Biofuel co-products as livestock feed - Opportunities and challenges

Micro-algae for fuel and use of spent biomass for feed and for other uses 435FIGURE 4Different forms of energy production from micro-algal biomassBiochemicalConversionFermentationAnaeobicDigestionEthanol, Acetone,ButanolMethane, HydrogenGasificationFuel GasMicroalgal biomassThermochemicalConversionPyrolysisBio-oil, CharcoalLiquefactionBio-oilChemicalReactionTrans-esterification/HydrocrackingBiodieselDirectCombustionPower GenerationElectricitySource: from Wang et al., 2008.the micro-algal concentrate can yield different liquid fuels;this process uses Fischer-Tropsch synthesis technology. Thecrude product obtained is called ‘Syn-gas’, which can beconverted to various fuel derivatives by further processing,such as hydrogenation.USE OF MICRO-ALGAE FOR FOOD, FEED ANDBIO-ACTIVESFood applications of micro-algaeThe algal biomass remaining after extracting the hydrocarbonsand lipids is a valuable co-product rich in nutritionallyimportant metabolites for food and feed purposes. It isused for food applications, and also for feed applicationsin various industries, such as fish aquaculture and poultry,as well as in the nutraceutical market for both human andanimal consumption. This section highlights the possibilitiesfor utilization of algal biomass for feed and as a source ofother valuable constituents. Such value addition would beof relevance not only to utilize all the co-products in a usefulmanner, but also as affording eco-friendly technologyalternatives for the production of various nutrients and bioactivesapart from direct food applications.Micro-algae with their immense chemical diversity providean seemingly unlimited source for various applications in thefood industry (Table 6). Algal products ranging from wholebiomass to nutraceuticals like carotenoids and PUFAs are utilizedin the food industry. The safety of these algae has beenevaluated and commercial use approved in several countries.Many reviews are available detailing the potential uses ofmicro-algae as food sources (Venkataraman et al., 1980;Becker, 2004; Pulz and Gross, 2004; Spolaore et al., 2006;Ravishankar et al., 2008; Plaza et al., 2009; Milledge, 2010).Micro-algae as a source of vitaminsMicro-algae also represent a valuable source of nearly allessential vitamins (e.g. A, B 1 , B 2 , B 6 , B 12 , C, E, nicotinate,biotin, folic acid and pantothenic acid). Vitamin B 12 is mainlysynthesized by certain bacteria that are associated withthe gut flora of animals, contributing to the requirement ofthis vitamin. Since plants have no ability to synthesize vitaminB 12 because of the absence of cobalamin-dependentenzymes, strict vegetarians (vegans) are at risk of developingvitamin B 12 deficiency, and hence need to dependupon vitamin B 12 -fortified foods or vitamin B 12 -containingdietary supplements to meet the requirement. Spirulinaplatensis is one of the most widely consumed cyanophyceanforms used as a food supplement and containssubstantial amounts of vitamin B 12 . Because the vegetariandiet does not contain vitamin B 12 , S. platensis, along withother nutrients, helps in meeting the recommended dailyrequirement of vitamin B 12 in the vegetarian diet, and alsoof meeting the requirement of needy individuals with variedfood habits or health status (Kumudha et al., 2010). Otherwater-soluble vitamins, including Vitamin C, riboflavin and