Recovering High Value Acids from Anaerobic Co-digestion of Municipal Solid and Grease Interceptor Waste Using an Electrically Driven Separation Process
Investigators: North Carolina State University and University of North Carolina at Chapel Hill
Re-engineering the anaerobic co-digestion (co-AD) of organic-rich, municipal solid waste (MSW) to yield high-value chemical products could dramatically change the economics of co-AD technologies. Conventional co-AD, in which two distinct waste streams are digested together (e.g., food waste and wastewater solids), generates methane gas (CH4). However, the low market value of CH4 ($160/ton) translates into a long return on initial capital investment and limits revenue generation that could help offset maintenance and operating costs. Shutting down the biological pathways to CH4 production in co-AD (via inhibition of methanogenesis) can result in the production of volatile fatty acids (VFAs) without compromising solids destruction goals. For example, research at NCSU has shown that increasing grease interceptor waste (GIW) loading beyond certain thresholds during co-AD with waste activated sludge can stop CH4 production and lead to generation of the VFAs acetic, propionic, butyric, and valeric acids. These VFAs have current market values in the range of $525 (acetic acid) to $6,000 (valeric acid) per ton and are therefore significantly more valuable than CH4. While the knowledge of how to operate co-AD to generate VFAs exists, the primary challenge facing implementation of this approach is the lack of effective methods to separate and recover VFAs from co-AD.
The overall goal of the proposed research is to demonstrate the technical feasibility of recovering VFAs from co-AD using electrochemical methods. To accomplish this overall goal, the following specific objectives will be pursued:
- To determine how the composition of organic-rich, solid waste mixtures impacts VFA production during co-AD.
- To measure VFA recovery efficiencies and rates using an electrochemical-based separation process.
- To build and test a scalable electrochemical cell (e-cell) design that will be used to validate VFA recovery from co-AD effluents.