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 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).

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