Effect of membrane properties in a membrane rotating biological contactor for wastewater treatment

Abstract

Membrane fouling is a major drawback of almost all pressure-driven membrane processes that limit their widespread application. This study compares the biological and the hydraulic performances of polyvinylidene fluoride (PVDF) and polysulfone (PSF) membranes when used as external filtration for polishing of a rotating biological contactor (RBC) effluent and as an integrated part in a membrane rotating biological contactor (MRBC). MRBC is an upgrade of the conventional RBC, in which the disk rotations are used not only to provide biological aeration but also as an inherent mechanism for membrane fouling control. Results showed that high biological performances were achieved irrespective of the membrane materials. The steady-state permeabilities of the membranes in MRBC are higher than external filtration by 92.4% and 19.7% for the PVDF and PSF membrane respectively. In the MRBC, smaller membrane-to-disk gaps and high disk rotational speed improve permeability for both membranes reaching the values of 297 and 173 L/(m2 h bar) for PVDF and PSF membranes, respectively. Full-scale energy consumption projection results show that the MRBC consumes only one-fourth of the energy of a referenced membrane bioreactor. The PVDF membrane outperforms PSF membrane thanks to the effective fouling control that maximize the throughput of a lower intrinsic resistance of the PVDF membrane. It implies that apart from membrane material, other operational parameters can still be optimized to further enhance the MRBC performance.