Intermittent backwashing and relaxation are mandatory in the membrane bioreactor (MBR) for its effective operation. The objective of the current study was to evaluate the effects of run-relaxation and run-backwash cycle time on fouling rates. Furthermore, comparison of the effects of backwashing and relaxation on the fouling behavior of membrane in high rate submerged MBR. The study was carried out on a laboratory scale MBR at high flux (30 L/m2·h), treating sewage. The MBR was operated at three relaxation operational scenarios by keeping the run time to relaxation time ratio constant. Similarly, the MBR was operated at three backwashing operational scenarios by keeping the run time to backwashing time ratio constant. The results revealed that the provision of relaxation or backwashing at small intervals prolonged the MBR operation by reducing fouling rates. The cake and pores fouling rates in backwashing scenarios were far less as compared to the relaxation scenarios, which proved backwashing a better option as compared to relaxation. The operation time of backwashing scenario (lowest cycle time) was 64.6% and 21.1% more as compared to continuous scenario and relaxation scenario (lowest cycle time), respectively. Increase in cycle time increased removal efficiencies insignificantly, in both scenarios of relaxation and backwashing.

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