PROGRAMME

Multi-residue analysis of various classes of contaminants of emerging concern (CECs) present in wastewater, along with improvements in analytical methodologies, may allow for future application of promising wastewater tracers, thus providing wastewater treatment plant (WWTP) operators and regulatory authorities with a more definitive toolbox to assess contamination associated with wastewater discharge and reuse practices. In June 2020, the Regulation EU 2020/741 of the European Parliament and of the Council of 25 May 2020 on minimum requirements for water reuse was published (EU, 2020). With the increasing drive from both policy and practice to facilitate treated wastewater reuse in agricultural irrigation, there is an urgent need to identify and characterize the risks associated with the occurrence of CECs in treated wastewater. In this study, a quantitative target screening of 200 CECs in 24-hour composite wastewater influent and effluent samples was performed. The wastewater samples were collected, in April 2018 during 7 consecutive days, from the 5 largest WWTPs located in 4 major cities of Cyprus, employing (i) conventional activated sludge (CAS) process followed by chlorination, (ii) membrane bioreactor (MBR) technology and (iii) MBR technology followed by chlorination. The methodology included a generic solid-phase extraction protocol which was followed by an Ultra-High Performance Liquid Chromatography coupled with Quadrupole-Time of Flight Mass Spectrometry (UHPLC-QTOF-MS/MS) method, and post-acquisition data treatment (Gago-Ferrero et al., 2020). The 200 target compounds comprised 185 pharmaceuticals and related metabolites and transformation products, 10 industrial chemicals and 5 artificial sweeteners. In total, 63 CECs were detected in influent and effluent wastewater samples. Metformin, valsartan, diclofenac, sucralose and acesulfame were among the most abundant compounds in influent samples, while sucralose, diclofenac, guanylurea, valsartan, carbamazepine and benzotriazole were among the most abundant compounds in effluent samples. The parent molecules of clarithromycin, citalopram and metformin were transformed upon CAS and MBR treatment and their associated TPs, N-desmethyl clarithromycin, N-desmethyl citalopram, and guanylurea were detected in effluent samples. Interestingly, N4-acetyl sulfamethoxazole was detected only in MBR effluents, while guanylurea in both CAS and MBR, indicating that enzymatic activity may differ in the two processes leading to different TPs. A qualitative approach to assess the bioavailability in soil was applied for the 5 most abundant compounds in effluent samples. This approach, described by Revitt et al. (2021), combines data and expert judgement to assess the likelihood of occurrence and the magnitude of impact contributing to the assessment of the risks related to wastewater reuse for irrigation.