Performance of septic tanks for pharmaceutical removal and their impact to river water quality.

Pharmaceuticals enter surface water after incomplete removal in wastewater treatment works (WWTWs) and are known for their potential ecotoxicological hazard to the environment. Septic tanks (STs) treat wastewater of individual houses and small communities in rural and semi-urban areas and are an understudied pathway of surface water contamination. Therefore, the aim of this research was to understand the performance of STs for pharmaceutical removal and their impact to river water quality. A methodology for the analysis of 68 pharmaceuticals, including prescription and over-the-counter drugs, related metabolites, hormones, and other human wastewater marker (emerging contaminants; ECs), by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) in ST influent and effluent, total suspended solids (TSS), sludge and river water was developed. Five community STs and the receiving rivers were studied over 12 months. Concentrations were similar in influent and effluent, exceeded those previously found in centralised WWTWs and surpassed freshwater predicted no-effect concentrations (PNECs) for some pharmaceuticals and samples. Hence, dilution of the ST discharges is required to mitigate environmental hazard. Influenced by the small contributing population, monthly variability was high, especially for pharmaceuticals with acute use, e.g., antifungals. Generally, the contribution of TSS to the total pharmaceutical concentration was small, but high contributions of TSS were for example observed for fluoroquinolone antibiotics and antidepressants. Approximately half of pharmaceuticals are chiral, existing as two or more enantiomers with differences in their environmental occurrence, fate, and toxicity. For 26 chiral pharmaceuticals, the enantiomer composition of ST was determined. Most pharmaceuticals were found racemic in wastewater, containing the same amount of both enantiomers. However, a strong enantioselectivity in influent and effluent was for example found for fluoxetine, naproxen, citalopram, omeprazole, and cotinine. The similar enantiomeric composition of ST influent and effluent suggests that unlike in aerobic WWTWs, no enantioselective degradation occurs in STs. Potentially, the unchanged enantiomeric composition in ST wastewater, can be used to distinguish between pharmaceutical discharges from STs and other WWTWs in the environment, e.g., naproxen. A wide range of ECs were also detected in rivers upstream and downstream of the ST discharge points, and concentrations increased by up to 95% downstream. In general, hazards in the rivers were low. However, PNECs were exceeded for ibuprofen, diclofenac and ciprofloxacin in few samples. Overall, the similarities in number of compounds detected, concentrations, and enantiomeric composition, indicate that STs are less effective in removing pharmaceuticals than centralised WWTWs. Alternative wastewater treatment might be needed at locations with low dilutions. Finally, pharmaceuticals were analysed in influent and effluent of twelve pilot-scale STs (control, insulated, 20°C and 30°C) to assess the temperature effect on removal, as biodegradation is influenced by microbial activities and can increase with increasing temperature. For most pharmaceuticals, no temperature effect was found. However, lower concentrations of metformin and sanitary determinands at 30°C, highlight the potential for a seasonal effect for some pharmaceuticals. Higher temperatures above 30°C may further enhance the removal. In summary, STs contribute to pharmaceutical concentrations in rivers, but due to the mostly high dilutions, hazards are low.

Grantor dc:publisher.institution

Robert Gordon University

Year dc:date.issued

2025

Author dc:creator

• Wilschnack, Kai

Advisor dc:contributor.advisor

• B. Petrie and K. Yates

• Wastewater treatment
• Environmental pollutants
• Emerging contaminants
• Pharmaceuticals
• Rivers
• Water quality
• Ultra high-performance liquid chromatography (UHPLC)
• Tandem mass spectrometry (MS/MS)
• Predicted no‑effect concentrations (PNECs)

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:3216999
https://doi.org/10.48526/rgu-wt-3216999

Author Identifier

0009-0007-5970-0465

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:3216999