Microalgae grow in soil unfit for agriculture and livestock and in lakes or ponds located in inhospitable lands, such as deserts, which are usually unsuitable for generating any kind of food. Microalgae can double their biomass in a period of 3.5 days, achieving high yields (Chisti, 2007). After harvesting and drying of the biomass, the final state of the product is a powder. According to the chemical composition of microalgae, the biomass may have several applications.
1.15.1 Food
In the 1950s, the increase in world population and the prediction of insufficient protein supplement for humans led to the search for alternative and unconventional sources of nutrients. Microalgae emerged as candidates for this purpose. Research has been directed to- ward the development of functional products—food additives such as vitamins, antioxidants, highly digestible proteins, and essential fatty acids. Microalgae can supply several of these nutrients, and they have potential health benefits (Cavani et al., 2009; Petracci et al., 2009).
Microalgae are currently used in the form of tablets, capsules, or liquids. These microor- ganisms can be incorporated into pastas, cookies, food, candy, gum, and beverages (Liang et al., 2004). Due to their varying chemical properties, microalgae can be applied as a nutri- tional supplement or as a source of natural proteins, dyes, antioxidants and polyunsaturated fatty acids (Spolaore et al., 2006; Soletto et al., 2005).
The Laboratory of Biochemical Engineering (LEB) at the Federal University of Rio Grande (FURG) in southern Brazil has developed research projects since 1998 that study the cultiva- tion ofSpirulinaon a pilot scale on the banks of the Mangueira Lagoon, as additives to meals for children of the region. Products that are easy to prepare, store, and distribute and that are highly nutritious and accepted by the consumer have been developed here.
These products include instant noodles, pudding, powdered mixture for cake, cookies, chocolate milk powder, instant soup, isotonic drinks, powdered gelatin, and cereal bars.
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1.15 APPLICATIONS OF BIOMASS
These products will be prepared at the Center for Enrichment of Foods withSpirulina(CEAS) located at the university. In Camaqua˜ (Brazil), the company Olson produces organicSpirulina capsules for importation.
1.15.2 Drugs
Many algae produce antibiotics such as acrylic acid found inPhaeocystis poucht.This anti- biotic inhibits the growth of gram-positive organisms. The phenols found in macro- and microalgae have antimicrobial activity.
The microalgaScenedesmus obliquushas been used in postoperative recovery, assisting in coagulation of the skin surface. The extracts of the diatomAsterionella notatahave an antifun- gal and antiviral activity. Toxic algae have been used as a depressant vessel, similar to tetro- dotoxin found in fish (Richmond, 1990).
Another drug obtained from microalgae is phycocyanin, a natural antioxidant that, when combined with caloric restriction, can contribute to mitigating the aging process. Free radicals are partly responsible for the human aging process (Finkel, 2003). The oxidative damage caused by free radicals has been linked to several diseases such as heart disease, atheroscle- rosis, lung problems, Alzheimer’s, and Parkinson’s. The DNA damage caused by free radicals plays an important role in the processes of mutagenesis and carcinogenesis.
1.15.3 Biopigments
Microalgae have three main pigments: chlorophyll that absorbs blue light; red carotenoids that absorb blue and green light; and phycobilins that absorb green, yellow, and orange light.
These pigments have been used as natural colorants in food products. In many countries biodyes have replaced artificial dyes, which are currently prohibited.
b-carotene is a carotenoid found in all higher plants and algae. b-carotene acts as pro- vitamin A and may be used as a natural food color. Phycolibins are water-soluble pigments and are found only in red algae or cyanobacterias. Most members of cyanophyceae contain blue pigment (phycocyanin), although several species may also contain erythrin. Phycoery- thrin and phycocyanin can be used as natural pigments in food, medicine, and cosmetics, avoiding the use of artificial pigments that are carcinogenic (Richmond, 1990).
1.15.4 Biopolymers
Since 1940, the most widely used plastics have been polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(ethylene terephthalate) (PET), and poly(vinyl chloride) (PVC).
Despite advances, plastics processing and manufacturing generate two major problems:
the use of nonrenewable resources to obtain their raw materials and large quantities of waste generated for disposal.
Biodegradable plastics degrade completely within three to six months when attacked by microorganisms, depending on the environmental conditions. The polyhydroxyalkanoates (PHAs) are natural polyesters consisting of units of hydroxyalkanoic acids with similar prop- erties to petrochemical plastics (Jau et al., 2005).
18 1. AN OPEN POND SYSTEM FOR MICROALGAL CULTIVATION
The polyhydroxyalkanoates are produced as a reserve of carbon and energy accumulated within the cells of various microorganisms such as microalgae. Among the PHAs, polyhydroxybutyrate (PHB) and its copolymer polyhydroxybutyrate-co-valerate (PHB- HV) are synthesized by cyanobacteria when exposed to specific conditions of cultivation (Sharma et al., 2007).
The degradation rate of PHB and PHB-HV depends on many factors, some related to the environment, such as temperature, moisture, pH, and nutrient supply, and others related to the biopolymer itself, such as composition, crystallinity, additives, and surface area. Due to its physical and chemical properties, PHB is easily processed in equipment commonly used for polyolefins and synthetic plastics (Khanna and Srivastava, 2005).
1.15.5 Biofuels
Microalgae are a potential source of fermentable substrate. According to the conditions of cultivation, microalgal biomass can provide high levels of carbon compounds. These com- pounds are available directly for fermentation or after pre-treatment and may be used for eth- anol production.
Biogas is the product of the anaerobic digestion of organic matter and can be obtained from domestic sewage, animal waste, solid waste, or aquatic biomass, such as macro- and microalgae (Omer and Fadalla, 2003; Gunaseelan, 1997). The type of digestion using microalgal biomass processes can eliminate the biomass harvesting and drying and the asso- ciated costs (Vonshak, 1997).
The fatty acids that microalgae produce can be converted into biodiesel, which is a renew- able, biodegradable, nontoxic, and environmentally friendly fuel. Biodiesel has the advantage that it emits 78% less carbon dioxide when burned, 98% less sulfur, and 50% of particulate matter emissions (Brown and Zeiler, 1993).
Another promising biofuel is hydrogen. Photobiological hydrogen production can be in- creased according to the carbon content in the biomass. The microalgae are candidates for such a process because they produce hydrogen under certain conditions and can be grown in closed systems, allowing the capture of hydrogen gas (Benemann, 1997). This biomass can be burned to produce energy because the calorific value of these microorganisms is greater than that of some charcoals.
1.15.6 Biofertilizers
The greatest issue in agriculture nowadays is the availability of chemical fertilizers at af- fordable costs. Nitrogen fixation has been acknowledged as the limiting factor in food pro- duction. The concept of using cyanobacteria to fix nitrogen is based on the ability of these microalgae to grow in soil.
The microalgae Nostoc, Anabaena, Oscillatoria, Cylindrospermun, and Mastigocladus Tolypothrixform heterocysts and can fix nitrogen aerobically. Nonheterocyst-forming fila- mentous microalgae, such as Oscillatoria and Phormidium, can fix nitrogen in the absence of oxygen and in the presence of nitrogen and carbon dioxide. Filamentous forms without heterocysts, such asTrichodesmium, may fix nitrogen aerobically (Richmond, 1990).
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1.15 APPLICATIONS OF BIOMASS
The heterocysts, which are specialized in aerobic nitrogen fixation, are the site of the en- zyme nitrogenase, which catalyzes the conversion of nitrogen into ammonia. Nitrogen-fixing cyanobacteria were isolated in soils from various cities in South Asia, India, and Africa.
In that study, 33% of 2,213 soil samples collected in India contained cyanobacteria. Microalgae such asNostoc, Anabaena, Calothrix, Aulosira, and Plectonema were found in soils in India, while Halosiphon, Scytonema and Cylindrospermum were observed in the other regions (Richmond, 1990).