Greenhouse gas reduction and nitrogen conservation during manure composting by combining biochar with wood vinegar

The constant greenhouse gases (GHGs) and ammonia emissions during pig manure (PM) composting have made large contributions to air pollution and global temperature rise. This study aimed to evaluate the addition of biochar (B) and wood vinegar (WV) to reduce GHGs emissions and improve nitrogen retention and microbial activities during PM composting. Different treatments, carried out under a 1:2 ratio (dry weight) of PM and sawdust mixture with the addition of B (5%) and various proportions of WV, include a control treatment (CT) without the addition of B and WV and, B, B+0.5%WV, B+1.0%WV, B+1.5%WV, and B+2.0%WV treatments. The results indicated that the addition of B could accelerate the composting process in contrast to CT. In addition, various amounts of WV with B decreased NH₃, CO₂, CH₄ and N₂O emissions by 18.82-35.88%, 1.38-15.39%, 16.98-62.73%, and 4.47-19.91%, respectively. Furthermore, in contrast to the B treatment, WV addition was more effective in decreasing GHGs and NH₃ emissions, and the B+1.0% WV treatment displayed the lowest nitrogen loss (2.12%) and GHGs emissions (11.62 g/kg). The bacterial community analysis demonstrated that synergistic application of WV and B can increase the relative abundance of Proteobacteria which can contribute to nitrogen fixation and reduction of nitrogen loss. The results proved that combining B with WV can be a feasible strategy to effectively reduce GHGs emissions and improve nitrogen conservation in the composting industry.