Composting pig manure with nano-zero-valent iron amendment: Insights into the carbon cycle and balance.

[Display omitted] • Effect of NZVI on composting carbon cycle and carbon balance was investigated. • A NZVI-regulated composting C cycle was experimentally demonstrated. • NZVI addition increased CO 2 and CH 4 emissions by 51% and 128% respectively. • NZVI addition enhanced bacteria promoting hygiene of final product. The effectiveness of nano-zero-valent-iron (NZVI) addition during composting of pig manure (PM) was investigated. Different dosages of NZVI were mixed with PM substrate during a 50 days composting process. The results revealed that the higher share of NZVI addition, the higher OM degradation rate is. On contrary, it was observed that the higher share of NZVI addition, the lower the fulvic acid and the humin degradation rate is. Meanwhile, NZVI amendment increased the CO 2 and CH 4 emissions by 29–47 % and 53–57 %, respectively. The in-depth analysis showed that NZVI addition increased the activity of Sphaerobacter and Luteimonas , which eventually led to the degradation of hard-to-degrade OM faster. Additionally, NZVI was found to increase the filtration of microorganisms, reducing the toxicity and hygiene of compost products. No significant improvement in humic substance enhancement was observed during composting with NZVI addition but improved OM degradation. [ABSTRACT FROM AUTHOR]