Long-Term Performance of a Pilot-Scale Gas-Sparged Anaerobic Membrane Bioreactor under Ambient Temperatures for Holistic Wastewater Treatment

Concerns regarding ambient temperature operation, dissolved methane recovery, and nutrient removal have limited the implementation of anaerobic membrane bioreactors (AnMBRs) for domestic wastewater treatment. This study addresses these challenges using a pilot-scale gas-sparged AnMBR, with post-treatment recovery of dissolved methane and nutrients. Operating under ambient temperatures for 472 days, the AnMBR achieved an average effluent quality of 58 ± 27 mg/L COD and 25 ± 12 mg/L BOD5 at temperatures ranging from 12.7 to 31.5 °C. The average total methane yield was 0.14 ± 0.06 L-CH4/g-COD fed, with 42% of the total methane dissolved in the permeate. Dissolved methane removal using a hollow fiber membrane contactor achieved an average removal efficiency of 70 ± 5%, producing effluent dissolved methane concentrations of 3.8 ± 0.94 mg/L. The methane recovered from gaseous and dissolved fractions could generate an estimated 72.8% of the power required for energy neutrality. Nutrient recovery was accomplished using coagulation, flocculation, and sedimentation for removal of sulfide and phosphorus, followed by a clinoptilolite ion-exchange column for removal of ammonia, producing effluent concentrations of 0.7 ± 1.7 mg-S/L, 0.43 ± 0.29 mg-P/L and 0.05 ± 0.05 mg-N/L. The successful integration of AnMBRs in a treatment train that addresses the critical challenges of dissolved methane and nutrients demonstrates the viability of the technology in achieving holistic wastewater treatment.