An insight into the removal of fluoroquinolones in activated sludge process: Sorption and biodegradation characteristics

Abstract

The detailed sorption steps and biodegradation characteristics of fluoroquinolones (FQs) including ciprofloxacin, enrofloxacin, lomefloxacin, norfloxacin, and ofloxacin were investigated through batch experiments. The results indicate that FQs at a total concentration of 500μg/L caused little inhibition of sludge bioactivity. Sorption was the primary removal pathway of FQs in the activated sludge process, followed by biodegradation, while hydrolysis and volatilization were negligible. FQ sorption on activated sludge was a reversible process governed by surface reaction. Henry and Freundlich models could describe the FQ sorption isotherms well in the concentration range of 100-300μg/L. Thermodynamic parameters revealed that FQ sorption on activated sludge is spontaneous, exothermic, and enthalpy-driven. Hydrophobicity-independent mechanisms determined the FQ sorption affinity with activated sludge. The zwitterion of FQs had the strongest sorption affinity, followed by cation and anion, and aerobic condition facilitated FQ sorption. FQs were slowly biodegradable, with long half-lives (>100hr). FQ biodegradation was enhanced with increasing temperature and under aerobic condition, and thus was possibly achieved through co-metabolism during nitrification. This study provides an insight into the removal kinetics and mechanism of FQs in the activated sludge process, but also helps assess the environmental risks of FQs resulting from sludge disposal.

Assessment of a Ficus benjamina wood chip‐based aerated biofilter used for the removal of metformin and ciprofloxacin during domestic wastewater treatment

“…These authors indicated that higher mixed liquor suspended solids (15 000 mg L –1 ) increased quinolone removal efficiency, mainly by sorption processes. Wang et al assessed the removal of several fluoroquinolone compounds including ciprofloxacin in a laboratory‐scale sequencing batch reactor with an aerobic suspended growth. After 50 h of reaction, the overall removal was 78–91%, indicating that the sorption process is the primary removal pathway for fluoroquinolones.…”

Effect of Sedimentation and Aeration on Antibiotic Resistance Induction in the Activated Sludge Process

“…After sterilization by autoclaving, the fluoroquinolone concentrations tended to increase, particularly for activated sludge (up to 10 times) indicating a release of the antibiotics from the solid fraction to the liquid fraction. Lindberg et al [26] and Wang et al [27] also found the tendency of norfloxacin to be accumulated in sludge particles. While the negative values of the log octanol-water partitioning coefficient (logK ow ) of the examined quinolones in the literature (e.g.…”

“…On the other hand, at this pH range, the fluoroquinolones are positively charged or neutral because the fluoroquinolones first pK a value and the isoelectric point are between this pH range [27]. In this pH range, zwitterions of the fluoroquinolones have been found to have the strongest affinity to sludge particles than either the cation or anion, thus contributing the largest portion of chemical species adsorbed in the sludge [27].…”

“…While the negative values of the log octanol-water partitioning coefficient (logK ow ) of the examined quinolones in the literature (e.g. logK ow of ciprofloxacin: −1.10, levofloxacin: −0.42, lomefloxacin: −1.13, nalidixic: 0.15, norfloxacin: −0.95, ofloxacin; −0.47) indicate that they are hydrophilic [27][28][29] our results showed that using logK ow alone is inadequate to explain the higher concentration of quinolones in the solid than in the liquid fraction of the wastewater. Mechanisms other than hydrophilicity are a better explanation for the fluoroquinolone sorption to sludge particles.…”

“…When mechanisms other than hydrophilicity are dominant, pH and redox condition at which the process condition occur can influence the sorption [27,30]. At neutral pH, which is similar to typical wastewater pH of 6.5 − 7.5, sludge particles are dominated by negatively charged carboxyl groups [31].…”