Fe/BC co-conditioners with environmental and economic benefits on composting: reduced NH3 emissions and improved fertilizer quality

Abstract

The significant volatilization of NH₃ during aerobic composting causes nitrogen (N) losses and environmental risks. Both iron (Fe) and biochar (BC) can influence the N conversion process in composting. Fe application can delay the maturation of materials, while biochar can enhance the quality of organic fertilizer. The combination of these two conditioners may help decrease NH₃ emissions and improve organic fertilizer quality. Therefore, this study investigates the effects of different doses of FeCl₃ and BC on NH₃ emissions and organic fertilizer quality during composting. The results demonstrated that Fe/BC co-conditioners reduced the accumulation of NH₃ emissions during composting by 11.1–48.2%, increased the total nutrient content by 0.6–15.3%, and enhanced economic and environmental benefits by 0.1–23.6 $ t⁻¹. At the high-temperature stage of composting, Fe/BC co-conditioners decreased the pH by 0.3–1.2, but there was no significant difference compared to the control at the end of composting, and they did not affect compost maturation. The structural equation model analysis suggested that the reduction in NH₃ emissions was related to ammonia-oxidizing bacteria (AOB), NH₄⁺–N, and total nitrogen (TN). As a result, the Fe/BC co-conditioners reduced NH₃ emissions by lowering the pH at the beginning of composting and increasing the content of NH₄⁺–N. This study concludes that Fe/BC co-conditioners could complement each other to significantly reduce NH₃ emissions and improve the quality of organic fertilizers.

Graphical Abstract