Modeling for sustainability: Life cycle assessment application to evaluate environmental performance of water recycling solutions at the dwelling level

The reduction in drinking water consumption, also through the reuse and recycling of unconventional sources of water, has been identified as one of the goals of the sustainable development. This study focuses on evaluating and comparing the environmental impacts attributable to the use of source of water supply, such as rainwater harvesting and greywater recycling, alternative to the traditional one. The environmental impacts of both positive (reduction of the potable water consumption, stormwater runoff mitigation, wastewater reduction, etc.) and negative factors (system complexity, double network, tank, pump system, etc.) have been evaluated through the combined use of two models. The first is a Life Cycle Assessment (LCA) model, developed by means of Simapro software and based on Recipe 2008 method. The second is a hydrological model, realized with the EPA SWMM software. Models have been used to estimate the environmental impact of the following scenarios: (i) Business-As-Usual; (ii) rainwater harvesting system; (iii) greywater recycling system. Those scenarios have been applied to several configuration of single dwellings and apartment buildings. The Life Cycle stages evaluation showed how energy consumption for distribution system plays a critical role in the overall environmental performance of the solutions proposed, as well as use intensity of the technology. For greywater recycling system, the application of 1 m3 storage and treatment system serving thirty population equivalent results in a net positive impact, while for rainwater harvesting system, the high use intensity should be combined with an alternative reuse for recycled water, i.e. washing machine supply, to obtain an overall environmental benefit.