Biogeochemical Cycling of Phosphorus, Nitrogen, and Carbon during the Provision of Global Sanitation Integrated with Resource Recovery

The new paradigm in the wastewater (sanitation) sector is to not only safely manage pollutants to protect human health and the environment, but also recover valuable resources such as nutrients (i.e., phosphorus and nitrogen). Sanitation technologies that meet the needs of the 2.4 billion people of the world without access to basic or safely managed sanitation services can be deployed in a decentralized or centralized manner. All technologies have the ability to recover globally critical nutrients to varying degrees. Passive decentralized sanitation technologies such as pit toilets and septic tanks can integrate fecal sludge management to recover nutrients. Ecological toilets (e.g., composting toilets) can be designed and operated to contain, process and recover solid human excrement and urine. Likewise, centralized sanitation technologies that integrate conventional wastewater treatment with water reuse may not only reduce greenhouse gas emissions but also reduce the direct discharge of nutrients to surface water while creating beneficial products from "waste." This study presents results of an investigation that assesses the technology-based biogeochemical cycles of phosphorus, nitrogen, and gaseous carbon emissions with provision of decentralized and centralized sanitation that are integrated with resource recovery. Material flow diagrams for phosphorus, nitrogen, and gaseous carbon emissions (CO2 and CH4) were developed for three decentralized technologies (pit and composting toilets, septic tanks), and one centralized resource recovery scenario (sewered toilet followed by waste stabilization pond integrated with water reuse). The system boundary was assumed to occur immediately around the technology. For example, we only accounted for biochemical transformations in a latrine pit or septic tank and did not consider any attenuation provided after the contents left the infrastructure and entered the surrounding soil environment. The results from the material flow diagrams were extrapolated and grouped by World Bank region to understand how resource recovery impacts global biogeochemical flows. Our hope is to provide important insight to decision makers on how to meet multiple Sustainable Development Goals (SDGs) through global sanitation provision that integrates resource recovery.