pH Monitoring to Improve Early Detection of Contamination in Cooling Water System at Rönnskär Smelter Site : A case study to reduce marine emissions

Sammanfattning

The industrial marine emissions remain an environmental challenge and require continuous collective efforts to support a more sustainable industrial sector. Mining and smelter operations contribute to the industrial sector’s environmental impact, partly due to the use and discharge of large water flows. The purpose of this degree project was to improve the cooling water monitoring strategy of Boliden AB’s smelter site Rönnskär by investigating how pH sensors could be used as indicators of contamination in the cooling water system and thereby reduce the marine emissions from the site. The study was conducted as a case study, combining site-specific data collection and experimental methods, including cooling water network mapping, interviews with personnel, analysis of a historical contamination event, scenario-based emission reduction calculations, laboratory dilution experiments and in-field pH signal characterization. The results suggest that the current monitoring strategy had limitations regarding early detection and source localization of contamination, particularly due to the complexity of the cooling water network. Legacy infrastructure has caused challenges from a structural and organizational perspective. A proposed monitoring system with increased spatial resolution was developed, consisting of pH sensors located closer to potential contamination sources. The dilution experiment indicated that the pH sensors respond to relatively small additions of acidic process water (0.005%), suggesting that pH may serve as an early indicator of contamination in the cooling water system. Field measurements quantified pH signal characteristics (𝜇 = 7.60, 𝜎 = 0.03) and were used to develop an alarm logic for pH deviations. The analysis of a historical contamination event and the scenario-based emission reduction calculations indicate that reductions of 32-80% are possible, depending on the time to detect contamination. Overall, the work showed that pH-based monitoring can provide a practical and technically feasible strategy for improving cooling water emission control at Rönnskär and the finished work could be linked to the SDG 6 and SDG 14. Further work is suggested to validate sensor locations, ensure reliable data transmission and expand the strategy to support long-term operation.