Optimization of membrane bioreactors by the addition of powdered activated carbon

•MBR (BAC) has better fouling control than the MBR (AS) with constant replacement of PAC.•The aged BAC would deteriorate the membrane filtration performance.•Without PAC, MBR with longer SRT has better fouling control at modest fluxes.•With PAC addition, the shorter SRT gave better fouling control.•Relatively fine PAC operated at short SRTs has better fouling control for MBR (BAC). It was found that with replenishment, powdered activated carbon (PAC) in the membrane bioreactor (MBR) would develop biologically activated carbon (BAC) which could enhance filtration performance of a conventional MBR. This paper addresses two issues (i) effect of PAC size on MBR (BAC) performance; and (ii) effect of sludge retention time (SRT) on the MBR performance with and without PAC. To interpret the trends, particle/floc size, concentration of mixed liquor suspended solid (MLSS), total organic carbon (TOC), short-term filtration properties and transmembrane pressure (TMP) versus time are measured. The results showed improved fouling control with fine, rather than coarse, PAC provided the flux did not exceed the deposition flux for the fine PAC. Without PAC, the longer SRT operation gave lower fouling at modest fluxes. With PAC addition, the shorter SRT gave better fouling control, possibly due to greater replenishment of the fresh PAC.