Multicriteria Suitability Index for Prioritizing Early-Stage Deployments of Wastewater-Derived Fertilizers in Sub-Saharan Africa

Recycling nutrients from wastewater could simultaneously decrease the carbon intensity of traditional ammonia supply chains and increase the accessibility of local fertilizer. Despite the theoretical potential, techno-economic viability of wastewater nutrient recovery in sub-Saharan Africa has been poorly characterized at subnational scales. This work proposes a multicriteria suitability index to describe techno-economic viability of wastewater-derived fertilizer technologies with district-scale resolution. This index, with a range from 0 to 1 (highest suitability), incorporates key drivers, including population density, soil conditions, sanitation levels, and fertilizer prices. We found that suitability varies widely within and across countries in sub-Saharan Africa and that the primary limiting factor is the absence of sanitation infrastructure. Regions with a minimum of 10% cropland area and a suitability index of at least 0.9 were identified as highly suitable target regions for initial deployment. While they comprise only 1% of the analyzed area, these regions are home to 39 million people and contain up to 3.7 million hectares of cropland. Wastewater-derived fertilizer technologies could deliver an average of 25 kg of nitrogen per hectare of cropland, generating additional food equivalent to the annual consumption of 6 million people. Screening for high suitability can inform selection of effective lighthouse demonstration sites that derisk technology deployment and promote the transition to a more circular nutrient economy.

Automated summary

This study proposes a multicriteria suitability index to evaluate the techno-economic viability of wastewater nutrient recovery technologies. The results show that suitability varies widely across sub-Saharan Africa, with the main limiting factor being the lack of sanitation infrastructure. Highly suitable target regions for initial deployment have been identified, which have significant cropland area and population. Wastewater-derived fertilizer technologies can provide a substantial amount of nitrogen, equivalent to the food needs of millions of people.