27 / 2021-06-26 14:53:18

Adding appropriate proportion of phosphogypsum to ensure the composting process of the rice-husk system with urea as the N source and promote the utilization of composting products as the substrate

composting; Phosphogypsum; C/N; Nitrogen loss; Substrate utilization.

To explore the effectiveness of urea as N source instead of poultry manure in the rice husk compost system, and promote the substrate utilization of compost product, 0%(RUP0), 10%(RUP10), 20%(RUP20) and 30%(RUP30) of phosphorgypsum were added in the rice husk urea composting system, and were compared with rice husk chicken manure (RCP0). Results showed that the RCP0 treatment could successfully complete the maturity fermentation, but the high EC value of the composting product limited substrate utilization. Compared with RCP0 treatment, the RUP0 treatment significantly reduced the EC value of composting, but the C/N ratio was uncoordinated during the start-up stage of composting, which affected the fermentation process. In the rice husk urea composting system, added proper ratio of phosphorgypsum could ensure the appropriate C/N ratio at the start-up stage of composting and promote the smooth fermentation of composting. At the end of composting, the seed germination indexes of RUP10 and RUP20 were 96.63% and 85.98%, respectively. However, when the additive amount was 30%, the high-temperature period of composting (≥50℃) was significantly shortened (only 3d). After composting, the GI value was only 77.18%, and the content of water-soluble NH₄⁺-N was higher than the maturity standard (＜400 mg·kg^-1). In all treatments, only RUP10 and RUP20 compost product met the requirements of ideal seeding substrate; the content of heavy metals did not exceed the requirements of NY525-2021 standard of China, but the addition of phosphogypsum still increased the risk of heavy metals in composting. In conclusion, urea could replace poultry manure as N source for co-composting with rice husk, added phosphogypsum could maintain the appropriate C/N ratio in the start-up stage of composting and ensure the smooth fermentation. It is suggested that the amount of phosphogypsum should be 10% ~ 20%.