Development of an Integrated Methodology for Fouling Control in Membrane Bioreactors

The most serious drawback in wastewater treatment using membrane bioreactors (MBRs) is membrane fouling, which gradually leads to membrane permeability decrease and efficiency deterioration. This work is part of a research project that aims to develop an integrated methodology for membrane fouling control, using specific chemicals which enhance the coagulation and flocculation of compounds responsible for fouling, hence reducing biofilm formation on the membrane surface and limiting the fouling rate acting as a pre-treatment step. For this purpose, a pilot- scale plant with fully automatic operation achieved by means of programmable logic controller (PLC) has been constructed and tested. The experimental set-up consists of four units: wastewater feed unit, bioreactor, membrane (side-stream) filtration unit and permeate collection unit. Synthetic wastewater (BOD=1000 mg/L) was fed as the substrate for the activated sludge (F/M=0.2 kg BOD/kg MLVSS∙d). The dissolved oxygen (DO) concentration of the aerobic tank was maintained in the range of 2-3 mg/L during the entire operation by using aerators below the membrane module. Backflushing steps of 1 min were performed periodically after 10 min of filtration. Membrane reversible and irreversible fouling was pre-assessed in terms of filterability tests and SMP (soluble microbial product) concentration measurements conducted in mixed liquor samples before and after the addition of commercial and composite coagulants. Membrane fouling results in increased treatment cost, due to high energy consumption and the need for frequent membrane cleaning and replacement. Due to the widespread application of MBR technology over the past few years, it becomes clear that the development of a methodology to mitigate membrane fouling is of paramount importance. The present work aims to develop an integrated technique for membrane fouling control in MBR systems and, thus, contribute to sustainable wastewater treatment.