Ozonation of membrane bioreactor effluent for landfill leachate treatment.

Ozonation of leachate effluent obtained from a Membrane Bioreactor (MBR) process treating a medium-aged landfill leachate was investigated. The sequence of ammonia stripping, membrane bioreactor, and ozonation was used in the experiment. Ozonation of the MBR effluent showed reduction in Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) with an increase in five days Biochemical Oxygen Demand (BOD5) concentration. About 73% of COD could be removed at an ozone (O3) dosage of 4.2 mg O3 mg COD(-1). The biodegradability indicated by BOD5/COD ratio increased from 0.03 to 0.08 after ozonation at optimum ozone condition. While analyzing the molecular weight distribution, the fraction of molecular weight (MW) greater than 50 kDa of MBR effluent was transferred to MW 10-50 kDa (38%) at an ozone dosage of 810 mg O3. When O3 dosage was increased to 2,025 mg O3, a rapid change occurred in MW > 50 kDa fraction. This fraction was completely broken down into lower molecular weight fractions. This indicates partial degradation of landfill leachate by ozonation. The colour removal from the leachate was found to be greater than 95%. When the ozonated leachate was recirculated into the MBR system, along with an improvement in the performance of MBR, overall COD removal increased from 78% to 83%. Further, the ozone consumption decreased from 6.1 to 3.4 mg O3 mg COD(-1) removed, thus reducing the ozone requirement.