Membrane fouling reduction and improvement of sludge characteristics by bioflocculant addition in submerged membrane bioreactor

The effectiveness of a green bioflocculant (Gemfloc®) on enhanced performance of a submerged membrane bioreactor (SMBR) was evaluated in terms of membrane fouling reduction and sludge characterization. Two MBRs were operated parallelly in this study, namely conventional MBR (CMBR) and MBR with Gemfloc® addition (MBR-G). Results showed mitigated membrane fouling through Gemfloc® addition in terms of cake layer formation and pore blocking. When compared to the CMBR, in spite of more extracellular polymeric substances (EPS) presented in activated sludge, the MBR-G demonstrated less soluble microbial products (SMP), larger sludge flocs, higher zeta potential and greater relative hydrophobicity of sludge flocs, which decreased cake layer resistance and pore blocking resistance. The reduced cake layer resistance in the MBR-G could be also ascribed to less growth of suspended biomass, lower sludge viscosity, as well as less EPS, SMP and biopolymer clusters in the cake layer. In addition, a modified resistance-in-series model was employed by considering SMP and mixed liquor suspended solids. The simulated results implied that the model could predict the influence of sludge characteristics on membrane fouling behavior of the SMBR.