Biofuel co-products as livestock feed - Opportunities and challenges

424Biofuel co-products as livestock feed – Opportunities and challengesMAIN MESSAGES Depletion of fossil fuels is leading to an energy crisisand highlighting the need for development of renewableenergy sources Micro-algae, being photo synthetic with a high abilityto produce hydrocarbons and lipids, offer multipleadvantages as a source of bio-energy through harnessingsolar energy, with the additional advantagesof CO 2 sequestration and providing an eco-friendlyalternative to meet energy requirements. In addition to providing bio-energy molecules, algaeare good source of nutrients and health promotingsubstances, as well as valuable metabolites that areunique and of high commercial value. The algal biomass after extraction of bio-combustiblematerials can be used as feed for fish, poultry andanimals. Development of eco-friendly and easily adaptableeconomic process for mass cultivation of biomass leadingto net energy gain and their utilization towardsvarious applications is discussed. A biorefinery approach to utilizing various fractionsof algal biomass has been proposed to make processesmore economical, with a bias towards energyproduction, biochemicals and feed in an eco-friendlymanner utilizing algal biodiversity and harnessingsolar energy.productivity than higher plants, make them a potential andeconomically viable resource for renewable fuel production(Gouveia and Oliveira, 2009). Large-scale algal cultivationhas been developed for various purposes and the biomasscan be harvested frequently as algae can have very shortdoubling times, ranging from 4 to several days. Further,some of the micro-algae accumulate lipids up to 50 percentof the dry weight in certain growth conditions. The lipidaccumulation in micro-algae is influenced by light intensity,culture pH, availability of nutrients, dissolved oxygenconcentrations and several other environmental factors.Apart from lipids, some micro-algae, such as Botryococcus,accumulate long-chain hydrocarbons that have propertiessimilar to petroleum hydrocarbons (Metzger and Largeau,2005; Dayananda et al., 2007b). Also, certain micro-algaeoccur in extreme environmental conditions, like brackishand high saline waters, acidic or alkaline lakes, and at chillingtemperatures. These extremophilic micro-algae can beexploited for the production of novel compounds of commercialand functional importance.The preliminary step, and an important part of sustainablemicro-algal technology, is extensive germplasm collectionand biodiversity screening for the production of lipidsand hydrocarbons. Furthermore certain parameters, likebiomass productivity, lipid or hydro-carbon content anddaily yield, and possibility of co-product generation mustbe considered for viable micro-algal technology applications(Subramaniam et al., 2010). Micro-algae chosen after initialstudies under controlled conditions must be evaluated fortheir performance in outdoor and scaled-up conditions.Large-scale cultivation methodologies involve optimizationof media for high biomass and lipid yields, and adjustingphysical parameters like light requirements, culture mixing,supply of CO 2 , etc. (Pulz, 2001). Use of simple and inexpensivenutrient sources and re-usability of media should beconsidered in assessing potential for sustainable mass cultivation.Apart from mass cultivation, development of simpledownstream processing must be critically evaluated, includingharvesting procedures, processing the biomass for lipidor hydrocarbon extraction, and converting crude extractsto combustible fuels. Existing technology using energyintensivemethods, such as centrifugation and ultra filtrationfor harvesting, and extraction methods like oil expelling orFrench pressing, has proven unviable for renewable energyproduction (Brennan and Owende, 2010). Nevertheless, itis increasingly evident that algae can be exploited for nutritionallyand nutraceutically important metabolites for foodand feed applications owing to their content of vitamins,proteins, pigments, fatty acids, sterols and polysaccharides.The potential of micro-algae as a source of antiviral, antitumour,antibacterial, anti-HIV agents and as food additiveshave also been well established (Cardozo et al., 2007).Production of bio-energy through photo synthetic systemsis gaining strength and has a great future since itis renewable and eco-friendly. However, for any type ofbio-energy production, systems need to be developed thatoperate in an economical manner in terms of total energygain per unit area. A careful analysis of the present daytechnologies for utilizing algal biomass for energy productionindicate that they do not take into account the totalenergy audit. One needs to look at the whole process fromthe point of view of net energy gain, addressing cultivationto utilization of the biomass for the production of lipids,hydrocarbons and other useful constituents. In addition tothe target molecules for fuel generation, co-products couldbe of utility for food and feed, as well as a source of chemicalsof importance to humankind. Utilization of sea waterwould address the water requirements for cultivation ofbiomass, which otherwise would compete with agriculture,potentially leading to water conflicts. Therefore, utilization