Energy Efficient Ethanol Stillage Treatment using a Bio-Electrochemical System

Reducing energy and water intensity of fuel-ethanol production is a critical national need, particularly if we are to realize the renewable fuel standards of 2010 mandating 36 million gallons of renewable fuels by 2022. Because the ethanol tolerance of yeasts used in commercial cellulosic ethanol production is around 7-9% by volume, 10-14 gallons of stillage are created for every gallon of ethanol produced, resulting in billions of gallons of wastewater per year. Yet existing stillage treatment solutions are costly and energy intensive. Bio-electrochemical systems (BES) that can generate electricity during stillage treatment have the potential to greatly improve both the economics and carbon intensity of fuel-ethanol production. Phase I feasibility analysis demonstrated for the first time, to our knowledge, the ability of bio-electrochemical systems to reduce BOD in ethanol stillage while generating electricity directly. A proprietary cell achieved a maximum power density of 3.5 W/m3 on un-pretreated ethanol stillage at columbic efficiencies of 31% while removing 0.42 KG COD/m3day. A multi-discipline, physics-based Metlab model demonstrated lower 10-year discounted cost of ownership versus competing systems at performances similar to those achieved in the lab, based in part on benefits not fully considered in the academic literature. This Phase II project builds on Phase I results to optimize performance and demonstrate a scaled BES-based stillage treatment solution in partnership with some of the largest ethanol producers in the world. The project is divided into four major tasks: Broaden Scope: Expand validated stillage streams to include cellulosic ethanol. Detailed Design: Verify design concepts developed to minimize cost at larger scale; modulate key parameters to minimize internal electrical and hydraulic resistances to increase treatment rates. Process Optimization: Pilot design in proposed process configuration to validate performance and determine proper pre-treatment characteristics. Pareto-Optimization: Incorporate empirical results into our multi-objective technical and economic model to identify pareto-optimal solutions, validate pilot economics, and inform future scaling efforts. The end result will be commercial validation of a scalable BES treatment process with the potential to radically reduce the cost and energy intensity of ethanol stillage treatment. Such a process could be used as a retrofill to older ethanol plants, incorporated into the ramp-up for cellulosic ethanol production, and also applied to other fermentation-based industries such as brewing.