algal biofilms Algal Biotechnology

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

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.

algal biofilms
Fig1 Algae Biofilm on stones

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).

Fig 5 Mixotrophic cultivation of algae biofilm
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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Microalgae: A Powerful Tool for Climate Change and Water Pollution Mitigation Algal Biotechnology

Microalgae: A Powerful Tool for Climate Change and Water…

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 CO2, 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 CO2 emissions. 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 CO2 emissions, 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 CO2 in 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 CO2 levels 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 CO2 concentrating 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 CO2 concentrating 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 CO2 concentrating 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 & CO2 Sequestration.

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 CO2 Sequestration 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 MCO2 and 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 CO2 Mass 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 CO2 capture 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 CO2 concentration 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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Challenges in microalgae production Algal Biotechnology

Critical Challenges in Microalgae Cultivation Industry and Its Operation

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.

Challenges in microalgae production

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

  1. A continuous source of CO2, nutrients for algae cultivation
  2. Need for a robust and sturdy strain with high biomass productivity
  3. Non-tedious cultivation system which is easy to operate and has less maintenance cost
  4. Simple microalgae flocculation techniques for easy harvest
  5. 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

  1. Kannan, D. C., & Magar, C. S. (2022). Microalgal biofuels: Challenges, status, and scope. In Advanced Biofuel Technologies (pp. 73-118). Elsevier.
  2. 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
  3. 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
  4. 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
  5. 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
  6. 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

  1. Mostafa, S. S. (2012). Microalgal biotechnology: prospects and applications. Plant science, 12, 276-314.
  2. INTREEGUE Photography, Wageningen, Netherlands – September 22, 2020: Algae unit for Algae production as sustainable alternative biomass to produce fuel, oil, and protein.
  3. 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.
  4. 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

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