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 (NH) via volatilization. Effectively reducing NH volatilization is vital for advancing aerobic composting and protecting the ecological environment. Herein, two crystal types of MnO (α-MnO and δ-MnO) 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-MnO (34.6%) can more effectively reduce NH accumulation than δ-MnO (27.1%). Moreover, the combination of WHC and MnO better reduces NH volatilization (48.5-58.9%) than the combination of WPC and MnO (15.8-40.1%). The highest NH volatilization reduction effect (58.9%) is achieved using the combination of WHC and δ-MnO. Because the added WHC and δ-MnO promote the humification of the compost, the humic acid to fulvic acid ratio (HA/FA ratio) dramatically increases. The combination of WHC and δ-MnO doubled the HA/FA ratio and resulted in a net economic benefit of 130.0 RMB/t. Therefore, WHC and δ-MnO co-conditioning can promote compost decomposition, improving the quality of organic fertilizers and substantially reducing NH volatilization.