Unveiling the Hidden World of Algal Biofilms: Nature’s Microscopic…

October 31, 2023October 31, 2023
by everflow

Biofilms are clusters of microorganisms that adhere to each other and a solid surface where water is present for extended periods. In nature, people often refer to photosynthetic biofilms as periphytic or algal biofilms, which consist mostly of algae, cyanobacteria, and heterotrophic bacteria living in symbiosis. In addition to these primary members, biofilms often contain additional microorganisms like flagellates and desmids and non-biological elements like silt, sand, and minerals.

Algae, which are chlorophyll-containing organisms, are widespread and lack traditional roots, stems, and leaves (Kesaano M, Sims RC et al., 2014). Biofilms are intricate communities of microorganisms that form on any surface, enclosed within a matrix of extracellular polymeric substances (EPS). These biofilms typically consist of unicellular or simple filamentous organisms, often known as microfouling or slimes. In specific conditions, such as high water flow or exposure to toxins, macroalgae like Enteromorpha and Ectocarpus can exhibit stunted growth on anti-fouling surfaces. In such cases, these algae may adapt by adopting a more compact growth form or integrating into the microfouling slime layer. The term “algal biofilms” refers to communities primarily dominated by microalgae that colonize well-lit surfaces when moisture and nutrients are present (Leadbeater BS et al., 1992, Jarvie HP, Neal C, et al., 2002).

Adherence and Attachment

Two methods can achieve microalgae immobilization: passive immobilization, accomplished through natural or induced biofilm formation, and active immobilization, achieved by trapping the cells within hydrogel polymer matrices. Researchers have utilized various immobilization media, including alginates, carrageenans, and polyacrylamide gel, for various purposes (Muñoz et al., 2009; de-Bashan and Bashan, 2010; He and Xue, 2010; He et al., 2014; Gagliano et al., 2017). Immobilization based on these polymeric matrices provides low mechanical strength and can result in restrictive diffusion of the substrate (Qureshi et al., 2005; Moreno-Garrido, 2008). This approach capitalizes on microalgae’s natural tendency to form biofilms.

Inorganic and organic compounds adhere to the surface of a substrate, creating a conducive environment for microbial growth (Qureshi et al., 2005; Stephens et al., 2015). Once microalgae and bacteria establish themselves on the surface, they secrete extracellular substances comprising nucleic acids, proteins, polysaccharides, and phospholipids. These substances serve a dual purpose: enhancing adherence to the substrate and simultaneously capturing and concentrating essential nutrients required for cell growth (Mohsenpour et al., 2021; Qureshi et al., 2005).

Algal Biofilm Habitats: Nature’s Adaptive Colonizers

In natural ecosystems such as rainforests, deserts, and ocean floors, algal biofilms are commonly present on surfaces like river stones (see Fig. 1), seashores, garden walls, tree bark, reed stems, and bamboo pipes. These microalgal biofilms thrive when they have sufficient moisture and light, and people typically collect them by scraping. They can grow on various materials, including plastics such as polyvinylchloride, polyethylene, polyurethane polymethyl methacrylate, polystyrene, polycarbonate, and polyamide; and other materials such as glass, cardboard, and ceramic tiles.

Notably, algal biofilms exhibit adaptability to environmental changes, maintaining colonies on surfaces and detaching either as single colonies or in clumps.

Composition of algal biofilms

The polysaccharide matrix called EPS embeds microorganisms in biofilms, providing cohesion and enabling component interactions (Flemming & Wingender et al., 2010).

Nutrients and dissolved gases diffuse through the boundary layer above the biofilm, then through the EPS matrix to reach biofilm cells, while waste gases and products either recycle within or diffuse outward. Surfaces concentrate charged particles and molecules, potentially serving as nutritional sources due to mineral and organic content. Various inorganic and organic molecules accumulate on surfaces, and particle-associated bacteria exhibit higher nutrient uptake rates, as shown by (Paerl and Merkel et al.,1982).

Diatoms are common early colonizers in algal biofilms, often making up the majority of associated bacteria and other unicellular organisms (Jackson & Jones, 1988). Single-celled diatoms are known for their silica frustules and their golden brown appearance, which is attributed to the fucoxanthin pigment present in their chloroplasts. They vary in size and attachment mechanisms (Daniel et al., 1987). Just a few diatom cells can start surface attachment, multiplying to form a compact biofilm.

In freshwater environments, green algae and cyanobacteria, particularly in aerial conditions, can dominate algal biofilms (Grant et al., 1982). For instance, Pleurococcus, a green unicellular alga, thrives in damp conditions on various surfaces. Trentepohlia, a filamentous green alga, can disfigure exterior surfaces in humid regions (Wee & Lee et al.,1980). Cyanobacteria, though usually minor, can become dominant due to their resilience and nitrogen-fixing abilities.

The biofilm is a dynamic community in equilibrium with its environment, undergoing growth, death, sloughing, and regeneration processes similar to bacterial biofilms but with less organization (see fig 2).

mature algal biofilms — Fig 2 Mature Algal Biofilm

Factor affecting algal biofilm.

The development and adhesion of algal biofilms are influenced by various factors, including the physico-chemical characteristics of the substrate, operational parameters (see fig 3), the specific microalgal strain employed, and the interactions between microalgal cells, the substrate, and the liquid medium.

factors affecting algal biofilms — Fig 3 Factors Affecting algal biofilm

Light

Light is essential for algal photosynthesis and microalgal growth. Green algae dominate in high-light conditions during early colonization, while heterotrophic bacteria thrive in low-light environments. Diatoms often prevail in light-limited algal biofilms.

Increasing photon flux density (PFD) enhances growth rates in planktonic algae, but excessive PFD can result in photoinhibition and photooxidation, leading to culture stagnation or demise. Microalgae have the capacity to adjust to changing light intensities to optimize efficiency and protect against photodamage. The specific threshold for photoinhibition or light limitation varies among biofilm communities.

Under high irradiance, thick biofilms dominated by green algae resembling Scenedesmus were observed. Biofilms cultivated in a similar light range exhibited higher cellular nutrient content compared to those grown under higher light regimes. Algal Biofilms cultured under low irradiance using the same inoculum were thinner, more compact, and featured a wider variety of species, including cyanobacteria.

Hultberg et al. demonstrated that light quality has a direct impact on biofilm formation when using monochromatic illumination, suggesting the potential for enhanced cellular growth and lipid content through light quality optimization.

Temperature

Temperature plays a pivotal role in microalgal growth, biomass production, and biochemical processes. The optimal temperature range for microalgal cultivation typically spans from 20°C to 25°C. Below 16°C, growth slows down, while exceeding 35°C can be fatal for certain species. High temperatures, depending on the species, can stimulate cell growth, adhesion, and EPS production, promoting the formation of biofilms (Qureshi et al., 2005).

Claquin et al. (Claquin et al.; 2008) conducted research highlighting temperature’s significant impact on marine microalgae, influencing growth and the secretion of transparent exopolymeric particles (TEP) due to shifts in microbial and grazing activities (Honda Y, Matsumoto J, et al., 1983). Temperature also affects algal growth rates, species composition, and grazing activity within biofilm communities(Rao TS et al.; 2010). Tuchman and Blinn (1979) observed a rise in algal densities as temperature increased.

The Arrhenius relationship elucidates how temperature influences algal growth rates under consistent light and optimal nutrient conditions(Goldman JC et al.; 1974, Raven JA et al.; 1988). Biofilms grown in thin water layers are more sensitive to temperature fluctuations compared to suspended cultures (Posadas et al., 2013).

Furthermore, temperature stress and the accumulation of calcium can have adverse effects on EPS production in algal cells (Domozych, et al., 2007). Fica and Sims (2016) determined that elevating wastewater temperature (7–27°C) and increasing organic carbon levels (300–1,200 mg L−1) significantly enhance biomass growth in algae-based biofilm systems. Temperature serves as the precise conductor orchestrating the dynamics of microalgae.

Nutrients

The abundance of algal species within biofilms is strongly influenced by nutrient concentration and light intensity, with a preference for algal dominance under conditions of high inorganic and low organic carbon levels(Unnithan VV et al.; 2014).

Nutrient availability plays a pivotal role in shaping algal growth, biofilm characteristics, succession patterns, and species composition (Nils RP et al.; 2003, Sekar R et al.; 2002). Environments enriched with biodegradable organic matter tend to favor the development of heterotrophic biofilms, whereas phototrophic biofilms thrive in response to light and the presence of inorganic nutrients (Hillebrand H et al.; 2002, Olapade OA et al.; 2006). The transport of nutrients to algal cells occurs through a concentration boundary layer via diffusion mechanisms.

Nitrogen and phosphorus availability exert distinct influences on microalgal metabolism. In instances of nitrogen starvation, microalgae pivot towards the production of lipids and/or carbohydrates as opposed to proteins (Gojkovic et al., 2020). There exists a mutual reliance between nitrogen and phosphorus uptake, with green algae initially dominating biofilms in nitrogen-deficient conditions, followed by diatoms, and ultimately cyanobacteria. The presence of phosphorus enhances nitrogen uptake, and in the presence of nitrogen, excess phosphorus can be absorbed by algae, a phenomenon known as luxury uptake (Bougaran et al., 2010)t.

Monod’s Kinetic Expression in Algal Biofilm Research

Monod’s kinetic expression finds application in algal biofilm research to elucidate growth patterns concerning nutrient concentrations and to predict rates of substrate utilization. For instance, Hill et al. 2009 established a growth saturation threshold of 25 μg/L soluble reactive phosphorus (SRP) for algal growth in stream biofilms.

Microalgae harness dissolve for in-organic carbon sources such as CO2 (aq) and HCO3 − found in wastewater, along with atmospheric CO2, and organic carbon derived from bacterial degradation (E. Posadas et al.; 2013, L.B. Christenson et al.; 2011).

Carbon, nitrogen, phosphorus, and silicon (for diatoms) are pivotal elements governing microalgae growth. The ratios of C:N:P serve as valuable indicators of nutrient limitation within algal communities, with the Redfield ratio (106:16:1 molar basis) representing a characteristic benchmark for optimally growing phytoplankton (R.S. Stelzer et al.; 2001, H. Hillebrand et al; 1999)

Elevated levels of nitrogen and phosphorus, coupled with increased inorganic carbon concentrations and heightened light intensity, augment the accumulation of photosynthetic biomass and its relative proportions in comparison to non-photosynthetic biomass. Additionally, advanced cultures and elevated temperature and nutrient loading rates contribute significantly to an upsurge in the proportions of cyanobacteria within photosynthetic biofilms.

pH

The pH level plays a crucial role in nutrient availability, including factors such as the solubility of ammonium and phosphate ions, as well as the formation of precipitates. Elevated pH values, typically at 9 or above, can trigger the formation of calcium phosphate, rendering it inaccessible to microalgae (Laliberté et al., 1997). Conversely, a decrease in pH levels can influence enzymatic activities, albeit depending on the specific microalgal species, thereby decelerating cell growth and product production.

Furthermore, pH values determine the charge of functional groups present on the surface of microalgae, consequently affecting their capacity to bind substances such as heavy metal ions.

CO2

Carbon stands as an indispensable element vital for the growth and productivity of microorganisms. Photoautotrophic organisms like microalgae possess the capacity to employ light energy to photosynthetically convert carbon dioxide (CO2) into biomass (S.B. Patwardhan et al.; 2022). Additionally, microalgae can utilize soluble carbonates as a carbon source for cellular growth, either via direct uptake or by catalyzing the conversion of carbonate into free carbon dioxide through enzymatic carboanhydrase activity.

Hence, the availability of an appropriate level of CO2 is imperative for the proper growth and metabolic activities of microalgae. Deviations from this optimum CO2 level, whether below or above, can exert adverse impacts on growth and productivity (W. Blanken et al 2014, B. Clement-Larosiere et al.; 2014). For instance, CO2 concentrations falling below the optimal level may result in carbon limitation, thereby retarding growth and productivity. Conversely, upon the introduction of an elevated concentration of CO2, microalgae assimilate a portion of the carbon through photosynthesis. Simultaneously, the excess carbon is converted into carbonic acid (H2CO3), which subsequently induces acidification of the medium.

Substratum

Algal adhesion studies primarily explore surface characteristics and material composition’s influence on biofilm formation to enhance cell attachment and biofilm growth. Ozkan and Berberoglu (2013) found differences in cell attachment between green algae and diatoms related to surface hydrophobicity, a concept emphasizing hydrophobic entities’ preference for each other to minimize water contact (Palmer et al., 2007).

Surface texture is crucial; rough or porous surfaces, with increased surface area and shear force protection, promote higher cell attachment (Gross et al., 2016; Huang et al., 2018). Increasing surface roughness, as suggested by Cao et al. (2009), creates slower flow zones that aid algal settlement. Studies by Huang et al. (2018) and Kardel et al. (2018) demonstrated weaker shear stress on grooved surfaces, influencing cell attachment based on groove shapes.

Material properties matter. Christenson and Sims (2012) found superior algal growth on cellulose-based natural polymer surfaces over synthetic polymers on various substrates. Sekar et al. (2004) observed greater attachment of certain algal species to hydrophobic surfaces (e.g., titanium, perspex, stainless steel), with exceptions for copper and its alloys, which hindered attachment due to toxicity (aluminum and admiralty brass).

Hydrophobicity

Hydrophobicity is a factor that affects the surface of the algal cell and substrate, for this reason considered an interface and a cellular factor. In diverse multi-species microbial biofilm, the presence of fimbriae, proteinaceous bacterial appendages rich in hydrophobic amino acids, can increase cell surface hydrophobicity (Barros et al., 2018). Flagellated cells show an increased ability to attach to surfaces. Flagellar motility may serve to overcome initial electrostatic surface repulsion (Bullitt and Makowski, 1995; Qureshi et al., 2005; Krasowska and Sigler, 2014). However, the microalgae biofilm on a hydrophilic surface might decrease and then increase with the increasing concentration of DOMs(dissolvable organic matter) and inorganic salts. Furthermore, many studies have shown that the DOMs can adsorb onto the substratum surface, leading to the development of surface conditioning films (Hwang et al., 2012)

Flow Velocity

The flow velocity of the liquid medium housing the algal biofilm plays a pivotal role in governing both cellular growth and attachment dynamics. This is primarily attributed to the liquid medium’s essential function as a source of vital nutrients for sustaining microalgal cells. However, it is imperative to acknowledge that elevated flow velocities can impose shear stress upon the biofilm (P. Choudhary et al.; 2017).

Furthermore, it is well-documented that turbulent flows occurring within the liquid medium have the potential to induce the detachment of cells from the biofilm, leading to a subsequent reduction in the overall thickness of the biofilm (L. Katarzyna et al.; 2015). It is noteworthy that the specific arrangement of microalgal biofilms may involve their placement within a rotational environment, resulting in periodic exposures to gaseous and liquid phases. This unique configuration introduces an added layer of complexity to the intricate interplay between flow velocity, shear stress, and the dynamics of microalgal cell growth and attachment within the biofilm milieu.

Extracellular polymeric substances (EPS)

Extracellular Polymeric Substances (EPS) in algal biofilm communities consist of polysaccharides, proteins, nucleic acids, lipids, and humic acids (A.M. Romani et al.; 2008, F. Di Pippo et al .; 2009) influencing their physical and chemical properties. EPS serves as nutrient reservoirs, with embedded enzymes breaking down EPS and inert solids (Sutherland IW et al.; 1999), and they act as ion exchange resins, trapping nutrients through sorption (Flemming HC et al.; 2007, Wolfaardt GM et al; 1999). EPS roles include facilitating cell movement (D.J. Smith et al.; 1998), preventing cell desiccation, protecting against toxins (J.V. Garcia-Meza et al.; 2005), and providing structural stability (I.W. Sutherland et al.; 2001).

Environmental Factors Influencing EPS Production

Microalgae adjust EPS production in response to environmental factors during biofilm formation. Light intensity significantly affects EPS accumulation (H. Ge et al.; 2014), e.g., Nostoc sp. produces more EPS at 206.20 mg/g DW under 80 μE.m^−2.s^−1 compared to 155.49 mg/g DW at 40 μE.m^−2.s^−1 .

Adhesion materials enhance EPS production in diatom Amphora coffaeformis (Becker K et al .; 1996). Growth materials influence EPS, as shown by Shen et al. (H. Ge et al.; 2014), and increased nutrient levels, especially nitrogen, boost EPS in diatom and green algae. Operational factors like light, temperature, nutrients, and culture density affect both biomass and EPS secretion. Li et al. noted EPS concentrations of 1.25 and 1.75 g.L^−1 with C/N ratios of 0.96 and 12.82, respectively (.H. Li, L. Ji et al.; 2020).

Young, grazed algal biofilms exhibit high EPS-to-biomass ratios for survival (C. Barranguet et al.; 2005). Cyanobacteria and diatom biomass correlate positively with EPS in wastewater-based biofilms. Light is linked to EPS production, and even in darkness, some species like Cylindrotheca closterium, Navicula perminuta, and Nitzschia sigma secrete EPS using stored glucan as a carbon source (D.J. Smith et al.; 1998).

Wastewater algal biofilms face grazing and changing conditions, necessitating species selection for EPS production and carbon management.

Species interaction

Natural biofilms encompass a diverse array of microbial constituents, including fungi, algae, protozoa, flagellates, and bacteria ( B.S.C. Leadbeater et al.; 1992, F. Di Pippo et al.; 2009). Within photosynthetic biofilms, one finds a myriad of algae, bacteria, cyanobacteria, protozoa, and multicellular microorganisms. Notably, diatoms, green algae, and filamentous algae play substantial roles in contributing to biofilm biomass, displaying both autotrophic and heterotrophic capacities (Liang Y,Sarkany N et al; 2009). The bacterial component encompasses cyanobacteria and heterotrophic and autotrophic bacterial species.

Within algal biofilm, organisms engage in symbiotic interactions where heterotrophic bacteria serve as a source of carbon dioxide for photosynthetic organisms, thereby enabling the production of biomass and oxygen during respiration. Furthermore, excreted carbohydrates, vitamins, and organic compounds serve as vital nutrients for both algae and bacteria. This nutrient exchange is facilitated by the initial colonization of bacteria, which expedites the formation of algal biofilms (G. Roeselers et al.; 2007, É. Ács et a.; 2007).

Developmental Stages and Species Succession

The developmental stage of a biofilm exerts a discernible influence on species succession, resulting in alterations in the relative abundance and proportions of algae, bacteria, and extracellular polymeric substances (EPS) . In the early stages of photosynthetic biofilm formation, a higher proportion of EPS and bacteria is observed in comparison to algae and cyanobacteria, a phenomenon colloquially referred to as “conditioning”. Subsequently, following the establishment of the EPS matrix, algae exhibit rapid growth in the upper layers of the biofilm, thereby prompting bacteria to form aerial colonies in competition for essential nutrients.

Succession Patterns in Algal Groups

Biofilm maturity also exerts discernible effects on the dominance of specific algal groups. Diatoms are found to predominate in the early stages of biofilm development (typically within the first 15–20 days), while filamentous chlorophytes become more prevalent in later stages (Besemer K, Singer et al.; 2007, Johnson Reet al.; 1997). Some investigations have suggested a succession pattern characterized by an initial dominance of green algae during the early phase (1–4 days), followed by diatoms during the subsequent phase (5–9 days), and ultimately giving way to cyanobacteria during the third phase (10–15 days) (Sekar R et al.; 2004). Cyanobacteria are identified as late successional microorganisms (Zippel B et al.; 2005) with their distribution and prevalence being influenced by a multitude of factors (Rao TS et al.; 2010, Barranguet C et al.;2005, Sekar R et al.; 2004 ).

The presence of grazers, including Chironomids, Gastropods, Trichopteran larvae, Ephemeropteran larvae, and crustaceans, has a pronounced impact on reducing algal biomass throughout the seasons, with summer exhibiting the most significant effects (Hillebrand H et al.; 2001). Notably, filamentous species and chain-forming diatoms are more susceptible to grazing than single-celled algae species (Hillebrand H et al.;2002).

The succession of algal species within photosynthetic biofilms is governed by a complex interplay of factors, including light intensity, temperature, nutrient concentrations, and shear rates, with seasonal variations playing a pivotal role in shaping these dynamics see fig 4.

algal biofilms applivation — Fig 4 Different factors for algal biofilm and its application

Metabolic pathway

Metabolic pathways in microalgae cultivation are influenced by the availability and form of nutrients, primarily driven by the assimilation of available carbon (Markou G et al., 2014). These pathways play a crucial role in enhancing biomass production and shaping the composition of intracellular metabolites like proteins, lipids, and pigments. They rely on inputs such as light and carbon sources (Wang J et al.,2014).

Heterotrophic cultivation of microalgae is considered the most promising approach for achieving higher biomass yield and optimizing biochemical composition (Chen F. et al.,1996, Yang C et al.,2000). Generally, there are three distinct metabolic pathways in microalgae, determined by their nutritional requirements for growth and valuable biochemical production.

The main cultivation conditions are photoautotrophic cultivation, heterotrophic cultivation, and mixotrophic cultivation.

Photoautotrophic cultivation

The photosynthetic pathway involves converting sunlight and carbon dioxide into energy and cellular carbon dioxide, directing biochemical production in microalgae (Burkholder JM et al., 2008).

In photoautotrophic cultivation, microalgae exhibit varying lipid contents, ranging from 5% to 68%, depending on the species (Chen CY et al.; 2011). To boost lipid content during growth, nitrogen or nutrient limitations can be applied (Mata TM et al.,2010). The highest reported lipid productivity in microalgae under photoautotrophic conditions reached 179 mg/L/d using Chlorella sp. with 2% carbon dioxide and 0.25 vvm aeration (Chiu SY et al.; 2008).

Heterotrophic cultivation

Heterotrophic cultivation involves microalgae using organic compounds as both carbon and energy sources (Chojnacka K et al.; 2004). Some microalgae species can thrive in both photoautotrophic and heterotrophic conditions.

Only a few microalgae species have succeeded on a large scale in the heterotrophic mode (Lee DU et al.; 2001), but it is more efficient in terms of cell production per unit energy compared to the autotrophic mode (Yang C et al.; 2000). For instance, Chlorella protothecoides experienced a 40% increase in lipid content when shifting from photoautotrophic to heterotrophic cultivation ( Xu H et al.; 2006).

Microalgae can utilize various organic carbon sources during growth, including sucrose, glucose, lactose, galactose, glycerol, and fructose (Liang Y et al.;2009). Some microalgal species are obligate heterotrophs and are cultivated in heterotrophic mode, especially for lipid and pigment production from wastewater. This approach allows for achieving high cell densities, up to 100 g/L, facilitating microalgae biomass harvesting (Morales-Sánchez D et al.; 2015).

Mixotrophic cultivation

Mixotrophic cultivation combines autotrophic and heterotrophic modes, enhancing microalgae growth and resource utilization (Burkholder JM et al.; 2008). Microalgae use organic carbon compounds and CO2 as carbon sources, recycling CO2 during phototrophic conditions when light is available (Mata TM et al.; 2010). This approach aids global carbon dioxide reduction by utilizing carbon dioxide for microalgae growth. Industrial wastewater serves as a carbon source when combined with a light source, offering an efficient and cost-effective microalgae cultivation method (see fig 5).

Conclusion

Algal biofilms, a captivating realm within microbiology and environmental science, showcase intricate communities of microorganisms residing within a matrix of extracellular polymeric substances (EPS). Dominated by microalgae, cyanobacteria, and heterotrophic bacteria, these biofilms are versatile colonizers, populating a range of surfaces where moisture and light are abundant, from river stones to plastic surfaces and tree bark. Their ability to thrive and adapt in diverse conditions, using three primary metabolic pathways (photoautotrophic, heterotrophic, and mixotrophic cultivation), underscores their resourcefulness.

Beyond their aesthetic appeal, algal biofilms play an active ecological role. They contribute to water purification, nutrient cycling, and the production of valuable biomass and bioactive compounds, reflecting the dynamic nature of natural ecosystems. In a world grappling with environmental challenges, algal biofilms offer hope and insight, serving as a model of resilience. These microorganisms, without traditional plant structures, harness the power of photosynthesis, adapting to changing conditions, and exemplifying the ingenuity and tenacity of life.

Algal biofilms are not just subjects of scientific inquiry; they are living testaments to the intricate interplay of microorganisms in nature, demonstrating the remarkable potential for adaptation and survival. In a changing world, their adaptability and resourcefulness inspire us to explore and understand the complex relationships within ecosystems.

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Uncategorized

Environmental Benefits of Wastewater Treatment by Algae

October 3, 2023October 4, 2023
by everflow

Introduction

Wastewater treatment is a critical process for preserving environmental quality and human health. Traditional methods have been effective but can be resource-intensive and less environmentally friendly. Enter phycoremediation, a revolutionary approach that employs algae to clean wastewater while offering a myriad of ecological advantages. In this article, we’ll explore the environmental benefits of wastewater treatment by algae, delving into its ecological advantages, potential for carbon sequestration, and habitat restoration.

Phycoremediation: A Green Revolution in Wastewater Treatment

Phycoremediation, or the use of algae for wastewater treatment, is gaining prominence as an eco-friendly, cost-effective, and sustainable solution. Unlike conventional treatment methods, which often rely on chemicals or mechanical processes, phycoremediation leverages the natural capabilities of algae to absorb, assimilate, and remove contaminants from water. Beyond its primary goal of wastewater purification, phycoremediation provides several ecological advantages.

Nutrient Removal and Eutrophication Mitigation

One of the most significant environmental benefits of phycoremediation is its ability to remove excess nutrients from wastewater. Nutrient pollution, particularly the presence of nitrogen and phosphorus compounds, can lead to eutrophication in aquatic ecosystems. Eutrophication causes harmful algal blooms, oxygen depletion, and the decline of aquatic life.

How Algae Help:

Algae are exceptional at nutrient uptake. They thrive on nitrogen and phosphorus, two primary culprits in nutrient pollution. By cultivating algae in wastewater, these organisms absorb and store excess nutrients, effectively reducing the nutrient load in treated water. This nutrient removal mitigates the risk of eutrophication in downstream water bodies, restoring balance to aquatic ecosystems.

Carbon Sequestration: Algae as CO2 Sponges

In addition to nutrient removal, algae have a remarkable capacity for carbon sequestration. As photosynthetic organisms, they capture carbon dioxide (CO2) from the atmosphere during photosynthesis and convert it into organic biomass. This process effectively locks away carbon and helps mitigate greenhouse gas emissions.

The Role of Algae in Carbon Sequestration:

Photosynthesis: Algae are among the most efficient photosynthesizers on Earth. They capture CO2 and transform it into organic matter, including lipids, proteins, and carbohydrates.
Biomass Growth: As algae multiply and grow, they continue to capture CO2 and store it in their biomass.
Harvesting Potential: Algal biomass can be harvested and converted into biofuels, bioplastics, or other valuable products, effectively sequestering carbon while producing renewable resources.

By incorporating algal cultivation into wastewater treatment, we purify the water and contribute to carbon sequestration, mitigating the impacts of climate change.

Habitat Restoration and Biodiversity Enhancement

Phycoremediation also offers opportunities for habitat restoration and the enhancement of biodiversity in aquatic environments. Algae play a crucial role in marine food webs, serving as a primary food source for many organisms, including zooplankton and small fish. The ecological advantages include:

Enhanced Trophic Dynamics: As algae proliferate in treated wastewater, they support the growth of zooplankton and other herbivores. This, in turn, attracts higher trophic-level species, promoting biodiversity.
Aquatic Habitat Improvement: By reducing nutrient pollution and harmful algal blooms, phycoremediation helps create healthier aquatic habitats, benefiting fish and other aquatic organisms.
Restoration of Native Species: The removal of pollutants and excess nutrients facilitates the recovery of native aquatic species, promoting the resilience of natural ecosystems.

Economic Benefits and Sustainable Resource Use

Beyond its environmental advantages, phycoremediation offers economic benefits and opportunities for sustainable resource use. These include:

Resource Recovery: Algal biomass harvested from wastewater can be converted into valuable products such as biofuels, bioplastics, animal feed, and even pharmaceuticals. This resource recovery helps offset the costs of wastewater treatment and promotes a circular economy.
Cost Savings: Phycoremediation can be more cost-effective than traditional wastewater treatment methods, especially in rural or decentralized systems. It requires fewer energy inputs and chemical additives.
Energy Production: Some algal species are excellent candidates for biofuel production, offering a sustainable source of renewable energy.

Challenges and Considerations

While phycoremediation offers numerous ecological advantages, it’s essential to consider the challenges associated with its implementation:

Species Selection: Choosing the suitable algal species for a specific wastewater treatment application can be crucial for success. Different species have varying capabilities and growth requirements.
Monitoring and Control: Managing algal cultures and maintaining optimal growth conditions require careful monitoring and control of environmental parameters.
Harvesting and Processing: Efficient methods for harvesting and processing algal biomass are essential to maximize resource recovery.
Regulatory Compliance: Regulations governing the use of algae in wastewater treatment and the discharge of treated water must be adhered to.

Conclusion: Harnessing Algae for a Sustainable Future

Phycoremediation, with its ecological advantages, holds tremendous promise for wastewater treatment and environmental restoration. By harnessing the natural capabilities of algae to remove nutrients, sequester carbon, enhance biodiversity, and produce valuable resources, we take a significant step towards a more sustainable and ecologically balanced future. As we continue to explore innovative solutions to address environmental challenges, phycoremediation stands out as a shining example of how science and nature can work hand in hand to benefit both the environment and society.

Bio Remediation/ Phycoremediation

Phycoremediation Innovations: New Approaches to Algae-Based Wastewater Treatment

September 29, 2023September 29, 2023
by everflow

Introduction

In the realm of wastewater treatment, a green revolution is taking place, and it’s powered by algae. Phycoremediation, the use of algae for wastewater treatment, is gaining traction as a sustainable, cost-effective, and environmentally friendly approach. Recent advancements in phycoremediation technology and research are pushing the boundaries of what’s possible, offering innovative solutions to the global water pollution crisis. In this article, we will explore the latest breakthroughs in phycoremediation, their potential impact on the industry, and how these innovations are revolutionizing the way we treat wastewater.

The Algae Revolution: Why Phycoremediation Matters

Wastewater treatment is a pressing global challenge. Traditional methods often involve chemicals or energy-intensive processes, leading to high operational costs and environmental concerns. Phycoremediation, powered by the remarkable capabilities of algae, presents a compelling alternative.

Algae, including microalgae and macroalgae, are photosynthetic organisms that thrive in aquatic environments. They can absorb nutrients, heavy metals, and even certain organic pollutants, all while producing oxygen. This unique combination of capabilities makes algae ideal candidates for wastewater treatment. Here, we delve into recent innovations in phycoremediation that are reshaping the field.

Innovations in Algae Strain Selection

One of the fundamental aspects of phycoremediation is selecting the right algae species for the job. Recent advancements in strain selection are enhancing the efficiency and effectiveness of algae-based wastewater treatment.

Traditionally, researchers relied on naturally occurring algae strains for treatment. However, advancements in genetic engineering have allowed scientists to modify algae strains for enhanced pollutant removal. For example, researchers have created genetically modified algae strains with an increased capacity to absorb heavy metals or break down specific organic pollutants.

In addition to genetic engineering, advanced screening techniques are being used to identify native algae strains that possess exceptional pollutant-removal capabilities. These strains can then be cultivated and used for efficient and natural wastewater treatment.

Breakthroughs in Algae Cultivation Techniques

The scalability of algae-based wastewater treatment has always been a concern. Recent innovations in algae cultivation techniques are addressing this challenge, making large-scale phycoremediation projects more feasible.

Photobioreactors: Photobioreactors are enclosed systems that provide controlled conditions for algae growth. Recent improvements in photobioreactor design have increased the productivity of algae cultivation. These systems allow for precise control of environmental variables like temperature, light intensity, and nutrient supply, resulting in higher biomass yields.
Algae Farming: Large-scale algae farming has become more practical due to innovations in pond and raceway designs. Advanced monitoring and automation systems now equip algae ponds, enabling efficient nutrient delivery and biomass harvesting. The development of floating algae platforms has also expanded the potential for algae farming in various water bodies.
Wastewater Integration: Researchers are exploring the integration of algae cultivation systems with existing wastewater treatment facilities. Incorporating algae ponds into the treatment process naturally treats wastewater while simultaneously generating valuable algal biomass for various applications.

Enhanced Nutrient Removal

Nutrient pollution, particularly excess nitrogen, and phosphorus, is a major concern in wastewater. Algae possess a renowned ability to assimilate and remove nutrients from water. Recent advancements are making this process even more efficient.

Algae-Bacteria Symbiosis: Researchers have discovered symbiotic relationships between algae and certain bacteria that enhance nutrient removal. These bacteria can convert ammonia into nitrate, a form of nitrogen that algae can more readily absorb. This synergy between algae and bacteria has the potential to significantly improve nutrient removal in phycoremediation systems.
Nutrient Recovery: Beyond removal, recent research has focused on nutrient recovery from algal biomass. Techniques like pyrolysis and hydrothermal liquefaction can convert algal biomass into nutrient-rich biochar or liquid fertilizers. In agriculture, people can use these products to close the nutrient cycle and reduce the need for synthetic fertilizers.

Algae-Based Biosensors for Monitoring

Effective monitoring is crucial for the success of phycoremediation projects. Recent innovations involve the development of algae-based biosensors that can provide real-time data on water quality.

Algae biosensors use changes in the fluorescence or growth of algae in response to specific pollutants as indicators of water quality. These biosensors are highly sensitive and can detect pollutants at low concentrations. They offer a cost-effective and eco-friendly solution for the continuous monitoring of water bodies, ensuring the efficiency of phycoremediation processes.

Algae for Value-Added Products

The potential of algae extends beyond wastewater treatment. Recent advancements are unlocking the possibilities of turning algal biomass into valuable products.

Biofuels: Algae are known for their high oil content, making them a promising source of biofuels. Advances in extraction and conversion technologies are improving the viability of algal biofuels as a sustainable energy source.
Food and Pharmaceuticals: Some algae species are rich in essential nutrients and bioactive compounds. Research is ongoing to develop algae-based products in the food and pharmaceutical industries. People can use algae for nutraceuticals, dietary supplements, and even plant-based proteins.
Bioplastics: Algae-derived bioplastics are gaining attention as an eco-friendly alternative to conventional plastics. Researchers are exploring ways to produce biodegradable plastics from algal biomass.

Implications for the Wastewater Industry

The innovations in phycoremediation are poised to have a profound impact on the wastewater treatment industry. Here are some key implications:

Sustainability: Algae-based wastewater treatment is inherently sustainable, as it relies on natural processes. As advancements continue, it’s likely to become an even more eco-friendly alternative to traditional treatment methods.
Cost-Effectiveness: The scalability and efficiency of modern algae cultivation techniques are making phycoremediation increasingly cost-effective. This could lead to reduced operational costs for wastewater treatment plants.
Resource Recovery: The ability to recover valuable resources from algal biomass, such as nutrients and biofuels, can create new revenue streams for wastewater treatment facilities.
Real-Time Monitoring: Algae-based biosensors offer a means of continuous monitoring, helping treatment plants respond rapidly to changes in water quality.
Versatility: Phycoremediation can be applied to a wide range of wastewater types, from municipal sewage to industrial effluents. Its versatility makes it a valuable tool in addressing various pollution challenges.

Challenges and Future Directions

While the recent innovations in phycoremediation are promising, several challenges remain:

Strain Optimization: Fine-tuning algae strains for specific contaminants and environmental conditions is an ongoing process.
Regulatory Frameworks: Regulations governing the use of genetically modified algae and the discharge of treated wastewater need to be developed and standardized.
Scale-Up: Scaling up phycoremediation projects for industrial use requires overcoming technical and logistical challenges.
Public Awareness: Raising public awareness about the benefits of algae-based wastewater treatment is essential for widespread adoption.
Long-Term Sustainability: Ensuring the long-term sustainability of phycoremediation projects, including the prevention of algal blooms, is critical.

Conclusion

Phycoremediation is at the forefront of sustainable wastewater treatment solutions, and recent innovations are pushing the boundaries of its potential. From enhanced algae strains and cultivation techniques to nutrient recovery and real-time monitoring, these breakthroughs are revolutionizing the field. The implications are far-reaching, offering a greener, more cost-effective, and versatile approach to addressing water pollution challenges. While challenges remain, the future of phycoremediation holds promise, transforming the way we treat and value our most precious resource — water. As society continues to grapple with water pollution and environmental sustainability, the algae revolution is a beacon of hope on the horizon.

Bio Remediation/ Phycoremediation

Case Studies: Successful Wastewater Treatment through Bioremediation

September 29, 2023September 29, 2023
by everflow

Wastewater treatment is a pressing global concern, as the discharge of untreated or inadequately treated wastewater poses severe environmental and public health risks. While conventional wastewater treatment methods play a crucial role in addressing this issue, innovative and sustainable alternatives like bioremediation have gained prominence. In this article, we explore real-world case studies of successful wastewater treatment projects that have harnessed the power of bioremediation, shedding light on their outcomes and the valuable lessons learned.

Case Study 1: The Hudson River PCB Cleanup

One of the most iconic bioremediation projects took place along the Hudson River in the United States. The river had been contaminated with polychlorinated biphenyls (PCBs), a group of toxic industrial chemicals, released into the water by General Electric (GE) factories over several decades.

The Problem: PCBs had accumulated in the sediment, posing a significant threat to aquatic life and human health. Conventional dredging and disposal methods were considered, but they were costly and environmentally damaging.

Bioremediation Approach: GE collaborated with environmental scientists to implement a natural, environmentally friendly solution. They introduced a PCB-degrading bacterium called Dehalococcoides into the contaminated sediment. This bacterium had the unique ability to break down PCBs into harmless byproducts under anaerobic conditions.

Outcomes: Over time, the bioremediation approach significantly reduced PCB levels in the sediment. Native microorganisms also played a role in the cleanup. The project demonstrated that bioremediation could effectively remediate PCB-contaminated sites, offering a more sustainable alternative to traditional methods.

Lessons Learned: This case study emphasized the importance of selecting the right microorganisms for the specific contaminants present in the environment. It also highlighted the need for ongoing monitoring and adaptive management to ensure the success of bioremediation projects.

Case Study 2: The Tianjin Binhai New Area Oil Spill

In 2010, a catastrophic oil spill occurred in the Tianjin Binhai New Area in China, resulting in the release of thousands of tons of crude oil into the Bohai Sea. The spill posed a severe threat to marine ecosystems and coastal communities.

The Problem: Conventional cleanup methods, such as mechanical skimming and chemical dispersants, were insufficient to address the scale of the oil spill. The contamination persisted, endangering marine life and local economies.

Bioremediation Approach: Chinese authorities, in collaboration with environmental experts, decided to employ a bioremediation technique using naturally occurring oil-degrading bacteria. These microorganisms would break down the oil into less harmful substances.

Outcomes: Over time, the oil-degrading bacteria multiplied and effectively consumed the oil. This natural process significantly reduced the oil’s impact on the marine ecosystem. The success of the bioremediation approach minimized ecological damage and allowed for a quicker recovery of the affected areas.

Lessons Learned: The Tianjin Binhai New Area oil spill demonstrated the efficacy of bioremediation in addressing large-scale oil contamination. It highlighted the importance of promptly identifying and utilizing native oil-degrading bacteria to expedite the cleanup process.

Case Study 3: Rhizofiltration in Mining Wastewater

Mining operations often generate highly contaminated wastewater, particularly from metal and metalloid-rich ores. Rhizofiltration, a bioremediation technique that uses the roots of plants to absorb and accumulate contaminants, has shown promise in remediating mining wastewater.

The Problem: A gold mine in South Africa was facing a significant challenge with its wastewater, which contained elevated levels of heavy metals like arsenic, lead, and cadmium. Traditional treatment methods were expensive and generated chemical sludge.

Bioremediation Approach: Researchers introduced certain hyperaccumulator plants with a high affinity for heavy metals to the wastewater ponds. The plants absorbed the metals through their roots, effectively removing them from the water.

Outcomes: Over time, the plants accumulated substantial quantities of heavy metals, reducing the pollutant levels in the wastewater. The approach not only cleaned the water but also provided an opportunity to recover valuable metals from the plant biomass.

Lessons Learned: This case study highlighted the potential of rhizofiltration as a cost-effective and sustainable method for treating mining wastewater. It emphasized the importance of selecting appropriate plant species for specific contaminants and maintaining a balance to prevent overloading the plants.

Case Study 4: The Lake Washington Cleanup Project

Lake Washington in Seattle, Washington, USA, faced severe pollution problems in the mid-20th century due to untreated sewage discharges. The lake had become a cesspool, with low oxygen levels and high nutrient concentrations.

The Problem: Lake Washington was experiencing eutrophication, a process where excessive nutrients lead to harmful algal blooms and oxygen depletion, threatening aquatic life.

Bioremediation Approach: Authorities and scientists undertook an ambitious bioremediation effort, which involved diverting sewage to a wastewater treatment plant and allowing the lake’s natural ecosystem to recover. This process reduced nutrient inputs and allowed the lake to gradually cleanse itself.

Outcomes: Over several decades, the lake’s water quality improved significantly. Oxygen levels increased, harmful algal blooms diminished, and native fish populations rebounded. The project demonstrated that, in some cases, nature’s ability to self-cleanse can be harnessed through appropriate management.

Lessons Learned: The Lake Washington Cleanup Project showcased the importance of holistic, long-term approaches to bioremediation. It underscored the need for combining bioremediation techniques with prudent management practices to achieve lasting results.

Conclusion

These case studies exemplify the success and potential of bioremediation as a sustainable and effective approach to wastewater treatment. From remediating PCB-contaminated rivers to cleaning up oil spills and addressing mining wastewater challenges, bioremediation has proven its worth in diverse real-world scenarios. The lessons learned from these projects emphasize the importance of careful planning, monitoring, and adaptability when applying bioremediation techniques. As we continue to seek environmentally friendly solutions to our wastewater woes, these case studies provide valuable insights into the promising future of bioremediation.

Bio Remediation/ Phycoremediation

Green Algae to the Rescue: Phycoremediation for Sustainable Wastewater…

September 29, 2023September 29, 2023
by everflow

Microalgae: A Powerful Tool for Climate Change and Water Pollution Mitigation

Introduction

The environmental impact of untreated or poorly treated wastewater is undeniable. Pollution of our water bodies, contamination of drinking water sources, and the destruction of aquatic ecosystems are just some of the dire consequences. In response to this growing crisis, we urgently need innovative and sustainable approaches to combat wastewater treatment. One such promising solution is phycoremediation, a process that harnesses the power of green algae to remove pollutants from wastewater. In this article, we will delve into the potential of green algae in wastewater treatment, highlighting its environmental advantages and diverse applications.

Understanding Phycoremediation

Phycoremediation, often referred to as algae-based wastewater treatment, is a natural and eco-friendly method that utilizes various species of green algae to purify wastewater. These algae, primarily belonging to the Chlorophyta division, are proficient in photosynthesis, enabling them to absorb nutrients and pollutants while releasing oxygen, making them nature’s own water purifiers.

The Environmental Advantages of Phycoremediation

Nutrient Uptake: One of the key environmental benefits of phycoremediation is its capacity to remove excess nutrients from wastewater. Algae are voracious consumers of nutrients such as nitrogen and phosphorus, which are often the culprits behind water pollution and harmful algal blooms. By absorbing these nutrients, algae help prevent eutrophication in receiving water bodies, thereby safeguarding aquatic ecosystems.
Carbon Sequestration: Green algae have a unique ability to remove carbon dioxide (CO2) from the atmosphere through photosynthesis. This not only reduces greenhouse gas emissions but also promotes carbon sequestration, aiding in the fight against climate change.
Toxic Metal Removal: Some species of green algae have demonstrated a remarkable capability to accumulate heavy metals and other toxic substances from wastewater. This feature makes them invaluable in the treatment of industrial effluents contaminated with heavy metals like lead, cadmium, and mercury.

Applications of Green Algae in Wastewater Treatment

Municipal Wastewater Treatment: Green algae-based systems are increasingly being incorporated into municipal wastewater treatment plants as an efficient and cost-effective means to reduce nutrient levels. These systems not only enhance the quality of treated effluent but also reduce the environmental impact of wastewater discharge.
Industrial Wastewater Treatment: Industries generating wastewater with high levels of nutrients or heavy metals can benefit from phycoremediation. Algae also can be cultivated in wastewater ponds or reactors, where they absorb pollutants, rendering the water suitable for safe discharge or even reuse in industrial processes.
Agricultural Runoff Remediation: Agricultural runoff laden with fertilizers and pesticides is a significant source of water pollution. Constructed wetlands also can deploy green algae to absorb excess nutrients, providing a natural buffer against pollution in agricultural areas.
Aquaculture Wastewater Treatment: In aquaculture, the buildup of nutrients and organic matter in water can be detrimental to fish health. Phycoremediation can be used to maintain optimal water quality in aquaculture systems, benefiting both fish health and the environment.

Challenges and Future Directions

While the potential of green algae in wastewater treatment is promising, there are challenges to address. These include optimizing algae cultivation methods, scaling up systems for larger applications, and ensuring the effective harvesting of algae biomass.

In the future, research into genetically modified algae strains with enhanced pollutant-uptake capabilities and increased resistance to adverse environmental conditions could further improve the efficiency of phycoremediation.

Conclusion

Green algae, with their remarkable ability to remove pollutants, sequester carbon, and promote water quality, hold immense promise in the realm of wastewater treatment. As we confront the pressing issues of water pollution and sustainability, phycoremediation emerges as a green, cost-effective, and also ecologically sound solution. Therefore, by harnessing the power of these microscopic organisms, we can work toward cleaner waterways, healthier ecosystems, and a more sustainable future for all. Phycoremediation is not just a rescue; it’s a step towards a brighter and cleaner tomorrow.

Also Read: An Advancements in Algae Cultivation: A Vital Component of Algal Technology

Bio Remediation/ Phycoremediation

Biofilms: A Dynamic Community in Equilibrium with the Environment

September 11, 2023September 12, 2023
by everflow

Biofilm, a complex assembly of microbial cells anchored to surfaces within a polysaccharide matrix, forms a harmonious and organized microbial community. This strategy enables microorganisms to thrive in favorable conditions, avoiding displacement by currents. Comprising cells and extracellular polymeric substances, biofilms exhibit dynamic equilibrium with their surroundings, cycling through growth, death, and regeneration.

Microorganisms gain remarkable advantages from biofilm cultivation, including protection from harsh conditions, enhanced resilience to stress, and cooperative metabolic and gene expression adjustments. Microorganisms thriving in biofilms exhibit an astonishing ability to adapt, demonstrating a captivating collective and synchronized behavior that intrigues both scientists and enthusiasts. (Donlan et al., 2002; Chmielewski and Frank et al., 2004; Van Houdt and Michiels et al., 2010). Multispecies biofilms are prevalent in nature, significantly impacting ecosystems (Donlan et al., 2002; Hall-Stoodley et al., 2004).

1. Microbial Biofilm Formation: A Complex Developmental Process in Bacteria

Biofilm formation is a captivating process wherein bacteria transition from single cells to structured multicellular communities. These parallels other bacterial developmental processes like sporulation (Dunny GM, Leonard BA. Et al.,1997), fruiting body formation (Plamann L et al.,1995, Shimkets et al.;1999, Wall D et al.,1999), and stalked-cell formation (Fukuda AK et al.,1977, Hecht GB et al., 1995, Trun NJ et al.,1990, Quon KC et al., 1996, Wu J et al.,1997). In nature, biofilms exist as diverse microbial communities, with bacteria joining, departing, exchanging genetic material, and occupying specific niches, resembling complex cities rather than developed organisms.

1.1 Biofilm Formation in Non-Motile Species

In non-motile species, during favorable conditions for biofilm formation, bacteria increase adhesin expression, enhancing stickiness for cell-to-cell and cell-to-surface adherence (Gotz, 2002). Surface proteins like Bap(biofilm-associated protein) in staphylococci aid cell interactions and matrix creation (Lasa and Penades et al., 2006). Similar proteins exist in other species, often with repeated domains undergoing recombination within the bap gene, yielding variable-length proteins (Latasa et al., 2006). Additionally, species that lack motility also generate exopolysaccharides (EPS), which subsequently become crucial constituents of the extracellular matrix. An illustrative instance of this is the production of PIA(Polysaccharide intercellular adhesion )/PNAGS (Poly-N-acetylglucosamine )EPS by the gene products originating from the ica operon in staphylococcal species. Thus, altered surface proteins and EPS production are key in initiating biofilm formation in non-motile bacteria.

1.2 Biofilm Formation in Motile Species

In motile species, conducive conditions trigger bacteria to adhere to a surface, lose motility, and form biofilms. An extracellular matrix binds them together. Flagella are vital for biofilm initiation; flagella-minus mutants show reduced biofilm formation (Pratt and Kolter et al., 1998; Watnick and Kolter 1999; Lemon et al., 2007). Listeria monocytogenes recover initial adhesion with directed movement, indicating motility’s role in overcoming repulsion for biofilm formation (Lemon et al., 2007). The initial surface encounter leads to transient adherence, determining stable biofilm development or return to planktonic state.

2. Genetically Distinct Stages of Biofilm Formation

Biofilm formation can be divided into five genetically distinct stages:

1. Initial surface attachment

2. Monolayer formation

3. Migration to form multilayered microcolonies

4. Production of extracellular matrix

5. Biofilm maturation with characteristic three-dimensional architecture (O’Toole et al., 2000)(fig 1).

Fig 1 Decoding Bacterial Biofilms: Approaches to Regulate and Control

3. Regulatory Variations in Biofilm Formation

In numerous motile bacteria, initial surface attachment relies on flagella-mediated motility. However, specific Gram-negative bacteria require type IV pili-associated surface motility for microcolony and three-dimensional architecture formation. Notably, this motility is absent in Gram-positive bacteria, except for Clostridia ssp. (Varga et al., 2006; O’Toole et al., 2000)

4. Extensive Cellular Differentiation in Biofilm Environment

Once the bacteria have successfully adhered to the surface, they begin producing an extracellular matrix. This matrix serves as a crucial organizational element, enabling the formation of structured communities within the biofilm. As a result, extensive cellular differentiation can occur within the biofilm environment.

5. Biofilm Composition and Architecture

Its composition hinges on the inoculum’s characteristics, while external factors like substrate, nutrients, competition, and grazing shape colonization and growth (Baier et al., 1980; Characklis & Cooksey et al., 1983; Marshall et al., 1985).

The architecture of biofilm is shaped by hydrodynamics, nutrients, bacterial motility, communication, exopolysaccharides, and proteins. Altered biofilm morphology in mutants lacking components of extracellular polymeric substances (EPS) illustrates their impact. Exopolysaccharides in Vibrio cholerae and colanic acid in Escherichia coli influence three-dimensional biofilm formation.

5.1 Biofilm Architecture in Bacillus subtilis

In the case of Bacillus subtilis biofilm, the matrix consists of an exopolysaccharide and the secreted protein Tas A, both of which are essential for maintaining the structural integrity of the matrix and facilitating the development of biofilm architecture resembling fruiting body-like structures (Fig 2).

6. Factors affecting the formation of biofilm.

Biofilms form at interfaces of aqueous or gaseous phases and substratum surfaces in diverse systems. Metabolic substrates required for growth must be accessible in the aqueous phase (e.g., medical catheters) or between aqueous and solid phases (e.g., minerals). Nutrient quantity and ratios in the liquid phase impact growth-limiting factors (van Loosdrecht et al., 2002).

Biofilm development is influenced by factors like temperature, pH, Oxygen levels, hydrodynamics, osmolarity, ions, nutrients, and biotic elements, collectively shaping bacterial behavior as mentioned in Fig 3 (van Loosdrecht et al., 2002).

6.1 The Relevence of EPS in Biofilm Composition

In biofilms, microorganisms make up less than 10% of the dry mass, with over 90% being the EPS matrix. EPS facilitates cell adhesion, cohesion, and interactions, including cell-cell communication, promoting the formation of micro consortia. It acts as an external digestive system, retaining enzymes to sequester nutrients from the water phase. Biofilm morphology varies, from smooth and flat to rough, fluffy, or filamentous, even forming mushroom-shaped colonies surrounded by water-filled voids. The structure adapts in response to nutritional changes, supporting diverse habitats and the coexistence of mixed-species consortia (Klausen et al., 2003).

Table 1 Function of EPS for Biofilm Formation ( Flemming HC, Wingender J et al., 2010)

6.2 Surface factor

Interactions between bacterial cell walls and surfaces are influenced by interfacial electrostatic and van der Waals forces (McClaine JW et al.,2002, Vigeant MA et al.,2002). Other factors, such as hydration forces, hydrophobic interactions, and steric forces, also impact cell attachment (Findenegg GH. JN Israelachvili et al., 1985). Hydrophobic interactions (low surface energy) and electrostatic interactions charge have been extensively studied.

6.2.1 Interactions Driving Bacterial Cell Attachment to Surfaces: Electrostatic Force

Electrostatic forces drive bacterial cell attachment to surfaces, given bacteria’s net negative charge (Soni KA et al., 2008, Katsikogianni MG et al 2010). Positively charged surfaces facilitate rapid attachment, while negative surfaces hinder it. Extracellular organelles aid in overcoming repulsion (Bullitt E et al., 1995). High ionic strength reduces charge effects. Bacterial cell walls expose functional groups interacting with substrates (Hong Y et al.,2008). Adsorbed molecules influence surface chemistry and charge, aiding adsorption and biofilm growth. Hydrophobic groups and organelles stabilize interactions after repulsion.

Biofilms form on various materials in contact with bacteria-containing fluids, influenced by surface roughness, chemistry, and conditioning films (Donlan et al., 2002). Hydrophobic surfaces promote faster attachment through interactions with flagella, fimbriae, and pili (Donlan et al., 2002; Donlan and Costerton et al., 2002). However, exceptions like Listeria monocytogenes prefer hydrophilic surfaces (Chavant et al., 200). Clinical isolates of Staphylococcus epidermidis favor biofilm formation on hydrophobic substrates (Cerca et al., 2005). Hydrophilic surfaces generally exhibit higher bacterial attachment than hydrophobic surfaces (Donlan, 2002).

6.2.2 High energy surface

Thermodynamic analysis of surface energies reveals insights into bacterial adhesion (Absolom DR 1983). Hydrophilic surfaces enhance bacterial adhesion when cell wall surface tension exceeds the surrounding liquid (Absolom DR et al.,1983). Fluorinated materials with large contact angles indicate low-energy surfaces (Absolom DR et al., 1983). Oxidation of fluorinated surfaces reduces initial bacterial attachment due to altered hydrophilic properties (Davidson CA et al., 2004). Bacterial attachment depends on surface free energy; high surface free energy surfaces like stainless steel and glass are more hydrophilic (Davidson CA et al., 2004). Biofilm growth depends on various factors, including nutrient concentrations and light availability, once bacterial cells adhere and achieve confluence.

6.3 Role of Biosurfactants in Bacterial Attachment and Biofilm Formation

Biosurfactants with antibacterial and antifungal properties are crucial for bacterial attachment to and detachment from oil droplets (Kim HJ et al., 2011 ). Research interest in environmentally friendly chemicals has grown, including biosurfactants (Kim HJ, Boedicker JQ, Choi JW, Ismagilov RF et al., 2008, Eun YJ et al.,2009 ). Microorganisms produce biosurfactants at the air-water interface, influencing surface tension and gas exchange in surface waters (Flickinger ST et al.,2011). Rhamnolipids, found in the EPS matrix of P. aeruginosa, act as surfactants, contributing to microcolony formation, bacterial migration, and biofilm dispersion (Boedicker JQ et al.,2009) (Vincent ME et al.,2010, Renner LD, Weibel DB et al.,2011) (Harmsen M et al., 2010).

6.4 Influence of Quorum Sensing (QS) on Biofilm Formation

Quorum sensing (QS) is a crucial regulatory mechanism for biofilm formation (Parsek and Greenberg 2005). Microorganisms release auto-inducers (AIs) that induce or repress QS-controlled genes, impacting biofilm structure and 3-dimensional organization (Steinmoen et al. 2002). QS also influences population size and dispersion in biofilms (Lewis et al., 2001; Davies et al., 2003; Jesaitis et al. 2003). Additionally, QS can induce behaviors and control group activities, affecting biofilm development and resistance to stress (Camilli and Bassler et al.,2006). Cell properties like hydrophilicity, fimbriae, and flagella also influence microbial attachment in biofilms.

6.5 Chemotaxis triggers biofilm formation

Chemotaxis is vital for biofilm formation in bacteria like Pseudomonas aeruginosa, E. coli, and Vibrio cholerae (O’Toole GA et al., 1998, Pratt LA et al.,1998, Watnick PI et al.,1999). Bacteria sense chemical stimuli, use flagella to swim toward nutrients, and attach to the substrate. Flagella and/or type IV pili are essential for initial cell adhesion, leading to microcolony formation (Stelmack PL et al.,1999). E. coli also utilizes type I pili for initial attachment. Bacterial chemotaxis aids biofilm growth and spread as it develops.

6.6 Importance of Horizontal Gene Transfer (HGT) in Microbial Communities

Horizontal gene transfer (HGT) is crucial for microbial evolution, facilitated by mobile genetic elements like plasmids, transposons, and bacteriophages (Koonin EV et al., 200) Bacterial biofilms show distinct gene expression compared to planktonic counterparts, influenced by the surface they settle on (Keyhani NO et al.,1996) HGT occurs within biofilms, allowing gene transfer between bacteria (Roberts AP et al.,1999).HGT also plays a significant role in animal evolution, diseases, and intercellular processes, like Agrobacterium transferring genetic material to plants (Guo M et al.,2019). Chemotaxis influences HGT, seen in Agrobacterium’s DNA transfer to plant cells (Guo M et al.,2019)., Niehus R et al.,2015). Other pathogenic bacteria also employ chemotaxis-derived HGT within host cells (Dougherty K et al.,2014 , Desmond E et al.,2007).

6.7 Interspecies Interactions in Bacterial Adhesion: Implications for Biofilm Stabilization and Commensal Relationships

McEldowney and Fletcher (McEldowney S, Fletcher M et al.,1987) showed that bacterial adhesion to a surface can affect other species differently, with negative, positive, or neutral outcomes. Inhibitory interactions may involve cell blockage or secretion of inhibitory macromolecules (Belas MR, Colwell RR et al.,1982).

6.7.1 Positive Interactions during Adhesion

Positive interactions during adhesion can result from bacterial products modifying the conditioning film or direct cell-to-cell contact. Dental plaque exemplifies direct interactions, where ligand-receptor interactions cause interspecies coaggregation (Kolenbrander PE et al., 1989). Hydroxyapatite attachment enhances the adhesion of co-aggregating pairs (Ciardi JE, McCray GF et al.,1987, Schwarz SU, Ellen RP 1987 ). Other interactions, like mutans streptococci adhering to immobilized oral bacteria, play a role in biofilm formation (Lamont RJ et al.,1990). Interspecies interactions are crucial during the initial stages of biofilm formation.

6.7.2 Neutral Adhesion Interactions

The attachment of one species to a substrate may not always be influenced by another species’ attachment (Cowan MM et al.,1991, McEldowney S et al.,1987). Neutral interactions could result from separate binding sites on the substrate for each species, including multiple high- and low-affinity sites within species (Gibbons RJ et al.,1983, Korber DR et al.,1994). For example, a nonmotile mutant strain of Pseudomonas fluorescens attached to glass independently of the parent strain, suggesting different binding sites (, Korber DR et al.,1994). Adhesion interactions depend on the surface and species involved (McEldowney S, Fletcher M et al.,1987), leading to variations in adhesion mechanisms for different substrates. Vibrio proteolytica’s adhesion to hydrophobic substrates was inhibited by proteases, while hydrophilic substrates were unaffected (Paul JH et al.,1985).

6.8 Commensal Interactions in Biofilm Stabilization

One intriguing aspect of biofilm stabilization is that it can be seen as a commensal interaction, where one species benefits from another’s ability to form a stable film.

6.8.1 Types of Commensal Interactions in Biofilms

Commensal interactions in biofilms occur when one population benefits without affecting the other. Oxygen consumption by aerobic/facultative microorganisms creates oxygen gradients, enabling the growth of obligate anaerobes (Costerton JW et al.,1994,De Beer D et al.,1994, Lewandowski Z et al.,1994). This interaction is crucial for sulfate-reducing bacteria growth in anaerobic microniches, contributing to microbially-induced corrosion (Hamilton WA. et al.,1985, Lee W, Lewandowski Z et al.,1993).

6.8.2 Commensalism in Dental Plaque Development

In dental plaque development, commensalism involving oxygen consumption occurs, with aerobic bacteria declining, and anaerobic Veillonella spp. predominating in deeper layers, while aerobic species dominate upper layers (Ritz HL et al.,1967 1969). Also in waste-water treatment biofilms, layering of aerobic and anaerobic bacterial species illustrates commensal interactions (Alleman JE, Veil JA et al.,1982). Other commensal interactions like substrate provision may be common in biofilms but require further research (Ritz HL et al.,1967).

7. Symbiotic Relationships and Enhanced Growth in Bacterial-Associated Algal Biofilms

Bacteria initiate EPS matrix formation in algal biofilms, leading to symbiotic relationships and competition with algae (Davis LS, Hoffmann JP et al.,1990, Mack WN et al., 1975). Studies show significant benefits of bacterial presence for algal recruitment and growth (Irving TE et al.,2011, Hodoki Y et al.,2005, Sekar R et al., 2004, Holmes PE et al., 1986). Algal biomass increases with rising pre-conditioned bacterial biofilm concentrations (Hodoki Y et al.,2005). Mixed community biofilms exhibit higher algal growth compared to pure algal cultures (Holmes PE et al., 1986).

Algae biofilms in non-sterile wastewater show increased thickness, switch to a sessile state, and resist shear stress better due to bacteria and EPS presence (Irving TE et al.,2011).Irving and Allen (Irving TE et al.,2011) demonstrated a nine-fold increase in algae biofilm thickness when grown on non-sterile secondary wastewater effluent compared to sterile wastewater. They also found that in the presence of unsterile wastewater, algae cells had a greater tendency to switch from a planktonic (free-floating) to a sessile (attached) state and exhibited enhanced resistance to shear stress.

Fig 8 Bacterial association with microalgae

8. Impactful Roles of Biofilm in Chemistry and Environmental Restoration

Biofilms are valuable in chemical synthesis processes, including ethanol, poly-3-hydroxybutyrate, and benzaldehyde production (Kunduru and Pometto, 1996; Li et al., 2006; Zhang et al., 2004). They also play essential roles in wastewater treatment, phenol bioremediation, and the degradation of dinitrophenols and toxic metals in environmental remediation (Lendenmann et al., 1998; Luke and Burton, 2001; Nicolella et al., 2000; Singh and Cameotra, 2004). Biofilms are highly resilient and serve as valuable tools for beneficial purposes in various chemical processes and environmental applications.

9. Conclusion

Biofilms represent dynamic and well-organized microbial communities that play a vital role in various ecological and industrial processes. They form through a complex developmental process, transitioning bacteria from a free-floating state to sedentary, multi-layered communities. The formation of biofilms involves various factors, such as surface characteristics, chemotaxis, and horizontal gene transfer, which contribute to the unique three-dimensional architecture and stability of these communities.
Interspecies interactions within biofilms further enhance their complexity, leading to commensal relationships and symbiotic associations that benefit different microbial species within the community. Bacteria initiate biofilm formation, and their presence fosters the recruitment and growth of algae, creating symbiotic relationships within mixed community biofilms.
The significance of biofilms extends beyond microbial interactions, as they also find applications in chemical synthesis and environmental restoration. Biofilms play crucial roles in wastewater treatment, bioremediation of contaminated sites, and the production of various chemicals, showcasing their potential as valuable tools for beneficial purposes.
Overall, the study of biofilms provides valuable insights into the intricacies of microbial communities, their interactions, and their adaptability to diverse environments. Understanding biofilm formation and behaviour can lead to the development of innovative strategies for improving industrial processes, environmental management, and human health. As researchers delve deeper into the world of biofilms, they uncover the fascinating intricacies of these dynamic microbial communities and their impact on the ecosystem and human activities.

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Algal Biotechnology

Microalgae: A Powerful Tool for Climate Change and Water…

July 4, 2023July 7, 2023
by everflow

Global climate change has emerged as a pressing global issue in contemporary times. The primary contributors to this phenomenon are the rising levels of greenhouse gases, predominantly originating from human activities and the operations of power plants (Watanabe Y, et., al; 2017).

Human activities, such as fossil fuel usage and industrial production, as well as natural processes involving the Earth’s oceans, soil, plants, animals, and volcanoes, release greenhouse gases, including CO_2, CH₄, and N₂O, into the atmosphere. However, since the Industrial Revolution, human activities have emerged as the primary contributors to greenhouse gas emissions (Baba Mohammad et al., 2015; Mirzaei et al., 2015).

Specific Sources of CO₂ Emissions

According to Le Quere (Le Quere et al. 2013, 2015), the combustion of fossil fuels, namely coal, natural gas, and oil, is responsible for about 87% of human-produced CO₂emissions. Among these fuels, coal combustion contributes to 43% of CO₂ emissions from fuel burning, followed by oil at 36% and natural gas at 20%. Power plants, vehicles, aircraft, and industrial facilities primarily use these fossil fuels to generate heat, electricity, and power. The largest share of man-made CO₂emissions, approximately 41%, originates from power generation and heating activities. Transportation ranks as the second largest source, accounting for around 22% of CO₂ emissions resulting from fossil fuel burning. Industries contribute approximately 20% of CO₂ emissions from fossil fuel combustion. Other human-related sources include deforestation and land-use changes, contributing to roughly 9%, and industrial processes like cement manufacturing, which account for around 4%.

The emission of CO₂ into the atmosphere involves not only human activities but also natural processes. According to a study conducted by Denman et al. In 2007, researchers found that natural sources significantly contribute to CO2 emissions. The Earth’s oceans, through the exchange between the ocean and the atmosphere, account for a substantial 42.84% of these natural emissions. Additionally, sources like plant and animal respiration, soil respiration, and decomposition contribute to 28.56% of the total CO₂ emissions generated naturally.

CO₂: A major Green House Gas

Research efforts are ongoing and focused on tackling global warming by actively mitigating greenhouse gas emissions. While carbon dioxide naturally exists as a greenhouse gas, the concentration of CO₂in the atmosphere has undergone a substantial increase because of industrialization and human activities (National Research Council et al.,2011; Siegenthaler U et al., 2005; Chang EH et al, 2003).

According to a report by the French National Center for Scientific Research, atmospheric CO₂levels have soared to 380 parts per million (ppm), marking a twofold increase compared to the previous century (Morais and Costa, et al.,2007). The notable surge in CO₂ concentration directly attributes to the combination of population growth and industrialization. Future projections indicate that by 2100, CO₂ emissions in the atmosphere could reach a staggering 26 billion tons, surpassing the emissions recorded in the past century by 18.5 billion tons (Chiu et al., 2008).

Power plants play a significant role in releasing CO₂ into the atmosphere through the combustion of fossil fuels (Benemann JR et al., 1993). To tackle the challenge of CO₂ emissions from this source, it is imperative to prioritize efforts in enhancing the efficiency of power plant generation and transitioning towards cleaner and more sustainable alternatives.

Biological CO₂ Sequestration Technology/Method

In 1990, the Research Institute of Innovative Technology for the Earth (RITE) launched the Biological CO₂ Fixation and Utilization Project under the sponsorship of the Ministry of International Trade and Industry (MITI). The New Energy and Industrial Technology Development Organization (NEDO) commissioned this pioneering initiative (Murakami, N, et al., 1996).

Among the array of available CO₂ capture methods, the biological approach stands out as an attractive alternative. This approach harnesses the power of photosynthesis, which enables the conversion of carbon dioxide into organic matter, fueled by sunlight as an energy source. In this regard, photosynthetic microorganisms have emerged as a preferred choice, owing to their remarkable characteristics. These microorganisms possess the unique ability to assimilate CO₂ into carbohydrates, lipids, and proteins using solar energy. They exhibit higher rates of CO₂ fixation compared to land plants and offer better compatibility for integrating CO₂ removal systems into industrial processes when compared to other photosynthetic systems involving higher plants.

Algae potential players for CO₂ Sequestration.

Within the realm of photosynthesis, there are two fundamental processes at play: the light-dependent reaction, which entails a series of intricate steps reliant on the availability of light, and the light-independent reaction, also recognized as carbon fixation. In the context of microalgae, they have developed a specialized mechanism known as the CO₂concentrating mechanism (CCM) to secure an ample reservoir of inorganic carbon required to support cellular growth and proliferation during the process of photosynthesis (Brueggeman et al., 2012).

The CO₂concentrating mechanism (CCM) plays a crucial role in microalgae by effectively increasing the concentration of CO₂ at the active site of the enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase oxygenase). These microorganisms possess specialized inorganic carbon transporters located in the plasma membrane and thylakoid membrane, each with varying affinities and flux rates for HCO₃ (bicarbonate) and CO₂ (Beardall and Raven, 2017). Carbonic anhydrase (CA) is responsible for converting HCO₃ into CO₂, and the proper functioning of both CA and the CCM is highly dependent on the availability of CO₂ (Zou et al., 2004; Zhou et al., 2016) See Fig 1.

Carbon-capture-mechanism-CCM-by-algae for climate change

As a result, the availability of CO2 intricately ties to the activity of these enzymes. While elevated CO₂ levels can promote the growth of algae, they may also impede the activity of carbonic anhydrase (CA) and the functioning of the CO₂concentrating mechanism (CCM) (Xia and Gao, 2005).

Microalgae surpass terrestrial plants in their efficiency in converting CO₂ into organic compounds. They exhibit approximately 10 times greater efficacy in CO₂ fixation compared to land plants.

Algae cultivation in Wastewater an alternative approach for wastewater treatment & CO₂Sequestration.

The combination of biological CO₂ fixation using microalgae and wastewater treatment presents significant advantages in terms of both economic feasibility and environmental sustainability. By cultivating microalgae in nutrient-rich wastewater, these microorganisms have ample access to the nutrients needed for their growth. As they flourish, microalgae absorb CO₂ and convert it into biomass, which can be utilized as a valuable feedstock for biofuel production (Kannan DC et., 2022, Magar et al., 2022).

The integration of CO₂ capture, wastewater treatment, and biofuel production creates a synergistic and compelling approach. It not only contributes to reducing CO₂ emissions by capturing and utilizing CO₂ but also addresses the crucial requirement for effective wastewater treatment. This combined strategy demonstrates a promising solution that not only helps mitigate climate change but also promotes the efficient utilization of resources while generating a valuable end product (Wang B et al., 2008).

The integration of microalgae in wastewater treatment presents a sustainable and eco-conscious solution that minimizes or eliminates the requirement for chemical treatments in wastewater plants. This groundbreaking technology utilizes the inherent abilities of microalgae to effectively extract nutrients, specifically nitrogen and phosphorus compounds, from wastewater. In addition to facilitating CO₂ capture through photosynthesis, this approach successfully tackles the pressing challenge of nutrient removal in wastewater.

Mechanism of Microalgae-based Wastewater Treatment

Microalgae offer an invaluable solution to address the challenge of microcontaminants found in wastewater effluents, which can pose significant risks when they enter drinking water treatment processes (Beelen ES et al., 2007). By efficiently eliminating these microcontaminants, microalgae greatly improve the overall quality of water. Additionally, microalgae play a vital role in reducing nutrient levels, such as carbon, nitrogen, and phosphorus, while simultaneously releasing significant amounts of oxygen. This dual action not only aids in the decomposition of organic matter by bacteria but also helps mitigate odor-related issues commonly associated with wastewater (De Pauw N et al., 1983).

The abundant availability of nutrients in municipal wastewater makes it an ideal resource for harnessing the potential of microalgae. Furthermore, the close proximity of wastewater treatment plants to power plants, which generate significant amounts of CO₂ in flue gases through the combustion of fossil fuels, further emphasizes the benefits of this approach. This strategic positioning enables the efficient utilization of readily available CO₂ resources.

Microalgae cultivation in wastewater presents versatile opportunities, allowing for the use of either open or closed systems. These approaches enable precise control over the growth media, optimizing the removal of nutrients from wastewater and maximizing the production of valuable microalgae biomass. This customized approach ensures effective and sustainable wastewater treatment while generating valuable resources in the form of microalgae biomass.

Open ponds

High-rate algal ponds, commonly known as HRAPs or raceway ponds, are the prevailing large-scale production systems in practice. These open, shallow ponds have been employed since the 1950s and utilize a paddle wheel to ensure the circulation of algae and nutrients. While raceway ponds are relatively affordable to construct and operate, their productivity is often hindered by challenges such as contamination, inadequate mixing, the presence of dark zones, and inefficient utilization of CO₂ (Chisti, 2007; Mata et al., 2010).

In theory, raceway ponds should achieve production levels of 50–60 g m−2 day−1, and there have been instances of reaching such levels in a single day (Sheehan et al., 1998). However, in practical applications, it proves difficult to attain even 10–20 g m−2 day−1 productivity (Shen et al., 2009). While the high evaporation rate of open ponds is often perceived as a limitation, it does provide some benefits by aiding in temperature regulation through evaporative cooling (U.S. DOE, 2010).

Moreover, the HRP system’s simplicity and symbiotic nature make it a perfect candidate for emulating natural ecosystems in laboratory and field settings, aligning harmoniously with the principles of ecological engineering (Cunningham M et al., 2010).

An important conclusion drawn from cost analysis studies conducted by the U.S. Department of Energy’s Aquatic Species Program was that there are limited prospects for alternative systems to replace the open pond approach, particularly when considering the need for low fuel costs (Sheehan et al., 1998).

Closed reactors

According to Chisti (2007), tubular photobioreactors are the exclusive type of closed systems used on a large scale. These reactors come in vertical, horizontal, and helical designs, with helical ones being regarded as the easiest to expand (Carvalho et al., 2006). In comparison to open ponds, tubular photobioreactors offer several advantages such as improved control over pH and temperature, better protection against contamination, enhanced mixing, reduced evaporation, and higher cell densities (Mata et al., 2010).

Reported productivities typically range from 20 to 40 grams per square meter per day (Shen et al., 2009). However, despite these benefits, tubular reactors have not gained significant usage due to various challenges. Issues such as the accumulation of toxic oxygen, unfavorable pH and CO₂ gradients, overheating, bio-fouling, and high material and maintenance costs have limited their widespread adoption (Mata et al., 2010; Molina Grima et al., 1999). Among these challenges, the removal of oxygen is considered one of the most difficult problems to overcome, particularly when scaling up the system. It effectively imposes limitations on the length of tubes or panels and necessitates a more complex or modular design (Carvalho et al., 2006

How Algae CO₂Sequestration Potential is Calculated?

To tackle the challenge of reducing CO₂ emissions, researchers have explored various avenues, which can be broadly divided into two groups: (i) methods based on chemical reactions and (ii) biological methods (Benemann JR et al., 1993, Wang B et al.,2008). Among these, biological processes have emerged as compelling solutions to combat global warming, attracting significant attention from the scientific community (Yun YS et al., 1997).

Chisti emphasizes that microalgal biomass typically consists of around 50% carbon, allowing for the capture of approximately 1.83 kg of CO₂ per kilogram of biomass produced (Chisti et al., 2007). In the field of CO₂ capture using microalgae, many studies rely on measuring CO₂ concentrations at the inlet and outlet of cultivation reactors. However, this approach may pose challenges as it does not guarantee that all consumed CO₂ is solely attributed to the growth of microalgae. Alternatively, estimating the carbon content can provide a more precise assessment of the CO₂ consumption by microalgae cells, assuming that the culture medium does not contain carbon sources other than CO₂ (Yun YS et al., 1997; Tang D et al., 2011).

Based on this premise, researchers can estimate the rate of CO₂ capture (RCO₂) using the following formula.

RCO₂ = P·CCO₂·MCO₂/MC,

where P represents biomass productivity (g L-1 day-1), CCO₂ denotes the carbon content of microalgae biomass obtained from CO₂, and MCO₂and MC correspond to the molecular weights of carbon dioxide and carbon, respectively.

CO₂ concentration and CO₂ uptake efficiency of Microalgae

The cultivation of photoautotrophic microalgae relies on carbon dioxide (CO₂) as the primary source of carbon. Despite the physiological significance of CO₂ concentration on microalgae cell growth, researchers have conducted limited research to analyze CO₂ uptake under relevant process conditions, indicating the need for further investigation (Cheng L et al., 2006). Atmospheric air contains minimal amounts of CO₂, which cannot sufficiently support microalgae cell growth due to limited mass transfer driving forces. To overcome this challenge, researchers can obtain CO₂ from pure sources or harness it from flue gases, thereby addressing the environmental concern associated with CO₂ capture (Acién Fernández FG et al., 2012).

Microalgae and cyanobacteria have the ability to adapt their photosynthetic properties, including the carbon concentrating mechanism (CCM), to high concentrations of CO₂ (Baba et al., 2011). Certain microalgae and cyanobacteria species, such as Chlamydomonas reinhardtii, can quickly acclimate to a CO₂ concentration of 20% within a few days (Hanawa et al., 2007).

When developed at air-equilibrated CO₂ levels, microalgae and cyanobacteria can effectively utilize low levels of dissolved inorganic carbon (DIC). Cyanobacteria actively increase calcite deposition at higher CO₂ concentrations, which plays a crucial role in CO₂ removal. This increase leads to a 1.5- to 2.5-fold enhancement in CO₂ fixation rates (Ramanan et al., 2009, 2010; Badger and Price, 1994).

Enhancing CO₂Mass Transfer with Microbubbles

Some of the important physical factors that change the mass transfer rate of CO₂ from the air to liquid are air bubble size, the pore size of the sparger, flow rate, air holding time of the liquid system, etc. Microbubble size is a very essential aspect to enhance the CO₂ mass transfer rate (McGinn PJ et al., 2011). However, high CO₂ concentrations hinder the growth of microalgae and cyanobacteria (Ramanan et al., 2010).

Previous research has reported that optimal CO₂ fixation occurs at concentrations ranging from 2% to 5% CO₂, with 3% CO₂ being approximately 489 times higher than the atmospheric CO₂concentration (Douskova et al., 2009; Ibn-Mohammed et al., 2013). These studies indicate that many algal strains may not require undermined haphazard high CO₂ feeding. Excess-supplied CO₂ mostly goes to waste, and it is necessary to determine the critical CO₂ concentration required by each strain.(Chaitanya Magar et al. 2019, Rambhiya, S. J. et al 2021).

Conclusion

In summary, the utilization of microalgae cultures presents a promising solution for both CO₂capture and biomass production. By cultivating microalgae in wastewater media, it becomes possible to remove significant pollutants from the wastewater while efficiently capturing CO₂ and converting it into valuable biomass feedstock. The selection of suitable algae strains and optimization of key parameters such as pH, temperature, and CO₂concentration is crucial in maximizing CO₂ fixation efficiency in biological systems. Certain algae species, such as Scenedesmus dimorphus, Scenedesmus incrassatulus, Chlorella sp., and Scenedesmus obliquus, demonstrate remarkable CO₂ fixation rates.

Moreover, integrating CO₂ capture from flue gases with microalgae-based wastewater treatment holds immense potential for sustainable biofuel production. This integrated approach offers the opportunity to address environmental concerns by capturing CO₂ emissions, treating wastewater, and producing valuable biofuel resources concurrently. To enhance the efficiency and effectiveness of microalgae cultivation, the development of comprehensive dynamic models becomes essential. These models should accurately depict the growth rates of microalgae under various limiting factors, enabling the design of optimized control systems and the identification of optimal operational conditions.

By advancing our understanding of the complex interactions and dynamics involved in microalgae-based systems, we can unlock the full potential of this technology. Ultimately, this will contribute to reducing reliance on fossil fuels, mitigating CO₂ emissions, and promoting a more sustainable and environmentally friendly approach to energy and wastewater management.

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Kannan DC, Magar CS. Microalgal biofuels: Challenges, status and scope. InAdvanced Biofuel Technologies 2022 Jan 1 (pp. 73-118). Elsevier.

XIA JR, GAO KS. Impacts of elevated CO₂ concentration on biochemical composition, carbonic anhydrase, and nitrate reductase activity of freshwater green algae. Journal of Integrative Plant Biology. 2005 Jun;47(6):668-75.

Wang B, Li Y, Wu N, Lan CQ. CO₂ bio-mitigation using microalgae. Applied microbiology and biotechnology. 2008 Jul;79:707-18.

Beelen ES. Municipal wastewater treatment plant (WWTP) effluents: a concise overview of the occurrence of organic substances. Association of River Waterworks-RIWA; 2007.

De Pauw N, Van Vaerenbergh E. Microalgal wastewater treatment systems: potentials and limits. Phytodepuration and the Employment of the Biomass Produced. Centro Ric. Produz, Animali, Reggio Emilia, Italy. 1983:211-87.

Chisti Y. Biodiesel from microalgae. Biotechnology advances. 2007 May 1;25(3):294-306.

Mata TM, Martins AA, Caetano NS. Microalgae for biodiesel production and other applications: a review. Renewable and sustainable energy reviews. 2010 Jan 1;14(1):217-32.

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Carvalho AP, Meireles LA, Malcata FX. Microalgal reactors: a review of enclosed system designs and performances. Biotechnology progress. 2006;22(6):1490-506.

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Acién Fernández FG, González-López CV, Fernández Sevilla JM, Molina E. Conversion of CO 2 into biomass by microalgae: how realistic a contribution may it be to significant CO₂removal?. Applied microbiology and biotechnology. 2012 Nov;96:577-86.

Baba M, Suzuki I, Shiraiwa Y. Proteomic analysis of high CO₂inducible extracellular proteins in the unicellular green alga, Chlamydomonas reinhardtii. Plant and cell physiology. 2011 Aug 1;52(8):1302-14.

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Chaitanya Magar, Sagar Rambhiya and Manjushri Deodhar, 2019. Evaluation of CO₂Removal Efficiency of Pseudanabaena limnetica (Lemm.) Komárek Grown in Na₂CO₃Enriched Seawater Medium in 60 L Airlift Flat Panel Photobioreactor. Journal of Environmental Science and Technology, 12: 186-196. DOI: 10.3923/jest.2019.186.196 (URL: https://scialert.net/abstract/?doi=jest.2019.186.196)

Photobioreators (PBRs)

An Advancements in Algae Cultivation: A Vital Component of…

June 3, 2023June 24, 2023
by everflow

Introduction and History of Commercial Algae Cultivation:

Algae’s usefulness in food, nutrition, and a variety of other industrial applications has long been recognized. With the rising demand for alternative energy sources, promising applications of algal biomass in biofuel generation have grown in significance. Apart from that, the issue of climate change and rising GHG emissions has driven the market for microalgae-based CO2 sequestration approaches in recent years. This has resulted in highly distinctive innovations in the algae business for improved mass culture. However, it is always interesting to examine the evolution and technological interventions that have occurred in the algae cultivation industry.

People in several parts of the world have been consuming microalgae and seaweed as a major food source for many centuries. Around 2000 years ago, the Chinese population solved the hunger issue by eating Nostoc, as documented by Janssen et al. in 2002. In 1519, Spanish scientist Hernando Cortez and Conquistadors discovered the microalgae Arthrospira platensis (Spirulina). Initially, it was farmed in Mexico’s alkaline lakes and on the African continent, but now it is commercially grown and collected worldwide. Algae cultivation also occurred in other locations, such as Lake Texcoco in the Valley of Mexico, during the sixteenth century. In 1964-65, Jean Léonard reported the sale of greenish, edible cakes in the local markets of Fort-Lamy in Chad, Africa (Sow, S., & Ranjan, S. 2021). To promote economic recovery during World War II, Japan actively promoted the consumption of proteinaceous algae.

Market of Microalgae

Despite this extensive history, researchers have only domesticated and produced a few wild microalgae species for human food and/or usage. These include Arthrospira platensis (Spirulina), Chlorella vulgaris (Chlorella), and Aphanizomenon. Until a few decades ago, nature’s water bodies rich in naturally growing microalgae were the only sources of consumable microalgae. However, microalgae culture, or artificial farming, is now performed worldwide, and the development of biotechnology to cultivate microalgae began in the middle of the last century (Wang, Y., et al 2021, Spolaore et al. 2006).

According to the research conducted by Dogma Jr. et al. in 1990, Asian countries have always been well known for their significant algae production for food purposes. In the 1980s, Naylor (1976) determined the production of seaweed by various Asian countries. Their estimate revealed that Japan, China, and Korea ranked at the top of the producers list, collectively producing 1,733,500.0 mt of seaweed. Conversely, the Philippines, Indonesia, and India were identified as low producers, with a combined production of approximately 28,000.0 mt of seaweed. During the 1980s, these Asian countries emerged as the major seaweed producers.

Development of the Algae Industry:

In the decades from 1940 onward the development of the algae cultivation industry occurred in the following chronology:

The year 1940-1950 – Beginning of commercial algae cultivation projects in European and Asian countries.
The year 1950-1960 – The issues first encountered and resolved into the practical aspects of mass cultivation involved essential nutrients, vigorous mixing, and the supply of CO₂.
The year 1960-1970 – Development in the design and operation of open ponds for mass cultivation and protein-rich microalgal biomass.
The year 1970-1980 – R&D for algae for biofuels and Production of algal biomass on a large scale. Growth of the market for algae-based products in Western countries.
The year 1980-1990 – Research on emerging products from algae biomass in pharmaceuticals, nutrients, cosmetics, biofuels, etc. Government agencies started supporting R&D programs for biofuels.
The year 1990-2000 – Development of a novel product market for algae-based products and commercial production of algal biomass for food, nutrition, and pharma applications.
The year 2000-2010 – Researchers primarily focused on researching mass algae cultivation based on photobioreactors and hybrid cultivation systems. They successfully developed novel algae cultivation systems and demonstrated their potential.
The year 2010-2020 – Development of newer industries in the algae sector. Importance algae in air and water treatment introduced along with biofuel production.
The current decade (2020-2030) – Novel emerging technology development for algae-based climate mitigation solutions is taking place. Emerging innovators and investors started developing GHG mitigation solutions along with multiple biofuels and cleantech options.

World Scenario of Algae Technology:

Human diets, functional components, cosmeceuticals, medicines, animal and aquaculture feeds, fatty acids, alginates, carotenoids, wastewater treatment, and biofuels are just a few of the biological and industrial applications for microalgal species. Companies sell cyanobacteria Arthrospira sp., and Chlorella vulgaris not only as protein-rich food ingredients and supplements but also as functional foods, and they generally regard them as safe (GRAS). Because of their high vitamin, mineral, and carotenoid concentrations. While annual global microalgae production is currently modest (5.0 104 tonnes dry matter) in comparison to macroalgae (seaweeds) production (7.5 106 tonnes dry matter), microalgae biomass and bio-actives extracted from it are of great nutritional and economic importance (values at USD 1.25 109 annually).

Importantly, researchers have yet to research, let alone commercialize, the vast majority of the tens of thousands of distinct species that make up the big, polyphyletic group of microalgae. As a result, there is enormous potential in researching and developing microalgae as sources of high-quality, sustainable protein for human meals and dietary supplements (www.bsb.murdoch.edu, McGill 2008, Javed and Farooq, 2013, Sankpa and Naikwade, 2013, Sarwer, A., et al. 2022).

Algae cultivation systems:

Algae can be cultivated in various types of systems, ranging from simple open ponds to complex photobioreactors. These systems have the potential to revolutionize the way we produce algae-based food, energy, and products while mitigating some of the environmental impacts associated with traditional production methods. In this article, we will explore various types of algae cultivation systems, and how they work on a large scale.

Algae cultivation systems are vessels that hold water as a medium and nourish algae by exposing them to plenty of light, which facilitates photosynthesis.

The basic algae cultivation system is equipped with:

Growth Vessel: The cultivation vessel with a larger surface area to receive maximum light energy. (Pond Height ≤30cm, Tube ID≤20cm) (Yadala, S., & Cremaschi, S. 2016, Torzillo, G., & Chini Zittelli, G. 2015)
Agitation: Mechanical or pneumatic way of vigorous agitation provided with baffles to avoid dead zones inside the system due to lack of proper agitation (de Souza Kirnev, P. C., et al. 2022)
Light Source: Suitable Natural or Artificial light source supplying Photosynthetic Photon Flux Density in the range of 26−700 µmol photons m⁻² s⁻¹ (Maltsev, Y. et al. 2021)
Nutrient Source: Providing necessary nutrients for large-scale algae cultivation projects is a challenging task. Algae Production utilizes mostly inorganic fossil-based NPK fertilizers for the same purpose, but the ever-increasing demand and decreased production could lead to fertilizer scarcity in the future.
CO₂ Supplementation: Traditionally, photoautotrophs obtain their major carbon source from dissolved CO2, which researchers supply by pneumatically feeding ambient air mixed with or without pure industrial CO2 gas.

Researchers develop algae cultivation systems that range from laboratory-scale experimental studies to outdoor massive production, depending on the scale. For laboratory-scale systems, they mostly use borosilicate glass, which is readily autoclavable for aseptic experimental studies. Additionally, researchers can utilize outdoor cultivation vessels that range from a simple open pond to a complex closed photobioreactor, based on the requirements of the algae strain being grown and the desired final product. The flowchart below presents a clear idea of the types of algae cultivation systems, which researchers classify based on the construction scale and the light source they utilize.

Laboratory Scale Algae Cultivation Systems

The successful algae cultivation process starts from a laboratory-scale inoculum development process that involves the transfer of unialgal or even axenic culture of algae from a sterile environment to outdoor non-sterile conditions in a step-by-step manner. This involves the utilization of smaller-level sterile glass liquid vessels like tubes, flasks, and bottles to some liter capacity laboratory scale PBR systems (Borowiak, D., et al.2020). Apart from scaleup, the laboratory-scale algae cultivation system with artificial light illumination can be a highly useful tool for experimentation and research purposes. In order to ensure the system is both efficient and effective, it is important to consider certain factors such as the lighting system and the autoclavability of the equipment.

1. All kinds of glass vessels to grow liquid cultures in a sterile condition

They are preferred over other materials because of their transparency, durability, and ease of cleaning. Here are some common types of glass vessels used in algae cultivation:

Culture Tubes:

Culture tubes have a straighter shape and a smaller volume. These systems are utilized for growing small volumes of algae in a sterile environment, serving as the initial transition point for transferring algal cells from a spent solid growth medium to a fresh sterile liquid medium.

Erlenmeyer Flask:

This is a conical-shaped glass vessel with a narrow neck and a wider base. The narrow neck helps to reduce evaporation and contamination. Researchers commonly use Erlenmeyer flasks for small-scale cultures of algae in the laboratory. These flasks are typically either screw-capped or covered with cotton to ensure the maintenance of internal sterile conditions.

Carboys:

Carboys are large glass containers with narrow necks and wide bases. They are used for growing large volumes of algae in a sterile environment. They are particularly useful for industrial-scale algae cultivation.

Fernbach Flask:

Fernbach flasks have a wider base and a shallower depth than Erlenmeyer flasks. They are used for growing algae cultures that require a lot of aeration, such as those that produce high levels of oxygen.

Bell Jars:

Researchers use bell jars, which are glass domes, to cover Petri dishes or other small glass vessels. These bell jars are employed to establish a sterile environment for growing algae cultures on a small scale.

Regardless of the type of glass vessel utilized, it is crucial to ensure proper cleaning and sterilization before use to prevent contamination of the algae culture. Due to their small sizes, researchers can easily clean, wash, and sterilize them using laboratory equipment. Therefore, basic laboratory glassware has become an important vessel for algae cultivation. As the scale-up process progresses in algae cultivation, larger systems are required to accommodate higher volumes of algae. The required systems for algae cultivation include the following: (Wikipedia contributors. 2023, February 1).

2. Cylindrical glass vessels

The cylindrical glass vessels, which are bioreactors made of glass, come equipped with the necessary provisions for agitation, temperature control, light illumination, aeration (CO2), and pH. These bioreactors provide a controlled environment for algae cultivation, allowing researchers to optimize the growth conditions and maximize productivity. They are generally of ≤20cm internal diameter making a light path length of 10cm when illuminated from all directions externally as per the standard recommended limit for light penetration. They are mostly illuminated externally with artificial light sources which can be regulated as per the need of the microalgal species growing in it.

This type of system is either mechanically or pneumatically agitated (or with the help of both options) depending upon the shear tolerance and aeration requirement of the microalgae in consideration. They provide optimal conditions for laboratory-scale studies to monitor the effect of light, temperature, and nutrients on algal biomass production as well as their primary and secondary metabolites. They can construct these cylindrical bioreactors to hold different volumes, ranging from milliliters to liters. However, for laboratory-scale studies, it is always operationally feasible to use cylindrical bioreactors with volumes less than 1L.

3. Glass Flat Panels

Glass Flat Panels are another essential type of laboratory-scale algae cultivation system. These panels serve as a thin clamber holding algae between two plates that offer a wide surface area for maximum light exposure for photosynthesis. The light path length through a flat panel is ≥10cm preferred when illuminated from one side. This could be doubled if illuminated from both sides. To ensure accurate experimentation, the panels must be able to withstand the conditions of the cultivation process, including exposure to artificial light and autoclaving.

Glass Panels for algae cultivation have the ability to withstand high temperatures and pressures during autoclaving. Therefore, researchers construct most flat panel systems using borosilicate glass materials and stainless-steel framing to create sturdy models for frequent sterilization processes. Due to its larger surface area, the flat panel system earns recognition for its exceptional light illumination capability. Researchers favor it for conducting experiments that examine the effects of varying light intensities and types on algal growth, lipid production, nutrient consumption rate, and photoinhibition studies.

Open Systems

An open system of algae cultivation involves the growth of algae in open shallow water streams which could be originating from the natural system or artificially prepared. In this system, researchers can cultivate algae in natural water bodies such as lakes, rivers, and oceans, as well as in artificial ponds constructed from concrete, plastic, pond liners, or a variety of materials. The open system of algae cultivation is simple and cost-effective, making it an attractive option for commercial production of algae-based products.

1. Water Lagoon

A lagoon, a type of aquatic ecosystem, is characterized by a shallow body of water that is separated from the open ocean using natural barriers such as sandbars, barrier islands, or coral reefs. An Australian company uses this algae cultivation system. Cognis Australia Pty Ltd is a well-known company that specializes in producing β-carotene from Dunaliella salina harvested from hypersaline extensive ponds located in Hutt Lagoon and Whyalla. These ponds are primarily used for wastewater treatment, and the production of D. salina is a secondary benefit (Spolaore, P., et al. 2006, Curtain, C. 2000, Campbell, P. K., et al. 2009).

2. Open Sea Cultivation (Seaweed)

Open sea cultivation is a method of cultivating seaweed in the open ocean, as well as on a coastal line in shallow water. The seaweed farming industry serves commercial needs for various products such as food, feed, pharma chemicals, cosmetics, biofuels, and bio-stimulants. Seaweed extracts act as bio-stimulants, reducing biotic stress and increasing crop production. Additionally, it presents opportunities for creating animal and human nutrition products that can improve immunity and productivity. Open ocean seaweed cultivation is an eco-friendly technology that doesn’t require land, fresh water, or chemicals. It also helps mitigate the effects of climate change by sequestering CO2.

The open sea cultivation method involves the use of rafts or ropes anchored in the ocean, where the seaweed grows attached to them. This method is widely used for commercial seaweed farming, as it allows for large-scale production and harvesting. The process of open sea cultivation of seaweed involves several steps. First, the intender identifies a suitable site in the ocean based on factors such as water depth, temperature, salinity, and nutrient availability. Once they choose a site, they anchor ropes or rafts in the water and attach seed pieces of seaweed to them using specialized equipment. The seaweed is then allowed to grow for several months, absorbing nutrients from the water and sunlight through photosynthesis. (Peteiro, C., et al. 2014).

3. Raceway Ponds

One of the most common and economic methods of large-scale algae cultivation is in open raceway ponds, which offer several advantages over other cultivation methods. An open raceway pond is a shallow, rectangular-shaped pond used for the cultivation of algae. Because it is designed to circulate water in a continuous loop or raceway, allowing algae to grow in a controlled environment. Open System is a low-cost method of algae cultivation, and it is relatively easy to construct and maintain. Researchers typically line the pond with a synthetic material, such as polyethylene (HDPE) or polyvinyl chloride, to prevent the loss of water and nutrients. They also equip the pond with paddlewheels or other types of mechanical devices to provide mixing and aeration (Klein, B., & Davis, R. 2022).

4. High Rate Algal Ponds (HRAPs)

High-Rate Algal Ponds (HRAPs) are a type of open algae cultivation system that has gained popularity in recent years due to their efficiency and low cost of operation. HRAPs (High Rate Algal Ponds) are shallow ponds, usually ranging from 0.1 to 0.4 meters deep, utilized for cultivating algae. Researchers equip these ponds with a paddlewheel or another type of mechanical agitation system to provide mixing and aeration, thereby facilitating algae growth. The use of HRAP systems is also recommended in wastewater treatment involving algae (Mehrabadi, A. et al. 2015, The Local Government Association-LGA of South Australia).

5. Revolving Algal Biofilm Reactor (RABR)

The use of revolving disks of polystyrene to produce algal biofilm to reduce nitrogen and phosphorus in municipal wastewater was originally described in the 1980s. (Przytocka-Jusiak et al., 1984). The goal of this research was to create a rotating algal biofilm (RAB) growing method that microalgae producers could use to easily harvest biomass. Algal cells grew on the surface of a substance that alternated between a nutrient-rich liquid phase and a CO₂-rich gaseous phase. Scraping biomass from the connected surface saved costly harvesting operations like centrifugation. Cotton sheets outperformed all other attachment materials in terms of algal growth, durability, and cost-effectiveness. Harvest frequency, rotation speed, and CO₂ levels were further tuned in a lab-scale RAB system.

The water content of the algal biomass from the RAB system was comparable to that of centrifuged biomass. When compared to a control open pond, an open pond raceway retrofitted with a pilot-scale RAB system resulted in significantly higher biomass productivity. The research indicates that the RAB system is an efficient algal culture system for convenient biomass harvesting and increased biomass productivity (Gross, M., et al. 2013).

RAB Systems by Gross-Wen Technologies:

Currently, industries primarily perform algal cultivation in open ponds or photobioreactors, where they suspend algal cells and harvest them through flocculation and centrifugation. They recently developed a novel attachment-based Revolving Algal Biofilm (RAB) culture system that enables easier biomass harvest and increased biomass productivity. The goal of this study was to assess the efficacy of the RAB system at the pilot scale (durability, algae growth, and shape). The RAB system was successfully tested for a year at a greenhouse plant in Boone, Iowa, USA. The RAB increased biomass productivity by 302% on average when compared to a typical raceway pond, with a maximum biomass productivity (ash free) of 18.9 g/m2-day achieved. The vertical RAB outperformed the triangle RAB in terms of productivity. The research reveals that the RAB, as an efficient algal growing method, has a high potential for commercialization. (Gross, M., & Wen, Z. 2014)

Productivity:

Gross-Wen Technologies have devised a Revolving Algal Biofilm (RAB) growth system, where they bond algal cells to a flexible material that undergoes rotation between liquid and gas phases. In this work, they created different configurations of the RAB system at pilot size by retrofitting the attachment materials to a raceway pond with a 2000-L capacity and an 8.5 m2 footprint area, as well as a trough reservoir with a 150-L capacity and a 3.5 m2 footprint area. The trough-based RAB system has a maximum productivity of 46.8 g m-2 day-1.

The RAB system shows higher water evaporation loss, the specific water consumption per unit of biomass generated was only 26% (raceway-based RAB) and 7% (trough-based RAB) of that of the control pond. This research demonstrates that the RAB system is an efficient algal culture system with a high potential for commercially producing microalgae with high productivity and efficient water use. (Gross, M., Mascarenhas, V., & Wen, Z. 2015).

Closed System- Photobioreactors (PBRs)

Closed systems or photobioreactors (PBRs) are commonly used in algae cultivation systems due to their numerous advantages over open pond systems. These systems are more efficient in terms of land and water usage and also provide greater control over environmental conditions, such as temperature, light, and nutrient supply. Two common types of closed PBRs are tubular and flat panel systems, but there are various designs and models suggested by many for the cultivation of different microalgae on a mass scale (Znad, H. 2020).

1. Tubular PBRs

Tubular PBRs consist of long, transparent tubes that are either vertically or horizontally oriented. Algae are grown inside the tubes, which are typically made of glass or plastic. The tubes are arranged in a helical or serpentine pattern to increase surface area for light exposure. The tubing can be either continuously or intermittently circulated to promote mixing and prevent stagnation. Researchers generally use tubular PBRs (Photobioreactors) for high-density cultivation and find them well-suited for species that require high light intensity. Controlling the temperature in tubular PBRs is a challenging task, typically accomplished by externally sprinkling deionized water. This sprinkling allows the tubes to cool down, subsequently reducing the temperature of the culture circulating inside them (Torzillo, G., & Chini Zittelli, G. 2015).

2. Flat panel PBRs

Flat panel PBRs (Photobioreactors) consist of researchers stacking a series of flat, transparent panels on top of each other to create a thin layer of liquid between them. They grow algae in this thin liquid layer while continuously circulating it to promote mixing and prevent stagnation. The panels, typically made of glass or plastic, can be arranged in various configurations to optimize light exposure. Researchers generally use flat panel PBRs for low-to-medium density cultivation and find them well-suited for species that require lower light intensity and maximum surface area for optimal light exposure. They control the temperature in the flat panel PBR system by cooling down the culture in the reservoir chamber using a chilled water jacket and by sprinkling cold water on the flat panel surface (Sierra, E. et al. 2008).

3. Plastic V-Shaped Bag

V-shaped plastic bags are commonly used in closed systems of algae cultivation for several reasons. These bags are made from high-density polyethylene (HDPE) and are designed to hold algae cultures in a closed environment, providing an ideal environment for algae growth. V-shaped plastic bags are effective for growing a variety of algae species, including Chlorella, Spirulina, and Nannochloropsis (Chen, Y. P., et al. 2021).

Chlorella vulgaris exhibited a higher growth rate and biomass yield when cultivated in V-shaped plastic bags compared to other-shaped plastic bags. Different designs of plastic bags based PBR are developed by sealing the plastic bags at different places that generated, flat bottom hanging plastic bags, V-shaped hanging plastic bags, horizontally laying plastic bags that serve the kind of flat PBR system, etc. Many plastics bag-based design is proposed but few are utilized on a commercial scale due to their productivity. The operation of plastic bags is tedious as they need to be replaced after every use to maintain sterility, which is a laborious task for large-scale facilities (Wang, B., et al. 2012, Huang, Q., et al. 2017).

Conclusion:

Algae cultivation technology is becoming an important commercial and economical asset in the algae mass cultivation industry. As the importance of different algal products is growing, their maas cultivation demand makes it necessary to improve and define newer cultivation concepts for significant production. The cultivation methods greatly influence the productivity of particular algae species and eventually, it affects the profit from the cultivation. Therefore, implementing a more economical, operationally feasible, sturdy, easy-to-maintain, and scalable algae cultivation system is becoming a critical aspect of microalgae cultivation practices.

For the growing market of microalgae-based products variety of commercial PBR systems are now coming into the market proving significant progress in this sector. For macroalgae or seaweed, open sea cultivation is becoming a way of the future for their cultivation, and lot many inventions from improving seaweed anchoring, maximum nutrients & CO2 absorption to reimplantation of lost coral reef is happening. Ultimately, the availability of plenty of coastal lines all over the world would play a very essential role in developing new concepts of sea farming of algae.

References:

Borowiak, D., Pstrowska, K., Wiśniewski, M., & Grzebyk, M. (2020). Propagation of Inoculum for Haematococcus pluvialis Microalgae Scale-Up Photobioreactor Cultivation System. Applied Sciences, 10(18), 6283.

Campbell, P. K., Beer, T., Batten, D., & Stream, T. B. (2009). Greenhouse gas sequestration by algae: energy and greenhouse gas life cycle studies. CSIRO Energy Transformed Flagship.

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Curtain, C. (2000). Plant Biotechnology-‐ The growth of Australia’s algal b-‐carotene industry. Australas Biotechnol, 10(3), 19-23.

References:

de Souza Kirnev, P. C., de Souza Vandenberghe, L. P., Soccol, C. R., & de Carvalho, J. C. (2022). Mixing and agitation in photobioreactors. In Innovations in Fermentation and Phytopharmaceutical Technologies (pp. 13-35). Elsevier.

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Gross, M., & Wen, Z. (2014). Yearlong evaluation of performance and durability of a pilot-scale revolving algal biofilm (RAB) cultivation system. Bioresource Technology, 171, 50-58.

Gross, M., Henry, W., Michael, C., & Wen, Z. (2013). Development of a rotating algal biofilm growth system for attached microalgae growth with in situ biomass harvest. Bioresource Technology, 150, 195-201.

Gross, M., Mascarenhas, V., & Wen, Z. (2015). Evaluating algal growth performance and water use efficiency of pilot‐scale revolving algal biofilm (RAB) culture systems. Biotechnology and Bioengineering, 112(10), 2040-2050.

Huang, Q., Jiang, F., Wang, L., & Yang, C. (2017). Design of photobioreactors for mass cultivation of photosynthetic organisms. Engineering, 3(3), 318-329.

Janssen M., Tramper J., Mur L.R., & Wijffels R.H. (2002). Enclosed Outdoor Photobioreactors: Light Regime, Photosynthetic Efficiency, Scale-Up, and Future Prospects. Biotechnology and Bioengineering, 81, 193-210. DOI: 10.1002/bit.10468.

Javed, T. and A. Farooq. 2015. Ignition of alkane-rich FACE gasoline fuels and their surrogate mixtures. Pro Comb Inst. 35(1): 249-257.

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Klein, B., & Davis, R. (2022). Algal Biomass Production via Open Pond Algae Farm Cultivation: 2021 State of Technology and Future Research (No. NREL/TP-5100-82417). National Renewable Energy Lab.(NREL), Golden, CO (United States).

Maltsev, Y., Maltseva, K., Kulikovskiy, M., & Maltseva, S. (2021). Influence of light conditions on microalgae growth and content of lipids, carotenoids, and fatty acid composition. Biology, 10(10), 1060.

McGill.R., 2008, A White Paper Prepared for the IEA Advanced Motor Fuels Implementing Agreement, Presented to the 35th Executive Committee Meeting May 2008. Vienna, Austria, page 2-7.

Mehrabadi, A., Craggs, R., & Farid, M. M. (2015). Wastewater treatment high-rate algal ponds (WWT HRAP) for low-cost biofuel production. Bioresource Technology, 184, 202-214.

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Peteiro, C., Sánchez, N., Dueñas-Liaño, C., & Martínez, B. (2014). Open-sea cultivation by transplanting young fronds of the kelp Saccharina latissima. Journal of Applied Phycology, 26, 519-528.

Przytocka-Jusiak, M., Ba̵szczyk, M., Kosińska, E., & Bisz-Konarzewska, A. (1984). Removal of nitrogen from industrial wastewaters with the use of algal rotating disks and denitrification packed bed reactor. Water Research, 18(9), 1077-1082.

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Sankpal, S. T., & Naikwade, P. V. (2013). Important bio-fuel crops: advantages and disadvantages. International Journal of Scientific & Engineering Research, 4(12).

Sarwer, A., Hamed, S. M., Osman, A. I., Jamil, F., Al-Muhtaseb, A. A. H., Alhajeri, N. S., & Rooney, D. W. (2022). Algal biomass valorization for biofuel production and carbon sequestration: a review. Environmental Chemistry Letters, 20(5), 2797-2851.

Sierra, E. & Acien, Gabriel & Fernández, J. & Garcia, J. & González-López, Cynthia & Molina-Grima, Emilio. (2008). Characterization of a flat plate photobioreactor for the production of microalgae. Chemical Engineering Journal. 138. 136-147. 10.1016/j.cej.2007.06.004.

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Wastewater Treatment

Can Carbon Diversion Unlock Energy Savings for WWTPs?

May 27, 2023May 30, 2023
by everflow

Utilities are actively working to decrease energy usage at wastewater treatment plants (WWTPs). They are increasingly interested in incorporating carbon diversion processes as a means to accomplish this goal. The market for carbon diversion is expanding, and in this regard, GWI (Global Water Intelligence) investigates the advantages and obstacles associated with its implementation.

Understand the carbon diversion in the context on WWTPs

Carbon diversion, also known as enhanced primary treatment, is gaining traction as a crucial tool in the water sector’s pursuit of energy efficiency. It offers utilities a means to maximize the value of their operations by simultaneously reducing aeration energy consumption and boosting biogas generation. Various carbon diversion methods are emerging in the market to achieve these dual benefits.

In wastewater treatment plants, aeration stands out as the most energy-intensive stage. It utilizes blowers to introduce air, creating optimal conditions for aerobic biological treatment processes. While crucial for effective wastewater treatment, this step offers significant potential for optimization to achieve strong results while minimizing energy usage.

Carbon diversion intervenes precisely at this point. It involves reducing the organic load on secondary treatment systems by diverting a higher portion of biochemical oxygen demand (BOD) towards the sludge line during primary treatment. Consequently, this reduces the aeration requirements for subsequent biological processes downstream.

Wastewater treatment plants, which employ anaerobic digestion, can capitalize on the additional benefit of carbon diversion by increasing biogas production by redirecting more organic matter to the sludge at an early stage of the treatment process. Depending on the operating conditions and the specific method of enhanced primary treatment employed, these plants could potentially achieve a 20-65% increase in biogas generation while simultaneously reducing aeration energy consumption by 10-30%.

How chemicals can important role in carbon diversion at WWTPs?

There are three types of carbon diversion methods: chemically enhanced, biologically enhanced, and filtration-based. Chemically-enhanced carbon diversion involves adding chemicals to clarifiers to promote faster settling of suspended solids. This process forms larger or heavier flocs that settle to the bottom of the tank, without requiring extensive infrastructure modifications.

However, the use of additional chemicals in chemically-enhanced carbon diversion incurs extra operational costs for utilities. These costs need to be carefully considered in relation to the benefits of reducing energy expenses for aeration. Another challenge with chemically-enhanced treatment is the difficulty of recovering chemically-bound phosphorus, which has become a significant concern for utilities, especially in Europe.

Ballasted clarification is a variation of chemically-enhanced primary treatment. It utilizes microsand or magnetic materials to enhance the settling of particles that would typically be too small to settle in traditional gravity-driven tanks. While chemical coagulants and flocculants are readily available, leading providers of ballasted clarification systems, such as Veolia Water Technologies, Evoqua, and WesTech Engineering, offer innovative solutions. These systems continuously reuse the materials that enhance the settling process, thereby reducing operational costs compared to purely chemical-based processes.

Infiltration technology to reduce chemical reliance

Utilities are increasingly seeking chemical-free solutions for carbon diversion. One emerging approach involves the use of filters to improve primary treatment by removing more suspended solids before biological processes. Researchers and wastewater treatment practitioners are employing various types and configurations of filters for this purpose, demonstrating promise in achieving desirable outcomes. Notably, cloth disc filters and compressible media filters have demonstrated effectiveness.

For instance, Aqua-Aerobic Systems has introduced the AquaPrime product, which is an adapted version of its tertiary disc filter. This innovative filter incorporates specially engineered cloth media and increased basin depth, making it well-suited for enhanced primary treatment applications.

Another technology addressing this need is the Proteus Primary filter developed by Tomorrow Water. This filter utilizes a cross-shaped media design that enhances the filtration surface area by 50%. Large-scale wastewater treatment plants in Korea have successfully implemented carbon diversion, as well as pilot projects in locations like Milwaukee in the United States. Additionally, Tomorrow Water offers the option of incorporating chemical enhancements into the filter to address the challenges posed by unpredictable peak flows resulting from climate change-induced wet weather events.

Advancements in biological processes – A potential alternative option.

Biological treatment processes for carbon diversion present a promising opportunity in the primary treatment market. Unlike physical and chemical processes that only eliminate suspended material, biological processes can also remove soluble matter, which constitutes a significant portion of municipal wastewater.

One prevalent configuration of biologically-enhanced primary treatment is the A-stage process. This approach involves establishing a small high-rate activated sludge system in the primary reactor. Bacteria within this system absorb soluble carbon from the wastewater without metabolizing it, ultimately settling into the waste sludge along with the excess carbon.

Another option is the A/B process, which represents a modification to the traditional activated sludge process. This method utilizes a combination of adsorption and bio-oxidation to divert carbon. The short retention time in the A/B process leads to reduced energy consumption for aeration, while soluble material is rapidly absorbed without being broken down.

Innovations within this market are focused on integrating treatment processes in novel ways. An exemplary instance is the alternating activated adsorption (AAA) clarifier, developed by NEWhub Corp. This technology combines the A-stage process with contact stabilization, directing the flow to the bacteria layer. Here, bacteria bind carbon to their surface and undergo biosorption. The AAA clarifier is particularly suitable for smaller treatment plants and has gained recognition in Europe, with plans to explore markets in the US and Australia.

Importance of the harmonization between different WWTPs processes for better results

Implementing enhanced primary treatment to reduce energy consumption is an attractive option, but utilities face a complex decision due to the crucial role of carbon in nutrient removal. If too much carbon is removed at the primary stage, additional carbon sources will be needed for biological processes to meet discharge standards.

The tightening of nutrient removal regulations worldwide highlights the importance of considering these standards. In Europe, for instance, the proposed updates to the Urban Waste Water Directive aim to significantly reduce total nitrogen and phosphorus limits. While utilities may prioritize efficiency and cost savings, their main focus will be on meeting these stringent regulatory limits.

Emerging methods of nutrient removal offer the potential to reduce carbon requirements in secondary treatment. One promising option is anaerobic ammonium oxidation, although widespread commercial adoption is still a distant goal. Nonetheless, it could eventually allow utilities to allocate more carbon to sludge. Currently, utilities must carefully balance the competing priorities of energy reduction and meeting strict nutrient removal requirements.

The immediate markets for carbon diversion are larger utilities in Europe, the US, and East Asia, where efforts to improve the sustainability and efficiency of wastewater treatment processes are gaining momentum. As more utilities adopt carbon diversion practices, they demonstrate how to harness the synergies that accelerate the development of energy-positive wastewater treatment plants with a smaller environmental footprint.

Reference: Original article (HOW COULD CARBON DIVERSION UNLOCK ENERGY SAVINGS FOR WWTPS? by AuqaTech) with Knowledge partner GWI published on Thursday, 11 May 2023.

Algal Biotechnology

Critical Challenges in Microalgae Cultivation Industry and Its Operation

March 1, 2023May 30, 2023
by everflow

The Algae industry is developing and growing every year with the increasing demand for various high-value algae products. Algae are a very important source in preparations of nutritional supplements, protein food, dietary fiber, essential fatty acids (Omega-3 Fatty acids, DHA, EPA), Gelling agents, cosmeceuticals, natural coloring pigments, animal feed, fertilizers, carotenoids, antioxidants, and many more. With the ever-increasing demand for pure products, the production demand for algae biomass is also high. Since the beginning, the Microalgae Cultivation industry facing several challenges associated with algae biomass production. That includes the challenges associated with water and land requirements, lab-to-land successful technology transfer and scaleup issues, issues related to algae cultivation systems, cost-effective fertilizers for algae cultivation, climate-related and environmental issues, related to the robustness of the selected strains and their productivity, etc. Here in this article, we are stipulating some of the above-mentioned issues and discussing the possible solutions to resolve them.

Water and land requirement

Algal biomass production requires a significant amount of water and land in order to be successful and yield a productive output. Algae are highly sensitive to environmental factors such as temperature, light, salinity, nutrients, grazers, and invaders, and therefore require an ideal growth environment to thrive. Many of these factors are influenced by the water source and location of the algae cultivation facility.

Water

Algal biomass production is water intensive due to the need for water for algae to photosynthesize, maintain the salinity of the water, and produce biomass. The amount of water needed for algal biomass production depends on the type of algae being grown, the size of the pond, the temperature, and other environmental factors.
The most viable water source is plentiful seawater. Not only is it accessible from many coastlines, but it also contains trace metal nutrients which reduce the need for additional supplementation, making it cost-effective. However, transporting seawater inland would be another costly affair. Moreover, for freshwater algae, this option will not be of any use. Also, evaporation accounts for a significant loss of water in open outdoor algal systems, and to compensate for this loss, volume make-up must be used (Kannan, D. C., & Magar, C. S. (2022)). For this having continuous freshwater sources is compulsory. In this, wastewater-based algae cultivation may have an important role to play.

Conventional as well as novel phycoremediation-based treatments could be implemented to clean the polluted water at STP/STP plants. Where produced algae biomass could be utilized for non-nutritive applications, such as biofuels, biofertilizers, and bioplastic production. Then this treated and pollution-free clean water will be utilized for good-quality biomass production for nutritional applications. This water source will also help to compensate for the evaporation loss of the water during the cultivation process. Wastewater is also known for its high content of Nitrogen and Phosphorus which could easily provide a sufficient amount of required nutrients when the addition of CO2 is performed.

Land

In horizontal construction, raceway ponds are carefully constructed to allow optimal exposure to sunlight for a productive output in algal biomass. It has been estimated that hundreds of hectares of land would be required to produce a sufficient amount of biomass for the industrially valued and marketable scale of algae products. Even for a phycoremediation-based wastewater treatment facility for any ideal Metropolitan city thousands of hectares of land would be required. This creates a big issue for the implementation of this technology, as this will compete with agricultural land. Also, scarcely available land in and around metropolitan cities makes it quite difficult to implement phycoremediation technology for cities.

To solve this issue non-arable lands such as wastelands, marginal lands, and desert regions near the sea coast, as well as wastelands near towns and industries, could be used for this purpose. However, this land must be properly identified through area-specific surveys and have adequate sunlight exposure and suitable climatic conditions to ensure successful algal production. (Kannan, D. C., & Magar, C. S. (2022) loc. Cit.). Apart from these alternative land sources, major modifications in cultivation systems to hold larger volumes in vertical systems will help to reduce the need for tremendous land. However, it may lead to the costly vertical design of the cultivation system.

Designing and constructing of algae cultivation system

The major types of algae cultivation systems are segregated into two types, Open (ponds) and Closed (Photobioreactors or PBRs) systems. Conventionally major algae cultivation is done in a very cost-effective manner using a raceway pond system. But to achieve good productivity and quality biomass, PBR always proved to be the best. Both systems have their own pros and cons, which are discussed in the following context.

Open and Closed System of Algal Biomass production

Open system- Raceway Pond

The open raceway pond system has advantages in the areas of investment and operation cost, but its weaknesses can’t be ignored. Bacterial contamination is a major issue, as the microalgae grown in such a system are exposed to the external environment, leading to the failure of growth or contamination of the culture media or wastewater (Mantovani et al., 2020). Furthermore, there is no temperature regulation present, so the external environment, such as temperature and illumination, can significantly affect the growth and treatment of wastewater with microalgae (Ras et al., 2013; Talbot et al., 1991). In some cases, the low temperature and poor illumination in winter can impede microalgae growth and microalgae-based nutrient removal in aquaculture effluent, thus limiting the practical application of open raceway pond systems.

Closed system—Photobioreactors

PBRs are of various types, viz. flat panel, tubular, plastic V-shaped tubes, air-lift PBR, acrylic/polycarbonate tray systems, biofilm-based vertical systems, etc. A novel type of system is still under exploration and the design and scale-up of photobioreactors is the topic of continuous development with innovative ideas. In closed systems, three key areas for improvement have been identified. Efficient lighting processes, efficient supply of carbon dioxide and oxygen removal, and energy consumption for adequate mixing (Clemens, 2009).

Light delivery is the most challenging problem when it comes to photobioreactor scale-up. Surface-lit photobioreactors require a large surface area to volume ratio to ensure enough light transmission to support photosynthesis (Janssen et al., 2003). The construction of extensive transparent surfaces is expensive and difficult and can lead to photo-inhibition of cells located closer to the surface as well as photo-limitation of cells in the center of the vessel, reducing productivity (Gris et al., 2014). To overcome these issues, researchers have proposed alternative internal lighting approaches, such as plastic light guides (Zijffers et al., 2008) or internal fluorescent bulbs surrounded by glass containers (Ogbonna et al., 1996).

comparison of open and closed algae culture

Microalgae culture integrity and sustainable development with biorefinery concept

Microalgae cultivation for biofuel production purposes needs the maintenance of some stringent environmental conditions for high lipid-producing microalgae strains. The production of high-value metabolites from microalgae poses major technological challenges, such as low biomass and product yield, as well as high costs associated with the cultivation and downstream processing. To create an efficient biorefinery, strategies must be developed to improve the cultivation process and reduce energy costs in the downstream processing of metabolites. To achieve this, an economic analysis must be conducted to understand the feasibility of the biorefinery, and metabolically engineered strains should be developed to increase biomass and secondary metabolite production. Metabolic engineering and bioprocess strategies can be employed to create genetically modified microalgal strains with high lipid and biomass production for food and nutraceutical applications, thereby reducing the energy and cost associated with the process.

Contamination by other fastidious microorganisms, invaders, and algae grazers makes mass-scale cultivation unrealistic

Contamination by other microorganisms can reduce the yield of algal biomass, and can also introduce pathogens and toxins that can be harmful to humans. In addition, algae grazers can consume the algae, thus reducing the yield. Cross-contamination of other local microalgae species is a common issue in cultivation plants and required frequent culture changes to maintain the culture strength. This increases the maintenance cost of the whole system. Mass-scale cultivation of algal biomass is difficult to achieve due to these challenges. To avoid this issue various solutions are undertaken that involve the use of antimicrobial agents, and acid treatment for bacterial and protozoan invaders and grazers. The use of detergent liquids and biosurfactants for maintenance work to avoid contamination issues is also another way for exploration. Use of mechanical separators and shear treatments where algae are not harmed but grazers are easily removed from the cultivation systems.

Challenges associated with efficient biomass harvesting and pre-treatment at low cost

The cultivation of algae-based biofuel requires an efficient harvesting technology to obtain higher yields. Algae which do not have gravity sedimentation ability/or require a longer duration for gravity settling mostly creates issues for harvesting. This requires the utilization of centrifugation of ultrafiltration systems to separate algae from the water. Unfortunately, existing harvesting methods are not economical and energy-efficient in removing algae from growth media.

Additionally, there are several pre-treatment steps for different industrial applications of algae. Also working on the optimization of appropriate treatments is necessary. This will also ensure the optimal product extraction in the end with desired quality. Many times, these processes can also be expensive and energy intensive. This makes it difficult to implement them on a commercial scale and also to find a suitable alternative. Through innovative research, it is always seeking to find suitable, cost-effective alternative solutions to harvest algae and process it further for extraction procedures at the industrial level.

Algae Pre-treatment for product recovery

Different products require different pre-treatment methods; mechanical and chemical methods are utilized for lipid and pigment extraction. Aqueous extracts give proteins and hydrophilic color pigments. Enzymatic and chemical methods, such as cellulase treatment and acidic hydrolysis help with the degradation of cellulose, hemicellulose, and starch. Finally, the sugar broth produced is utilized for bioethanol production. Different forms of biomass require different methods of pre-treatment and it needs to be optimized for higher yields from the biorefineries. Indeed, it is a difficult task given all the variables that come into play. Play such as biomass quality, principal component, the pressure generated during mechanical pressing, pH, temperature, and reaction times.
The other important challenges in pre-treatment procedures are associated with chemical loss, the efficiency of the method, loss of principal components in the final product, degradation of the quality of the product and by-product, undesirable modification of the product, etc.

Other Challenges in Microalgae Cultivation Industry include

A continuous source of CO₂, nutrients for algae cultivation
Need for a robust and sturdy strain with high biomass productivity
Non-tedious cultivation system which is easy to operate and has less maintenance cost
Simple microalgae flocculation techniques for easy harvest
Simplified and cost-effective harvest method to avoid biomass loss or degradation of biomass quality during harvesting

Summary and Conclusion

Algal biomass production has the potential to become a viable biorefinery concept along with renewable energy resources, but it is still developing. Despite recent advances in algal cultivation, there are several challenges ahead that will need to be resolved before algal biomass becomes a widespread source of renewable energy. Various alternative solutions are also proposed for various technical obstacles from mass cultivation to product harnessing steps. But finding the most suitable solution for each challenge is mandatory.

References

Kannan, D. C., & Magar, C. S. (2022). Microalgal biofuels: Challenges, status, and scope. In Advanced Biofuel Technologies (pp. 73-118). Elsevier.
Clemens, P. (2009). Design principles of photo-bioreactors for the cultivation of microalgae. Eng. Life Sci. 9, 165–177. doi:10.1007/s00449-013-0898-2
Janssen, M., Tramper, J., Mur, L. R., and Wijffels, R. H. (2003). Enclosed outdoor photobioreactors: light regime, photosynthetic efficiency, scale-up, and future prospects. Biotechnol. Bioeng. 81, 193–210. doi:10.1002/bit.10468
Gris, B., Morosinotto, T., Giacometti, G. M., Bertucco, A., and Sforza, E. (2014). Cultivation of Scenedesmus obliquus in photobioreactors: effects of light intensities and light–dark cycles on growth, productivity, and biochemical composition. Appl. Biochem. Biotechnol. 172, 2377–2389. doi:10.1007/s12010-013-0679-z
Zijffers, J. W. F., Janssen, M., Tramper, J., and Wijffels, R. H. (2008). The design process of an area-efficient photobioreactor. Mar. Biotechnol. 10, 404–415. doi:10.1007/s10126-007-9077-2
Ogbonna, J. C., Yada, H., Masui, H., and Tanaka, H. (1996). A novel internally illuminated stirred tank photobioreactor for large-scale cultivation of photosynthetic cells. J. Ferment. Bioeng. 82, 61–67. doi:10.1016/0922-338X(96)89456-6

Image References

Mostafa, S. S. (2012). Microalgal biotechnology: prospects and applications. Plant science, 12, 276-314.
INTREEGUE Photography, Wageningen, Netherlands – September 22, 2020: Algae unit for Algae production as sustainable alternative biomass to produce fuel, oil, and protein.
Magar, Chaitanya & Deodhar, Manjushri, 2019, Construction of laboratory scale photobioreactor for sequestration of CO2 from industrial flue gases and utilizing biomass for biofuel production, Ph. D. Thesis, Dept. of Biotechnology, K.E.T.’s V. G. Vaze College of Arts, Science and Commerce, University of Mumbai.
Huang, Q., Jiang, F., Wang, L., & Yang, C. (2017). Design of photobioreactors for mass cultivation of photosynthetic organisms. Engineering 3 (3): 318–329.

Also Read: Algae-Based Biofuels an Alternative option for Fuel Security and Biofuel: Fuel of the Future