keywords ACTIVATED-SLUDGE ANAEROBIC-DIGESTION BIOHYDROGEN PRODUCTION ELECTROLYSIS CELL Environmental Sciences Environmental Sciences & Ecology FERMENTATION HYDROGEN-PRODUCTION Life Sciences & Biomedicine MICROBIAL FUEL-CELLS PRETREATMENT SEWAGE SINGLE-CHAMBER Science & Technology acetoclastic methanogenesis anaerobic digestion models bioanode reaction models bioelectrochemical systems energy recovery exoelectrogenic bacteria mesophilic anaerobic digesters wastewater sludge digestion