Biofuel co-products as livestock feed - Opportunities and challenges

423Chapter 24Cultivation of micro-algae for lipids andhydrocarbons, and utilization of spentbiomass for livestock feed and forbio-active constituentsG.A. Ravishankar, R. Sarada, S. Vidyashankar, K.S. VenuGopal and A. KumudhaPlant Cell Biotechnology Department, Central Food Technological Research Institute, Constituent laboratory of Council of Scientific and Industrial Research(CSIR), Mysore 570020, IndiaE-mail for correspondence: rgokare@yahoo.co.inABSTRACTThe demand for energy is ever increasing, and concurrently the depletion of fossil fuels has been so rapid that itcould lead to an energy crisis in the near future. At the same time, reducing the carbon footprint to mitigate globalwarming has been a subject of immediate attention. Production of energy through photosynthetic organisms suchas micro-algae by harnessing solar energy might be a viable solution to some of these issues. In pursuit of renewableenergy sources, efforts worldwide focus on identifying those organisms that can accumulate high quantitiesof biomass and produce molecules that can be converted to combustible materials. Economically viable processesfor large-scale cultivation and downstream processing of biofuel precursors, such as lipids and hydrocarbons, havebeen a challenge, requiring adoption of technologies needing reduced inputs of energy and chemicals. Prudentenergy audits to assess the viability of bio-energy processes are a necessity. The utilization of micro-algae for bioenergyproduction would be viable only when the whole process has a net energy gain, with complete utilizationof algal biomass for biofuel and the co-products thereof used to produce food, feed and chemicals. The spent algalbiomass—which is rich in proteins, carbohydrates, minerals and bio-active compounds—is ideal for feed applications.The paper outlines biorefinery approaches to integrated utilization of algal biomass for bio-energy, withco-production of valuable metabolites and nutrients as feed, with full utilization of all the fractions for economicviability of the process. These aspects are dealt with in detail in the various sections to provide a comprehensiveoverview of micro-algal technology for biofuel programmes vis-à-vis feed applications.INTRODUCTIONPhytoplankton are the most important and major biomassproducers in global aquatic ecosystems. Algaeare the primary producers, generating approximately52 000 000 000 tonne of organic carbon per year—almost50 percent of the total organic carbon produced annually(Field et al., 1998)—through photo synthesis utilizingsolar energy and converting CO 2 and other simpleinorganic compounds to myriad molecules (Chisti, 2007).These organisms populate the top layers of the oceansand freshwater habitats where they receive sufficient solarradiation for photo synthesis (Hader et al., 1998). Microalgaeare unicellular to filamentous in form, whereasmacro-algae or seaweeds are plant-like organisms. Microalgaelack roots, vascular systems, leaves and stems, andare autotrophic in nature and photo synthetic. They aregenerally eukaryotic organisms, although cyanobacteria—aprokaryotic assemblage—are included under algae due totheir similar photo synthetic and reproductive properties(Greenwell et al., 2009). The thalli of algae display a widerange of organization, ranging from single cells (Chlorellaspp.), through motile (Chlamydomonas spp., Dunaliellaspp.), colonial (Volvox spp., Botryococcus spp.), filamentous(Spirulina spp., Spirogyra spp.) and plant like (Chara spp.) togiant seaweeds (Postelsia spp., Fucus spp.). (Fritsch, 1935).Depleting fossil fuel reserves, with associated escalationin petroleum prices, has engendered huge demandfor development of technology for renewable fuels fromphoto synthetic organisms with a smaller carbon foot printand an overall positive energy balance. In this context,micro-algae could be a possible solution. Their ubiquitousdistribution and ecological adaptations give them certainadvantage over other groups. The ability to cultivatealgae under varied conditions, including using non-potablewaste water and operating in marginal areas, coupled withtheir photo synthetic efficiency and higher surface area