Removal of anti-inflammatory micropollutants in wastewater treatment plants

This research focuses on the assessment of removal potential of non-steroidal anti-inflammatory drugs (NSAIDs), frequently used non-prescribed drugs (i.e., diclofenac, ibuprofen, naproxen, ketoprofen, mefenamic acid and indomethacin) to treat the symptoms of pain and inflammation, in wastewater treatment plants (WWTPs). NSAIDs enter into the ecosystem mainly from wastewater treatment plants and they are potential toxic compounds in the receiving environments. This research has preceded with the determination of seasonal change during a year in the influent stream of two wastewater treatment plants. Removal efficiencies of the targeted NSAIDs were assessed in two different wastewater treatment plants and mostly detected anti-inflammatory micropollutants (i.e., ibuprofen, naproxen, diclofenac) were determined. For this purpose, composite samples (24-hour) were taken from two biological wastewater treatment plants located in the Marmara Region to screen NSAIDs' behavior during one year to characterize seasonal changes. NSAIDs' concentration in both influent and effluent of wastewater treatment plant have been measured and their removal efficiencies have been investigated. Apart from the seasonal variations, hourly samples were also taken in the summer (2-hour composite samples) to characterize their hourly variations. In order to evaluate yearly variations of NSAIDs in the sampled wastewater treatment plants, composite samples in the summer season were also repeated and analyzed after one year. Ibuprofen and naproxen concentrations have been observed at higher concentrations than the other micropollutants during four seasons in both of the wastewater treatment plants. Influent concentrations of ibuprofen and naproxen in the WWTP-1, which possess a UV disinfection unit, changed between 3-22 µg/L and 8-12 µg/L respectively. Moreover, their removal rates have been recorded higher than 93% and 96%. Influent concentration of ibuprofen and naproxen in the WWTP-2 have been detected as 5-9 µg/L and 8-17 µg/L, respectively. However, a decrease in the removal rate of ibuprofen and naproxen was observed in autumn and spring season in WWTP-2. Diclofenac concentrations observed in two WWTPs were relatively similar. The concentration of diclofenac in WWTP-1 and WWTP-2 was recorded as 0.4-1 μg/L and 0.2-1 μg/L, respectively. However, removal rate for diclofenac were ranged between 0-34% in both of the WWTPs. The influent concentration of ketoprofen were observed between 0.8-2.5 μg/L in both of WWTPs. High concentrations of ketoprofen were determined in autumn season. Removal rate of ketoprofen calculated between 0-70% in both WWTPs. Indomethacin and mefenamic acid could be measured in the range of nanogram. Influent concentration of indomethacin was measured as 30-110 ng/L in WWTP-1, and 20-120 ng/L in WWTP-2. Mefenamic acid concentration was 5-60 ng/L in WWTP-1 and 12-50 ng/L in WWTP-2. While indomethacin might be slightly removed in the autumn and spring seasons in WWTP-2, removal rate in summer was calculated a bit higher in WWTP-1. Mefenamic acid removal was not observed in both WWTPs. According to the results obtained with 2-hourly composite samples during a day, ibuprofen and chemical oxygen demand (COD) influent concentration profiles were similar. A similarity with the COD concentration profile and diclofenac concentration profile was not observed. A correlation analysis was performed between micropollutants and conventional parameters to determine if there is a correlation between these NSAIDs and conventional parameters in terms of influent concentrations as well as removal efficiencies. It was determined that the influent concentrations of diclofenac, indomethacin and naproxen were correlated with the influent concentrations of total suspended solids (TSS) and volatile suspended solids (VSS) parameters. Correlation evaluations were performed between concentrations of conventional parameters and NSAIDs. Moreover, correlations between the loads of these pollutants were also investigated. According to correlation analyses performed between the NSAIDs and conventional parameters based on influent loads of these parameters, a high correlation with COD and soluble COD (SCOD) parameters and NSAIDs have been determined. Moreover, naproxen and ketoprofen had positive correlation with all of the investigated conventional parameters. In terms of concentrations of NSAIDs and conventional parameters' concentrations, a correlation was observed for the naproxen concentration and TSS content in the influent wastewater. Thus, the amount of solid matter and especially COD and SCOD content of the wastewater may reflect some predictive information about the micropollutants loads. Based on the removal efficiencies, there was a positive correlation between naproxen, ibuprofen removal efficiencies and nitrogen, SCOD, TCOD removal efficiencies. Additionally, there was a correlation between SCOD and diclofenac removal efficiency. In the second part of this study, a fill and draw reactor was operated and fed with acetate with a sludge retention time of 20 days. The individual as well as synergic toxicity effect of diclofenac, ibuprofen and naproxen were investigated respirometrically. According to respirometric analyses, a decrease in the growth rate of heterotrophic biomass was determined as a result of the culture amendment with these selected micropollutants. Results reflected that the presence of these NSAIDs decreased the oxygen uptake rate and specific growth rate on readily biodegradable substrate. Respirometric analyses were carried out with the culture amendment with 500 μg/L of NSAIDs (individually and as a mixture) to investigate potential toxic effects on microbial community. It was observed that exposure to NSAIDs changes metabolic structure of biomass (i.e., specific growth rate). In the presence of 500 µg/L of ibuprofen, naproxen and diclofenac the calculated heterotrophic specific growth rates were 3.489, 2.999, and 3.049 day-1, respectively. Higher decrease in the specific growth rate was observed when the biomass was amended with diclofenac and naproxen. Whereas, biomass amendment with ibuprofen resulted in a decrease from 3.66 to 3.489 day-1 The highest drawback effect was observed when diclofenac and ibuprofen were introduced together. Diclofenac was determined as the most effective and ibuprofen was detected as the least effective NSAID on the microbial culture.