Aerobic Biological Treatment of Synthetic Municipal Wastewater in

Abstract: Membrane-coupled bioreactors (MBRs) offer many benefits compared to conventional biological wastewater treatment systems; however, their perfor-mance characteristics are poorly understood. Labora-tory-scale MBRs were used to study bacterial adapta-tions in physiology and community structure. MBRs were fed a mixture of starch, gelatin, and polyoxyethyl-ene-sorbitan monooleate to simulate the polysaccharide, protein, and lipid components of municipal wastewater. Physiological adaptations were detected by measuring ectoenzyme activity while structural dynamics were studied by denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments. As cell bio-mass accumulated in the MBRs, pollutant removal effi-ciency initially improved and then stabilized with respect to effluent concentrations of chemical oxygen demand, protein, and carbohydrate. Comparison of the MBR efflu-ent to filtered reactor fluid indicated that a portion of the observed pollutant removal was due to filtration by the membrane rather than microbial activity. The rates of ectoenzyme-mediated polysaccharide (-glucosidase) and protein (leucine aminopeptidase) hydrolysis became relatively constant once pollutant removal efficiency sta-bilized. However, the maximum rate of lipid hydrolysis (heptanoate esterase) concomitantly increased more than 10-fold. Similarly, -glucosidase and leucine amino-peptidase ectoenzyme affinities were relatively constant, while the heptanoate esterase affinity increased more than 30-fold. Community analysis revealed that a sub-stantial community shift occurred within the first 7 days of operation. A Flavobacterium-like bacterial population dominated the community (>50 % of total band intensity) and continued to do so for the remainder of the experi