Biofouling Aspects and Critical Flux Evaluation in an Intermittently Aerated and Fed Submerged Membrane Bioreactor

Abstract

Nowadays, much attention is being paid to environmental issues since legislation has become stricter. Membrane bioreactors (MBR) are non-conventional treatment systems that gain ground in wastewater processing. In this study, the operation of a 24 L submerged membrane bioreactor, treating municipal wastewater, was investigated under different organic loading rates and high mixed liquor suspended solids concentrations (up to 13 g/L). The system, consisting of a hollow fibre membrane for ultrafiltration (0.1 μm pore-size), was operated under intermittent aeration (30 min/30 min aeration - on & off) and periodic feeding at the beginning of the anoxic phase, while effluent was discarded at the end of the aerobic phase. The transmembrane pressure and operation processes were monitored and controlled by a programmable logic controller (PLC). Complete suspended solids removal was achieved throughout the entire operation and BOD and COD average removal values higher than 97 % and 93 % were determined. Moreover, TKN and NH4 +-N mean removal efficiencies were estimated to be higher than 77 % and 91 %, respectively, regardless of the increase in the organic loading rate and biomass concentration. No membrane fouling was observed since the submerged membrane bioreactor was operated below the critical flux. A 2nd order equation considering fouling and sieving phenomena was found to mathematically express critical flux. It is concluded that the MBR system could effectively operate without membrane fouling for a long period of time, even at high volumetric organic loading rates and high biosolids concentrations.