Microbial ecology and performance of nitrifying bacteria in an aerobic membrane bioreactor treating thin-film transistor liquid crystal display wastewater

This study was conducted to evaluate the long-term performance of an aerobic membrane bioreactor (MBR), treating TFT-LCD wastewater containing dimethyl sulphoxide (DMSO), monoethanolamine (MEA) and tetra-methyl ammonium hydroxide (TMAH), which are recognized as slow-biodegradable organic compounds containing nitrogen and can release significant amount of ammonia during biodegradation. Moreover, many studies have reported that certain organic compounds can potentially inhibit nitrification of AOB, but limited information is available regarding the effects of TFT-LCD wastewater compounds on nitrification performance and microbial ecology of nitrifying bacteria. In general, the aerobic MBR achieved satisfactory conversion efficiency for DMSO, MEA, TMAH, and ammonia, except that a sudden inhibition on MEA degradation was observed for a transition period when the influent feed switched from synthetic to real TFT-LCD wastewater. Furthermore, the terminal restriction fragment length polymorphism (T-RFLP) methodology was applied to monitor the microbial ecology of nitrifying bacteria in the aerobic MBR. The results suggested that Nm. marina or Nm. cummunis were the dominant AOB population in the aerobic MBR fed with synthetic TFT-LCD wastewater, while Nitrosospira became dominant in the aerobic MBR fed with real TFT-LCD wastewater. For the NOB population, both Nitrobacter and Nitrospira were present during this study. Finally, the results of batch experiments, which were conducted to evaluate the effects of DMSO, MEA, and TMAH on nitrification activity, indicated that MEA and TMAH became inhibitory to nitrifying bacteria at concentrations of 250 and 50 mg/L, respectively, while DMSO did not at concentrations up to 100 mg/L.