Effects of adding inoculants on improving the nitrogen content of compost by Meta analysis

Composting has been recognized as a pivotal technology for the resourceful management of organic waste. Much attention has also gained, due to its harmlessness, resourcefulness, and reduction of carbon emission. However, there is a serious and vast amount of nitrogen (a critical nutrient) loss during composting. Fortunately, microbial agents can be incorporated to mitigate this nitrogen loss. This research aims to delve into the various influencing factors on the nitrogen content (total nitrogen content, carbon-nitrogen ratio, ammonium nitrogen, and nitrate nitrogen) and loss (ammonia emission, and total nitrogen loss) during composting, including the type and source of microbial agents, the dosage of inoculation, the composting materials, the composting modes, and the scale of production. The results found that the inoculants added significantly enhanced the total nitrogen (19.34%), ammonium nitrogen (40.77%), and nitrate nitrogen (2.30%) content, while there was a decrease in the emission of ammonia (-14.91%), decreasing C/N (-37.87%) and the total nitrogen loss (-29.68%) at the same time. The microbial inoculants were also dominant in the preservation of nitrogen within the compost. Local inoculants (namely indigenous agents) were selected to be extracted from the composting environment. There was remarkable adaptivity in the same and complex environment. The best performance was achieved in improving the total nitrogen content of the compost (16.9%), compared with the other three types of inoculants. It was more favorable for nitrogen fixation and emission reduction in the composting process. In the addition of microbial agents at a rate of less than 2%, there was the most pronounced effect on the total nitrogen content and C/N ratio of the composts. This approach was contrary to the common belief that the higher quantities of microbial agents always yielded better performance. Interestingly, there was the most significant impact on the increase in ammonium nitrogen content, when the addition rate was less than 1%. Since cellulose was preferred to degrade microorganisms, the addition of inoculants accelerated the degradation of organic matter rather than nitrogen. Therefore, the content of organic matter was much lower than that of the total nitrogen in the compost. In addition, the C/N ratio was significantly reduced with the increasing dose range of inoculants. Much emphasis was also put on the type of composting raw materials. Materials with an initially low C/N ratio, such as poultry and livestock manure, failed to effectively respond to the addition of microbial agents for nitrogen fixation as other materials. Thus the inoculants added shared less effect on the total nitrogen content of compost than other types of raw materials. Furthermore, reactor composting was identified as an exceptional approach for nitrogen fixation and loss reduction. The best performance was achieved to conserve the nitrogen in compost with the exception of traditional composting. Therefore, the microbial agents in composting significantly enhanced the nitrogen content of the final product. The resources of the inoculant, especially local inoculants, shared the best effect on nitrogen conservation. The reactor was also the best way for composting than the conventional pile and windrow process.