The use of microalgae for municipal wastewater treatment has been a focus of research and development for decades as they have the ability to metabolize sewage more rapidly than bacterial treatments (Olguin, 2003). Through photosynthesis, algae assimilate nitrates, phosphates, and other nutrients present in the wastewater (http://www. algaewheel. com). In addition, the oxygen given off by algae is the pri­mary contribution toward the treatment of municipal wastewaters and industrial effluents (Metting, 1996). Wastewater treatment systems that rely on microalgae for oxygen production are dominated by chlorophytes (Metting, 1996).

Additionally, biomass from high-rate algal pond (HRAP) systems (such as animal wastewater and fish farm wastewater) can be harvested for use as animal feed; a con­cept that has been demonstrated by Lincoln and Earle (1990) and Metting (1996), as part of an integrated recycling system (IRS) (Olguin, 2003). Such a system would incorporate animal waste as an input and several by-products and high-value-added products (algae) as overall outputs. “Bioespirulinema,” a system carried out by Olguin (2003), has been operating effectively, and with a 4-year average Spirulina produc­tivity of 39.8 tonnes ha-1y-1. The average protein content of the ash-free Spirulina biomass was 48.39% dry weight; which is relatively high for a system where there are no nitrogen costs.

Low harvesting costs could be one of the key concepts in establishing the eco­nomic viability of the entire system. However, these applications remain in their infancy, and extensive research and development are needed. Successful technolo­gies and processes are available for wastewater treatment, such as the Advanced Integrated Wastewater Pond Systems (AIWPS) Technology, commercialized by Oswald and Green in the United States (Olguin, 2003). Phycoremediation with the employment of microalgae is a field with great promise and demand with so many regions in the world prone to eutrophication.

10.3 CONCLUSION

Since the use of microalgae to survive the famine in China some 2,000 years ago, the commercial applications of microalgae have been increasing rapidly. Of the many microalgal species that exist, a few species are stored in collections, and only a handful have been exploited for high-value products (Olaizola, 2003); hence, there are only a few high-value products in the marketplace (Milledge, 2011). The chal­lenge in progressing to commercialization can be overcome by focusing efforts on products with a huge market potential and a distinct competitive advantage in large markets such as food.

Algal biomass “health food” appears to be the main commercial product, fol­lowed by food additives in the form of carotenes, pigments, and fatty acids. Algal production within the health-food market has the highest sales value but is largely dependent on health benefits and proof of efficacy (Becker, 2007; Milledge, 2011). As natural additives, these commodities are superior to synthetic products, although there is much to consider regarding the economics, sustainability, and environmental perspectives of the production of each product (Harun et al, 2010; Milledge, 2011).

There are various factors to consider in developing manufacturing processes of high-value metabolites. These include ensuring that proper taxonomic treatment is applied such that efficient screening of the microalgae can be conducted—not only for the fastest growing species, but also for those organisms with desirable robust characteristics and valuable products. A key starting point is to expand the inven­tory of microalgal species represented in culture collections and cell banks (Pulz and Gross, 2004; Sekar and Chandramohan, 2008). Production systems are also an important factor to consider. The type of production system depends on the nature and value of the end-product (Metting, 1996). Currently, outdoor open-pond systems are the mainstream mode of microalgal cultivation (Spolaore et al., 2006). The most successful genera cultivated in open-pond systems are Spirulina, Dunaliella, and Chlorella. Microalgal products of high value and purity, such as isotopically labeled research compounds and reagent-grade phycobilins, are produced in photobioreac­tor systems (Metting, 1993; Millledge, 2011). Overall operating and maintenance costs of open-pond systems are lower compared to those of photobioreactors (which are restricted mainly to the production of high-value products). Ideally, open ponds make for a competitive cultivation alternative (Harun et al., 2010) and are likely to be the way for commercial cultivation of microalgae. The location of the pond, algal strain, light and CO2 availability, final product yield, and quality are important fac­tors to consider in open-pond cultivation systems.

Harvesting and metabolite recovery methods depend on the nature of the species and end-product. Centrifugation is probably the most reliable method of harvest­ing but, on the other hand, it is costly. Filtration and flocculation are cost-effective methods that are widely used for the harvesting of algal biomass. The cost of the downstream recovery process for such high-value, high-purity products contrib­utes to a significant portion of the overall production cost. For example, 60% of the total production cost of EPA is attributed to the recovery process of EPA (Grima et al., 2003), while biomass production only contributes approximately 40% of the total production cost. Thus, reducing the cost of downstream processing can signifi­cantly influence the overall economics of microalgal metabolite production (Grima et al., 2003).

Genetic modification of microalgae has been considered for improving the yield of valuable products at reduced costs (Milledge, 2011). The production of recom­binant proteins in microalgal chloroplasts has several attributes (Specht, 2010). Transgenic proteins can accumulate to much higher levels in the chloroplasts than when expressed from the nuclear genome; chloroplasts can be transformed with multiple genes in a single event due to multiple insertion sites (Specht, 2010). Furthermore, proteins produced in chloroplasts are not glycosylated (Franklin and Mayfield, 2005); this can be useful in the production of antibodies that are similar to native antibodies in their ability to recognize their antigens (Specht, 2010). To demonstrate the feasibility of human antibody expression in an algal system, a full — length IgG (Immunoglobulin G) antibody has been synthesized in the chloroplast of the green alga Chlamydomonas reinhardtii (Hempel et al., 2011). The ability to accumulate high-value compounds makes microalgae attractive for recombinant protein production; however, there are some factors that limit microalgal expres­sion systems (Gong et al., 2011). These include the lack of standard procedures for genetic transformation of commercially important microalgal species, limited availability of molecular toolkits for genetic modification of microalgae, and low expression levels of recombinant proteins (Surzycki et al., 2009).

The use of genetic modification may reduce the organic and natural appeal of specific algal products, especially when the product is to be applied in the food and feed industries. It is thus imperative to prioritize endeavors toward proper species selection and production process development. This is a preferred approach, rather than resorting to genetic engineering of microalgae. However, for specialized applications, such as for therapeutic and diagnostic purposes, the use of microalgae as bioreactors for the production of recombinant proteins may be advantageous.

Microalgae boast a range of high-purity, valuable products that have progressed successfully to commercialization in applications in the food, pharmaceutical, clini­cal research, and animal nutrition industries. The possible employment of microalgae in environmental applications (phycoremediaion and biofertilizers) provides poten­tial solutions to global warming and sustainable economic development. Although in their infancy, these applications hold significant promise, and with potential use in diagnostics and therapeutics, the range of applications continues to grow. However, for these industries to progress, it is important to start at grass-root levels in research. Exhaustive screening procedures must be conducted for specific species and products, while also considering the economics of upstream and downstream processes for individual products.

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