Biofuel co-products as livestock feed - Opportunities and challenges

Utilizing co-products of the sweet sorghum-based biofuel industry as livestock feed in decentralized systems 233 Produces feedstock on small farms, which tend to useland more efficiently than large farms. Co-products remain with the farmers. Reduces farm input needs through promotion of regionally-appropriate,low-input feedstock crops. Promotes equitable distribution and greater retention ofwealth by rural communities.CO-PRODUCTSThe processing options discussed above focus on the liquidcarbohydrate portion of the sweet sorghum, but do notaddress the use of grain, the solid bagasse and steam thatare generated during the pressing process, or the wastevinasse that is generated during the dewatering process.An ideal system will utilize as many crop components aspossible to create a closed-loop system (Worley, Vaughanand Cundiff, 1992).GrainCurrently the stalk from rainfed sweet sorghum grown inthe rainy season is the source of raw material for the decentralizedunits in India. The grain is considered a co-producthere as sweet sorghum is basically grown for productionof ethanol by fermenting extracted juice from the sugarystalks. Mould-affected grain can be used as raw material forethanol production, while mould-free grain can be used forhuman consumption. The primary product in DCU is syrup,which can be used either in ethanol production or in thefood and pharmaceutical industries.Grain from the rainy season crop is mostly mouldaffecteddue to rains during grain development, maturationand harvest. Grain and stover yield are statistically unrelatedin both hybrids and varieties (Blümmel et al., 2009). Stoveryield is directly proportional to realizable bagasse yield(Kumar et al., 2010). High grain yields could be associatedwith above average stover yields. In a recent comprehensiveinvestigation of grain-stover relationships in (non-sweet)sorghum cultivars tested by the Directorate of SorghumResearch (DSR), formerly the National Research Center forSorghum (NRCS), Hyderabad, India, during the 2002–2006period, Blümmel and co-workers (2010) observed thatgrain yields accounted for only 14 percent of the variationin stover yield, i.e. grain and stover yields in sorghum wereonly weakly positively associated. These findings suggestthat grain and stover yield should both be recorded in sorghumimprovement, since stover yields cannot be accuratelypredicted by grain yield measurements. Grain yields do notneed to be achieved at the expense of fodder for livestock orfeedstock for ethanol production, and vice versa.BagasseThe solid bagasse that remains after pressing sweet sorghumhas several potential uses. One potential use isas animal feed, directly after chopping or after ensiling(Linden, Henk and Murphy, 1987). It has also been usedas a source of pulp for the paper industry (Belayachi andDelmas, 1997). Another potential use of the bagasse is asa fuel source for the processing plant. With the addition ofa solid-fuel boiler, the bagasse can be used to provide processheat to run the plant. With its heating value it is likelyto require only 20–30 percent of the available biomass tofuel the plant (Bennett and Anex, 2009). In addition, processesfor conversion of lignocellulosic material to ethanolare becoming more economically viable, making sweetsorghum bagasse a possible source of biomass for such aprocess. Studies have demonstrated that a large portionof the insoluble carbohydrate (cellulose and hemicellulose)from sorghum can be readily converted to ethanol (Siposet al., 2009).Foam and frothLot of foam and froth is generated during juice boiling. Thiscan be collected separately and used to feed livestock or asorganic fertilizer.SteamThe steam generated during concentration of juice to syrupis a good source of energy, which can be used for severalpurposes, such as boiling water, which in turn can be usedto increase juice extraction, heat treatment of juice beforeboiling, etc., by installing the necessary equipment to capturethe outgoing steam.VinasseVinasse, also known as stillage, is the liquid co-productafter removal of the final products during sugar processing.In a distillation process, vinasse is the liquid remainingafter separation of ethanol. In the decentralized model ofsorganol production, the dewatering and/or distillation systemwill produce 10–15 litre of waste vinasse (distillate) forevery litre of ethanol produced in the later stages, dependingon the initial ethanol concentration of the fermentationbroth. The large volume generated and the high organicloading in the waste water make it a major environmentalchallenge for most commercial applications. Reports ofbagasse characterization for sugar cane feedstocks showbiochemical oxygen demand (BOD) levels ranging from25 to 60 g/L, with nitrogen levels from 300 to 2500 mg/Land phosphorus levels from 10 to 300 mg/L. The limiteddata on sweet sorghum bagasse show comparable results,with BOD = 46 g/L, nitrogen = 800 mg/L and phosphorus= 1990 mg/L (Wilkie, Riedesel and Owens, 2000). Due toits high BOD, disposal into waterways is not an option.One potential option is land application of the vinasse asirrigation water and fertilizer. Several reports suggest thatboth dilute and concentrated vinasse (from sugar cane)