Buffering phosphate mitigates ammonia emission in sewage sludge composting: Enhanced organics removal coupled with microbial ammonium assimilation

摘要

Ammonia emission is a challenge for sewage sludge composting, causing odor issues, indirect greenhouse gas emission and nitrogen loss in the mature compost. This study investigated the effectiveness of applying K2HPO4-KH2PO4 buffer to mitigate ammonia emission in sewage sludge composting. During the 34-day aerated composting experiment, adding 7.5 mg p.g(-1) DM (dry matter) K2HPO4-KH2PO4 buffer reduced the ammonia emission and total nitrogen loss by 45.4% and 41.8%, respectively. The enhanced nitrogen conservation by phosphate additive resulted from two complementary mechanisms: (1) phosphate buffering effect and (2) accelerated sludge extracellular polymeric substance (EPS) decomposition, thus improving microbial ammonium assimilation to convert ammonia-N to cell-protein. The extent of nitrogen conservation was found to be positively associated with activities of the key enzymes for microbial ammonium assimilation and relative abundance of the ammonium-assimilating Bacillus. In a summary, K2HPO4-KH2PO4 addition was proved as an effective strategy to reduce ammonia emission, promote organics removal and conserve nitrogen nutrients in the final compost product. (C) 2019 Elsevier Ltd. All rights reserved.