The iron and steel industry discharges large quantities of wastewater. The environmental impact of the wastewater is traditionally assessed from the quantitative aspect. However, the water quality of discharged wastewater plays a more significant role in damaging the natural environment. Moreover, comprehensive assessment of multi-pollutants in wastewater from both quality and quantity is still a gap. In this work, a total environmental impact score (TEIS) is defined to assess the environmental impact of wastewater discharge, by considering the volume of wastewater and the quality of main processes. To implement the comprehensively qualitative and quantitative assessment, a field monitoring and measurement of wastewater discharge volume and the quality is conducted to acquire pH, suspend solids (SS), chemical oxygen demand (COD), total nitrogen (TN), total iron (TFe), and hexavalent chromium (Cr(VI)). The sequence of TEIS values is obtained as steelmaking > ironmaking > sintering > hot rolling > coking > cold rolling and TN > COD > SS > pH > Cr(VI) > TFe. The TEIS of the investigated steel plant is 26.27. The leading process lies in steelmaking with a TEIS of 19.98. The dominant pollutant is TN with a TEIS of 15.00. Finally, a sensitivity analysis is performed to validate the feasibility and generalisability of the TEIS.
Environmental sensitivity areas need more investment to treat and process environmental pollution from waste drilling fluids than non-sensitivity areas because the former was closer to rivers, villages, farmlands, etc., which not only increased the burden of enterprises, but also constrained the sustainable development for oilfields. In order to overcome the challenge of treating waste drilling fluids in environmental sensitivity areas, harmless treatment technology and formulas for waste drilling fluids were developed and determined in this study. The basic formula was: 10.0% SD-4 + 2.5% SD-5 + 9.0% SD-6 + 7.0% SD-7. This technology broke through the traditional curing processing technology and it was successfully applied to two oil wells in Wenmi environmental sensitivity areas. The results showed that the main pollutants were below the requirements of related state environmental protection standard limits and had some porosity and soil-like characteristics. Therefore, the aim of harmless treatment and restoring drilling of waste drilling fluids was realized and the ecological environment of environmental sensitivity areas was well protected.
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