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© 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Hazardous substances used and produced by different industrial activities pose a potential risk to the environment and to human health. Different physicochemical and/or biological processes are used in industrial wastewater treatment; these methods, however, may not be effective in removing these substances. This study was carried out to comparatively evaluate the removal of hazardous substances through conventional wastewater treatment processes that are used by major industries in Turkey. A four-season monitoring study was carried out in textile manufacturing and leather production sectors, representing industrial activities in Turkey. Samples were analyzed for 45 priority substances defined by the European Union and 250 specific pollutants listed in the Turkish Regulation on Surface Water Quality. For both wastewaters, where biological treatment was performed after pretreatment, their characteristics showed that organics were almost completely removed. except for dichloromethane (44–51% removals) and dioxin and dioxin-like compounds (64–69% removals). Additionally, different removal ratios (16–97%) were obtained for metals; the poorer removal was observed for B, Ba, Ag, Sb, and Si. The remaining metals (Cu, Pb, Sb, V, Si for textile; Cr, Cu, Sb, Si for leather effluents) in the treated wastewaters were still higher than environmental quality standards (EQS) of receiving water bodies. The study revealed that existing treatment processes were not adequate for efficient hazardous substance removal and there is an urgent need to improve them. Finally, advanced treatment technologies were suggested for specific pollutants together with their unit treatment costs.

Many developing countries apply technology-based discharge standards that set quantitative limits on pollutant discharges. These standards do not inherently consider ambient constraints and, therefore, cannot guarantee to protect aquatic life from hazardous pollutants. It is a challenge for developing countries to enforce water-quality-based limits for wastewater discharges and guarantee the intended use of water. This study aims to develop a strategy that suits the needs of developing countries for a transition from technology-based discharge standards to water-quality-based discharge limits. To this end, a pilot monitoring program was carried in the Gediz River Basin in Turkey. Surface water, industrial, and urban wastewater samples were collected and analyzed for 45 priority pollutants identified by the European Union and 250 national river basin specific pollutants. The monitoring results revealed that the environmental quality standards (EQSs) were exceeded for 8 priority, and 28 specific pollutants. This finding indicated that the existing technology-based discharge standards are not satisfactory to guarantee the intended water quality, and there is a need for adopting a new strategy for the implementation of water-quality-based discharge limits in Turkey. As a widely applied approach for determining water-quality-based discharge limits, firstly, conservative mass balance with and without consideration of mixing zone was evaluated. The results indicated that this approach was not applicable due to the receiving environment concentrations being higher than the EQSs. As an alternative approach, the dilution methodology, which considers the level of dilution occurring at the immediate discharge point, was tested. The results proved that the dilution methodology is the most appropriate strategy for developing countries with relatively poor surface water quality to improve the water quality to the level where the conservative mass balance approach can be applicable.