Commercial-scale co-composting of wood-derived biochar with source-selected organic fraction of municipal solid waste

This full-scale trial aims to systematically examine the effect of the addition (10 % DW ratio) of wood-derived biochar produced at 700 °C on the composting of source-selected organic fraction of municipal solid waste (OFMSW) and compare it with an identical treatment without biochar addition. The study mainly focused on (i) composting process performance, including compost quality, and (ii) gaseous emissions (ammonia, methane, nitrous oxide, volatile organic compounds (VOC) and odor emissions) from the two experimental piles, in which representative areas within each pile were identified as independent regions (n = 6) for sampling, obtaining over 1300 independent gas sampling data points. During the first 50 days, biochar contributed to a more sustained thermophilic temperature compared to the control (average 47 and 38 °C, respectively). Over the 80 days of composting, biochar significantly (p < 0.003) decreased methane (from 0.17 to 0.05 kg CH₄ Mg⁻¹ OFMSW) and ammonia (from 0.57 to 0.35 kg NH₃ Mg⁻¹ OFMSW) emissions. The differences in VOC emission from the two treatments were only significant (p < 0.001) during the maturation phase (from day 50 onwards) with average values of 35 and 175 g C-VOC day⁻¹, for the biochar and control treatments, respectively. Odor emissions were smaller in the presence of biochar (1.1E + 0.6 vs. 1.9E + 0.6 ou Mg⁻¹ OFMSW). The agronomic value of the resultant biochar co-compost was similar to that of the control compost. Biochar can thus contribute to climate change mitigation, not only through CO₂ removal, but also through the reduction of non-CO₂ greenhouse gases emissions during composting, while also decreasing the odor impact of the plant on nearby residents.