Energy-efficient wastewater treatment plants (WWTPs) utilize systems like high-rate activated sludge (A-stage) system to redirect organics from wastewater are redirected into energy-rich sludge (A-sludge). Anaerobic membrane bioreactors (AnMBRs) offer lower footprint and higher effluent quality compared to conventional digesters. In this study, the biological treatment and the filtration performances of AnMBRs for A-sludge digestion under mesophilic and thermophilic conditions were comparatively evaluated through lab-scale experiments, mass balancing and dynamic modeling. Under thermophilic conditions, a higher COD fraction of the influent sludge was converted into methane gas than under mesophilic conditions (65% versus 57%). The energy balance indicated that the surplus energy recovery under thermophilic conditions was less than the additional energy required for heating the AnMBR, resulting in a more than three-fold higher net energy recovery under mesophilic conditions. Therefore, operating an AnMBR for sludge digestion under mesophilic conditions has a higher potential to improve the energy balance in WWTPs.

BACKGROUND: Membrane technology is used for the treatment of produced water enabling high permeate quality to meet discharge standards or potable and irrigation water quality standards. In this study, the effect of hybrid membrane-activated carbon processes on the performance of nanofiltration (NF) and reverse osmosis (RO) membrane systems treating mixed oil and gas field produced water was investigated. Different pre-treatment alternatives including combinations of microfiltration unit and powdered activated carbon (PAC) or granular activated carbon (GAC) systems were applied prior to nanofiltration and reverse osmosis processes. RESULTS: The activated carbon process increased chemical oxygen demand (COD) and conductivity removal efficiencies due to the organic matter and ion adsorption capacity of activated carbon. PAC addition gave the best removal efficiencies for COD, whereas highest conductivity removals were obtained in studies with GAC addition. CONCLUSION: Differences obtained in the performance of different pre-treatment alternatives based on targeted pollutants and membrane characteristics confirmed synergetic/antagonistic effects between pre- and final membrane treatment.