Effects of pharmaceuticals on the fouling propensity of membrane bioreactor: Case of iodinated X-ray contrast media

Membrane bioreactor (MBR) has shown promising results in the abatement of pharmaceuticals, however, its fouling propensity has continued to put challenges in its wide-scale applicability. The present study is the first study that investigated the MBR fouling behaviour in the presence of iodinated X-ray contrast media (ICM). The study found that ICM aggravated the fouling issue by reducing the filtration cycle by 21 % and enhancing the production of key foulants- extracellular polymeric substances (EPS) and soluble microbial products (SMP). Size exclusion chromatography (SEC) results revealed the presence of a higher molecular weight (MW) organics in the EPS in ICM dosed phase. Also, excitation-emission matrix (EEM) contours of EPS showed that the exposure to ICM seemed to stimulate the secretion of aromatic proteins comprising tryptophan (28.7 %) and tyrosine (22.07 %) compared to the non-ICM dosed phase (25.10 % for tryptophan and 20.39 % for tyrosine). The floc size of the sludge was found to increase to 67.6 +/- 10.2 mu m from 22.4 +/- 4.8 mu m in the presence of ICM as a result of increased EPS content. Further, ICM addition resulted in a slight reduction of the sludge microbial activity (similar to 10 %). ICM also changed the microbial dynamics of the sludge by enriching the abundance of biofilm forming phyla such as Bacteroidetes and TM7. The findings of this study provide fundamental insights into the fouling propensity of MBR in presence of ICM, and highlight that the changes caused in the EPS secretion profile would be responsible for enhanced fouling.