Post-digestate composting benefits and the role of enzyme activity to predict trace element immobilization and compost maturity. (October 2021) - Gurmessa, Biyensa
Graphical abstract: Highlights: Pilot level aerobic co-composting of digestate and biogas feedstocks was conducted. Composting reduced C/N ratio, release of trace elements, and phytotoxicity. Enzyme activities were influenced by OM content and release of trace elements. Enzyme activities could be compost maturity indicators. Abstract: 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 co-composting 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 α-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.