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Process Design of Wastewater Treatment for the NREL Cellulosic Ethanol Model
Author: Thomas Steinwinder, Everett Gill, Matthew Gerhardt
Date: 9/211
Contract No. DE-AC36-08GO28308, Subcontract Report, NREL/SR-5100-51838, September 2011

The National Renewable Energy Laboratory (NREL) is evaluating a novel process for the production of ethanol from the cellulosic feedstock, corn stover. This process results in a liquid by-product stream that must be treated with the goal of reusing the effluent water in the production process, thus minimizing waste and the impact of this process on the environment. In the Statement of Work (SOW), NREL describes the treatment concept as consisting of anaerobic treatment of condensed pretreatment vapors, boiler and cooling tower blowdown streams, and filtered beer stillage followed by aerobic treatment. The biogas captured in the anaerobic process, the surplus biological sludge, as well as the captured lignin would be burned in a biomass boiler to generate steam and ultimately electricity from a steam turbine. The treated effluent would be recycled to the ethanol fermentation process. Since the development of this conceptual design in 1998, NREL has updated the fermentation process which has caused changes to the resultant process wastewater. In general the wastewater contains high concentrations of organic compounds, measured as chemical oxygen demand (COD) and biochemical oxygen demand (BOD). It also contains high concentrations of ammonia-nitrogen (NH3-N). The treatment process developed for this wastewater must provide the capacity to reduce the levels of these constituents sufficiently for recycle. It should be noted that this evaluation was performed for a specific corn stover using dilute acid pretreatment. Changes to the corn stover source and/or method of pretreatment may result in changes to the conclusions summarized in this document. As a secondary objective, energy in the form of biogas could be recovered during anaerobic treatment and used to meet or supplement the facility energy demand.

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