Biochar addition reduces non‐CO₂ greenhouse gas emissions during composting of human excreta and cattle manure

Abstract

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.

Effective Carbon Dioxide Mitigation and Improvement of Compost Nutrients with the Use of Composts’ Biochar

“…So far, the most popular substrates for biochar production have been waste biomass with a high proportion of organic matter. However, the amounts of biochar added to compost to effectively remove CO 2 could even be 19% [23], while the production efficiency of such wood biochars is extremely low-up to 90% weight loss during production [24]. This has made the addition of such biochars less effective.…”