Study On Optimization In Submerged Membrane Bioreactor Operating Conditions And System Design

Submerged membrane bioreactor (SMBR) technology is regarded a key option of wastewater treatment in the future, which combines the activated sludge treatment and membrane separation process. Although a lot of SMBR treatment plants have been commissioned in the world, high costs and membrane fouling are the bottlenecks of this promising technology. To the disadvantages of SMBR in operation, particularly for the lack experiences in the Chinese membrane modules application, this dissertation assessed the aspects such as operation performance, membrane fouling characters, membrane cleaning, energy costs, and membrane module. Through this study, treatment qualities, energy consumption, membrane module would be balanced to an optimal working conditions and it was expected to provide evidences for full-scale SMBR.Firstly, based on 262 days multistage experiments, an orthogonal analyzing model of SMBR implementation was established. The results showed that, the mix liquid suspended solid had the largest effect on membrane fouling and followed by air to water ratio and on/off ratio. In addition, the optimal operation performance was recommended from effluent qualities and membrane fouling.Secondly, mathematical methods were used in analyzing membrane fouling development in multistage experiment. It was shown that membrane fouling in SMBR is characteristic by two stages development profile. In the first stage, microscopic depositing and clinging on the membrane surface had taken a majority of fouling. And cake layer forming with a transfer membrane pressure (TMP) rapid rise was the remarkable character in second stage. According to this theory, a maintenance chemical in-line cleaning protocol was suggested in this study for the first time, which could avoid high pressure working conditions and prolong membrane life. To ensure security in chemical in-line cleaning, the damages in chemical backwashing to microorganism were appraised. Sodium hypochlorite was recommended in soak chemical cleaning. And soaking temperature and time were also important for flux recovery.Thirdly, aiming to reducing of high energy cost, a concept of loading distribution which could combine the virtues of two style aeration systems in SMBR was introduced. The concept could not only maintain low fouling rate but also reduce energy consumption. With lab-scale experiment and aeration calculation model, the total aeration rates were simulated in different working conditions. What's more, the concept of loading distribution could optimize energy consumption in SMBR.At last, for the first time, a mathematic model which based on the theory of fiber axial non-uniform distributed fouling was proposed. With this model, membrane fouling and flow rate per energy consumption in SMBR was optimized. Then, it could be concluded that increasing fiber lumen diameter and reducing fiber length were benefit for fouling controlling. Furthermore, through simulated analyzing, optimal fiber dimension in working condition was presented. Finally, an experiment of reactor configuration influencing membrane fouling was carried out, which showed that air lift design could prevent membrane fouling in some degree. The results provided preliminary basis materials for integrated module design.