Improvement of sulfamethoxazole (SMX) elimination and inhibition of formations of hydroxylamine-SMX and N4-acetyl-SMX by membrane bioreactor systems.

Sulfamethoxazole (SMX) has frequently been detected in aquatic environments. In natural environment, not only individual microorganism but also microbial consortia are involved in some biotransformation of pollutants. The competition for space under consortia causing cell-cell contact inhibition changes the cellular behaviors. Herein, the membrane bioreactor system (MBRS) was applied to improve SMX elimination thorough exchanging the cell-free broths (CFB). The removal efficiency of SMX was increased by more than 24% whether under the pure culture of A. faecalis or under the co-culture of A. faecalis and P. denitrificans with MBRS. Meanwhile, MBRS significantly inhibited the formation of HA-SMX, and Ac-SMX from parent compound. Additionally, the cellular growth under MBRS was obviously enhanced, indicating that the increases in the cellular growth under MBRS are possibly related to the decreases in the levels of HA-SMX and Ac-SMX compared to that without MBRS. The intracellular NADH/NAD+ ratios of A. faecalis under MBRS were increased whether thorough itself-recycle of CFB or exchanging CFB between the pure cultures of A. faecalis and P. denitrificans, suggesting that the enhancement in the bioremoval efficiencies of SMX under MBRS by A. faecalis is likely related to the increases in the NADH/NAD+ ratio. Taken together, the regulation of cell-to-cell communication is preferable strategy to improve the bioremoval efficiency of SMX.