Activated Carbon Addition to a Submerged Anaerobic Membrane Bioreactor: Effect on Performance, Transmembrane Pressure, and Flux

This study examined the effect of the addition of activated carbon to three, 3 L submerged anaerobic membrane bioreactors (SAMBRs) in terms of chemical oxygen demand (COD) removal, flux, and transmembrane pressure (TMP). The feed was a synthetic substrate with a COD of $460\mathrm{mg}{\mathrm{L}}^{-1}$ , with one reactor run as a control, one with $1.7\mathrm{g}{\mathrm{L}}^{-1}$ of powdered activated carbon (PAC), and the third with $1.7\mathrm{g}{\mathrm{L}}^{-1}$ of granular activated carbon (GAC). While COD removal was high in all reactors $(>90\%)$ , in comparison to the control (SAMBR1), the average COD removal in SAMBR2 (PAC) increased by 22.4%, while SAMBR3 with GAC was not significantly better. Because PAC has a significantly greater surface area per mass than GAC, it is probable that this difference was primarily due to the greater absorbance of fine colloidal particles and high molecular weight organics onto the carbon surface. These effects manifested themselves by SAMBR2 having lower TMPs and higher fluxes than both SAMBR3 and SAMBR1. Volatile fatty acids in the effluent from all three SAMBRs were extremely low $(<18\mathrm{mg}{\mathrm{L}}^{-1})$ , even during step changes in hydraulic retention tune, and most of the soluble COD in the effluent was soluble microbial products. Biochemical methane potential assays showed that biomass in the SAMBRs was less active than the seed sludge, and it appears that the addition of activated carbon to Reactors SAMBR2 and SAMBR3 provided a solid support for growth, and hence reduced floc breakage.