Profile of priority substances and toxicity assessments of wastewater treatment plants in Istanbul

Abstract

Wastewaters formed due to anthropogenic activities around urban areas pose a threat to aquatic environments. The growth in industrial activity along with the worldwide urban migration, as well as the threat posed by climate change, increase the extent of pollution. The discharge of the treated or untreated wastewaters is reported to cause a threat to their receiving water environments. Conventional wastewater treatment plants (WWTPs) are constructed to minimize the nutrient loads of macropollutants (C, N, and P) entering the receiving water bodies. As, removal of some of the emerging contaminants (ECs) or micropollutants present in wastewaters is found to be incomplete in conventional wastewater treatment processes, traces of those non-biodegradable ECs were reported to be found in the receiving environments. The presence of ECs, even in very low concentrations (pg/L - ng/L) in the water environments could cause adverse effects on humans and the ecosystem. In addition to industrial emissions, domestic discharges along with urban runoffs are main contributors of ECs in WWTPs. Understanding the presence, sources and transport of the micropollutants and ECs in wastewaters is important for assessing their impacts, and hence can help their reduction and management in the receiving environment. Micropollutants that have shown toxic, persistent, bioaccumulative, and ubiquitous properties and have been identified in aquatic environments, are designated as priority substances (PSs) by the EU Water Framework Directive (WFD). EU Member States are required to identify the presence of PSs in surface waters, in order not to exceed threshold levels specified by the Environmental Quality Standards (EQS) dictated by WFD. The Turkish Ministry of Forestry and Water Affairs adopted the aforementioned quality standards for the PSs in surface waters in 2012, and updated them in 2016. Since WWTPs are known to be main point sources of ECs entering the receiving water bodies, investigating the occurrence of PSs in wastewaters of Istanbul has generated valuable information. This thesis aims at understanding the occurrences of PSs in the wastewaters of the megacity of Istanbul as well as assessing WWTP effluents as sources of PSs in receiving environments. The thesis also includes the acute toxicity assessment of the same wastewaters. The scope of the study includes the wastewaters of the seven largest WWTPs, a hospital wastewater and leachate of a landfill treatment plant in Istanbul. The results of the PSs analyses allowed estimation of risks posed by the PSs in the WWTP effluents. Lists were formed to PSs showing sufficient risk (RQ>1), and their inclusions are recommended in the surveillance monitoring programs for the effluents of advanced treatment, as well as mechanical treatment. The regulators undertaking environmental risk assessments in the initiation of monitoring programs for the protection of the Sea of Marmara, Bosphorus and the Black Sea may utilize the findings of this study. Chapter 2 provides general information on the background of the study that is related to the aim and objective of the study. Chapter 3 comprises of information regarding the study area as well as methods on the description of all the experiments conducted through this study, namely analyses of PSs, toxicity analyses and physiochemical analyses. Chapter 4 Results and Discussion, provides information on the results of the experiments conducted through this study (PSs analyses, toxicity analyses and physiochemical analyses), as well as discussion of those results. Chapter 5 provides a summary of the whole thesis. The References section includes the complete bibliography. The Appendix includes tables, figures and pictures.