Dynamic membrane bioreactor for wastewater treatment: Operation, critical flux, and dynamic membrane structure

This research investigated the characteristics of the dynamic membrane bioreactor (DMBR) for wastewater treatment, including operation performance, critical flux of dynamic membrane (DM), and structure of the cake layer. Various analytical methods were used. The DMBR exhibited excellent pollutant-removal efficiencies, and the critical flux of DM was in the range of 70-75 L/m(2)h. The DM operated at sub-critical flux exhibited longer filtration time and smaller flux decline in the filtration process. The DM formed by activated sludge exhibited a hierarchical structure, and the order of mean particle size of three cake layers was as follows: top cake layer < middle cake layer < bottom cake layer. Protein (PN) was the major part of extracellular polymeric substances (EPS) in the three layers and its concentration did not show obvious decline from the top cake layer to the bottom cake layer, whereas the quantity of polysaccharides (PS) exhibited an increased tendency, which was also proved by confocal laser scanning microscopy (CLSM) image analysis. Total EPS (T-EPS) content did not show obvious variations among the three cake layers. The middle cake layer contained the most high-molecular weight (MW) substances with MW larger than 160 kDa and the bottom cake layer contained the lowest high-MW substances. The light bound EPS (TB-EPS) was the major content of T-EPS in the residual substances on the backwashed stainless steel mesh. The quantity of PN attached to the mesh was much greater than that of PS. More residual substances were attached on the outer support mesh. Residual substances of the inner support mesh were mainly attached on the intersection of the two stainless steel wires, whose interaction was enhanced by the inorganic ions. (C) 2013 Elsevier B.V. All rights reserved.