Enhanced copper passivation in pig manure composting through iron nanoparticle amendment.

As the world's leading producer of pigs, China is now experiencing large-scale pollution derived from agricultural usage of untreated pig manure, where passivation of metal toxicity in pig manure is a major challenge. Here, the effect of green synthesized iron nanoparticle (G-nFe) addition on copper (Cu) transformations during thermophilic aerobic composting of pig manure was investigated. The results revealed that following addition of G-nFe passivation of active Cu forms, including exchangeable (EXC-Cu), carbonate-bound (CARCu), and iron and manganese oxide-bound (IMOCu) Cu increased by 66.8, 47.5, and 15.4 %, respectively. The fraction of Cu bound to organic matter (OM-Cu) also increased with composting and was influenced by G-nFe dose. Notably, addition of 500 mL kg G-nFe increased OM-Cu to 52.9 %. Residual Cu (RESCu) concentrations initially rose within the first five days of composting, followed by a subsequent decline, demonstrating that G-nFe addition had dual effects: firstly, an initial 31.3 % increase in RES-Cu five days post-G-nFe addition; and secondly, a subsequent 60.9 % reduction over the entire composting process. Furthermore, OM, Humus and Fourier transform infrared (FTIR) analysis confirmed that the increase in OM-Cu, coupled with G-nFe, facilitated the transformation of Cu into OM-Cu fractions post-composting. This work thus provides new insights into how iron nanomaterials can increase passivation of metal ions during composting.