The contradictory roles of tightly bound and loosely bound extracellular polymeric substances of activated sludge in trimethoprim adsorption process.

Extracellular polymeric substances (EPS) of activated sludge are a mixture of high molecular weight polymers secreted by microorganisms, which have the double structure of tightly-bound EPS (TB-EPS) in inner layer and loosely-bound EPS (LB-EPS) in outer layer. The characteristic of LB- and TB-EPS were different, which would affect their adsorption of antibiotics. However, the adsorption process of antibiotics on LB- and TB-EPS was still unclear yet. Therefore, in this work, the roles of LB-EPS and TB-EPS in adsorption of a typical antibiotic-trimethoprim (TMP) at environmentally relevant concentration (25.0 µg/L) were investigated. The results showed the content of TB-EPS was higher than that of LB-EPS, which was 17.08 and 10.36 mg/g VSS, respectively. The adsorption capacity of raw, LB-EPS extracted and both LB- and TB-EPS extracted activated sludges for TMP were 5.31, 4.65 and 9.51 µg/g VSS, respectively, which indicated LB-EPS had positive effect on TMP removal, while TB-EPS had negative effect. The adsorption process can be well described by a pseudo-second-order kinetic model (R2 > 0.980). The ratio of different functional groups was calculated and the CO and C-O bond might be responsible for the adsorption capacity difference between LB- and TB-EPS. The fluorescence quenching results indicated that tryptophan protein-like substances in LB-EPS provided more binding sites (n = 0.36) than that of tryptophan amino acid in TB-EPS (n = 0.1). Furthermore, the extend DLVO results also demonstrated that LB-EPS promoted the adsorption of TMP, while TB-EPS inhibited the process. We hope the results of this study were helpful for understanding the fate of antibiotics in wastewater treatment systems.

The erythromycin sorption removal at environmentally relevant concentration based on molecular imprinted polymer: Performance and mechanism.

The antibiotic pollution emerged in different environments has raised a great concern. Adsorption is an effective method to solve the problem. However, conventional adsorbents are not always efficient for antibiotic removal with interferences. Therefore, in this study, molecularly imprinted polymer (EMIP) with selective adsorption ability was prepared to remove a typical antibiotic-erythromycin (ERY) at environmentally relevant concentration. The specific surface area of EMIP was 265.62 m2/g with large pore volume, small pore size and hydrophobic surface. The adsorption capacity of EMIP was increased from 211.08 to 4015.51 µg/g when the concentration of ERY was increased from 5.00 to 100.00 µg/L. The isothermal adsorption process was fitted well with the Langmuir model. The adsorption kinetic could be well described by the pseudo-second-order model. With co-existing of interferences, the imprinting factor for ERY was 2.57, which demonstrated EMIP had good adsorption selectivity. After five consecutive adsorption-desorption experiments, the adsorption capacity of EMIP was still over 80%. The results of molecular dynamic simulation showed the adsorption energy between ERY and EMIP was high, which was favorable for ERY adsorption removal. Hopefully, the results of this study could provide new insights for trace antibiotic removal by molecular imprinting polymers in different aqueous environments.