No abstract

The United Nations' Sustainable Development Goals (SDGs) recognize that current sanitation gaps must be closed to better serve those without access to safely managed systems (Target 6.2: universal sanitation coverage) and those connected to sewers without wastewater treatment (Target 6.3: halving the proportion of untreated wastewater). Beyond mitigating environmental and health concerns, implementing resource recovery sanitation systems could simultaneously improve the availability of agricultural nutrients (SDG 2) and household energy (SDG 7). This study estimates the potential for global, regional, and country-level resource recovery to impact nutrient and household electricity use through 2030. We distinguish impacts from newly installed sanitation systems (to achieve universal coverage), newly treated wastewater systems (to halve the proportion of untreated wastewater), and existing system replacement, while also considering urban and rural disparities and spatial colocation of nutrients with agricultural needs. This work points toward country-specific strategies for deriving the greatest benefit from sanitation investments while also identifying overarching trends to guide international research efforts. Globally, potential nutrient gains are an order of magnitude larger than electricity (a small fraction of total energy), and considerable impacts are possible in the least-developed countries, six of which could double or offset all projected nutrient and electricity use through newly installed sanitation systems.

Urban growth in low- and middle-income countries has intensified the need to expand sanitation infrastructure, especially in informal settlements. Sanitation approaches for these settings remain understudied, particularly regarding multidimensional social–ecological outcomes. Guided by a conceptual framework (developed in parallel with this study) re-envisioning sanitation as a human-derived resource system, here we characterize existing and alternative sanitation scenarios in an informal settlement in Kampala, Uganda. Combining two core research approaches (household survey analysis, process modeling), we elucidate factors associated with user satisfaction and evaluate each scenario’s resource recovery potential, economic implications, and environmental impacts. We find that existing user satisfaction is associated with factors including cleaning frequency, sharing, and type of toilets, and we demonstrate that alternative sanitation systems may offer multidimensional improvements over existing latrines, drying beds, and lagoons. Transitioning to anaerobic treatment could recover energy while reducing overall net costs by 26–65% and greenhouse gas emissions by 38–59%. Alternatively, replacing pit latrines with container-based facilities greatly improves recovery potential in most cases (e.g., a 2- to 4-fold increase for nitrogen) and reduces emissions by 46–79%, although costs increase. Overall, this work illustrates how our conceptual framework can guide empirical research, offering insight into sanitation for informal settlements and more sustainable resource systems.

Sanitation remains a global challenge, both in terms of access to toilet facilities and resource intensity (e.g., energy consumption) of waste treatment. Overcoming barriers to universal sanitation coverage and sustainable resource management requires approaches that manage bodily excreta within coupled human and natural systems. In recent years, numerous analytical methods have been developed to understand cross-disciplinary constraints, opportunities, and trade-offs around sanitation and resource recovery. However, without a shared language or conceptual framework, efforts from individual disciplines or geographic contexts may remain isolated, preventing the accumulation of generalized knowledge. Here, we develop a version of the social-ecological systems framework modified for the specific characteristics of bodily excreta. This framework offers a shared vision for sanitation as a human-derived resource system, where people are part of the resource cycle. Through sanitation technologies and management strategies, resources including water, organics, and nutrients accumulate, transform, and impact human experiences and natural environments. Within the framework, we establish a multitiered lexicon of variables, characterized by breadth and depth, to support harmonized understanding and development of models and analytical approaches. This framework’s refinement and use will guide interdisciplinary study around sanitation to identify guiding principles for sanitation that advance sustainable development at the nature-society interface.

Recovering human-derived nutrients from sanitation systems can offset inorganic fertilizer use and improve access to agricultural nutrients in resource-limited settings, but the agronomic value of recovered products depends upon product chemistry and soil context. Products may exacerbate already-compromised soil conditions, offer benefits beyond nutrients, or have reduced efficacy depending on soil characteristics. Using global spatial modeling, we evaluate the soil suitability of seven products (wastewater, sludge, compost, urine, ammonium sulfate, ammonium struvite, potassium struvite) and integrate this information with local recovery potential of each product from sanitation systems that will need to be installed to achieve universal coverage (referred to here as “newly-installed sanitation”). If product recovery and reuse are colocated, the quantity and suitability of nutrient reuse was variable across countries. For example, alkaline products (e.g., struvite) may be particularly beneficial when applied to acidic soils in Uganda but potentially detrimental in the southwestern United States. Further, we illustrate discrepancies across soil data sets and highlight the need for locally accurate data, knowledge, and interpretation. Overall, this study demonstrates soil context is critical to comprehensively characterize the value proposition of nutrient recovery, and it provides a foundation for incorporating soil suitability into local and global sanitation decision-making.