Understanding the Role of Extracellular Polymeric Substances on Ciprofloxacin Adsorption in Aerobic Sludge, Anaerobic Sludge, and Sulfate-Reducing Bacteria Sludge Systems

Extracellular polymeric substances (EPS) of microbial sludge play a crucial role in removal of organic micropollutants during biological wastewater treatment. In this study, we examined ciprofloxacin (CIP) removal in three parallel bench-scale reactors using aerobic sludge (AS), anaerobic sludge (AnS), and sulfate-reducing bacteria (SRB) sludge. The results showed that the SRB sludge had the highest specific CIP removal rate via adsorption and biodegradation. CIP removal by EPS accounted up to 35. 6 +/- 1.4%, 23.7 +/- 0.6%, and 25.5 +/- 0.4% of total removal in AS, AnS, and SRB sludge systems, respectively, at influent CIP concentration of 1000 mu g/L, which implied that EPS played a critical role in CIP removal. The binding mechanism of EPS on CIP adsorption in three sludge systems were further investigated using a series of batch tests. The results suggested that EPS of SRB sludge possessed stronger hydrophobicity (proteins/polysaccharides (PN/PS) ratio), higher availability of adsorption sites (binding sites (n)), and higher binding strength (binding constant (K-b)) between EPS and CIP compared to those of AS and AnS. The findings of this study provide an insight into the role of EPS in biological process for treating CIP-laden wastewaters.