Maintaining the ratio of hydrosoluble carbon and hydrosoluble nitrogen within the optimal range to accelerate green waste composting

Abstract The recalcitrance of green waste, caused by its high lignocellulose content, is a technical challenge for accelerating green waste composting. Adjusting the initial ratio of total carbon and total nitrogen (TC/TN) to the optimal range of 25–30:1 is a common strategy to accelerate the composting process. However, because microorganisms can only utilize hydrosoluble nutrients directly, we investigated whether maintaining the ratio of hydrosoluble carbon and hydrosoluble nitrogen (HC/HN) within the optimal range through continuous urea addition can better accelerate green waste composting. We conducted a pilot-scale composting experiment, in which the aforementioned maintaining started at the beginning of composting, or after the thermophilic phase. The results demonstrate that maintaining the optimal HC/HN ratio starting at both periods can, to some extent, direct the TC/TN ratio toward 25–30:1, and can also significantly improve heat generation, pH, lignocellulose degradation, and humification. Moreover, lignin degradation was improved by 3.15–7.33%, cellulose degradation was improved by 6.48–8.15%, and carbon content of humus was increased by 7.19–16.13%. Although the maturity assessment showed that none of the final compost reached maturity within the limited experimental period (48 days), based on the promoted lignocellulose degradation and humification, we conclude that maintaining the HC/HN ratio within the optimal range is a more efficient method to accelerate green waste composting, compared to the initial TC/TN adjustment only once.