Degradation of carbon disulphide (CS₂) in soils and groundwater from a CS_{2 -}contaminated site

This study is the first investigation of biodegradation of carbon disulphide (CS2) in soil that provides estimates of degradation rates and identifies intermediate degradation products and carbon isotope signatures of degradation. Microcosm studies were undertaken under anaerobic conditions using soil and groundwater recovered from CS2-contaminated sites. Proposed degradation mechanisms were validated using equilibrium speciation modelling of concentrations and carbon isotope ratios. A first-order degradation rate constant of 1. 25 × 10-2 h-1 was obtained for biological degradation with soil. Carbonyl sulphide (COS) and hydrogen sulphide (H2S) were found to be intermediates of degradation, but did not accumulate in vials. A 13C/12C enrichment factor of -7. 5 ± 0. 8 ‰ was obtained for degradation within microcosms with both soil and groundwater whereas a 13C/12C enrichment factor of -23. 0 ± 2. 1 ‰ was obtained for degradation with site groundwater alone. It can be concluded that biological degradation of both CS2-contaminated soil and groundwater is likely to occur in the field suggesting that natural attenuation may be an appropriate remedial tool at some sites. The presence of biodegradation by-products including COS and H2S indicates that biodegradation of CS2 is occurring and stable carbon isotopes are a promising tool to quantify CS2 degradation

Climate change mitigation potential in sanitation via off-site composting of human waste

Approximately 4.5 billion people lack access to safely managed sanitation globally, and 1 billion live in slums, often relying on anaerobic waste containment in pit latrines. Providing access to safely managed sanitation may lead to reduced GHG emissions and thus simultaneously address both Sustainable Development Goals. Here we measure cumulative GHG emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) during the off-site composting of human waste to estimate scalable emission factors. We find that CH4 emission factors are one to two orders of magnitude smaller than IPCC values for other excreta collection, treatment and disposal processes. After accounting for GHG emissions throughout the sanitation cycle, including transport, urine and compost end-use, the climate change mitigation potential is 126 kg of CO2-equivalent per capita per year for slum inhabitants. If scaled to global slum populations, composting could mitigate 3.97 Tg CH4 yr−1, representing 13-44% of sanitation sector CH4 emissions