Simultaneous mitigation of greenhouse gases and ammonia by boric acid during composting: Emission reduction potentials and microbial mechanisms

Greenhouse gases (GHGs) and ammonia (NH 3 ) are the main gas pollutants emitted during composting. This study used boric acid (H 3 BO 3 ) as an additive to simultaneously mitigate GHG and NH 3 emissions during composting and produce boron-rich organic fertilizer. The results showed that high dose of boric acid (1425 mg/kg) simultaneously reduced carbon dioxide (16.4%), methane (97.0%), nitrous oxide (91.7%), and NH 3 (27.1%) emissions in the composting process, resulting in the lowest carbon and nitrogen losses and global warming potential. However, low doses of boric acid (75 and 375 mg/kg) promoted nitrous oxide emissions and had limited emission reduction effects on other gases. Pearson correlation analysis showed that Corynebacterium, Planococcus, norank_f_MWH-CFBk5, Ruminofilibacter , norank_o_Actinomarinales and Truepera are key bacterial genera strongly associated with gas emissions. The results of principal co-ordinates analysis, network analysis, and structural equation modeling collectively indicated that the high dose of boric acid mitigates GHG and NH 3 emissions by undergoing chemical reactions, altering physicochemical properties, and reshaping bacterial communities. This study provides an innovative approach for synchronously mitigating GHG and NH 3 emissions and producing high value-added boron-rich organic fertilizer.