Different crystalline manganese dioxide and biochar co-conditioning aerobic composting: Reduced ammonia volatilization and improved organic fertilizer quality

Aerobic composting is a sustainable and effective waste disposal method. However, it can generate massive amounts of ammonia (NH3) via volatilization. Effectively reducing NH3 volatilization is vital for advancing aerobic composting and protecting the ecological environment. Herein, two crystal types of MnO2 (α-MnO2 and δ-MnO2) are combined with biochar (hydrochar (WHC) and pyrochar (WPC), respectively) and used as conditioners for the aerobic composting of chicken manure. Results reveal that α-MnO2 (34.6%) can more effectively reduce NH3 accumulation than δ-MnO2 (27.1%). Moreover, the combination of WHC and MnO2 better reduces NH3 volatilization (48.5-58.9%) than the combination of WPC and MnO2 (15.8-40.1%). The highest NH3 volatilization reduction effect (58.9%) is achieved using the combination of WHC and δ-MnO2. Because the added WHC and δ-MnO2 promote the humification of the compost, the humic acid to fulvic acid ratio (HA/FA ratio) dramatically increases. The combination of WHC and δ-MnO2 doubled the HA/FA ratio and resulted in a net economic benefit of 130.0 RMB/t. Therefore, WHC and δ-MnO2 co-conditioning can promote compost decomposition, improving the quality of organic fertilizers and substantially reducing NH3 volatilization.