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‐d thermophilic composting experiment with human excreta, and separately with cattle manure, mixed with kitchen scraps, teff [Eragrostis tef (Zuccagni) Trotter] straw, sawdust, and biochar (BC) 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 was >60 °C for 7, 6, 5, and 8 consecutive days for treatments containing human excreta, human excreta amended with BC, cattle manure, and cattle manure amended with BC, respectively, suggesting a final compost product free of pathogens. The compost mixture with cattle manure and BC reached a significantly higher temperature than the same variant without BC, with a maximum value of 65.9 °C on Day 6. For all treatments, final germination index values >100% indicated compost maturity and the absence of phytotoxic substances. Biochar addition reduced losses of organic matter (18−23%), C (33−42%), and 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.

Ecological sanitation combined with thermophilic composting is a viable option to transform human excreta into a stabilized, pathogen-free, and nutrient-rich fertilizer.In combination with suitable bulking materials such as sawdust and straw, and additives such as biochar, this could also be a suitable waste management strategy for reducing greenhouse gas (GHG) emissions. In this study, we conducted a 143-days thermophilic composting of human excreta or cattle manure together with teff straw, organic waste, and biochar to investigate the effect that biochar has on GHG (CO 2 , N 2 O, and CH 4 ) and NH 3 emissions. The composting was performed in wooden boxes (1.5 × 1.5 × 1.4 m 3 ), GHG were measured by using a portable FTIR gas analyzer and NH 3 was sampled as ammonium in an H 2 SO 4 trap. We found that the addition of biochar significantly reduced CH 4 emissions by 91% in the cattle manure compost, and N 2 O emissions by 56%−57% in both humanure and cattle manure composts. Overall, non-CO 2 GHG emissions were reduced by 51%−71%. In contrast, we did not observe a significant biochar effect on CO 2 and NH 3 emissions. Previous data already showed that it is possible to sanitize human fecal material when using this composting method. Our results suggest that thermophilic composting with biochar addition is a safe and cost-effective waste management practice for producing a nutrient-rich fertilizer from human excreta, while reducing GHG emissions at the same time. INTRODUCTIONAn estimated 4.5 billion people worldwide live without access to safe sanitation facilities, and either defecate in the open, or in toilets or pit latrines where excreta are disposed of in situ without any adequate treatment (WHO, 2019a,b). The Abbreviations: BC, biochar; CM, cattle manure control; CM+BC, cattle manure amended with biochar; GHG, greenhouse gases; HM, humanure control; HM+BC, humanure amended with biochar; MC, moisture content; WGCF-NR, Wondo Genet College of Forestry and Natural Resources.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Lack of sanitation is the underlying cause of many diarrheal infections and associated deaths. Improving sanitation through the set-up of ecological sanitation dry toilets, followed by the thermophilic composting of human excreta, could offer a solution. In addition, treating the excreta via thermophilic composting allows us to recycle the nutrients to be used as fertilizer for agriculture. However, for this purpose, the compost should be free of pathogens. We conducted a thermophilic composting trial over 204 to 256 days with human excreta, along with vegetable scraps and teff straw, with and without biochar. A sawdust–cattle manure mixture with the same supplements served as a control treatment. To evaluate the hygienic quality of the mature compost, the bacterial indicators Escherichia coli and Salmonella were assessed using the cultivation-based most probable number method. In addition, Ascaris lumbricoides eggs were quantified through light microscopy. The amount of detected E. coli was below the thresholds of German and European regulations for organic fertilizer. Salmonella and Ascaris eggs were not detected. No significant differences between the treatments were observed. Thus, the composting process was efficient in decreasing the number of potential human pathogens. The mature compost fulfilled the legal regulations on organic fertilizer regarding potential human pathogens.