Final Report: Bio-Electrochemical Systems for Ethanol Wastewater TreatmentEPA Contract Number: EPD10029
Title: Bio-Electrochemical Systems for Ethanol Wastewater Treatment
Investigators: Silver, Matt
Small Business: Cambrian Innovations / previously known as IntAct Laboratories, LLC
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2010 through August 31, 2010
Project Amount: $46,770
RFA: Small Business Innovation Research (SBIR) - Phase I (2010) RFA Text | Recipients Lists
Research Category: SBIR - Emission Reductions and Biofuels , Small Business Innovation Research (SBIR)
This project evaluated the technical and economic feasibility of using bio-electrochemical systems (BESs) to treat bio-ethanol wastewater (e.g., stillage). Because the ethanol tolerance of yeasts used in commercial cellulosic ethanol production is approximately 7-9 percent by volume, 10-14 gallons of stillage are created for every gallon of ethanol produced. This results in billions of gallons of wastewater every year that must be treated. Despite new process designs that increase efficiency of stillage treatment for corn ethanol, older corn ethanol plants and future cellulosic ethanol designs suffer from expensive and energy-intensive treatment options. Solutions that can treat stillage while generating energy could have a profound effect on the greenhouse gas (GHG) emissions and economic viability our nation's ethanol value chain.
This project validated for the first time, both experimentally and computationally, the feasibility of utilizing BES technology to generate electricity directly from the treatment of ethanol stillage. Based on newly discovered bacteria that can interact electrically with electrodes, BESs can produce electricity directly from the oxidation of organic wastes. Beyond generating value-added electricity and reducing GHG emissions, BES systems reduce total suspended solids (TSS) production and reverse the energy demand versus competing technologies such as aerobic digestion. In addition to proving technical and economic feasibility, the project identified promising product and process designs for Phase II R&D and subsequent scale up.
The Phase I project combined an experimental study with detailed systems analysis. Five different process wastewater streams from two different ethanol production facilities were tested in proprietary BESs using mixed and pure cultures. Measurements were taken for chemical oxygen demand (COD), biological oxygen demand (BOD), nitrate, and ammonium levels, as well as voltage, current, and power. These measurements were used to derive treatment rates, coulombic efficiency, and related parameters of interest.
Building on the experimental work, a detailed systems analysis evaluated economic feasibility. Interviews with biofuels experts and corporations identified promising process configurations and a multidiscipline physics-based matlab model was created to compare BES cost and performance to competing systems.
Stretch goals for the Phase I project include utilizing biological cathodes in addition to biological anodes, and varying process parameters. Based on these stretch goals, a novel approach to scaling the technology more quickly was identified and will be patented provisionally.
IntAct's 6-month study successfully demonstrated, for the first time to its knowledge, the feasibility of using bio-electrochemical systems for the treatment of ethanol stillage. For IntAct's preferred process design, the mixed culture achieved a sustained treatment rate of 130 mg COD/L/day (130 g/m3/day) resulting directly from BES activity. This corresponded to a maximum power density of 3.5 W/m3 at 0.23 V, and a maximum coulumbic efficiency of approximately 31 percent. BOD5 analysis indicated a BOD/COD ratio of between 0.079 and 0.52 depending on the stillage stream, indicating high variability in the selected feedstock digestibility. Similar total treatment rates with these streams indicated divergent columbic efficiencies, suggesting that future research should examine the impact of pre-treatment and stream variation in more detail. Pure culture experiments did not produce comparable results to the mixed culture experiments. Preliminary tests with biological cathodes are promising.
The systems analyses indicated that in at least one process configuration the 10-year discounted cost of a BES system can be far less than competing systems at performance rates similar to those achieved in the laboratory. Specifically, the BES system should outperform competing technologies at volumetric currents of between 16.6 and 17.5 Amps/m3, corresponding to power outputs of between 6.1 W/m3 and 12.5 W/m3. The low power outputs needed for economic feasibility derive from accounting for benefits not normally considered rigorously in the academic literature. These estimates are sensitive to a range of factors that should be investigated in more depth in Phase II. Tax credits and other incentives were not yet considered.
Despite the lack of optimization of wastewater pre-treatment or cell design, IntAct's BES system was able to obtain treatment rates that are on the fringe of target treatment rates for commercialization. The project as a whole demonstrated that InAct's proposed approach could achieve economic viability given a few improvements. Future R&D should focus on reducing internal resistance, modifying pre-treatment, improving cost estimates, and modeling new process designs that may enhance the economics of the system.
This research can be used to develop a detailed process and product design for a scaled BES system to replace energy-intensive stillage treatment designs, particularly for older corn-ethanol and future cellulosic plants. In addition to creating a system for ethanol stillage treatment, the technology could be used to reduce the energy intensity of wastewater treatment in adjacent fermentation-based industries such as breweries, wineries, and renewable fuels.
Towards that end, IntAct undertook significant commercialization efforts during Phase I R&D. IntAct conducted a detailed market analysis and discussed piloting with representatives from a range of potential corporate partners in both the United States and abroad. In August 2010, IntAct signed an agreement for exclusive distribution rights in a certain geographic area with a large foreign company. Further, another large company expressed interest in partnering in Phase II and licensing the technology. IntAct will continue to refine the best business case for further commercialization through Phase II R&D.