The lack of sanitation infrastructure, combined with the adoption of inadequate sanitation practices and technologies, poses a major problem in many low-income countries such as Haiti. The resulting fecal contamination often causes health and environmental issues, increasingly threatening human health and ecosystem balances. Addressing fecal contamination necessarily involves the implementation of sanitation systems and technologies (and practices) adapted to the local context to effectively manage household excreta. However, the selection of these sanitation systems must be based on scientific evidence to avoid creating pollution transfers.
This doctoral thesis primarily aims to evaluate the health and environmental impacts of the main autonomous sanitation systems and technologies used in tropical low-income countries, with a particular focus on Haiti, in order to identify the most environmentally efficient solutions and those that could be improved. Life cycle assessment (LCA), as a holistic and multi-criteria environmental evaluation method, is used as the methodological tool to achieve this goal. LCA helps to identify the sanitation systems and technologies that are most beneficial in terms of health and the environment, while avoiding pollution transfers. Additionally, quantitative microbial risk assessment (QMRA) is used as a complementary tool to assess microbial health risks, which are not covered by LCA. The functional unit considered is the management of one ton of wet fecal sludge in Haiti over a one-year period.
A total of fifteen scenarios representing the most common on-site sanitation systems were developed by combining three toilet types, initially manual and then mechanical evacuation, and five sludge treatment and/or valorization technologies. Each on-site sanitation system consists of three components: toilet, evacuation, and treatment. The three toilets considered are the ventilated improved pit (VIP) latrine, the container-based toilet (CBT), and the flush toilet (WC). For the evacuation, the initial sludge emptying is carried out using a Gulper pump (except for scenarios involving a CBT), while a sewage truck subsequently collects the sludge to transport it to a treatment plant located 10 km from the collection point. For treatment, the technologies considered are a biodigester, a composter, a lagoon system, unplanted drying beds (UDB), and planted drying beds (PDB).
To model the examined sanitation systems and technologies, a life cycle inventory based mainly on interviews, weighing campaigns, and bibliographic research was conducted. The OpenLCA software and ecoinvent databases version 3.7 were used for modeling. The Impact World+ and IPCC 2013 GWP 100a methods were employed for the life cycle impact assessment. System expansion was applied, in accordance with ISO 14044 standards, to allocate the environmental benefits resulting from the production of compost, biogas, and biosolids to the system.
The results show that among the sanitation technologies examined, the WC is the most harmful to the environment, while the CBT is the least harmful. The toilet use phase was identified as the most impactful stage of the life cycle, accounting for more than 90% of the total impact of each sanitation system examined. Toilet paper, wood shavings, greenhouse gas (GHG) emissions from the biodegradation of sludge in toilets, and water were identified as the main hotspots. Regarding intensive treatment technologies, the biodigester is more impactful than the composter, while for extensive technologies, PDB are considered the most impactful, followed by UDB and lagoons.
As for the sanitation systems, two broad categories were considered based on the presence of either intensive or extensive sludge treatment technologies downstream. In systems equipped with an intensive sludge valorization technology, Scenario 1 (VIP-Evacuation-Composting) was identified as overall the most beneficial, while Scenario 6 (WC-Evacuation- Biomethanization) was the most impactful. In the case of systems equipped with an extensive sludge treatment technology, Scenario 6 (VIP-Evacuation-Lagoons) and Scenario 4 (VIPEvacuation- UDB) were overall the least impactful, with these two scenarios being interchangeable. Conversely, Scenario 8 (WC-Evacuation-PDB) was identified as the most impactful.
To improve the examined sanitation systems and technologies, the study recommends using locally produced toilet paper made from recycled paper, using ash and/or sawdust as litter instead of wood shavings in CBT, using water-saving WCs, and a locally manufactured Gulper pump to avoid directly entering the pits during emptying.
Two separate QMRA studies were conducted to assess microbial risks related to the use of CBT and to the manual emptying of pits by emptiers, called “bayakous.” The results reveal a high risk for CBT users and an extremely high risk for the bayakous, exceeding the acceptable risk threshold set by the USEPA (10-4 per person per year). These studies recommend mitigation measures, including the use of personal protective equipment, the adoption of manual pumps to avoid entering the pits, and the professionalization of the bayakou occupation to improve health safety and working conditions.
| Date | 20 Nov 2024 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Frédéric Monette (Supervisor) |
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