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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]

In this study, a submerged membrane was installed in a bioreactor to treat N-riched wastewater and obtain high biomass productivity. Chlorella vulgaris was cultivated under mixotrophic, heterotrophic, and photoautotrophic conditions in different kinds of nitrogen sources (nitrate and ammonium) to compare the microalgae growth and nutrient removal in a membrane bioreactor. Further, the respirometric and photosynthetic activities of microalgae were investigated to evaluate the viability of microalgae in different conditions. The highest biomass productivity was obtained under mixotrophic cultivation in ammonium source (0.230 ± 0.009 gr/L d). Moreover, with this type of cultivation and nitrogen source, specific oxygen uptake rate (SOUR) was higher than oxygen product rate (SOPR). However, SOPR improved in mixotrophic cultivation using nitrate source. In both nitrogen source types, the photosynthetic activity of mixotrophic microalgae was reduced at high cell density. Compared favorably with other cultivation types, mixotrophic microalgae could achieve high N and P removal rates (about 23.64–28.84 and 4.38–5.08 mg/L d, respectively). In all cultivation types (except photoautotrophic condition with nitrate source), N and P removal amounts were assimilated to biomass. Based on the obtained results, membrane bioreactor containing mixotrophic microalgae would be the most useful system for application in N-riched wastewater treatment systems. [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]

Membranebioreactors (MBRs) are becoming more suitable alternativesfor conventional wastewater treatment devices. The performance ofa pressure-driven MBR is dominantly affected by the hydrodynamic conditionsof the system. This study was conducted to investigate various hydrodynamiccharacteristics including shear stress, cross-flow velocity, and membranefouling resistance, using computational fluid dynamics (CFD). Simulationof two- and three-phase flow for a flat-sheet submerged membrane modulewas carried out, and the results were compared with the experimentaldata. The CFD simulation was implemented to analyze the fluid-flowpattern, shear stress on membrane surfaces, and cross-flow velocitybetween membranes at various mixed liquor suspended solid concentrationsin the bioreactor. It was shown that the cross-flow velocity playsan important role in the membrane fouling and determination of thecritical particle diameter. To achieve an optimal operating condition,the critical particle diameter was calculated at different air flowrates and permeate fluxes. The CFD results showed that the outermostmembranes are more prone to fouling because of the lower shear stresson their surface as well as the lower cross-flow velocity betweenthem and the module wall. Moreover, the effect of the air bubble diameteron the air and liquid shear stress was investigated to determine anoptimal bubble size. [ABSTRACT FROM AUTHOR]

A new mathematical model is proposed based on filtrationmechanisms for the prediction of fouling in airlift immersedmembrane bioreactors (iMBRs). The cake formation on the membrane surface through constant pressure filtration process in the iMBR was explained by a proposed cake filtration mechanism which assumes that no particle enters the pores when forming the cake layer on the membrane surface. The cake porosity reduction due to diffusion of particles was described by an intermediate blocking mechanism. Experimental study of fouling was also performed in a lab-scale airlift flat-sheet iMBR operating at constant vacuum. The mixed liquor suspended solid (MLSS) concentration was changed within the range of 5000 to 15000mg/L, while the superficial air velocity was varied between 32 and 128m³/m²/h. The presented model includes two parameters, that is, ultimate filtration resistance and initial rate of cake formation. The effect of the MLSS concentration and superficial air velocity on the parameters of the proposed model was studied. The results obtained from the model demonstrated that the ultimate filtration resistance and the initial rate of cake formation are more sensitive to the aeration rate at lower superficial velocities. It was also shown that the ultimate filtration resistance has a linear relation with MLSS concentration. A good agreement exists between the results of the model and the experimental data. The proposed model also showed a better compatibility with the experimental data compared to other fouling models available in the literature. [ABSTRACT FROM AUTHOR]

Abstract: This work investigates filtration performance of mesh filter bioreactor for synthetic municipal wastewater treatment. Critical flux is measured by flux stepping method and the effect of aeration rate on the critical flux is investigated. The long term monitoring of trans-filter pressure evolution at sub and super-critical fluxes is performed. The analysis of resistance is achieved by determination of resistances and microscopic observation of bio-cake. Cake resistance values vary from 78% to 92% of total filtration resistance for sub and super-critical fluxes. The effect of variations of specific aeration demands (SADm: 0.5–6m3/m2 h) on suspended solid of effluent, turbidity of filtrate, filtration resistance, and zeta potential of biomass is evaluated. The results show that filtrate quality is decreased when the aeration rate increases. It is attributed to stable formation of dynamic membrane. A rather clear filtrate, less than 18 NTU of turbidity, is obtained for SADm 0.5m3/m2 h. The results also show that the total filtration resistance of the sub-critical flux significantly decreases with increasing aeration intensity until SADm 2m3/m2 h and thereafter slightly decreases. It is also shown that the variations of zeta potential of biomass with aeration rate highly correspond to the alterations of filtration resistance. [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]