Enzyme augmentation of an anaerobic membrane bioreactor treating sewage containing organic particulates

Hydrolytic enzymes offer the potential for enhancing the hydrolysis of organic particulates, which tends to be rate limiting in the anaerobic treatment of particulate containing wastewaters. In this study, the effects of enzyme augmentation on the biological performance of a laboratory submerged anaerobic membrane bioreactor (AnMBR) were investigated. A hydrolytic enzyme blend containing proteases, amylases and lipases was added to the bioreactor daily at doses ranging from 0.9 to 18 mL/g of influent COD to enhance the hydrolysis of organic particulates and soluble macromolecules. Enhanced enzymatic hydrolysis resulted in the reduction of total and volatile suspended solids by approximately 19% and 22%, respectively, on the average. Overall COD removal efficiency was unaffected while the average biogas production increased from 0.27 to 0.34 L/g of influent COD. Additionally, the concentrations of bound extracellular polymeric substances (EPS) and soluble microbial products (SMP) decreased and increased respectively, suggesting the enzymatic hydrolysis of EPS to SMP. Low enzymatic activities were detected throughout the entire study, probably due to the instability of free enzymes in the bioreactor environment. Nevertheless, membrane retention of exogenous enzymes within the AnMBR is an inherent feature, as evidenced by size exclusion chromatography.