Post-digestate composting benefits and the role of enzyme activity to predict trace element immobilization and compost maturity

The current study evaluated the quality of agricultural waste digestate by composting or co-composting with biogas feedstock (maize silage, food processing waste, or poultry litter). Temperature, phytotoxicity, C/N ratio, water extractable trace elements, and 14 enzyme activities were monitored. Temperature dropped earlier in digestate and maize silage co-composting pile, reducing time to maturity by 20 days. Composting and cocomposting reduced phytotoxicity and C/N ratio, but increased immobilization of Al, Ba, Fe, Zn, and Mn at least by 40% in all piles. All the enzyme activities, except arylsulfatase and alpha-glucosidase, increased at the maturity phase and negatively correlated with organic matter content and most of trace elements. Post-digestate composting or co-composting with biogas feedstock is a promising strategy to improve digestate quality for fertilizer use, and selected enzyme activities can be indicators of compost maturity and immobilization of trace elements.

Automated summary

The study showed that co-composting digestate with maize silage can shorten the maturity time but increase the immobilization of some trace elements. Additionally, certain enzyme activities were negatively correlated with organic matter content and most trace elements, indicating their potential as indicators of compost maturity and trace element immobilization.