Transient Performance of MBR with Flux Enhancing Polymer Addition

Abstract

The polymeric membrane performance enhancer (MPE50) was applied in two parallel submerged membrane bioreactors to test its effect on membrane fouling. Although the flux enhancer showed significant benefit, the effect of dosage termination caused a dramatic drop in performance relative to the control. The MBRs were compared in three carefully controlled runs performed over 155 days. The total organic carbon (TOC), EPS, and particle size data were collected at regular intervals during the entire operation. In run 1, after a start-up period of 62 days, a stable state was achieved in both MBRs. In run 2, a one-off 400mg/L MPE and 15mg/L MPE daily maintenance dosage were applied in one reactor for 60 days. The ocritical fluxo determined by the flux stepping test was increased by 50% from 20 LMH to 30 LMH after the addition of MPE. Long-term experiments were implemented at three separate levels of constant flux, namely 20, 30, and 40 LMH. At the flux of 20 LMH (below the ocritical fluxo of both reactors with and without MPE), the performance in both reactors was similar. At the flux of 30 LMH (above the ocritical fluxo of the MBR without MPE but below the ocritical fluxo of the MBR with MPE), the addition of MPE was found to mitigate membrane fouling. At a flux of 40 LMH (above the critical flux for both reactors), the TMP rise in the MBR with MPE was slower than the MBR without MPE, although the performance of both MBRs was poor. The performance differences correlated with the increase in the particle size distribution of the activated sludge as well as the low level of SMP and EPS (mainly polysaccharides) concentrations in the supernatant during steady state. In run 3, after terminating the MPE addition, the membrane performance was found to be significantly worse than the MBR without MPE, which suggests that the continuous maintenance dose of MPE is essential upon MPE application to the MBR.