Emissions and transport of pharmaceutical residues from three wastewater treatment plants in Saudi Arabia and the associated risk for the aquatic environment

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Date
2022
Authors
Alharbi, Obaid
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University College Cork
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Abstract
Pharmaceuticals are known to be poorly removed by wastewater treatment plants (WWTPs) and their wastewater-born residues could find their way to the environment and cause a potential environmental risk. This research investigates the occurrence of sixteen pharmaceuticals in three different WWTPs in Riyadh, Saudi Arabia. Removal efficiency, and the potential risk posed to the environment, together with seasonal variations of the target compounds in these different WWTPs was studied. The wastewater discharged by the studied WWTPs could be used for different purposes, like recharging groundwater and/or irrigation of crops, and therefore the leaching behaviour of the selected pharmaceuticals when applied to soils was investigated in the laboratory using soil columns. In total 144 wastewater samples over 12 months and 80 samples from the soil column experiments were collected and analysed. Samples were extracted and analyzed using either solid phase extraction (SPE) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) or ultrasound-assisted extractions (UAE) combination with LC-MS/MS for wastewater and soil samples respectively. Of the 16 investigated pharmaceuticals, ten and five pharmaceuticals were detected in the studied WWTP influents and effluents respectively. The highest concentrations measured in the influents of these WWTPs were for caffeine and acetaminophen (> 1000 μg L-1) followed by ciprofloxacin, metformin, ofloxacin, diclofenac, atenolol, cefalexin, trimethoprim and baclofen (< 1000 μg L-1). This is the first-time baclofen has been reported in the environment and was found here at concentrations ranging between 0.33 and 2.82 μg L-1 in WWTP influent. The two larger WWTPs (H and M) received relatively higher levels of pharmaceuticals than the smaller WWTP (KSU). The highest concentration of the five compounds detected in the studied WWTP effluents never exceeded 34 μg L-1. The investigated pharmaceuticals generally exhibited seasonal variations that were more obvious in the WWTP influents than in the effluents and were more obvious in autumn and winter. Mass loadings in the inputs and outputs of the detected compounds in the larger WWTPs were significantly (p ≤ 0.5) higher than for the small scale WWTP. There were very few significant correlations between the physiochemical parameters of the collected samples and the operational parameters of the WWTPs, and the observed concentrations of the studied pharmaceuticals in the studied WWTP influents and effluents. The average removal efficiencies of the pharmaceutical compounds were estimated to be ≥70%, with caffeine and acetaminophen eliminated almost completely at 99%. Removal efficiency of studied pharmaceuticals showed no significant differences (p ≤ 0.5) between the different studied WWTPs, regardless of the differences in their tertiary treatment processes. The removal efficiency of baclofen was found to be high between, 81% and 97%, and showed a significant correlation with the ambient air temperature and a weak correlation with TSS removal. The environmental risk was estimated to be high to moderate for the majority of the detected compounds in WWTP influents, particularly for ofloxacin and acetaminophen. Likewise, the ecological risk was estimated as high to medium for all five compounds detected in the WWTP effluents, especially for antibiotic compounds. Ultimately, the risk assessment results support the need for urgent action on managing the release of these compounds from the studied WWTPs to decrease their environmental impact in surrounding environments. Due to widespread use of WWTPs effluent in Saudi Arabia, the possibility of pharmaceuticals migrating from the unsaturated zone (soil) and contaminating groundwater was investigated using laboratory-scale soil column experiments. Most the investigated pharmaceuticals had a high affinity for soil particles and tended to accumulate in the top 5 cm of the soil column. Therefore, no migration of these compounds to groundwater is anticipated in the natural environment, with the possible exception of caffeine and cephalexin because they were found in the leachate at extremely low concentrations. Overall, this research has increased knowledge on the occurrence and effects of pharmaceuticals in Saudi Arabia, highlighting their presence in three selected WWTPs and the potential risk to the environment from their presence in wastewater. The research also raises concerns surrounding the release of pharmaceutical compounds that routinely enter the environment from WWTPs in Saudi Arabia. The results obtained from this work provide new information that could contribute to the formulation and implementation of future regulations for wastewater discharges, wastewater quality and emerging contaminants.
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Keywords
Pharmaceuticals , Wastewater treatment plants , Environmental risk assessment , Removal efficiency , Antibiotics , Non-steroidal anti-inflammatory , Mass loading , Seasonal variation , Soil leaching
Citation
Alharbi, O. 2022. Emissions and transport of pharmaceutical residues from three wastewater treatment plants in Saudi Arabia and the associated risk for the aquatic environment. PhD Thesis, University College Cork.