Microalgae in Other Applications

Commercial large-scale production of microalgae started in the early 1960s in Japan with the culture of Chlorella as a food additive, which was followed in the 1970s and 1980s by expanded world production in countries such as USA, India, Israel, and Australia (Pulz and Scheinbenbogen, 1998;Borowitzka, 1999; Spolaore et al., 2006).

1.10.1 Health food and human food

The human consumption of microalgae biomass is limited to very few species due to the strict food safety regulations (Pulz and Gross, 2004), commercial factors, market demand and specific preparation. Among the abundant species of microalgae, Chlorella, Spirulina and Dunaliella dominate the market. Microalgae biomass is marketed in tablet or powder form as food additives generally in the health food market, which is expected to remain a stable market (Spolaore et al., 2006).

Chlorella is also used for medicinal value such as protection against renal failure and growth promotion of intestinal lactobacillus (Yamaguchi, 1996). Suggested health benefits including efficacy on gastric ulcers, wounds and constipation together with preventive action against both atherosclerosis and hyper-cholesterol and antitumor activity. Dunaliella salina, is exploited for its β-carotene content of up to 14% (Metting, 1996).Spirulina (Arthrospira) is used in human nutrition because of it high protein content and excellent nutrient value (Spolaore et al., 2006). Many companies have been producing ‘‘nutraceuticals’’ (food

supplements with claimed nutritional and medicinal benefits) made from Spirulina, such as in DIC in Japan and China, and Cyanotech in Kona and Hawaii.

1.10.2 Animal feed and aquaculture

Microalgae are an important food source and feed additive in the commercial rearing of many aquatic animals (Borowitzka, 2006). Over 30% of the current world algal production is sold for animal feed and over 50% of the world production of Spirulina is used as feed supplements (Spolaore et al., 2006).

Specific algal species are suitable for preparation of animal feed supplements. Algae species such as Chlorella, Scenedesmus and Spirulina have beneficial aspects including improved immune response, improved fertility, better weight control, healthier skin and a lustrous coat (Pulz and Gross, 2004). However, prolonged feeding at high concentrations could be detrimental (Spolaore et al., 2006) especially in relation to cyanobacteria.

1.10.3 Carotenoids and astaxanthin

Algae contain carotenoids, yellow orange or red pigments, that include β-carotene a substance converted by the body to Vitamin A. The most important uses of carotenoids are as food colorants and as supplements for human and animal feeds (Becker, 1994; Spolaore et al., 2006).

Astaxanthin is another carotenoid that can be derived from algae, Haematococcus, and is principally used in fish farming and as a dietary supplement or antioxidant. Natural

astaxanthin is preferred for example in carp, chicken and red sea bream diets due to enhanced natural pigment deposition, regulatory requirements and consumer demand for natural

products (Spolaore et al., 2006).

1.10.4 Polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) are essential for human development and physiology (Hu et al., 2008), and have been proven to reduce the risk of cardiovascular disease (Ruxton et al., 2007). Currently, fish and fish oil are the main sources of PUFA but application as a food additive are limited due to possible accumulation of toxins, fish odor, unpleasant taste, poor oxidative stability, the presence of mixed fatty acids and not suitable for vegetarian diets (Pulz and Gross, 2004).

Microalgal PUFA has many other applications such as additives for infant milk formula.

Elsewhere, chickens have been fed with special algae to produce omega-3 enriched eggs (Pulz

and Gross, 2004). Currently, docosahexaenoic acid (DHA) is the only algal PUFA that is commercially available, because algal extracts are still not competitive sources of

eicosapentaenoic acid (EPA), γ-linolenic acid (GLA), and arachidonic acid (AA) against other primary sources (Spolaore et al., 2006).

1.10.5 Microalgae in wastewater treatment

Wastewater rich in CO2 provides a beneficial growth medium for microalgae because the CO2 balances the Redfield ratio (molecular ratio of carbon, nitrogen and phosphorus in

marine organic matter, C:N:P = 106:16:1) of the wastewater allowing for faster production rates, reduced nutrient levels in the treated wastewater, decreased harvesting costs and increased lipid production (Lundquist, 2008).

Several applications in wastewater treatment have been reported. For example,

Sawayama et al. (1995) used B. braunii to remove nitrate and phosphate from sewage after primary treatment along with the production of hydrocarbon-rich biomass. Martínez et al.

(2000) achieved a significant removal of phosphorus and nitrogen from urban wastewater using the microalgal S. obliquus. They were able to achieve 98% elimination of phosphorus and a complete removal (100%) of ammonium in a stirred culture at 25°C over 94 and 183 h retention time, respectively. Gomez Villa et al. (2005) experimented with outdoor cultivation of microalgal S. obliquus in artificial wastewater, and achieved final dissolved nitrogen concentrations which were 53% and 21% of initial values in winter and summer, respectively.

Yun et al. (1997) successfully grew C. vulgaris in wastewater discharge from a steel plant to achieve an ammonia (NH3)bioremediation rate of 0.022 g L^-1 NH3 per day. To improve efficiencies, Muñoz et al. (2009) found the use of a biofilm attached onto the reactor walls of flat plate and tubular photobioreactors improved BOD5 removal rates by 19% and 40%, respectively, when compared with a control suspended bioreactor for industrial wastewater effluent. The retention of algal biomass showed remarkable potential in maintaining optimum microbial activity while remediating the effluent.

For processing of hazardous or toxic compounds, it is possible to use microalgae to generate the oxygen required by bacteria to biodegrade pollutants such as polycyclic aromatic hydrocarbons (PAHs), phenolics and organic solvents. Photosynthetic oxygen from

microalgae production reduces or eliminates the need for external mechanical aeration (Muñoz and Guieysse, 2006). Chojnacka et al. (2004) found that Spirulina sp. acted as a biosorbent, thus was able to absorb heavy metal ions (Cr³⁺, Cd²⁺ and Cu²⁺). Biosorption properties of microalgae depended strongly on cultivation conditions with photoautrophic

species showing greater biosorption characteristics.