Designing sustainable faecal sludge treatment systems for small cities in Sub-Saharan Africa

Abstract

More than 80 per cent of wastewater from human activities is discharged into the rivers or sea without any pollution removal, and the Sustainable Development Goals (SDGs) aim to halve this proportion and increase recycling and reuse globally by 2030. Treatment plants in Sub-Saharan Africa often fail due to lack of operating funds, poor regulation and poor design that does not take into account human factors. The failure of treatment plants can also be put down partly to the funding structures for management, which are often dependent on the disposal tariffs charged. Without sufficient regulation and enforcement, which is often lacking in Sub-Saharan Africa, this often leads to illegal disposal of faecal sludge. Due to the nutrient content and energy potential of wastewater, there is increasing focus on reuse of faecal sludge in ways that can contribute funds for maintenance and incentivise good management of treatment facilities. This research investigates potential designs for the re-use of faecal sludge in small cities in Sub-Saharan Africa to ensure proper treatment. Conducting two case studies using qualitative and quantitative methods, the research looks at the potential for re-use to be scaled up in Sunyani, Ghana and Mzuzu, Malawi, and whether different designs can ensure good management. Building upon the research investigation into how previous designs have failed in case studies, the research also investigates the use of agent-based modelling (ABM) as a modelling approach to explore social and technical aspects of sanitation systems to predict how different designs and management approaches can work. In Sunyani, biogas was the most acceptable option to customers whilst also providing a good business model to fund faecal sludge treatment, either as a decentralised system at public toilets where the fresh sludge is better for biogas production, or centrally at the existing disposal site. The success of biogas as a model that can fund maintenance and ensure good management would depend on the faecal sludge quality of public toilet sludge in the city and the investment level required and how any operating approach would work between the government and private sector. In Mzuzu, two main approaches to faecal sludge re-use exist currently: the implementation of Skyloos as above ground household toilets which provide compost, and a central disposal site from which compost is illegally harvested. At disposal, farmers remove sludge from the ponds and apply it untreated directly onto agricultural land. At times, private sector emptying services do not use the ponds, but also apply untreated sludge to agricultural land. Skyloos were found to have varying levels of success from different Non- Governmental Organisation (NGO) projects, with key sustainability issues being the availability of financing mechanisms, management between landlords and tenants and the trust of and engagement with implementing organisations. Existing approaches to waste management and re-use were found to be inaccessible and not working when implemented for the poorest and people with disabilities. Adopting re-use of faecal sludge in agriculture in Malawi would require improved marketing of sanitation options, financing options for households to incentivize adopting the technology, not targeting to poorest households and people with disabilities, and an improved management model for the treatment site to ensure safe disposal and production of compost. Looking at ABM as a way of modelling faecal sludge treatment systems in Sub- Saharan Africa, two models of different approaches in Mzuzu were developed to look at scaling up Skyloo toilets and managing the treatment plant. Both models demonstrate the potential of ABM to incorporate social and technical aspects into predicting the performance of different designs and approaches. The success and use of modelling depends on the quality of data that can be collected before implementing system approaches. Overall the thesis presents different models of treatment and re-use that can work and contribute to operating and maintenance of systems. It is unlikely that any design system will be so profitable that the treatment and re-use of sludge will be able to ensure good management without regulation, so the success of designs depends on relationships between the government and private sector and households in small cities.