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The aim of this study is the synthesis of a magnetic nanocomposite membrane to reduce fouling in a magnetic membrane bioreactor. To this end, Fe 3 O 4 nanoparticles with an approximate size of 60–70 nm were settled into the polysulfone ultrafiltration membrane matrix through blending of Fe 3 O 4 nanoparticles with the dope solution. Nanocomposite membranes containing 0–0.11 wt% Fe 3 O 4 nanoparticles submerged in the magnetic bioreactor system in which the MLSS was considered between 8000–16,000 g/L and the magnetic field intensity was 40–160 mT. The results showed that an increase in the concentration of nanoparticles reduced the filtration resistance as much as 48% and developed the COD removal as much as 24% and increased the flux as large as 30%. The presence of a magnetic field around the bioreactor reduced the total filtration resistance as much as 68% and increased the COD removal as much as 34% due to the production of some changes in the membrane morphology and the sludge properties. Comparing the performance of the synthesized nanocomposite membranes with a MICRODYN-NADIR commercial membrane sample showed that magnetic nanocomposite membranes possess 30% higher flux, 27% lower filtration resistance, 41% higher COD removal compared to a commercial membrane. [ABSTRACT FROM AUTHOR]

Highlights: [•] Presence of cations in MBR removes colloids, soluble biopolymers and induces bioflocculability of activated sludge. [•] Introduction of different multivalent metallic cations is a way of fouling mitigation in MBRs. [•] Pore blocking and cake layer permeability of membrane hydraulic resistance decreased with charge density. [•] Membrane fouling was correlated to biopolymers concentration and mean flocs size of activated sludge. [Copyright &y& Elsevier]

Abstract: In this study membrane fouling was studied in a novel airlift oxidation ditch membrane bioreactor (AOXMBR) working under various high organic loading rates (OLRs). The results confirmed the high performance of AOXMBR in terms of Chemical Oxygen Demand (COD) removal, even at very high OLRs. The role of the membrane barrier appeared to be significant when the COD in the supernatant was high under such conditions. In addition, the study confirmed the performance of the AOXMBR was better in comparison with the conventional activated sludge as such colloid matters cannot be retained via a simple secondary settling step. Also, on-line viability measurement of the activated sludge illustrated that the fouling increased with a decrease in the viability of the activated sludge. The results showed that the qualitative change of the activated sludge affected the fouling phenomenon. The membrane fouling dynamics analysis pointed out the relationship between cause of the membrane fouling and MBR operating conditions. Adsorption in pores appeared to be the dominant cause when any biofilm or deposit was present on the membrane surface. On the other hand at high OLR in the absence of any deficiency (oxygen deficiency, large pH variations etc.) for the microbial population the biofilm played the dominant role consequent, whereas with drastic decreases of OLRs -due to significant cell lysis – external and reversible deposits appeared as the dominant cause of membrane fouling. [Copyright &y& Elsevier]

Abstract: In this study, experiments and computational fluid dynamics were used to evaluate the fouling of membrane surfaces. Based on the resistance-in-series model, the total filtration resistance (R t ) was divided into cake resistance (R c ), adsorption resistance (R a ), internal-plugging (pore-blockage) resistance (R pb ) and intrinsic-membrane resistance (R m ). The values of each resistance and their relative percentages as a function of the operating parameters were experimentally determined. The effect of inlet air-flow rate and the baffle angle on the resistances were also investigated. It was then shown that the permeate flux and resistances could be related to the wall shear stresses of air and liquid flows at the membrane surface. Average shear stress was found to increase by increasing the air-flow rate. The change in baffle angle from 90° to 85° increased the shear stress of air on the membrane surface. At low air-flow rates there was a lower meandering of air as well as the area of the membrane, which is not subject to high-shear increases. The shear stresses of air and liquid on the membrane surface were determined by computational fluid dynamics and correlations were proposed for estimating each resistance of the membrane from these shear stresses. [Copyright &y& Elsevier]

Abstract: The effects of sludge viability on process performance and membrane fouling in a membrane bioreactor were investigated. A laboratory-scale submerged membrane bioreactor (SMBR) containing a flat-sheet microfiltration membrane was used at various percentages of living cellular flocs and dead cells. The effect of live to dead cells ratio on the extracellular polymeric substances (EPS) concentration was also studied. The proportion of dead cells affected the type of EPS in the mixed liquor as well as hydrophobicity of activated sludge. Tightly bound EPS (TB-EPS) mitigated membrane fouling, whereas loosely bound EPS (LB-EPS) caused severe membrane fouling. The results show that the content of TB-EPS and LB-EPS increases with dead cells portion. Furthermore, the ratio of TB-EPS to LB-EPS was presented as an important parameter in MBR performance. It was showed that this ratio is a good representative of flocculability of activated sludge and fouling intensity. Compared to the live cells, the dead cells had lower hydrophobicity and induced membrane fouling so that membrane permeability of the viable activated sludge was twice of the dead cell culture. The potential of zone settling velocity (ZSV) to be considered as a key parameter in MBR operation was also reported. [Copyright &y& Elsevier]