Compost's biochar as a practical odor mitigation strategy for the composting industry

Composting is a widely adopted method for the treatment of organic waste globally. It is relatively easy to implement and offers the added benefit of producing fertilizer. However, a significant drawback is the emission of odorous compounds. This study investigates the potential of using biochar derived from compost as an odor mitigation strategy during semi-technical scale composting of green waste. Experiments were conducted using 15 Mg compost piles over a six-week period, with compost's biochar added at rates of 0 %, 3 %, 6 %, and 9 % (dry matter basis). The compost's biochar was produced via pyrolysis at 550 °C. The results indicate that the addition of 6–9 % compost's biochar enhanced pile temperature and oxygen availability. These improvements contributed to an overall reduction in volatile organic compound (VOC) emissions by 28–32 %, with reductions of up to 50 % observed during the first week of composting – when VOC emissions are typically at their highest. The most pronounced mitigation effects were observed for two major VOC families: (1) terpenes and terpenoids and (2) ketones and aldehydes. Given the common challenge of odor emissions and low compost quality in many composting facilities, this study highlights a promising strategy for simultaneously improving process performance and product quality through the reuse of compost's biochar.