Comparison of life cycle impacts between wetland and rainwater harvesting systems

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Constructed wetland helps to improve the environmental and social values of the inhabited catchments and their downstream natural water bodies. However, the environmental impacts due to its construction necessitate evidence of how beneficial it would be once operational compared to other water-sensitive urban design (WSUD) components. The study has simulated the reduction of pollutants and runoff in a wetland. Consequently, environmental impacts were estimated using the life cycle assessment (LCA) approach. The catchment settings with and without wetlands were compared with the environmentally viable rainwater harvesting (RWH) systems. Potable supply using watermain was included in the catchment settings to have a common basis for their evaluation, which was not considered in the existing literature. The study demonstrates that the runoff impacts (operational) of the catchment having a watermain (without a wetland system) are 3.6–4.5, 4.0, 3.2–4.7, and 2.7–3.5 times of catchment with wetland-only on ecotoxicity-marine, ecotoxicity-freshwater, human toxicity-carcinogenic, and eutrophication categories. For the same systems, the net impacts (fabrication & installation + operational) of all undertaken impact categories are 3–28.6 times. In contrast, the net impacts of the residual runoff generated by the most viable RWH systems after supplying household demands (i.e., % reliability of the RWH tanks) are mostly 2.3–30.5 times the net impacts of the catchment having wetland-only. In an equivalent assessment, the catchment net impacts of the watermain system (with wetland) as times of impacts of RWH systems are 0.2–0.91 times on eutrophication, ozone depletion, ecotoxicity-marine (in lower series of RWH), and ecotoxicity-freshwater. In contrast, those systems are mostly 1.02–3.12 times on human toxicity-carcinogenic, global warming, ecotoxicity-terrestrial and higher series of ecotoxicity-marine impact categories. The study suggests that wetland or RWH is suitable if emission prevention to water or air is emphasized.