Biogas Production from Steam-Treated Municipal Solid Waste Wastewater

Biogas production from steam process wastewater carrying the organic fraction of municipal solid waste (MSW) was investigated in a bench-scale system comprised of an anaerobic completely stirred tank reactor (AnCSTR), an anaerobic filter (AnF), and an aerobic trickling filter (ATF). The AnCSTR received rinse water that contains pulp fibers that are derived from MSW. The AnF received the same rinse water from MSW process wastewater; however, the pulp fibers were not present. The ATF received effluent from the AnCSTR and AnF in fed-batch mode. Biogas production was observed at 0.02–0.29 and 0.04–0.47 kg CH₄ · m⁻³ day⁻¹ in the AnCSTR and AnF systems, respectively. Chemical Oxygen Demand (COD) removal efficiency was observed at 20% in the AnCSTR and up to 86% in the AnF operating at 10- to 12-day hydraulic retention time (HRT). Introduction of digester sludge in the feed at day 173 (2 days HRT) increased gas production rate in the AnCSTR from 0.13 to 0.29 kg CH₄ · m⁻³ day⁻¹ but did not significantly affect gas production rate in the AnF. The ATF stage removed 96% of dissolved COD. System stability was demonstrated in the AnF by full recovery of biogas production after operating the reactor under starvation conditions for 7 days. The average specific removal rate observed in the AnCSTR (k _ms = 0.098 day⁻¹) was one order of magnitude lower than previously observed values using organic kitchen waste (k _ms = 0.27 day⁻¹). On the other hand, organics removal rate kinetics in the AnF (k _ms = 0.25 day⁻¹), were similar to the previously observed value from the organic kitchen waste. The system treated the organic portion of steam process MSW wastewater with concomitant biogas production with as low as 0.01 mg COD · L⁻¹ in the final effluent from the ATF.