Greenhouse gas emissions from different containment system in Dhulikhel Municipality in Nepal

Abstract

On-site sanitation systems (OSS), are commonly used in low and middle-income countries (LMICs) like Nepal because of their practicality and economic feasibility. These systems are vital for ensuring access to basic sanitation, which is essential for both human health and the environment. However, they can significantly contribute to greenhouse gas (GHG) emissions through the microbial breakdown of faecal sludge via anaerobic and aerobic processes. Onsite containments are responsible for the majority of the GHG emissions occurring in the whole sanitation value chain. Therefore, this study intends to estimate the GHG emissions from different onsite containments prevailing in Dhulikhel Municipality using updated 2019 Intergovernmental Panel on Climate Change (IPCC) Guidelines. It was observed that 2.33 Gg CO₂ eq-per year is being emitted annually from Dhulikhel municipality from the containment systems and open defecation. A total of 2.32 Gg CO₂ eq-per year is contributed by methane (CH₄) emission from containment and rest of from nitrous oxide (N₂O) emissions from the open defecation solely. Similarly, the annual per capita CH₄ and N₂O emissions (from OD) from the onsite containments prevailing in Dhulikhel were computed as 67.52 kg CO₂-eq per person per year and 18.39 kg CO₂-eq per person per year respectively. A comparison of the emission was made between the containments that were emptied once and those which were never emptied. Paired sample t-test showed that emptied containments are likely to emit lesser CH₄ emissions compared to those which are never emptied (p-value<0.05). Similarly, a comparison of emissions was conducted between sealed and unsealed containment systems. Sealed containment systems were found to produce significantly lower GHG emissions compared to unsealed systems (p-value < 0.05). The design and typology of containment structures play a critical role in influencing emissions from different systems. However, our national statistics and other reports do not include precise and clear typological definition which have underestimated the emission originating from different kind of containment units.