Enhanced excreta-based biochar: a novel source of organic fertilizer in the Guatemalan highlands

Communities in the highlands of Guatemala are currently struggling with insufficient access to effective sanitation. Water born solutions, often referred to as the “flush and forget model” of human excreta management, cannot be adequately delivered to the rapidly growing peri-urban regions growing across the area. The consequences of the insufficient collection and treatment of this waste are worsening human and environmental health outcomes. Concurrently, smallholder farmers in the region struggle to supply their soil with sufficient quantities of plant nutrients to avoid growing yield gaps. Even when capable of utilizing required amounts of chemical fertilizers, there is no clear option available to maintain soil organic carbon; typically relied upon organic inputs such as animal manure are available in only insufficient quantities.

To deal with the sanitation challenge facing communities in the region, Mosan, an NGO based in the Lake Atitlan region of Guatemala has, for the last several years, piloted a novel approach to sanitation provision. Utilizing an on-site urine diversion system that focuses on the capture, processing, and valorization of excreta, this resource-oriented approach, in addition to providing households with the means to safely manage generated excreta, yields a novel organic fertilizer. Using two treatment processes, alkaline dehydration for urine and pyrolysis for the feces, Mosan can produce an enhanced biochar product that could have the potential to sustainably improve soil health and fertility for small holder highland farmers in the region. Working in partnership with Mosan and Vivamos Mejor, and agricultural development organization based in Guatemala, the Sustainable Agroecosystems group at ETH Zurich has been testing the potential of this novel source of organic fertilizer.

Over the last eighteen months, this interdisciplinary team of researchers, community activists, and farmers has managed two experimental sites in the region. The first focused on the incorporation of enhanced biochar into a potting mix used to grow tree seedlings used for reforestation efforts in the region. The second, a participatory farmer field trial, was designed to compare the yield increases of maize fertilized with enhanced biochar to that grown with chemical fertilizer (urea). In addition to observing no significant differences in the growth performance of the seedlings, or the yield increases of the maize grown with the excreta-based biochar compared to the standard alternatives, our team also observed positive changes to several soil physical and chemical properties in the field trial. Given these results, we argue that a socio-technical transition towards a circular rural-urban system, one predicated on nutrient capture and reuse of currently underutilized organic waste sources such as human excreta, would simultaneously improve human and environmental health outcomes in urban areas, while also increasing long term soil health and fertility in outlying rural ones.