Biofuel co-products as livestock feed - Opportunities and challenges

440Biofuel co-products as livestock feed – Opportunities and challengeswater footprint of bio-energy from some of the agriculturalcrops and concluded that the water footprint is high andnot competitive enough.Norsker et al. (2011) calculated the micro-algal biomassproduction costs for three different production systemsoperating at commercial scale: open ponds, horizontaltubular photo bioreactors and flat-panel photo bioreactors.The resulting biomass production costs for these systemswere € 4.95, € 4.15 and € 5.96 per kilogram, respectively.The parameters included for the costing were irradiationconditions, mixing, photo synthetic efficiency of systems,medium, carbon dioxide costs and dewatering. Optimizingproduction with respect to these factors resulted ina price of € 0.68/kg. They conclude that at this cost,micro-agal-based biofuel production is promising andcompetitive. Lundquist et al. (2010) thoroughly assessedthe technical and engineering systems involved in biofuelproduction from micro-algae. The biomass productionsystems considered are those for biofuel production orfor waste water treatment, with outputs as biogas, orbiogas and oil, and a farm size of 100 or 400 ha. Themajor technical assumptions were 25 percent recoverablelipid content, biomass yield of 22 g DM/m 2 /day (80 t/ha/year) and a resulting oil yield of 20 000 L/ha/year. CO 2was supplied from a flue gas source. According to theirreport, the overall production costs for biofuel productionas a co-product of waste water treatment was of higheconomic feasibility, at US$ 28/barrel of oil or US$ 0.17/kwh electricity produced through biogas generation.However, in the case of biofuel or biogas productionas the major objective based on waste water treatment,the system was very costly, at US$ 332/barrel of oiland US$ 0.72/kwh electricity generated through biogas.Their recommendations include use of bio-flocculationfor harvesting biomass, online extraction of oil from wetbiomass, and emulsification of oil, which together wouldreduce operating costs by 20–25 percent, avoiding thesteps of drying and extraction.BIOREFINERY APPROACH IN MICRO-ALGALUTILIZATIONA bio refinery is an integrated approach to biomassconversion processes to produce fuels, power and valueaddedchemicals from biomass. The biorefinery is analogousto today’s petroleum refinery, which produces multiple fuelsand products. The first step in the biorefinery concept iscultivation of micro-algae, with limited inputs and avoidinguse of nutrient chemicals like fertilizers. If the productionsystems are intended for biofuel production, nutrientrichsources of waste water can be utilized. This systemis advantageous in terms of the natural treatment of thewaste water, which could be recycled for algal cultivation orused for irrigation. Industrial effluents like distillery wastesor sewage ponds are good nutrient sources. Since microalgaeare better CO 2 sinks than higher plants, flue gasesfrom industry can be used as a source of CO 2 . Alternatively,if biomass production systems involve generation ofvaluable co-products, then cultivation systems utilizingmarine ecosystems like coastal and estuarine areas aremore economical in operational terms. Solar generatedpower can be effectively utilized in operating racewayponds and pumping the culture for further downstreamprocessing. The spent media can be utilized as a sourceof exopolysaccharides that have many potential bio-activeproperties. Lipid-rich diatoms like Cylindrotheca closterium,Thalassiosira pseudonana and Skeletonema costatumproduce extracellular polysaccharides that can be harvestedfor further applications (Urbani et al., 2005; Li et al., 2011),and also recycled for algal cultivation.There are different ways of realizing economic valuefrom micro-algal spent biomass after oil extraction. Thebest option would be to achieve complete utilization ofthe biomass for maximum energy recovery by variousconversion technologies, such as biomass gasification andthermochemical processes that generate syngas, whichcan be combusted or can be converted to chemicals likealcohols, ethers, etc. Pyrolysis can be employed where anoil-like liquid is produced that can be processed to fuels.Anaerobic fermentation of spent biomass yields methane,and power generation from these co-processes enhancesthe sustainability of micro-algal derived biofuels.The second option is utilization of glycerol generatedfrom the trans-esterification process of conversion ofcrude algal lipids to biodiesel. Glycerol can be usedas feed for generation of biomass. Pyle, Garcia andWen (2008) used a biodiesel-derived crude glycerol as asource of carbon for heterotrophic production of DHAby Schizochytrium limacinum, with comparable yields toother feeds. Glycerol is a highly reduced carbon sourcethat can be converted to many industrially importantcompounds, including 1,3-propanediol, dihydroxyacetone,succinic acid, propionic acid, ethanol, citric acid, pigments,polyhydroxyalconate, squalene and bio surfactants by use ofbacterial genera like Klebsiella, Citrobacter, Enterobacter,Clostridium, Propionibacterium, Anaerobiospirillum andEscherichia. (Yazdani and Gonzalez, 2007; Silva, Mack andContiero, 2009).Another option is recovery of polysaccharides andproteins from mono-algal cultures grown in cleanenvironments for use as animal feeds. Animal feeds canuse spent biomass with low lipids but with high contentof micronutrients such as minerals, anti-oxidants, proteinsand vitamins, in supplementation of rations for fish, poultryand other livestock. Some enhancement of the spentbiomass might be required for greater efficacy as feedsupplement. The residual biomass could be used as soil