Comparison of development scenarios of a black water source-separation sanitation system using life cycle assessment and environmental life cycle costing

The objective of the study is to compare different development scenarios of a black water source-separation sanitation system (BWS) that could be environmentally and economically more viable than a conventional system (CONV). Scenarios performance is evaluated using life cycle assessment and environmental life cycle costing. System boundaries include the processes related to the collection and treatment of wastewater and organic kitchen refuse collection and the recycling of by-product (digestate/sludge and biogas) produced in the treatment step. The BWS scenario that entails a vacuum toilet flow-volume reduction to 0.5 L/flush results in significantly higher performances than the ones of CONV for the climate change and resources indicators, while involving a significantly lower performance with regards to human health and a comparable cost. The BWS scenario based on digestate mass reduction with reverse osmosis and acidification prior to its transport to farmland achieves comparable performances to the ones of CONV for all indicators. The BWS scenario with digestate treatment by means of phosphorus precipitation (struvite) and nitritation-anammox reactors gives performances that are comparable to the ones of CONV for all indicators, with the exception of climate change, for which this scenario has a significantly lower performance if the electricity is produced by hydropower. When single-pathway scenarios are combined, the multi-pathway scenarios thus created can produce results that are significantly superior to the CONV result for the climate change, resources and human health indicators although the cost remains comparable.