Opportunities and barriers to recovering value from faecal sludge in sub-Saharan Africa

Abstract

Pit latrines are the most common sanitation systems used in sub-Saharan African cities. The rapid expansion and densification of urban areas has led to an urgent need for sustainable management practices which safely remove and transport faecal sludge from pit latrines to treatment facilities. Transformation into compost or soil conditioner can add further value by recovering nutrients for agriculture. This thesis examines key opportunities and barriers to faecal sludge management and value recovery using the city of Blantyre (Malawi), as a case study. Socio-technical interactions and technological innovations are examined at three points in the ‘faecal sludge value chain’: removal of faecal sludge from pit latrines, treatment with novel composting systems, and public acceptability of the derived compost. Menstrual waste, which is commonly found in pit latrines, can obstruct pit emptying devices; the first objective was therefore to quantify menstrual waste entering pit latrines and identify its behavioural drivers. Surveys and interviews established that substantial quantities of cloth and pads are discarded in pit latrines, but socio-cultural sensitivities inhibit disposal elsewhere. Biological composting methods, such as use of black soldier fly larvae (BSFL) (Hermetia illucens), offer novel faecal sludge treatment strategies; the second objective was therefore to investigate the effectiveness of BSFL composting. Laboratory experiments examined the die-off of faecal indicator organisms in faecal sludge and vegetable waste in the presence of BSFL and found reductions in Escherichia coli but not in Enterococcus faecalis. Lack of public acceptability is regarded as a critical barrier to recovering agricultural nutrients from faecal sludge; the third objective was therefore to assess public acceptability and willingness to pay for human-excreta-derived fertiliser (HEDF). Surveys revealed that almost all people were willing to buy maize grown in HEDF, and buy HEDF to use on their farms, provided that they were able to view a sample of the product. The thesis highlights the importance of understanding cultural norms and behaviours of beneficiaries in order to design effective and sustainable interventions, and how the siloed nature of sanitation and solid waste management obscures their important interconnections. Overall, presence of solid waste in pit latrines remains one of the most significant and complex obstacles to economic and efficient recovery of faecal sludge, whilst public acceptability is often underestimated, and novel treatment solutions remain promising but require further investigation.