Cradle-to-Gate LCA of Water Treatment Alternatives : A case study performed for Norrvatten’s future waterwork expansion
Abstract: Norrvatten is a municipal association which owns a water treatment plant capable of supplying good quality drinking water to the consumers in the associated neighbouring municipalities. After preliminary investigations for the future year of 2050, there were estimates which suggest a potential water quality degradation in the lake which supplies the raw water for treatment due to uncertain future climatic conditions and other forms of pollutions from the surrounding. There is also a forecast of future population increase in the respective neighbouring municipalities of Stockholm county, which consequently increases the demand for additional quantity of supplied drinking water. The supplied drinking water, which even though is currently acceptable by the standards set by Swedish Food Agency, still requires additional advanced treatment techniques in order to provide an upscale to its quality. This increase in water quality can be achieved by increasing the natural organic matter removal treatment techniques in the water treatment plant by implementing more chemical and microbiological barriers. Norrvatten has proposed several alternative water purification methods, out of which one of them can be implemented in the water treatment plant, after an expansion in the capacity of the plant to achieve all the above-mentioned requirements. A case study has been performed at Norrvatten in Stockholm, Sweden for evaluating the environmental performance of the proposed treatment alternatives. This study adopts a cradle-to-gate life cycle assessment methodology to analyze the alternatives using stand-alone and comparative assessment methods. An explicit focus is given with the selection of 15 different environmental categories to assess the related environmental burdens. The various hotspots identified from the analysis is investigated and identified to find the associated trade-offs with the alternatives under study. Additional parameter changes have been made in the alternatives to apprehend how the impacts change accordingly. The various hotspots identified from the results of the study were, the utilization of granular activated carbons for filtration, the consumption of aluminium sulphate for coagulation, the consumption of soda if iron chloride is selected as the main coagulant, the consumption of electricity in the WTP by nanofiltration process, hydropower from pumped storage and the use of heavy trucks for transporting chemicals from suppliers to the site. Other aspects and assumptions from conducting a sensitivity analysis indicated that there are possibilities to decrease the impacts through the following changes. By switching the main coagulant from aluminium sulphate to iron chloride to decrease the major resource depletion and human health impacts with a trade-off increase in impacts from an increased production of soda for chemical consumption. By switching the current purchase of electricity, from a green energy mix to the Swedish grid mix, to greatly improve the environmental performance of the treatment plant. This energy change was observed to result in the reduction of global warming potential from CO2 emissions. Other changes which can be implemented to reduce the overall environmental impacts are switching from fuel- based transportation trucks to electric trucks and switching chemical suppliers from outside Sweden to suppliers located near or within Sweden, closer to the water treatment plant.
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