Studies Of The Membrane Fouling Behavior In Forward Osmosis Membrane Bioreactor

Osmosis membrane bioreactor (OMBR), as a new emerging technology, has a bright prospect in wastewater treatment, while the membrane fouling behavior of OMBR has not been explored. In this paper, we studied the influences of activated sludge properties on flux behavior and the characterization of the cake layer in OMBR.In this paper, two models were developed to predict the flux decline rate involving activated sludge properties through the employment of partial least squares (PLS). The presented models owned good goodness-of-fit, robustness and predictive power. The osmosis pressure of the activated sludge played a dominant role in the flux decline, attributing to its strong negative impact on initial flux as the draw solution concentration was the same. The higher the initial flux was, the faster the flux declined. The solute and bound polysaccharides had negative relationships with the flux decline rate, which was due to their positive impact on the activated sludge osmosis pressure as well as the polysaccharides were not the dominant foulant. The relative hydrophobicity (RH) affected the flux decline positively due to the hydrophobicity of the FO membrane. Bound and solute protein affected the flux decline rate through their positive impact on RH as well as they were the primary foulant for their hydrophobic nature. MLSS and mean sludge particle size (MPS) had positive relationships with flux decline rate due to activated sludge with higher MLSS containing more foulant and tiny pores structure of the forward membrane active layer.In the study of the characterization of the cake layer formed in OMBR, the results indicate that the bigger particles would deposit on the membrane earlier, as the OMBR running, the particles in the bioreactor turned small, and then the smaller particles would deposit on the membrane. The cake layer formed on the membrane has well strength and it was easy to flush away from the membrane. The SEM analysis exhibited that the side contacted to the FO membrane of the cake layer was very smooth and the flushed FO membrane was very clean with little foulant on it. This is because the osmosis membrane has small roughness and tiny pores, so the foulant can’t enter into the membrane pores and connected loosely with the membrane. In the cake layer,51%weight percent was biofoulant and49%weight was inorganic foulant. We can see that biofoulant and inorganic matter have strong impacts on membrane fouling process. The main components of biopolymers were identified as proteins and polysaccharide materials by the FTIR. The examination by EDX demonstrated that Si, Ca, Mg, Al and Fe were the major inorganic elements in fouling cake. Therefore, during the operation of OMBRs, the biopolymers and inorganic matter in the bioreactor should be controlled to minimize membrane fouling.