Simultaneous saccharification and fermentation process for ethanol production from steam-pretreated softwood: Recirculation of condensate streams

Wastewater from fuel ethanol production plant represents a considerable potential pollutant. Treatment is an essential operation in the overall conversion of lignocellulosic to ethanol. This significantly reduces the effluent volume, and reduces the need of fresh water. Present work concerns a simultaneous saccharification and fermentation (SSF) process for ethanol production from steam-pretreated softwood. Within this process, the effect of recirculation of the condensate from the evaporation of the stillage stream was investigated. The condensate employed in this study represents the condensate of four evaporators connected in series, with each evaporator producing a condensate corresponding to 14% of the process stream after distillation of the SSF broth. The investigation demonstrated that it was possible to replace 100% of the fresh water used in the process (except for the steam used in the pretreatment), by recirculation of all the condensate fractions together, without affecting the ethanol yield and the productivity in SSF. A significant factor was the absence of lactic acid production, which is sometimes observed when the pretreated material is diluted with fresh water. The prospect of using condensate to replace fresh water offers an attractive means of reducing the cost of wastewater management and thereby improving the overall economic feasibility of the process.