[Effects of soluble microbial product on the performance of submerged membrane bioreactor].

The behaviors of soluble microbial products (SMP) and SMP effects on an operational process of submerged membrane bioreactor (SMBR) were studied. Within 90 days performance period, total organic carbon (TOC), molecular weight distributions (MWDs), specific oxygen uptake rate (SOUR)were periodically monitored. The dead-end filtration tests were used to indicate the SMP effect on membrane fouling. Experiment results showed that the concentration of SMP in SMBR supernatant obviously accumulated. As the operation time was prolonged, the concentrations of SMP with MW > 10,000 remarkably increased in SMBR supernatant. Compared with the SMP of MW < 1,000, the SMP with MW > 10,000 obviously affected sludge activity and membrane fouling, but did not significantly influence the SMBR effluent.

[Effect of aeration intensity on the filterability of mixed liquor in membrane bioreactor].

The influence of aeration intensity on membrane fouling in membrane bioreactors (MBR) was to investigate. Two lab-scale MBR with aeration intensity of 500 and 100 L/h were operated for 60 days at a constant permeate flux. The dead-end filtration tests were conducted to confirm the mixed sludge filterability under each condition. The effect of aeration intensity on relative molecular mass distributions of SMP, the particle size distributions (PSD) of flocs and the quantity of extracellular polymeric substances (EPS) in MBRs were also tested. The results show that large aeration intensity has a negative influence on the filterability of mixed sludge in MBR. Further research finds that the large aeration intensity results in the increase of soluble microbial products (SMP) with a relative molecular mass (M(r)) > 10 000 in supernatant, which obviously affects the filtration of mixed sludge. It is also found that small particles in the range of 1-10 microm and the concentration of EPS in flocs remarkably increase under high aeration intensity of 500 L/h.

[Comparison of sludge filtration characteristics between a membrane bioreactor and a conventional activated sludge process].

According to the filtration characteristics of sludge, a comparison between a membrane bioreactor (MBR) and a conventional activated sludge process(CAS) was carried out under similar conditions. Experiment results show that the filtration resistance in MBR was 2 to approximately 3 times of that in CAS. The contribution of supernatant resistance to filtration resistance was about 90% both in CAS and in MBR. The test on resistance distribution showed the cake resistance made up 87.30% and 94.18% of total resistance in CAS and MBR, respectively.