Combined effects of amoxicillin and copper on nitrogen transformation and the microbial mechanisms during aerobic composting of cow manure.

Pollutants in livestock manure have a compound effect during aerobic composting, but research to date has focused more on single factors. This study investigated the effects of adding amoxicillin (AMX), copper (Cu) and both (ACu) on nitrogen transformation and the microbial mechanisms in cow manure aerobic composting with wheat straw. In this study, compared with CK, AMX, Cu, and ACu increased NH3 cumulative emissions by 32.32%, 41.78% and 8.32%, respectively, due to their inhibition of ammonia oxidation. Coexisting AMX and Cu decreased the absolute abundances of amoA/ nxrA genes and increased the absolute abundances of nirS /nosZ genes, but they had an antagonistic effect on the changes in functional gene abundances. Pseudomonas and Luteimonas were enriched during the thermophilic and cooling periods due to the addition of AMX and ACu, which enhanced denitrification in these two groups. Moreover, adding AMX and/or Cu led to more complex bacterial networks, but the effect of the two pollutants was lower than those of the individual pollutants. These findings provide theoretical and experimental support for controlling typical combined pollution with antibiotics and heavy metals in livestock manure.