Essential Factors Of An Integrated Moving Bed Biofilm Reactor- Membrane Bioreactor:Adhesion Characteristics And Microbial Community Of The Biofilm

In this paper, an integrated moving bed biofilm reactor -membrane bioreactor (IMBBR-MBR) was used to treat synthetic wastewater, the removal mechanism of CODCr and NH3-N and the adhesion characteristics and microbial community of the biofilm in the system were presented. IMBBR-MBR not only has the merits of the moving bed biofilm reactor (MBBR) but also has the merits of the membrane bioreactor (MBR).The operation of IMBBR-MBR was divided into two steps:the first step, the system was started on November 19,2014 and kept running for 81 days, the of the regular including CODCr, NH3-N and TP of the inflow of the system, the MBBR area, the MBR area and the effluent of the system were measured to study the removal efficiency and the removal mechanism of the system; the second step, the system was started on March 16, 2015 and kept running for 51 days, the adhesion characteristics and microbial community of the biofilm in an integrated moving bed biofilm reactor -membrane bioreactor (IMBBR-MBR) and further evaluated their variations over operational time were studied by using atomic force microscope (AFM) and high-throughput sequencing. The main results of this study could be summarized as following:The IMBBR-MBR system started by using quick mud hanging membrane with 3500 mg/L inoculation sludge concentration, intermittent running and 24 hours hydraulic retention time (HRT). Seven days later, the system turned to successive running with 8 hours HRT. During the operation of system, a dissolved oxygen meter was used to present the every 10s DO concentration of the MBBR area and the data were transferred to the computer. Results have shown that:During the first operation, the CODcr concentration of the effluent was all lower than 20 mg/L, especially some was lower than 1.33 mg/L. The removal rate of CODCr was all higher than 80%, the best removal rate of NH3-N was 99.65%, but the removal rate of TP was only about 50%. The MBBR area removed major of CODcr and NH3-N and the MBR area had the function for deep processing to make the higher quality water; During the second operation, With multiple methods, including atomic force microscopic (AFM) observation, high-throughput sequencing of the V3-V4 region of 16S rRNA gene, and the analysis of surface roughness and EPS composition in the biofilm, the physic-chemical characteristics and microbial community of the biofilm on carriers were comprehensively illuminated, which showed their dynamic variety along with operational process. The roughness of biofilm on the carriers increased very quickly to a maximum value at the start-up stage, then, decreased and varied to become a flat curve, which exhibited a smooth biofilm on the surface after its mature. As an important component in biofilm, extracellular polymeric substances (EPS) were responsible for agglomerating microorganisms to form a microbial consortia, but only tightly-bond EPS (TB-EPS) have a significantly positive correlation with the adhesive force of biofilm. The development of biofilm could be divided into three categories, during which, the microbial community contained in biofilm experienced a series succession, whose biodiversity gradually decreased along with the operational time going, and Gammaproteobacteria were the most dominant microbial species in class level at the last stage.Overall, the results presented comprehensive understanding regarding the varying tendency of the basic characteristics in biochemical property and microbial community of the biofilm in a pilot-scale combined MBBR-MBR. This paper provides the basic theory for the engineering application of IMBBR-MBR.