Distribution And Mass Transfer Of Dissolved Oxygen In A Multi-habitat Membrane Bioreactor

In this paper, a multi-habitat membrane bioreactor (MHMBR) was used to treat synthetic domestic wastewater to carry out systematic experiment and study. Compared with the conventional activated sludge process, the multi-habitat membrane bioreactor has the conventional MBR’s advantages of high concentrations of activated sludge, long SRT, good water quality and low sludge yield. Moreover, the multi-habitat membrane bioreactor with a multi-habitat environment combining oxic, anoxic-anaerobic, and transition environment between the oxic and the anoxic-anaerobic environment, can meet the survival needs of different microbial species, thus it is greatly improving the diversity of microorganisms within the system. So while maintaining good performance of the bioreactor, the ability of nitrogen removal by multi-habitat membrane bioreactor is enhanced.The multi-habitat membrane bioreactor in this study was used to treat synthetic domestic wastewater to investigate the treatment effect and operation conditions. The ability of nitrogen removal of this system was mainly analyzed during the experiment. In the meantime, DO values of different zones were timely, continuously, automatically and simultaneously monitored to observe distribution of DO and formation process of multi-habitat in the bioreactor. The running performance of this bioreactor was analyzed as well. Besides the above research purposes, the present investigation also focused on determining the factors influencing the volumetric oxygen mass transfer coefficient at high concentrations of activated sludge. The main contents of this study could be summarized as following:The multi-habitat membrane bioreactor was continuously operating for 125 days without any sludge discharged, which began to culture microorganisms from inoculation biomass concentration of 3200 mg/L. For accurately reflecting the DO distribution within the MHMBR, three DO probes were installed, whose values reflected the DO concentrations in the oxic zone, the anoxic-anaerobic zone and the transition zone. All the three DO probes were connected to a computer to record the DO value of the corresponding zones simultaneously. The results indicated that the growth of biomass had an important influence on the distribution of dissolved oxygen. As the extension of operational time, the volumetric oxygen mass transfer coefficient (KLa) was generally decreased. With the difference in DO values, a complex environment combining oxic, anoxic-anaerobic, and transition environment between the oxic and the anoxic-anaerobic environment was produced within a single bioreactor, which provided a fundamental guarantee for stable and high water quality, especially the high total removal of TN. It showed that the average removal rates on COD was 94.14%, the effluent COD concentration maintained below 43.82 mg/L during the whole operation time, so the treatment system could resist the loading fluctuation. Along with the formation of the multi-habitat environment, the removal efficiency of TN could reach to 80.0%. Relatively stable and high removing efficiency of oxygen-consuming substances has verified the stability and the excellent performance of the bioreactor. However, this treatment process seemed to be not available in phosphorus removal, this was because that there was no sludge discharge during the whole operational period. As the extension of operational time, the amount of EPS was generally increased, which led to an increase in the apparent sludge viscosity of MLSS and a deteriorative effect on the membrane fouling.Finally the experimental results also indicated that aeration rate, the concentration and apparent viscosity of MLSS have different influences on KLa, but adjusting the viscosity is a feasible method to improve the mass transfer of dissolved oxygen in the bioreactor.