Fouling in Membrane Bioreactor Systems Treating Pharmaceutical Wastewater.

Abstract:

Membrane bioreactor (MBR) systems have emerged as promising technology to remove pharmaceuticals from wastewater. However, wide-scale applicability of MBR is largely limited due to fouling. Fouling is deposition of mixed liquor on membrane surface which results in clogging of membrane and reduction in permeation flux. Fouling is undesirable as additional cost and efforts are needed to clean the fouling layer and maintain the flux. Pharmaceuticals induce chemical stress in microbes, which alter the microbial metabolism and the sludge characteristics, thus exerting direct/indirect effects on fouling by interacting with foulants. Pharmaceuticals can aggravate fouling by enhancing the secretion of biopolymers such as extracellular polymeric substances (EPS) and soluble microbial products (SMP) – key foulants. EPS gets adhered to membrane surface and constitute a gel like three-dimensional matrix onto which foulants interact and contribute to fouling. Despite availability of literature, the interrelationship between pharmaceutical induced changes and fouling is to-date poorly understood. Studies are scarce which fractionate and characterize EPS/SMP molecules, and are often controversial. Additionally, sludge characteristics such as floc size have shown contradictory trends on adding pharmaceuticals. In this paper, we discuss the mechanism, knowledge gaps, and the pharmaceutically induced changes in activated sludge relevant to fouling.