Wastewater treatment for a biomass-to-ethanol process: System design and cost estimates

A wastewater treatment (WWT) system was designed for an enzyme-based process for converting lignocellulosic biomass to fuel ethanol. The bioethanol process included the following basic unit operations: biomass pretreatment, hydrolyzate conditioning, fermentation, cellulase production, product recovery, and energy recovery. Anaerobic digestion followed by aerobic treatment was selected as the best WWT strategy, and centrifugation and evaporation of the stillage was employed to minimize wastewater and optimize water recycling. For a 2000 dry tons/day biomass-to-ethanol plant, the capital cost estimate for a WWT system is about $10.4 million. The impact of capital costs and the associated operating expenses of the WWT system corresponds to 2.35c/L of ethanol or 6.6% of the total ethanol cost. The WWT strategy and cost estimates developed can be generally applicable to similar bioethanol plants.