Try Before You Buy – Bench-Scale Digestion Evaluation of Potential Co-Digestion Waste Streams

摘要

With limited digester capacity and the desire to increase digester gas production, GwinnettrnCounty Department of Water Resources initiated a research project with Hazen and Sawyer andrnGeorgia Institute of Technology to evaluate various fats, oils, and grease (FOG) and highrnstrength waste (HSW) streams for co-digestion. The bench-scale evaluation included wasternstream characterization, ultimate digestibility, continuous flow bench scale digester andrnbiological modeling with BioWin. During waste stream characterization, the solidsrnconcentration, carbonaceous oxygen demand (COD), along with pH and nutrient (nitrogen andrnphosphorus) concentration were measured. During the ultimate digestibility test, the CODrnconcentration and methane production was determined after a 90-day residence time. Thernultimate digestibility was used to compare the multiple waste streams to identify the streams thatrnproduced the most methane per volume of waste digested. Two waste streams, FOG and chewingrngum wastes, was used in the continuous, anaerobic, bench scale reactor. The waste streams werernco-digested with the plant’s primary and waste activated sludges at similar organic loading tornsimulate the full-scale digestion process. Each waste stream was co-digested individually andrnthen both waste streams were co-digester together. With each waste stream, the COD destructionrnand methane production exceeded the expected values of each individual waste stream from thernultimate digestibility tests. The continuous bench scale reactor was modeled using a calibratedrnBioWin model by EnviroSim that matched the theoretical and underestimated the observed CODrndegradation and methane production.