ENHANCING GREENHOUSE GAS MITIGATION AND ECONOMIC VIABILITY OF ANAEROBIC DIGESTION SYSTEMS: ALGAL CARBON SEQUESTRATION AND BIOPLASTICS PRODUC

Over 9 million dairy cows generate an estimated 226 billion kg (249 million tons) of wet manure and produce approximately 5.8 billion kg of CO2 equivalents annually in the U.S. (BSSC 2008; Liebrand & Ling 2009). For an average 10,000 head dairy, decomposition of this organic waste produces ∼6,000 tons of CH4, 74 tons of N2O, and 130,000 tons of CO2 per year, or ~290,000 tons of CO2 equivalents (USEPA 2011). These emissions constitute approximately 2.5% of the annual production of greenhouse gasses (GHGs) in the United States, and make dairies one of the largest single industry sources of GHG in the US (USEPA 2011). Anaerobic digestion (AD) can significantly reduce dairy GHG emissions by enhancing CH4 generation and capturing and converting CH4 to CO2 in a generator while producing electricity and offsetting farm energy usage. AD biogas could be used to generate >6,800 GWh/yr in power, roughly equivalent to the average annual electricity usage of 500,000 to 600,000 homes (U.S.EPA 2010). Recognizing the potential of ADs to mitigate GHG emissions and produce power, in January 2009, the Innovation Center (IC) for U.S. Dairy announced a voluntary goal to reduce GHG emissions 25% by 2020. Central to achieving this goal is the construction of approximately 1,300 new ADs, which the EPA estimates could reduce U.S. CH4 emissions by 90%. Despite industry support behind broad AD deployment, the on-the-ground reality is that AD projects are not always commercially feasible, due in part to generally low electricity rates. Perhaps more importantly, ADs emit relatively large quantities of GHGs in the form of CO2. Thus, new strategies are necessary to improve AD economics and consequently promote the adoption of AD as a mitigation strategy to achieve the ICs GHG reduction goals. To enhance dairy carbon (C) sequestration, this project will advance a novel integrated manure-to-commodities system that converts pre-fermented manure to bioenergy, sequesters carbon by converting volatile fatty acid (VFA)-rich fermenter supernatant to bioplastics, and sequesters AD effluents (CO2, nitrogen, phosphorus) by producing algae that can be harvested and returned to the AD to enhance PHA production and enhance overall C-sequestration. GHG reduction and C sequestration will be quantified and used to parameterize a system model and web-accessible management decision tool that will be developed at the Idaho National Laboratory. Research product and decision tool dissemination along with workforce and student training will be facilitated by connecting to an on-going, USDA funded outreach and education effort centered on biofuel literacy led by the University of Idaho's McCall Outdoor Science School (MOSS). The outcomes and impacts of this project will include changes in the agricultural knowledge system. Change in knowledge will come from applied research developing a novel approach to GHG reduction and economic development. Change in action will come from experimentally-based information generation and development of data driven decision tools with potential to lead to change in actions by agricultural producers.