Navigating Multidimensional Social-Ecological System Trade-Offs across Sanitation Alternatives in an Urban Informal Settlement

Assessing the Relative Sustainability of Point-of-Use Water Disinfection Technologies for Off-Grid Communities

Point-of-use (POU) water disinfection technologies can be adopted to provide access to safe drinking water by treating water at the household level; however, navigating various POU disinfection technologies can be difficult. While numerous conventional POU devices exist, emerging technologies using novel materials or advanced processes have been under development and claim to be of lower cost with higher treatment capacity. However, it is unclear if these claims are substantiated and how novel technologies compare to conventional ones in terms of cost and environmental impacts when providing the same service (i.e., achieving a necessary level of disinfection for safe drinking water). This research assessed the sustainability of four different POU technologies (chlorination using sodium hypochlorite, a silver-nanoparticle-enabled ceramic water filter, ultraviolet mercury lamps, and ultraviolet light-emitting diodes). Leveraging open-source Python packages (QSDsan and EXPOsan), the cost and environmental impacts of these POU technologies were assessed using techno-economic analysis and life cycle assessment as per capita cost (USD·cap-1·yr-1) and global warming potential (kg CO2 eq·cap-1·yr-1). Impacts of water quality parameters (e.g., turbidity, hardness) were quantified for both surface water and groundwater, and uncertainty and sensitivity analyses were used to identify which assumptions influence outcomes. All technologies were further evaluated across ranges of adoption times, and contextual analysis was performed to evaluate the implications of technology deployment across the world. Results of this study can potentially provide valuable insights for decision-makers, nonprofit organizations, and future researchers in developing sustainable approaches for ensuring access to safe drinking water through POU technologies.

Centralized or Onsite Testing? Examining the Costs of Water Quality Monitoring in Rural Africa

Rural water systems in Africa have room to improve water quality monitoring. However, the most cost-effective approach for microbial water testing remains uncertain. This study compared the cost per E. coli test (membrane filtration) of four approaches representing different levels of centralization: (i) one centralized laboratory serving all water systems, (ii) a mobile laboratory serving all systems, (iii) multiple semi-centralized laboratories serving clusters of systems, and (iv) decentralized analysis at each system. We employed Monte Carlo analyses to model the costs of these approaches in three real-world contexts in Ghana and Uganda and in hypothetical simulations capturing various conditions across rural Africa. Centralized testing was the lowest cost in two real-world settings and the widest variety of simulations, especially those with water systems close to a central laboratory (<36 km). Semi-centralized testing was the lowest cost in one real-world setting and in simulations with clustered water systems and intermediate sampling frequencies (1-2 monthly samples per system). The mobile lab was the lowest cost in the fewest simulations, requiring few systems and infrequent sampling. Decentralized testing was cost-effective for remote systems and frequent sampling, but only if sampling did not require a dedicated vehicle. Alternative low-cost testing methods could make decentralized testing more competitive.

Shared sanitation in informal settlements: A systematic review and meta-analysis of prevalence, preferences, and quality

Shared sanitation facilities are not considered a type of basic sanitation by the WHO/UNICEF Joint Monitoring Programme (JMP), though they may be the only alternative to open defecation in urban informal settlements. Additionally, JMP indicators for sanitation do not cover aspects related to the quality of shared sanitation, such as those outlined in the Human Right to Water and Sanitation (HRTWS) framework. Data on the prevalence of shared sanitation within informal settlement areas is limited, and there is a need to understand user preferences, experiences, and barriers to the use of shared sanitation to inform effective policy and practice. This systematic review aims to summarize the prevalence and number of households sharing sanitation in informal settlements globally, as well as user experiences and barriers to successful implementation of shared sanitation. We included studies available in English and published after January 1, 2000. We retrieved 4741 articles from seven databases and included a total of 167 relevant publications. Among included studies, 54 reported the prevalence of shared sanitation in informal settlements, and 138 studies reported on user perceptions and experiences related to shared sanitation quality. A meta-analysis of studies reporting the prevalence of shared sanitation in informal settlements globally revealed an estimated overall prevalence of 67% [95% CI: 61%-73%]. Commonly reported user preferences included cleanliness to promote continued use of shared facilities, privacy with a lockable door, facilities for menstrual hygiene management, safety and protection against violence, 24/7 access, proper lighting, and shared responsibility for facility management - which align with the HRTWS framework and represent barriers to shared sanitation use. Based on the findings of this review, we recommend including the number of households or people sharing a sanitation facility in monitoring of shared sanitation quality, locating sanitation facilities within compounds, where applicable, and promoting safety, dignity, and privacy of all users in the development of shared sanitation quality indicators.

Enhancing the nitrogen and phosphorus content of faecal-derived biochar via adsorption and precipitation from human urine

Urine diversion in toilets is a promising strategy to maximise nutrient recovery and produce low-cost urine-derived fertilisers. There are various methods for nutrient recovery from urine, including precipitation and adsorption onto porous media, such as biochars. This study uses faecal-derived biochars to produce and, for the first time, comprehensively characterise enriched biochar fertilisers with the addition of fully hydrolysed undiluted human urine. The evolution of urea hydrolysis and nutrient content during urine storage was initially investigated over a 6-month storage period and NH4+ adsorption mechanisms studied under varying biochar doses and NH4-N concentrations. The process was further optimised by adding MgO to induce precipitation reactions, enabling the combined recovery of NH4+ and P. For NH4+ adsorption, experimental data exhibited a good fit to both the Freundlich (R2 = 0.989) and Langmuir (R2 = 0.974) isotherm models and the rate of the reaction was well described by a pseudo 2nd order kinetics model (R2 = 0.988). The NH4+ uptake was rapid during the initial 2 h of the reaction and the adsorption process reached completion after 24 h. The NH4-N adsorption capacity of the faecal-derived biochar was 19.8 mg/g and the main adsorption mechanism identified was ion exchange (K+ ↔ NH4+), as confirmed by XRD and ICP-OES. The effect of different biochar doses (0, 25, 50, 100 g/L) and MgO addition scenarios (Mg:P = 0, 1.5, 4) on N and P recovery showed that the combination of MgO (Mg:P = 1.5) with the lower biochar dose (25 g/L) produced the most NP-rich fertiliser product which was easily separated from the urine. Faecal-derived biochar had a limited adsorption capacity for P, with precipitation being the main mechanism for P recovery. When MgO was added to urine, >98% of total P was recovered via precipitation of struvite/struvite-K and substituted hydroxyapatite, as identified via SEM-EDX. Faecal-derived biochar was a successful carrier to recover the P-containing precipitates and facilitate liquid-solid separation after treatment. The findings of this study provide proof-of concept for the systemic management of source separated human excreta and pave the way for the production of marketable waste-derived fertilisers from on-site sanitation systems.

Advancing the Economic and Environmental Sustainability of the NEWgenerator Nonsewered Sanitation System

Achieving safely managed sanitation and resource recovery in areas that are rural, geographically challenged, or experiencing rapidly increasing population density may not be feasible with centralized facilities due to space requirements, site-specific concerns, and high costs of sewer installation. Nonsewered sanitation (NSS) systems have the potential to provide safely managed sanitation and achieve strict wastewater treatment standards. One such NSS treatment technology is the NEWgenerator, which includes an anaerobic membrane bioreactor (AnMBR), nutrient recovery via ion exchange, and electrochlorination. The system has been shown to achieve robust treatment of real waste for over 100 users, but the technology's relative life cycle sustainability remains unclear. This study characterizes the financial viability and life cycle environmental impacts of the NEWgenerator and prioritizes opportunities to advance system sustainability through targeted improvements and deployment. The costs and greenhouse gas (GHG) emissions of the NEWgenerator (general case) leveraging grid electricity were 0.139 [0.113-0.168] USD cap^-1 day^-1 and 79.7 [55.0-112.3] kg CO₂-equiv cap^-1 year^-1, respectively. A transition to photovoltaic-generated electricity would increase costs to 0.145 [0.118-0.181] USD cap^-1 day^-1 but decrease GHG emissions to 56.1 [33.8-86.2] kg CO₂-equiv cap^-1 year^-1. The deployment location analysis demonstrated reduced median costs for deployment in China (-38%), India (-53%), Senegal (-31%), South Africa (-31%), and Uganda (-35%), but at comparable or increased GHG emissions (-2 to +16%). Targeted improvements revealed the relative change in median cost and GHG emissions to be -21 and -3% if loading is doubled (i.e., doubled users per unit), -30 and -12% with additional sludge drying, and +9 and -25% with the addition of a membrane contactor, respectively, with limited benefits (0-5% reductions) from an alternative photovoltaic battery, low-cost housing, or improved frontend operation. This research demonstrates that the NEWgenerator is a low-cost, low-emission NSS treatment technology with the potential for resource recovery to increase access to safe sanitation.

Effect of modified waste introduction methods over short-term and long-term use of onsite sanitation systems

Insufficiently treated wastes contained within onsite sanitation systems (OSS) commonly used by disadvantaged and developing communities contribute to public and environmental health concerns, calling for practical alternative solutions. At the basic level, an improved understanding of the evolution of chemical and physical constituents under different waste introduction methods and for short-term and long-term operation is needed. While receiving non-dilute waste under mixed, unmixed, toilet paper exclusion, and urine diversion (UD) regimes, self-flushing OSS simulated using anaerobic digesters (ADs) were compared during three operational stages: (1) 0-1 month service for unsheltered encampments; (2) 1-3 month disaster relief scenario; and (3) ≥ 3 months representing refugee camps and long-term household use. Although stratification was found to promote suitable conditions for short-term use of self-flushing toilets, mixing increased beneficial biodegradation of organic constituents. Urine-containing ADs demonstrated a shift from sulfide to ammonia odor accompanied by high pH (> 8) after ~ 240 d. E. coli reduction following elevated nitrogen and dissolved solids levels pointed to decreased pathogen survival in ADs with urine. The benefits of bacterial disinfection, reduction of sulfurous odors, and heightened organics degradation in mixed, urine-containing ADs suggest this format as more desirable for prolonged use of self-flushing OSS over unmixed or urine-diverting formats.

DMsan: A Multi-Criteria Decision Analysis Framework and Package to Characterize Contextualized Sustainability of Sanitation and Resource Recovery Technologies

In resource-limited settings, conventional sanitation systems often fail to meet their goals-with system failures stemming from a mismatch among community needs, constraints, and deployed technologies. Although decision-making tools exist to help assess the appropriateness of conventional sanitation systems in a specific context, there is a lack of a holistic decision-making framework to guide sanitation research, development, and deployment (RD&D) of technologies. In this study, we introduce DMsan-an open-source multi-criteria decision analysis Python package that enables users to transparently compare sanitation and resource recovery alternatives and characterize the opportunity space for early-stage technologies. Informed by the methodological choices frequently used in literature, the core structure of DMsan includes five criteria (technical, resource recovery, economic, environmental, and social), 28 indicators, criteria weight scenarios, and indicator weight scenarios tailored to 250 countries/territories, all of which can be adapted by end-users. DMsan integrates with the open-source Python package QSDsan (quantitative sustainable design for sanitation and resource recovery systems) for system design and simulation to calculate quantitative economic (via techno-economic analysis), environmental (via life cycle assessment), and resource recovery indicators under uncertainty. Here, we illustrate the core capabilities of DMsan using an existing, conventional sanitation system and two proposed alternative systems for Bwaise, an informal settlement in Kampala, Uganda. The two example use cases are (i) use by implementation decision makers to enhance decision-making transparency and understand the robustness of sanitation choices given uncertain and/or varying stakeholder input and technology ability and (ii) use by technology developers seeking to identify and expand the opportunity space for their technologies. Through these examples, we demonstrate the utility of DMsan to evaluate sanitation and resource recovery systems tailored to individual contexts and increase transparency in technology evaluations, RD&D prioritization, and context-specific decision making.

A Qualitative Assessment of Place and Mental Health: Perspectives of Young Women Ages 18-24 Living in the Urban Slums of Kampala, Uganda

This paper examines the link between place and mental health using a qualitative assessment and focus group discussion with young women, ages 18 to 24 years of age, residing in three slums in Kampala, Uganda. The assessment, conducted in August of 2022, engaged 15 women who participated in Uganda Youth Development Drop-in center activities. The objective was to assess mental health and the link between place and mental health. Facilitated group discussions and photograph review yielded the following results. In terms of understanding their views of mental health and wellbeing, participants clearly focused on feelings. However, they also assessed resilience, the environment and a person's choice as relating to their mental health. Participants also found the physical spaces related to sports, education, worship, workplaces and green space to be linked to happiness. In terms of the attributes that were linked to sadness, participants listed the physical locations where drugs are sold, clubs for dancing and partying and also sanitation issues in the community. Participants frequently reported on the social environment and reflected on harassment, discrimination, alcohol use and criminal behavior that did not reflect a specific physical space, but rather the embedded social interactions they may face or observe by living in close proximity to hotspots for criminal activity. Given the dire shortages of mental health services and care that are available in this setting, a better understanding of young women's perceptions of place and mental health will be key for low-cost interventions and strategies to mitigate the contextual factors that may exacerbate mental illness.

Financial Viability and Environmental Sustainability of Fecal Sludge Treatment with Pyrolysis Omni Processors

Omni Processors (OPs) are community-scale systems for non-sewered fecal sludge treatment. These systems have demonstrated their capacity to treat excreta from tens of thousands of people using thermal treatment processes (e.g., pyrolysis), but their relative sustainability is unclear. In this study, QSDsan (an open-source Python package) was used to characterize the financial viability and environmental implications of fecal sludge treatment via pyrolysis-based OP technology treating mixed and source-separated human excreta and to elucidate the key drivers of system sustainability. Overall, the daily per capita cost for the treatment of mixed excreta (pit latrines) via the OP was estimated to be 0.05 [0.03–0.08] USD·cap^–1·d^–1, while the treatment of source-separated excreta (from urine-diverting dry toilets) was estimated to have a per capita cost of 0.09 [0.08–0.14] USD·cap^–1·d^–1. Operation and maintenance of the OP is a critical driver of total per capita cost, whereas the contribution from capital cost of the OP is much lower because it is distributed over a relatively large number of users (i.e., 12,000 people) for the system lifetime (i.e., 20 yr). The total emissions from the source-separated scenario were estimated to be 11 [8.3–23] kg CO₂ eq·cap^–1·yr^–1, compared to 49 [28–77] kg CO₂ eq·cap^–1·yr^–1 for mixed excreta. Both scenarios fall below the estimates of greenhouse gas (GHG) emissions for anaerobic treatment of fecal sludge collected from pit latrines. Source-separation also creates opportunities for resource recovery to offset costs through nutrient recovery and carbon sequestration with biochar production. For example, when carbon is valued at 150 USD·Mg^–1 of CO₂, the per capita cost of sanitation can be further reduced by 44 and 40% for the source-separated and mixed excreta scenarios, respectively. Overall, our results demonstrate that pyrolysis-based OP technology can provide low-cost, low-GHG fecal sludge treatment while reducing global sanitation gaps.

Sustainability Assessment for Wastewater Treatment Systems in Developing Countries

As the assessment of the economic, environmental, institutional, and social sustainability of wastewater treatment systems may have several conceivable goals and intended recipients, there are numerous different approaches. This paper surveys certain aspects of sustainability assessment that may be of interest to the planners of wastewater treatment systems. Here, the key criteria assess the system’s costs and financing, including its affordability for the users, the environmental impact, the benefits for health and hygiene, the cultural acceptance of the system and its recycled products, the technical functioning, and the administrative, political, and legal framework for its construction and operation. A multi-criteria approach may then be used to analyze possible trade-offs and identify the most suitable system for a certain location.

Defining Nutrient Colocation Typologies for Human-Derived Supply and Crop Demand To Advance Resource Recovery

Resource recovery from human excreta can advance circular economies while improving access to sanitation and renewable agricultural inputs. While national projections of nutrient recovery potential provide motivation for resource recovery sanitation, elucidating generalizable strategies for sustainable implementation requires a deeper understanding of country-specific overlap between supply and demand. For 107 countries, we analyze the colocation of human-derived nutrients (in urine) and crop demands for nitrogen, phosphorus, and potassium. To characterize colocation patterns, we fit data for each country to a generalized logistic function. Using fitted logistic curve parameters, three typologies were identified: (i) dislocated nutrient supply and demand resulting from high density agriculture (with low population density) and nutrient islands (e.g., dense cities) motivating nutrient concentration and transport; (ii) colocated nutrient supply and demand enabling local reuse; and (iii) diverse nutrient supply-demand proximities, with countries spanning the continuum between (i) and (ii). Finally, we explored connections between these typologies and country-specific contextual characteristics via principal component analysis and found that the Human Development Index was clustered by typology. By providing a generalizable, quantitative framework for characterizing the colocation of human-derived nutrient supply and agricultural nutrient demand, these typologies can advance resource recovery by informing resource management strategies, policy, and investment.

Navigating Data Uncertainty and Modeling Assumptions in Quantitative Microbial Risk Assessment in an Informal Settlement in Kampala, Uganda

Decision-makers in developing communities often lack credible data to inform decisions related to water, sanitation, and hygiene. Quantitative microbial risk assessment (QMRA), which quantifies pathogen-related health risks across exposure routes, can be informative; however, the utility of QMRA for decision-making is often undermined by data gaps. This work integrates QMRA, uncertainty and sensitivity analyses, and household surveys in Bwaise, Kampala (Uganda) to characterize the implications of censored data management, identify sources of uncertainty, and incorporate risk perceptions to improve the suitability of QMRA for informal settlements or similar settings. In Bwaise, drinking water, hand rinse, and soil samples were collected from 45 households and supplemented with data from 844 surveys. Quantified pathogen (adenovirus, Campylobacter jejuni, and Shigella spp./EIEC) concentrations were used with QMRA to model infection risks from exposure through drinking water, hand-to-mouth contact, and soil ingestion. Health risks were most sensitive to pathogen data, hand-to-mouth contact frequency, and dose-response models (particularly C. jejuni). When managing censored data, results from upper limits of detection, half of limits of detection, and uniform distributions returned similar results, which deviated from lower limits of detection and maximum likelihood estimation imputation approaches. Finally, risk perceptions (e.g., it is unsafe to drink directly from a water source) were identified to inform risk management.