LAUSR

Ecological sanitation via thermophilic composting could be a promising solution to the lack of sanitation and limited access to fertilizers, particularly in developing countries. Here, we conducted a 185-day thermophilic composting experiment with human excreta, and separately with cattle manure, mixed with kitchen scraps, teff straw, sawdust and biochar by using an appropriate-technology approach. We followed the dynamics of the most important macronutrients (N, P, K), temperature, moisture, pH, electrical conductivity, cation exchange capacity, as well as content of organic matter, organic C, Ca, Mg, and micronutrients throughout the process. Low N (<47%), P (<9%), K (<11%), Ca (<18%), and Mg (<21%) losses and the temperature profile indicated a well-functioning thermophilic composting process. Compost temperature reached values above 60°C for 7, 6, 5, and 8 consecutive days for treatments containing human excreta, human excreta amended with biochar, cattle manure, and cattle manure amended with biochar, respectively, suggesting a final compost product free of pathogens. The compost mixture with cattle manure and biochar reached a significantly higher temperature than the same variant without biochar, with a maximum value of 65.9°C on day 6. For all treatments, final germination index values >100% indicated compost maturity and absence of phytotoxic substances. Biochar addition reduced losses of organic matter (18-23%), C (33-42%), N (49-100%), and decreased the amount of extractable NO3 - (32-36%) in the final compost. The tested ecological sanitation concept via thermophilic composting is thus a promising strategy to improve access to cheap fertilizer by safe and sustainable sanitation and waste management. Thermophilic temperature during composting suggests a safe treatment of human excreta. Phosphorus and K were preserved during composting, while Ca and Mg losses were low (<18%). Biochar reduced losses of organic matter (18-23%), C (33-42%) and N (49-100%) during composting. Biochar amendment reduced extractable nitrate content of the mature compost by 32-36%. Recycling nutrients from human excreta by thermophilic composting can improve food security. This article is protected by copyright. All rights reserved.