BACKGROUND Membrane bioreactor (MBR) is commonly considered a promising technology for wastewater treatment due to its outstanding effluent quality, low sludge production, and smaller environmental footprint. However, membrane biofouling is regarded as the bottleneck of MBR processes preventing their universal application. Optimizing operating conditions and improving the antifouling properties of membranes have a substantial impact on the rate and characteristics of membrane fouling in MBR systems. RESULTS In this study, a two‐step process was performed to mitigate membrane fouling by optimizing sludge retention time (SRT) and organic loading rate (OLR) and improving membrane characteristics in an MBR system developed for the treatment of pharmaceutical wastewater. At first, pure membrane fouling and sludge characteristics were examined in three identical MBRs at different OLRs (40, 100, and 160 mg chemical oxygen demand(COD)/L.d) under various SRTs (7.5, 22.5, and 37.5 days). The investigation indicated that high protein concentration in loosely bound extracellular polymeric substances (LB‐EPS) caused more irreversible fouling at the OLR and SRT of 40 mgCOD/L.d and 7.5 days, respectively. In the second stage, a modified anti‐biofouling membrane was installed into the optimized submerged MBR at OLR = 100 mgCOD/L.d and SRT of 22.5 days for further mitigation of membrane fouling. Membrane fouling significantly reduced as the protein and gram negative bacteria on the surface of the modified membrane decreased. CONCLUSION The results showed that the reversible and irreversible membrane fouling were controlled successfully through the proposed optimization of operational conditions and by improving the membrane characteristics in MBR. Finally, the protein of LB‐EPS is a vitally important factor affecting the irreversible membrane fouling. © 2020 Society of Chemical Industry (SCI)

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Water plays a crucial role in every animate life. There are a multitude of problems that can be occurred without water; thereafter, mankind’s lives can be extinct. Several solutions should be implemented in order to protect water supplies and to treat water used in industries. Among solutions, wastewater treatment is sounded economical and convenient way to overcome water scarcity. Physical, chemical, biological, and mixed treatment systems provide ample opportunity to use water over and over again. However, by using nanotechnology in these systems wastewater treatment can reach much more quality and overcome their drawbacks. Nano-membranes in MBR technology is one of most appropriate treatment technologies that have such potential to postpone water shortage until several years.

BACKGROUND The effects of sludge retention time, organic loading rate, specific aeration demand per membrane area (SADm) and exploiting poly(vinyl chloride)/polycarbonate/modified silver nanoparticles (PVC/PC/MAg) nanocomposite membrane in membrane fouling and removal performance of submerged membrane bioreactors (SMBRs) were compared. A reference membrane bioreactor (R‐SMBR) having a pure PVC/PC hollow fiber membrane module and no operational condition improvement was used as a reference for comparison. RESULTS The results revealed that all of the parameters had a considerable influence on improving membrane fouling, among which optimizing SADm and installing nanocomposite membranes in the SMBRs had comparable performances. Although the nanocomposite membrane had excellent potential to boost the membrane flux up to 62% in comparison with the R‐SMBR, it did not play any noticeable roles in rectifying the removal efficiency of the SMBR. On the other hand, not only did SADm increase the membrane flux up to 55%, but it also increased about 5% of COD and 3% of NH4+‐N removal. CONCLUSIONS Sludge characteristics were not affected by membrane modification since the concentration of extracellular polymeric substances, soluble microbial products and mean particle size were 110 ± 1 mg g−1 VSS, 54 ± 1 mg L−1 and 50 μm, respectively, for both the R‐SMBR and the SMBR in which the modified membrane was installed. However, the operational parameters could also modify the treatment performance of the SMBRs by positively impacting on sludge characteristics besides mitigating membrane fouling. © 2021 Society of Chemical Industry (SCI).

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