Impacts of iron oxide nanoparticles on organic matter degradation and microbial enzyme activities during agricultural waste composting.

The effects of iron oxide nanoparticles (IONPs, including Fe2O3 NPs and Fe3O4 NPs) on composting were investigated through evaluating their influences on organic matter (OM) degradation, dehydrogenase (DHA) and urease (UA) activities, and quality of the final compost product. Results showed that composting amended with Fe2O3 NPs was more effective to facilitate OM degradation. At the end of composting, the total OM loss in T-C, T-Fe2O3 NPs and T-Fe3O4 NPs was 66.19%, 75.53% and 61.31%, respectively. DHA and UA were also improved on the whole by the amendment of IONPs, especially Fe2O3 NPs. Although relationships between enzyme activities and environmental variables were changed by different treatments, temperature was the most influential to variations of both DHA and UA in all treatments, which independently explained 75.1%, 34.7% and 38.4% of variations in the two enzyme activities in T-C, T-Fe2O3 NPs and T-Fe3O4 NPs, respectively. Compared with DHA, UA was more closely related to the environmental parameters. The germination index in T-C, T-Fe2O3 NPs and T-Fe3O4 NPs was 134.49%, 153.64% and 146.76%, and the average shoot length was 3.16, 3.87 and 3.45 cm, respectively, indicating that amendment of IONPs, especially Fe2O3 NPs, could promote seed germination and seedling growth. Therefore, composting amended with IONPs was a feasible and promising method to improve composting performance, enzyme activities as well as quality of the final compost product.