Microenvironment Characteristics And Membrane Fouling Control In Membrane Bioreactor For Municipal Wastewater Treatment

Membrane bioreactor (MBR) is a new technology combining biological treatment with membrane separation for sewage treatment. Research on MBR for municipal wastewater treatment was conducted both in laboratory and in sewage treatment plant. The following results are obtained:By comparison with conventional activated sludge process (CAS), pollutants removal characteristic and kinetic analysis were revealed detailedly. The blockage of membrane module in MBR enhances removal efficiency and ability to resist impact of pollutants, pH and temperature. Both ammonium-oxidizing and denitrifying reaction in MBR accord to zero-grade reaction formula, and the corresponding degradation rate constant was 2.2 and 2.5 times respectively over CAS. The nitrifying rule is not obvious in MBR. The amount of total bacteria, nitrifying bacteria, ammonium-oxidizing bacteria and denitrifying bacteria in MBR are higher than corresponding bacteria 1~2 order of magnitude in CAS separately.By 170 day's continuous running test, microenvironment characteristics were investigated in MBR for municipal wastewater treatment with no biomass wasting. It is found that sludge concentration levels off at around 7000 mg/L. Dehydrogenase activity and sludge subside characteristic in MBR are inferior to CAS at stabilizing period. Accumulation of soluble microbial products (SMP) is occurred in MBR but it could be degraded further along with test progressing. Mass loading is negative correlation with extracellular polymers (EPS) concentration. EPS is mainly composed of polysaccharide and protein, and the two attribute over 60% to total COD of EPS.The influence of particular microenvironment and operation parameters in MBR on effluent quality, microbial viability and operation stabilization was discussed generally. The effluent COD is increasing with the supernatant COD increasing while dehydrogenase activity is declining obviously during the middle operation period. Economic aeration intensity is exponential increasing with sludge concentration enhancing. Membrane fouling developing is varied with sludge concentration under economic aeration intensity and it would be accelerated with too high or too low sludge concentration.The microfauna community variety in MBR along with time going was investigated, and the indicative effect of microfauna on MBR operating was discussed meanwhile. Microfauna in MBR are changed from active sludge bacteria to middle active sludge bacteria with time. The pertinence between microfauna species, number and COD removal efficiency is not obvious. The amount of total microfauna and sarcodina has great influence on the removal efficiency of NH4+-N and TN.The relative contributions of suspended solids, colloids and dissolved molecules to filtration resistance...