A SYSTEMS-APPROACH FOR THE EVALUATION OF ETHANOL-PRODUCTION BASED ON FORAGES

A systems approach is proposed to simultaneously consider the agronomi c aspects of forage production and the processing aspects related to t he extraction of a glucose or xylose substrate, its fermentation into ethanol and the optimal utilization of co-products (protein meal, fibr ous residue). The energy to produce and transport forage on the farm w as estimated to be only 375 MJ/t dry matter (DM) when liquid manure wa s used and 1165 MJ/t DM when mineral fertilizer was used. An additiona l 126 MJ/t DM would be required to transport it to a processing plant. In contrast, whole-plant corn production using mineral fertilizer req uired about 3211 MJ/t DM, but it had a potential ethanol yield 3.2 tim es greater per unit area than perennial forage. A forage system with m echanical juice extraction resulted in 8-20% of the original forage dr y matter available in a liquid substrate with subsequent protein meal separation and the fermentation of soluble sugars into ethanol. Anothe r forage system with relatively complete conversion of cellulose and h emicellulose into simple sugars by thermal, acidic and enzymatic treat ments was estimated to produce 12-28 times more ethanol per unit area than the mechanically extracted juice. Complete conversion of perennia l forages would meet the petroleum industry's needs more consistently than simple extraction of soluble components. (C) 1996 Elsevier Scienc e Ltd.