Dynamics of microbial community and their effects on membrane fouling in an anoxic-oxic gravity-driven membrane bioreactor under varying solid retention time: A pilot-scale study.

Membrane fouling in a membrane bioreactor (MBR) is highly influenced by the characteristics of the influent, the mixed liquor microbial community and the operational parameters, all of which are environment specific. Therefore, we studied the dynamics of microbial community during the treatment of real municipal wastewater in a pilotscale anoxic-oxic (A/O) MBR equipped with a gravity-driven membrane filtration system. The MBR was operated at three different solid retention times (SRTs): 25, 40 and 10 days for a total period of 180 days in Nordic environmental conditions. Analysis of microbial community dynamics revealed a high diversity of microbial species at SRT of 40 days, whereas SRT of 25 days was superior with microbial richness. Production of soluble microbial products (SMP) and extracellular polymeric substances (EPS) was found to be intensely connected with the SRT and food to microorganism (F/M) ratio. Relatively longer operational period with the lowest rate of membrane fouling was observed at SRT of 25 days, which was resulted from the superior microbial community, lowest production of SMP and loosely bound EPS as well as the lower filtration resistance of larger sludge flocs. Abundance of quorum quenching (QQ) bacteria and granular floc forming bacterial genera at SRT of 25 days provided relatively lower membrane fouling tendency and larger floc formation, respectively. On the other hand, substantial amount of various surface colonizing and EPS producing bacteria was found at SRT of 10 days, which promoted more rapid membrane fouling compared with the fouling rate seen at other tested SRTs. To sum up, this research provides a realistic insight into the impact of SRT on microbial community dynamics and resulting characteristics of mixed liquor, floc size distribution and membrane fouling for improved MBR operation.

Removal and fate of emerging organic micropollutants (EOMs) in municipal wastewater by a pilot-scale membrane bioreactor (MBR) treatment under varying solid retention times.

This study investigates the removal and fate of 23 emerging organic micropollutants (EOMs) including a wide range of pharmaceuticals (antibiotics, ß-blockers, analgesics, diuretics, psychostimulants, antiepileptics, immunosuppressives, anticoagulants), and steroid hormones detected in municipal wastewater by a pilot-scale membrane bioreactor (MBR) plant at two different solid retention times (SRTs) of 60 and 21 days. Different removal efficiencies of the selected EOMs were observed and explained based on their physicochemical properties (such as distribution coefficient, log D; dissociation constant, pKa; solid-water distribution coefficients, and Kd) along with process operating parameters. The dominant removal mechanisms of EOMs were biotransformation and sorption onto the sludge, which were confirmed by the mass balance study. Moreover, changes in the sludge properties, as a consequence of different SRTs, were evaluated based on variations in soluble microbial products (SMP), extracellular polymeric substances (EPS), and capillary suction time (CST). Finally, the quality of the MBR effluent was compared with some established guidelines, which confirmed the fulfilment of water quality requirements for reuse purposes.

Influence of relaxation modes on membrane fouling in submerged membrane bioreactor for domestic wastewater treatment.

Relaxation and backwashing have become an integral part of membrane bioreactor (MBR) operations for fouling control. This study was carried out on real municipal wastewater to evaluate the influence of different operational strategies on membrane fouling at equivalent water yield. Four relaxation modes (MBR10+0, MBR10+1, MBR10+1.5 and MBR10+2) were tested to analyze membrane fouling behavior. For the optimization of relaxation modes, fouling rate in terms of trans-membrane pressure, hydraulic resistances and characteristics of fouling fractions were analyzed. It has been observed that cake layer resistance was minimum in MBR10+1.5 but pore blockage resistance was increased in all relaxation modes. Moreover, high instantaneous flux contributed significantly to fouling rate at the initial stage of MBR operations. Relaxation modes were also efficient in removing irreversible fouling to some extent. Under all relaxation modes, COD removal efficiency ranged from 92 to 96.5%. Ammonium and TP removal were on the lower side due to the short solids and hydraulic retention time.

Assessing membrane fouling and the performance of pilot-scale membrane bioreactor (MBR) to treat real municipal wastewater during winter season in Nordic regions.

In this study, the performance of a pilot-scale membrane bioreactor (MBR) to treat real municipal wastewater was assessed at low temperatures (7 to 20°C) in Nordic regions. First, the effect of low temperatures on membrane fouling was evaluated by monitoring trans-membrane pressure. A significant membrane fouling was observed when the sludge temperature inside the MBR unit was below 10°C with a 75% permeability drop, thus indicating high deterioration of the membrane performance at low temperatures. Moreover, increasing values of sludge volume index (SVI) during low temperatures showed high deterioration of sludge settleability. As for the pollution removal, MBR achieved high performances primarily for pathogens and emerging micropollutants. The average log reductions of 1.82, 3.02, and 1.94 log units were achieved for norovirus GI, norovirus GII, and adenoviruses, respectively. Among the four trace organic compounds (TrOCs), the average removal efficiencies of bisoprolol, diclofenac and bisphenol A were 65%, 38%, and >97%, respectively. However, carbamazepine was not efficiently removed (-89% to 28%). Regarding trace metals, an average removal of >80% was achieved for Cd, Pb, and V. For the rest of the metals, the removal capacities were between 30 and 60%.