Hydrodynamics of membrane bioreactors

Abstract

Membrane Bioreactors (MBRs) are used in wastewater treatment processes providing copious advantages such as superior effluent quality, smaller footprint, better disinfection capability, higher volumetric loading and less sludge production as compared to conventional wastewater treatment processes. However, the major drawbacks in MBRs include membrane fouling and high energy consumption caused by aeration in the processes. The development of Submerged Membrane Bioreactor (SMBR) in the late 80’s had shown reduction in the energy consumption with aeration to induce a cross-flow. In this study, investigation was carried out on the effect of centralized aeration on the membrane fouling behaviour under a constant permeate flux. The main purpose is to understand and optimise the hydrodynamic conditions in the bubble column reactor to minimise membrane fouling and to save on operating cost. Desirable membrane filtration performances were observed for bentonite suspension test at a constant flux of 71.66 L/m2∙hr and for yeast suspension test at a constant flux of 28.66 L/m2∙hr. Generally, the magnitude of membrane fouling rate (dTMP/dt) decreases with an increase in air flow rates, especially when the membrane module was placed close to the air sparger together with a moderately high aeration. Enhanced membrane filtration performance were observed in the study because strong turbulence can caused homogenous mixing and reduced concentration polarization. Lastly, in the yeast suspension test under a constant permeate flux of 28.66 L/m2∙hr, where dTMP/dt appeared steady and the rise was relatively slow.