Biogas production and feasibility of energy recovery systems for anaerobic treatment of wool-scouring effluent

Abstract

The technical and economic feasibility of anaerobic digestion to produce biogas at a small wool-scouring facility in the United States was examined. The facility will process 90,800kg (200,000 pounds) of greasy wool per year at maximum capacity. Biochemical methane potential experiments showed that anaerobic biodegradation of organic constituents in wool-scouring effluent (WSE) ranged from 17 to 75% on a chemical oxygen demand (COD) basis and produced 0.10–0.39L methane per gram of WSE COD added. Microbial inhibition was observed when initial WSE concentrations exceeded 1000mg COD/L. A laboratory-scale continuous reactor operated at organic loading rates of 100–200mg COD/L/day produced biogas with an average methane content of 75% and provided 72–78% removal of total WSECOD. Life cycle costing predicted that the best alternative for energy recovery at a small wool-scouring facility was to offset natural gas used to heat water for wool-scouring with biogas. Economic feasibility should increase with increasing COD removal, increasing natural gas price, and increasing cost to discharge to the municipal wastewater treatment works. The key anaerobic treatment design challenge will be to maximize WSE organic loading rates while minimizing microbial inhibition.