A Methodological Approach to the Assessment of the Greenhouse Gas Mitigation Potential of Container-Based Sanitation Systems

Abstract

Container-based sanitation (CBS) is a safely managed sanitation service designed for regions with limited sanitation and water infrastructure (WHO/UNICEF, 2018). CBS services replace unsafe sanitation practices in low- and middle-income regions and thus avoid greenhouse gas (GHG) emissions from uncontrolled degradation of excreta in the environment (Harroff et al., 2019). CBS provides waterless toilets with sealable containers that separate human excreta from human contact (= safely managed), regular collection and revalorization of excreta (CBSA, 2018). This service is less costly than conventional sewage systems, but there are recurring operational costs for which long-term revenue streams such as climate financing are needed (Coates & Gray, 2021; Russel et al., 2019; World Bank, 2019). The objective of this study was to develop a methodology that allows CBS projects to systematically quantify and monitor their GHG savings vis-à-vis unsafe sanitation solutions. The two main goals were 1) to quantify the GHG emissions in sanitation as accurately as possible; and 2) to minimize monitoring efforts for CBS projects that apply the methodology. A literature review on GHG emission pathways from sanitation systems was supplemented with key informant interviews with experts in sanitation and methodology development. A methodology was drafted, along with an Excel calculator. The methodology provides default values for the quantification of emissions from CBS projects as well as the sanitation systems they replace. An uncertainty analysis revealed that a significant uncertainty of emission savings is pertaining to the variability and categorization of the unsafe sanitation systems that are replaced by CBS. The methodology was applied to the Mosan social enterprise at Lake Atitlán in rural Guatemala. It was found that about ¾ of the local population use on-site sanitation and ¼ are connected to a sewage system. However, 70% of the sewage system discharges directly to Lake Atitlán. Implementation of one Mosan CBS toilet can mitigate 370 kg CO2-equivalents per year. Further development and authorization of the draft methodology is needed to consolidate these findings and unlock climate financing for CBS projects.