Biofuel co-products as livestock feed - Opportunities and challenges

278Biofuel co-products as livestock feed – Opportunities and challengesFIGURE 2Flowchart for the production of ethanol in the RUSBI approachConditioning of raw materialWaterCassavaS. potatoSweetsorghumWashing Grating Drying MillingLavado RalladoMilling JuiceFloursWetmassEnzymesMust preparationRaw mustHydrolisisOrganic-mineralFertilizersAnimalfeedSweet mustClarifiedeffluentsSolidresiduesYeastsFermentationFermentedmustCO 2VinassetreatmentVinasseDistillationBio-polymersStationary enginesClean-cook stovesCarsHydrated Ethanol(96%)TABLE 1Operating conditions in the early stages of hydrolysis andfermentation of the conventional process (LSF) for biofuelproductionParameterHydrolysisLiquefaction SaccharificationFermentationT (°C) 82–86 65–70 32pH 5.7–6.0 4.3 4.5Source: Genencor International web site (www.genencor.com)TABLE 2Operating conditions of the simultaneous hydrolysis,fermentation and sacharification process (SHF) for biofuelproductionParameterHydrolysis (Liquefaction +Saccharification)FermentationT (°C) 30–33 30–33pH 4.0–4.5 4.5Source: Genencor International Web site (www.genencor.com)gluco-amylase. Operating conditions conventionally usedfor this method are given in Table 1.In the SHF method, a mixture of enzymes is used tocarry out the saccharification of starch without the liquefactionstage. In this method, special enzymes are used(StarGen), that are able to perform the hydrolysis stageat room temperature, and allow the combination of thesaccharification and fermentation stages in one singlestep, because they work under the same conditions oftemperature and pH as the yeast (Saccharomyces cerevisiae).The operating conditions for this method are givenin Table 2.The RUSBI approach to producing bio-ethanol is basedon the SHF method, seeking to reduce processing time,power consumption and installation costs, since it doesnot need installation of a heat exchanger. After the SHFstep is finished, a fermented mash is obtained. To separatethe ethanol from this mash, a distillation stage is required,in which the ethanol evaporates at 78 °C. The ethanolvapours are captured and condensed, yielding ETOH andleaving the vinasse (Ospina et al., in press).BIO-ETHANOL PRODUCTION TRIALS WITH THERUSBI APPROACHThe work conducted by CLAYUCA with the RUSBI modelfor production of biofuel has focused on the optimizationof the enzymatic hydrolysis of starch in cassava (Cajamarca,2009), and on estimation of the efficiency in the productionof bio-ethanol from cassava flour, by calculating the massand energy balances in the process (Martínez, 2009). Someof the tests conducted with cassava flour and cassava rootsfor the production of ETOH using the SHF method at roomtemperature are presented in Table 3.Management of the vinasse co-product resultingfrom the bio-ethanol production processThe operation of a biofuel production process, such asETOH from cassava, generates a large quantity of effluent