Over 2.4 billion people globally lack access to improved sanitation which leads to millions of tons of nutrient-rich, but pathogenic, fecal waste being discarded directly into urban and rural ecosystems every year. Ecological sanitation (EcoSan) attempts to close the biogeochemical cycles of water, nutrients, and carbon associated with these untapped waste streams, while simultaneously sterilizing the pathogenic material. We collaborated with Sustainable Organic Integrated Livelihoods (SOIL) in Haiti to explore the potential of EcoSan projects to provide dual ecological and public health solutions and produce sellable compost to improve soil fertility in agroecosystems. We investigated the effects of compost pile management (cement-floor lining and sugarcane bagasse biofiter) on greenhouse gas emissions of methane (CH4) and nitrous oxide (N2O). Gas emissions were used to assess the climate mitigation potential of EcoSan versus other waste management options and as biogeochemical indices to highlight potential improvements in the process of composting fecal waste. Measurements were also replicated in a dense spatial grid that allowed us to explore the within-pile effects of compost biogeochemistry including oxygen, temperature, and moisture.
Results/Conclusions
Compost pile greenhouse gas fluxes were strongly affected by the presence or absence of a cement floor, mediated by differences in pile moisture, and also exhibited consistent spatial patterns within each pile likely associated with biogeochemical gradients in temperature and aeration. Methane was approximately 5x higher in the wetter, lined pile (15.5 ± 3.5 µmol CH4-C m-2 s-1) than in the drier, unlined pile (3.4 ± 1.7 µmol CH4-C m-2 s-1). The pattern was reversed for N2O but the lower CH4 emissions still dominated difference in 25- and 100-year global warming potentials between lining treatments. Within-pile CH4 emissions ranged from 0.1 µmol CH4-C m-2 s-1 to 68.7 µmol CH4-C m-2 s-1, with the lowest emissions along the pile edges, while the spatial pattern for N2O was also reversed. Our results demonstrate the importance of CH4 release during the thermophilic composting stage, while N2O emissions increased in later stages when compost was aerated by frequent turning. Overall climate-forcing effects of emissions were favorable relative to waste lagoons and illegal dumping in Haiti. Furthermore, our data suggest that management options to reduce pile moisture can greatly reduce CH4 emissions and improve nutrient retention during initial static composting. Our research with SOIL Haiti suggests that EcoSan can be an effective technology for broad and multifaceted sustainability across the dimensions of climate change, nutrient cycling, and waste management.