Effects of phosphogypsum and medical stone on nitrogen transformation, nitrogen functional genes, and bacterial community during aerobic composting

This study explored the effects of adding phosphogypsum (PPG), medical stone (MS), and both (PPM) during composting on nitrogen transformation, nitrogen functional genes, the bacterial community, and their relationships with NH3 and N2O emissions. AddingMS and PPMreduced NH3 emissions by 25.78-68.37% and N2O emissions by 19.00-42.86%. PPG reduced NH3 emissions by 59.74% but slightly increased N2O emissions by 8.15%. MS was strongly correlated with the amoA-dominated nitrification process. PPG and PPM had strong correlations with nirS- and nirK-dominated, and nosZ-dominated denitrification processes, respectively. PPM promoted nitrification and denitrification processesmore than PPG andMS. Different functional bacteria had key roles in nitrification and denitrification during different composting stages. Firmicutes probably contributed to the conversion and release of nitrogen in the thermophilic period, whereas Proteobacteria, Chloroflexi, Bacteroidetes, and other phyla might have played important roles in the cooling and maturation periods. PPM obtained the greatest reductions in NH3 and N2O release via the regulation of environmental variables, nitrogen functional genes, and the bacterial community. Overall, these results provide insights at a molecular level into the effects of PPG and MS on nitrogen transformation and NH3 and N2O emissions during composting. (C) 2020 Published by Elsevier B.V.

Automated summary

This study found that adding MS and PPM significantly reduced NH3 and N2O emissions, while PPG slightly increased N2O emissions. Different functional bacteria played key roles in nitrification and denitrification during different composting stages. PPM obtained the greatest reductions in NH3 and N2O release via the regulation of environmental variables, nitrogen functional genes, and the bacterial community.