Abstract
In many developing countries, including South Africa, water scarcity has resulted in poor sanitation practices. The majority of the sanitation infrastructures in those regions fail to meet basic hygienic standards. This along with the lack of proper sewage/wastewater infrastructure creates significant environmental and public health concerns. A self-sustained, waterless “Nano Membrane Toilet” (NMT) design was proposed as a result of the “Reinvent the Toilet Challenge” funded by the Bill and Melinda Gates Foundation. A “cradle-to-grave” life cycle assessment (LCA) approach was adopted to study the use of NMT in comparison with conventional pour flush toilet (PFT) and urine-diverting dry toilet (UDDT). All three scenarios were applied in the context of South Africa. In addition, a Quantitative Microbial Risk Assessment (QMRA) was used to reflect the impact of the pathogen risk on human health. LCA study showed that UDDT had the best environmental performance, followed by NMT and PFT systems for all impact categories investigated including human health, resource and ecosystem. This was mainly due to the environmental credits associated with the use of urine and compost as fertilizers. However, with the incorporation of the pathogen impact into the human health impact category, the NMT had a significant better performance than the PFT and UDDT systems, which exhibited an impact category value 4E + 04 and 4E + 03 times higher, respectively. Sensitivity analysis identified that the use of ash as fertilizer, electricity generation and the reduction of NOx emissions were the key areas that influenced significantly the environmental performance of the NMT system.
Highlights
Provision of sanitation facilities which meet the international baseline standards (UNICEF and WHO, 2017), constitutes a major problem in developing world
Goal and scope The goal of this life cycle assessment (LCA) study is to evaluate the environmental performance of the novel Nano Membrane Toilet (NMT) system and that of the conventional sanitation systems most commonly seen in developing countries, i.e. pour flush and urine diverting dry toilets (Rieck et al, 2013; African Water Facility, 2014)
As it can be deduced from the distribution of the environmental burdens and credits among the different life cycle phases, the use phase dominates the profile of the NMT system - without the consideration of the ash- by a percentage of 79%, which is mainly attributed to the NOX gases generated during the faeces gasification (Table S4 in supporting material)
Summary
Provision of sanitation facilities which meet the international baseline standards (UNICEF and WHO, 2017), constitutes a major problem in developing world. In sub-Saharan African countries only 28% of the population were reported to have access to at least a basic sanitation service in 2015 (UNICEF and WHO, 2017). This situation is compounded by the lack of proper sewerage and the poor operation and maintenance of the domestic faecal sludge management facilities (Wang et al, 2014). Source separation of urine can be achieved by waterless systems through a specific user interface design In this case, urine is sanitized in a storage tank and faeces are composted in a dehydration vault for a minimum period of 6 months (Tilley et al, 2014). The social acceptability of their use in agriculture varies considerably among the developing countries (Moilwa, 2007; Mugivhisa, 2015), in this environmental study the given products have been considered scientifically acceptable, to other relevant LCA studies (Kulak et al, 2017; Remy and Jekel, 2008; Flores et al, 2009)
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