| Dynamic Membrane Bio-Reactor (DMBR) has drawn great intention in recent years. Filtration process using a large aperture in the retina of the sludge layer formed on the surface play a role in retention and solid-liquid separation. Due to its low cost, the DMBR has high value for research and application. During the membrane filtration process, the filtration substances are retained or absorbed on the surface of membrane to form a layer of filtration cake. When this cake layer becomes thick, it would cause permeate decreasing and trans-membrane pressure (TMP) increasing. This phenomenon is called membrane fouling. Although the filtration cake could increase energy consuming, it could also help to retain finer particles and thus enhance the filtration performance of the system. Compared to common membrane, the dynamic membrane has better permeability. However, as with MBR systems, membrane fouling indicated by the undersirable increase of filtration resistance remains the most serious problem greatly impairing the performance of DMBR systems.In this study, the dynamic membrane formation on the surface of 90μm pore size nylon mesh in a DMBR for simulated municipal wastewater treatment was investigated. The results showed that the initial rate of flux and dynamic membrane formation was positively correlated. At stable operation condition of MLSS=4500mg/L and membrane flux=10L/(m~2·h), the average removal rates of COD and ammonia nitrogen were 92.4%, 93.1%, respectively. The dynamic membrane averagely removed 7.6% of COD, and 7.2% of ammonia nitrogen in the supernatant of the mixed liquor. This indicates that the removal of pollutants in DMBR was mainly attributed to the activated sludge mixture, but the dynamic membrane bio-degradation can also remove a small part of the pollutants. Extracellular polymeric substances (EPS) of sludge were mainly composed of proteins and polysaccharides, which accumulated in the reactor. Observation of microscopy showed that biological sludge mixture phase also changes with the running time. Sludge bulking and disintegration were observed during the different period of reactor operation. The formed dynamic membrane was detected by FTIR, and the main pollution substances on the membrane surface are polysaccharides and proteins.The dynamic membrane formation and membrane fouling characteristics of normal sludge, bulking sludge and deflocculated sludge were investigated in submerged nylon mesh DMBR, and the fouling mechanisms were explored from the aspects of EPS, relative hydrophobicity (RH), sludge viscosity (μ), Zeta potential and contact angle. The results showed that the bulking sludge could cause severe cake fouling due to adsorption and bridging of filamentous bacteria. The deflocculated sludge reduced the effective filtration area, which resulted from the deposition of colloidal particles and soluble matter that deposited on the membrane pore. Comparatively, the normal sludge had a slightly lower membrane fouling tendency and thus the best performance. It was also found that the EPS content and its composition, and the sludge morphology were the two major factors affecting sludge properties and fouling behaviors of DMBR. |
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