Evaluating the Fate of Several Micro-Pollutants in Wastewater Using Membrane Bioreactor and Conventional Activated Sludge Reactor

Safe water reuse depends on the understanding and control of micro-pollutants in wastewater treatment and effluent reuse practices. Micro-pollutant impacts on human health and other living organisms have promulgated extensive research on wastewater treatment technologies with varying levels of success. While each type of wastewater treatment systems has its own merit, they vary dramatically in their energy requirements, cost-benefits, sensitivity and reliability in removing a wide range of pollutants. In the reported study, membrane bioreactor (MBR) with relatively greater pore size and conventional activated sludge reactor (CAS) were evaluated for their ability to remove a few classes of micro-pollutants together. Two solid retention times (SRTs) of 9 and 18 days were used to investigate the removal efficiency of micro-pollutants. Micro-pollutants belong to pesticide (aldicarb), herbicide (atrazine and glyposate), anti-inflammatory drug (Ibuprofen) and psychoactive stimulant drug (caffeine) were introduced to influent at a 200-ėg L-1 concentration. Results showed that both aldicarb and caffeine biodegraded effectively (90-100%) under both SRTs with no obvious difference between reactors. For anti-inflammatory drug, ibuprofen, biodegradation rate fluctuated during lower and higher SRTs. The slightly greater removal efficiency at lower SRT (35%) disappeared at higher SRT (20%) in CAS probably be attributed to limited biomass settling characteristics at higher SRT in that reactor. Ibuprofen biodegradation efficiency was similar and about 40% at both SRTs in MBR. Minimal biodegradation of atrazine (<2%) was observed in CAS at 9 day SRT and did not improve even at higher SRT. Atrazine biodegradation was approximately 20% and 30% in MBR for lower and higher SRTs, respectively. Glyposate degradation fluctuated significantly between sampling times with no specific trend in both reactors. Among the less degradable pollutants atrazine and ibuprofen had high affinity to water while glyposate was biphasic. Despite the irregularity in herbicide biodegradation, the MBR system was comparatively more effective in removing atrazine than the CAS and generally offers smaller footprint and more stable performances for the tested micro-pollutants. These preliminary results demonstrate the challenge in removing recalcitrant micro-pollutants in biological treatment systems, and also point to the directions for future research and development of the treatment technologies to assure safe water reuse.