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Ensuring the effluent quality despite fluctuations in influent flow rate and organic load to municipal wastewater treatment plants is critical. This study investigated the performance of a membrane bioreactor (MBR) in handling hydraulic and organic loading shocks during wastewater treatment. The ability of the MBR to remove COD, BOD5, and turbidity from synthetic wastewater was evaluated at steady-state and after applying five levels of organic shock loads (1.5×-4×) and four levels of hydraulic shocks (1.2×-4.7×). Due to the short-term shock-loadings no discernible effect was observed on the mixed liquor suspended solids implying biological stability. The average COD removal in MBR exposed to organic and hydraulic shock loads was 93.8% and 94%, respectively, similar to average BOD5 removals of 94.4% and 93.6%. The membrane retained suspended particles well throughout the process. However, it became quickly fouled only by applying a strong hydraulic shock. The MBR guaranteed the quality of the effluent. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of zeolite for controlling the membrane fouling in a hybrid membrane bioreactor. A control membrane bioreactor without zeolite (CMBR) and a hybrid MBR with zeolite were studied, which were called 4 g L–1 zeolite (Z4-MBR), 8 g L–1 zeolite (Z8-MBR) and 12 g L–1 zeolite (Z12-MBR) within long- and short-term filtration experiments. On average, the Z4-MBR, Z8-MBR and Z12-MBR reduced soluble microbial products (SMPC) by 18.96%, 42.11% and 19.44%, respectively. Furthermore, the ZMBR systems developed lower operational trans-membrane pressure (TMP), lower zeta potential, increased the relative hydrophilicity of sludge and enhanced the concentration of EPS. Reduced membrane fouling and ease of membrane operation are concluded from this study. [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]

This study investigated the long-term filtration of mesh filter with the formed dynamic membrane in bioreactor. The trend of transmembrane pressure (TMP) variations highly corresponded to the thickness and compactness index of dynamic membrane. The dynamic membrane was fractionated by applying two cleaning protocols, that is, rinsing and chemical cleaning. The desorbed fraction, consisting of soluble microbial products (> 70%), provided a stickiness surface for formation of consecutive biomass layer which featured a high concentration of extracellular polymeric substances (> 75%). The chemical oxygen demand (COD) removal was 70%, 89%, and 92% for period of 0–26, 26–49, and 49–67 day, respectively, which indicated that further development of dynamic membrane increased the TMP without improvement in the effluent quality (TMP: 50–200 mbar, COD removal: 89%; TMP: 200–600 mbar, COD removal: 92%). The averageand TN removal was about 76% and 21%, respectively. The effluent turbidity fell less than 2 NTU after 26 days of filtration. [ABSTRACT FROM PUBLISHER]

This study presents a closed-loop process for forming pre-coated dynamic membrane used in membrane bioreactor. Powder-activated carbon (PAC) particles are suspended by using axial-flow agitator whilst simultaneously deposited upon the filter medium by cross-flow filtration. The revolution speed of agitator is varied in the range of 150–450 rpm. Computational fluid dynamic is used to calculate velocity and shear rate adjacent to membrane surface. The force balance of the particles considers the driving force of dynamic membrane formation, drag force due to negative pressure-driven of suction pump, lift force due to mechanical mixing, and adhesive force due to particle–particle interactions. The effect of two major terms including drag and lift forces on the porosity of dynamic membrane is systematically investigated. The lower drag force results in the higher porosity of dynamic membrane. The results also show that the denser dynamic membrane is formed when the lift force becomes lower. The porosity of dynamic membrane is ranged from 0.38 to 0.46 while the thickness of dynamic membrane is altered between 100 and 500 μm. A dimensionless immobilized parameter is derived to predict the formation of pre-coating dynamic membrane. The results obtained from modeling show that dynamic membranes formed at higher values of immobilization parameter have a more cohesive structure. The results obtained from the experiments and the model reveal that the thickness of 400 μm of PAC layer is considered as a stability threshold thereafter the structure of dynamic membrane becomes loose and unstable. The rejection capacity of dynamic membrane is also evaluated at different thicknesses by using Formazin solution. The results reveal that the turbidity of filtrate decreases with increasing the thickness of dynamic membrane. The results display that rejection capacity of pre-coating dynamic membrane is comparable to that of microfiltration membrane. [ABSTRACT FROM PUBLISHER]

This study focused on evaluating the effects of flocculant addition on the performance of membrane bioreactor (MBR). Two different flocculants, aluminum sulfate (alum) and polyaluminum chloride (PACl), were tested and the performance of MBR system in terms of COD removal, membrane fouling, and sludge properties was investigated. Addition of both flocculants resulted in significant reduction of membrane fouling rate and polyaluminum chloride was found more effective than alum. The sustainable filtration time at optimum dosage of alum and PACl was, respectively, 2.5 and 4.2 times more than that in control MBR which had no flocculant. Additionally, sludge oxygen uptake rate (OUR) improved in the presence of both flocculants and average OUR values obtained from flocculant-added membrane bioreactors was about 1.5 times more than that in control MBR. The results also revealed that there were no significant difference in COD removal of flocculant-added MBRs and control MBR and the treatment in all the three MBRs led to high COD removal efficiencies. [ABSTRACT FROM AUTHOR]

Highlights: [•] To develop formation process of self-forming dynamic membrane on mesh filter. [•] To optimize imposed flux and aeration rate for self-forming dynamic membrane. [•] To evaluate efficiency of dynamic membrane bioreactor in removal of COD and TDS. [•] To investigate the preferable cleaning method for recovery of fouled mesh filter. [•] To characterize dominant chemical matter in dynamic membrane using FTIR analysis. [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]

Rheological characterization is of crucial importance in sludge management both in terms of biomass dewatering and stabilization properties and in terms of design parameters for sludge handling operations. The mixed liquor suspended solid (MLSS) and coagulant concentration have a significant influence on biomass properties in biological wastewater treatment systems and in particular in membrane bioreactors (MBRs). In this work the rheological behavior of the biomass in a MBR operated under different MLSS was studied. The range of MLSS in the bench scale MBR was 3800 mg/l to 15200 mg/l. The rheological properties were measured over time and the apparent viscosity was correlated with the concentration of suspended solids under steady-state conditions. Furthermore, a correlation was obtained between sludge viscosity and permeate flux. Results showed that viscosity of activated sludge affects the membrane fouling tendency in an exponential relation between viscosity and fouling in the investigated range in membrane bioreactor. Also coagulants cause reduction of activated sludge viscosity and hence membrane fouling. [ABSTRACT FROM AUTHOR]