Effects of humic acid modified oyster shell addition on lignocellulose degradation and nitrogen transformation during digestate composting

Abstract The aim of this work was to investigate the performance of a novel humic acid modified oyster shell (MOS) bulking agent on the digestate composting. MOS was prepared by immobilizing humic acid onto oyster shell using solid phase grafting method, and then applied to the composting process. Results showed more obvious degradation of lignocellulose was observed in the MOS treatment, which was probably due to the high relative abundance of Actinobacteria. Moreover, the addition of MOS could significantly preserve NH4+ and reduce the NO3− generation with the decreasing abundance of ammonia-oxidizing bacteria and archaea. Besides, adding MOS reduced the N2O emission by 59.63% compared with the control. After composting, excitation-emission matrix fluorescence spectra demonstrated that the humification degree as well as compost maturity was enhanced with MOS added.