| dc.description.abstract | The Membrane bioreactor (MBR) is the combination of the activated sludge process and the membrane technique process. With the effective filtrating function of the membrane unit, the suspended solid (SS) in the effluent of an MBR can be reduced to a very low concentration, hence eliminating the requirement of a secondary clarifier. This combination could further simplify the complicated operation requirements of the traditional wastewater secondary treatment facilities and is beneficial to the economic aspects of a treatment process for its less land demand.
In this study, we first surveyed the impact of different hydraulic retention time (HRT) on an MBR. With a fixed sludge retention time (SRT=10 days), pH value (6.8~7.1), dissolved oxygen concentration (DO=5mg/L) and varied HRT (5, 10, 15, 20 hours), the MBR removed influent ammonia-nitrogen (NH4+-N) and chemical oxygen demand (COD) with high efficiency (100% and 94% respectively), and the best treatment efficiency was obtained with an HRT equaled to15 hours. However, the MBR didn’t display a function of phosphorus removal.
To further increase the nitrogen removing efficiency of the MBR system, an anoxic tank was added in the upper stream of the aerobic MBR, which formed a two-stage MBR. With varied reflux ratio of the aerobic tank effluent to the influent (0.5, 1.5 and 2.0 respectively), the two-stage MBR removed COD and NH4+-N significantly, but the removal of phosphorus was not largely increased (efficiency =25%). The best COD and NH4+-N removing efficiency was obtained with the reflux ratio of 1.5.
Utilizing the optimized HRT and reflux ratio, we further tested the two-stage MBR system with different sludge retention time (SRT=10, 20 and 30 days). Results showed that the two-stage MBR performed stably and the total nitrogen removal efficiency could reach 81% with a SRT of 30 days. Moreover, 16S rDNA analysis of the system showed that bacteria belonged to Proteobacteria and Planctomycetale groups existed in the microbial community of the two-stage MBR reactor. We also found aerobic denitrifier at varied SRT. | en_US |