A comparative life cycle analysis of Sol-Char and anaerobic digestion sanitation systems

In this study, we compared the Sol-Char sanitation system with an Anaerobic Digestion (AD) system using Life Cycle Assessment (LCA) to evaluate their environmental impacts. Since both systems offer opportunities for human waste treatment and resource recovery, understanding their performance is crucial. This comparison aims to determine their environmental impacts while considering diverse factors, such as energy production and nutrient recovery. The Sol-Char system demonstrated a superior life-cycle environmental performance, showing two to five times lower impacts in categories such as Climate Change (e.g., 127 kg CO₂-eq for the Sol-Char system while that 592 kg CO₂-eq for the AD system), Non-Renewable Energy Resources, Ionizing Radiation, Land Use, and Water Use. Both systems exhibited significant potential for resource recovery, with the Sol-Char system producing biochar and disinfected urine, and the AD system generating electricity, heat, and digestate. Updated LCA results, after byproduct application, indicated that both systems potentially have a net positive environmental impact (both with reductions exceeding −500 kg CO₂-eq per day). Nutrient recovery simulations using SAmpSONS2 revealed that the AD system performed better when utilizing multiple biomass sources. The nitrogen content in the solids was 20.25 kg/day after AD and 3.75 kg/day for the Sol-Char system. Our results highlight the Sol-Char system is a viable sanitation solution in rural areas. However, the study also identified key challenges, including the absence of uncertainty analysis and the need for a standardized framework that enables more consistent evaluations and comparisons across diverse sanitation systems and contexts.