The Use of Natural Minerals in a Pilot-Scale MBR for Membrane Fouling Mitigation

This study examines the effect of bentonite and zeolite concentration (0.25–5 g/L) on the membrane fouling of a fully automated, pilot-scale membrane bioreactor (MBR) treating high-strength synthetic municipal wastewater. Reversible fouling was estimated by sludge filterability measurements and irreversible fouling was estimated by the reduction of the carbohydrate fraction of soluble microbial products (SMPc), which are considered to be significant MBR foulants. Both minerals were added to biomass samples (during batch-mode experiments) which were obtained from the system’s aeration tank. Results showed that the optimal bentonite and zeolite concentrations were 3.5–4 g/L and 2.5–3.5 g/L, respectively. Interestingly, above these values, the addition of both minerals increased the examined fouling indices, i.e., the measured filterability times and the SMPc concentration, implying that they might act as foulants at high concentrations. Optical microscopy images of the biomass samples showed that the addition of minerals at the optimal concentrations did not affect significantly filamentous microorganisms, since filament index (FI) was practically unaffected (~2). Finally, regarding the system’s treating performance, it was found that the pilot-scale MBR can operate successfully with high-strength synthetic municipal wastewater, since remarkable behaviour was exhibited in terms of organics (BOD5, COD) and ammonium (NH4+-N) removal (>98%).