Effect of solids retention time on membrane fouling intensity in two-stage submerged anaerobic membrane bioreactors treating palm oil mill effluent

Abstract

Submerged anaerobic membrane bioreactors (SAnMBRs) treating palm oil mill effluent were analysed in terms of membrane fouling dynamics when working at three different sludge retention times (SRTs of 15, 30 and 60 d). The average permeate flux was fixed at 2.4 L x m(-2) x h(-1). During operation, the membrane was regenerated by using two steps: membrane wiping during each experiment as soon as trans-membrane pressure reached 125-130 mbars, and complete membrane cleaning including backwash and chemical cleaning at the end of each experiment when analysing the membrane surface and foulant material. Whatever the SRT, the cake formation was the dominant effect on membrane fouling dynamics. The concentration of suspended solids in the SAnMBRs, depending on the SRT, was then a determining criterion. Scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy indicated that fouled membrane surfaces were covered with a cake layer containing organic and inorganic elements whose concentrations were higher when working at a higher SRT; the higher concentrations of such elements gave to the cake layer a denser and more compact structure. In these experiments, the soluble fractions played a secondary role because of the dominant effect of cake layer structuring.

Treatment of Palm Oil Mill Effluent Using Membrane Bioreactor: Novel Processes and Their Major Drawbacks

“…According to this study, in a longer-term operation, a significant increase in fouling rate was observed due to the polarization effect [117]. In a different study, solid retention time (SRT) pose a strong influence on the rate of biofilm formation as a result of the protracted polarization of biomass and persisting interaction on the membrane surface [204]. At a longer SRT, the soluble microbial product (SMP) concentration is high which easily got accumulated onto membrane pore walls to initiate blockage [98,[203][204][205].…”

“…In a different study, solid retention time (SRT) pose a strong influence on the rate of biofilm formation as a result of the protracted polarization of biomass and persisting interaction on the membrane surface [204]. At a longer SRT, the soluble microbial product (SMP) concentration is high which easily got accumulated onto membrane pore walls to initiate blockage [98,[203][204][205]. In addition, longer retention of activated sludge encourages shifting of microorganism growing rate to endogenous phase and this may lower the F/M ratio.…”

Effect of mean cell residence time on transmembrane flux, mixed-liquor characteristics and overall performance of a submerged anaerobic membrane bioreactor

“…Later work by Huang et al [7] showed biofouling increased at both long and short MCRTs, with maximum flux rates being achieved at 60 days. Recent studies on two stage SAnMBRs treating palm oil mill effluent [27] showed that cake layer formation was directly linked to MLSS concentrations, and hence increased at longer MCRT, with a negative impact on membrane flux. Studies to investigate the effect of MCRT on membrane fouling and overall performance in AnMBR are scarce, however, and none has previously evaluated this using a gravitationally-mediated constant transmembrane pressure as reported here with the capacity for continuous measurement of flux rate.…”