Evaluation of fouling prevention methods in a submerged membrane bioreactor treating domestic wastewater

Membrane fouling is considered as the main drawback that currently restricts use of membrane bioreactors (MBR) in domestic wastewater treatment. Microbiological factors such as extracellular polymeric substances (EPS) and soluble microbial products (SMP) have a critical impact on sludge filterability of membrane surfaces. The effects of operating parameters and sludge characteristics on fouling were examined in a pilot-scale MBR treating domestic wastewater under alternating aeration and intermittent feeding conditions. EPS and SMP were measured under various operating conditions and their effects on membrane fouling were assessed. Both glycerol and biosolids addition resulted in carbohydrate EPS and SMP increase, whereas operating mixed liquor temperature above 19 degrees C drastically reduced membrane flux as the consequence of the enhanced microbial activity. The first transmembrane pressure derivative (dTMP/dt) proved to be a suitable indicator of critical flux since an acute raise in dTMP/dt occurred. The implementation of various fouling prevention methods, such as increased backwash flow rate, cross flow aeration, in situ mechanical cleaning, anoxic/aerobic phase duration ratio and offline intensive chemical cleaning, resulted in the improvement of membrane permeability (P). Moreover, the increase in anoxic/aerobic phase ratio accelerated membrane fouling.