Sustainable approach for enzyme augmentation in anaerobic membrane bioreactors

• Main Author: Loh, Carissa Mei Ling L.
• Other Authors: School of Civil and Environmental Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/53870
• Institution: Nanyang Technological University

Enhancing the hydrolysis of macromolecular extracellular polymeric substances and organic particulates with hydrolytic enzymes may potentially alleviate membrane fouling and solids accumulation in membrane bioreactors respectively. Prior studies investigating the effects of hydrolases on wastewater have been conducted, with positive results. As supplementing commercial enzymes may not be cost-feasible, in this study the recovery of hydrolases from wasted sludge was investigated. α-amylase, α-glucosidase and protease were recovered from wasted sludge via ultrasonication, and their activities quantified. An optimization study was carried out to determine the optimum ultrasonication intensity and duration for the maximum solubilization and recovery of enzymes. Next, the effects of recycling the recovered enzyme extracts were studied over a duration of two months, using three customized 500ml Erlenmeyer flasks as batch reactors – one augmented with recycled enzyme extracts from wasted anaerobic sludge, one augmented with recycled enzyme extracts from aerobic sludge, and one control. Biogas production was monitored on a daily basis, while sCOD, TSS and VFA analysis was done thrice a week. The optimum ultrasonication parameters for maximum enzyme recovery and maximum solubilization were determined to be 30 minutes at 65 W. It was found that ultrasonication results in 60-70% and ~40% reduction in TSS for anaerobic and aerobic sludge respectively, which may translate to potential downstream processing cost savings. The control bioreactor had a biogas production of 225ml/day, approximately 60% of which was methane gas. In contrast, the bioreactors augmented with recycled enzymes from anaerobic and aerobic sludge had biogas productions of 203ml/day and 85ml/day respectively. As it was observed that recycled enzymes exhibited a slight inhibition on the anaerobic process, the biodegradability was investigated, and the pseudo first-order hydrolysis kinetic constants were found to be 0.0141 d-1, 0.0276 d-1 and 0.0795 d-1 for the control, bioreactors augmented with anaerobic sludge-derived enzymes and aerobic sludge-derived enzymes respectively. The faster degradation kinetics for the two test bioreactors showed that despite initial signs of inhibition, as suitable microbial strains developed over time, the accumulated organic matter could be degraded.