Study On Carbon & Nitrogen Removal Performance And Biofilm Chatacteristics Of MABR For Municipal Wastewater Treatment

Membrane-aerated biofilm reactor( MABR) is a promising wastewater treatment technology. In this study, a series of novel and bench-scale MABRs were thoroughly investigated in terms of carbon and nitrogen pollutants removal performances under various working conditions, the shift process of bacterial and archaeal community in biofilms, the effects of functional microorganisms on the operation efficiency, and the assembles and regulation of microbial community in biofilm, based on the approach incorporating the traditional monitoring methods for wastewater and biofilm and high-throughout sequencing technology. The main results were summarized as follows:The biofilms in MABR performed excellent adsorption and oxidation abilities for COD regardless of low temperature, high salinity, poor air-supplying pressure, strong flow shock and high influent COD and NH4-N concentrations under conditions of 24-h HRT and good biochemical degradability in the batch experiment. However, the ammonia oxidation process was easily subjected to the inhibition of low temperature, low pressure and high influent NH4-N concentration. Meanwhile, simultaneous TN and NH4-N removal was ubiquitously observed although high salinity, to some extent, weakened the denitrification in biofilm. Moreover, the shortage of carbon resource resulting from the initially rapid COD removal in bulk could not affect the reduction of later TN because of the endogenous respiration and dead organisms as its carbon source in the oligotrophic phase. Meanwhile, aerobic denitrification occurred in biofilms under the most applied conditions in the research. In addition, the reactors always exhibited great performance of more than 90% removal rates of COD, NH4-N and TN, when the influent COD and NH4-N concentrations were 200-400 and 30-40 mg/L, respectively.The dominant organisms were comprised of Anaerolineae, Betaproteobacteria, Alphaproteobacteria, Gammaproteobacteria and Candidatus Nitrososphaera. The changing relative abundance of these microorganism exerted significant influence on the change of efficiency of MABR for domestic wastewater trearment.There were many kinds of organisms associated with nitrogen removal in biofilms, such as ammonia-oxidizing bacteria(AOB) or archaea(AOA) and denitrifying bacteria. Among them, Nitrosomonas was the main AOB which was easily subjected to the inhibition of low temperature, high salinity and low pressure. Candidatus Nitrososphaera was the major AOA which tended to survive in the above habitat, and probably played more important role in the nitrification than Nitrosomonas. The denitrifier mainly consisted of anaerobic Hydrogenophaga, aerobic Hydrogenophaga and photosynthetic Rhodobacter. These diverse nitrifiers and denitrifiers strengthed the nitrogen removal ability of MABR.The microbial success in biofilms was probably the joint effect of working conditions and ecology drift, of which working conditions were the main driving force affecting the change of climax community structure. Thus, the MABR performance could be optimized by regulating the microbial composition through the change of environment variables.The same condition exerted different influences on the bacteria and archaea in biofilms in MABR. And the weight of environmental factors on bacteria or archaea also differed remarkably. Among these variables, effects of salinity and temperature on bacterial community were higher than ones of influent COD, flow velocity, air-supplied pressure and influent NH4-N concentration, while the influences of temperature, flow velocity and salinity on archaeal community were greater than ones of influent NH4-N concentration, air-supplied pressure and influent COD concentration.