Hazardous events in membrane bioreactors - Part 2: Impacts on removal of trace organic chemical contaminants

In complement to the initial study assessing the impact of hazardous events on membrane bioreactor (MBR) bulk performances, detailed assessment of the consequences of similar events has now been conducted on the removal of a wide range of trace organic chemical contaminants. The investigated chemicals include 12 steroidal hormones, 4 xenoestrogens, 2 pesticides, 23 pharmaceuticals and personal care products. Under salinity, DNP, ammonia and organic carbon shock conditions, overall removal of hydrophobic chemicals (log D_pH7≥2.5) was not or only slightly affected. Since these chemicals are largely adsorbed to biomass, these results imply that biotransformation within the biomass structure itself was maintained. However, removal of hydrophilic chemicals (log D_pH7<2.5) was commonly observed to be impeded under shock load conditions, indicating loss of bioactivity. This was observed primarily for chemicals which have low or moderate biotransformability. In comparison, easily biotransformable chemicals were largely removed. The susceptibility of less readily biotransformable hydrophilic chemicals to shock loads was due to their reliance upon specific organisms or metabolic pathways for their biotransformation. The results of these experiments show that hydrophilic chemicals with low biotransformability (e.g., sulfamethoxazole, ketoprofen, gemfibrozil and naproxen) could be sensitive indicators for monitoring impacts of hazardous events on removal of trace organic chemicals by MBRs.