Use of Additives in Composting Promotes Passivation and Reduction in Bioavailability of Heavy Metals (HMs) in Compost

Abstract

Composting influences heavy metal (HM) speciation by transforming the exchangeable and reducible forms of HMs to oxidisable and residual forms, promoting the redistribution of HMs to a more stable form thereby reducing their mobility, leachability, and bioavailability. This enhances HM passivation hence reducing environmental contamination and possible HM-related toxicity. In this review, we explored the impact of additives/ameliorants on HM passivation during composting and the reduction in HM bioavailability in compost. Using additives in composting improved the passivation of HMs and reduced the bioavailability through several mechanisms. Additives may not reduce total HM concentration but reduce the bioavailable concentration, which is of importance in risk assessment. However, vermicomposting is exceptional, as it reduces total HM concentration. Improving humification and microbial activity is at the heart of HM passivation in composting. Overall, conditions and substances that promote humification, thermophilic phase, and improve microbial community structure enhance HM passivation in compost. Combining suitable composting additives depending on HMs of interest and vermicomposting the final compost is most likely to yield the best result in reducing HM bioavailability cum total concentration to achieve a safe final product.

Mikania micrantha Kunth and its derived biochar impacts on heavy metal bioavailability and siderophore-related genes during chicken manure composting

“…Despite its benefits, conventional composting methods only partially mitigate the accumulation of HMs (Chen et al 2019;Chung et al 2021;Zhang et al 2021a, b). Besides, the degree of bioavailability of HMs and their mobility in compost final products have a considerable impact on their probable accumulation and release into plants and soils (Ejileugha et al 2023). Lately, combining biochar into a composting matrix has arisen as a cost-effective and environmentally friendly approach to fostering humification, enhancing microbial activity, and reducing the bioavailability of Zn and Cu (Li et al 2021a, b;Zhou et al 2021;Nguyen et al 2022;Abdellah et al 2023a).…”