The absolute concentration and bioavailability of trace elements: Two vital parameters affecting anaerobic digestion performance of chicken manure leachate.

It is currently unclear whether trace elements (TEs) deficiency is due to low bioavailability or low absolute TEs concentrations, especially in high-pH anaerobic digestion (AD) systems. A mixed solution of TEs and EDTA-Na were used separately in mono-AD of chicken manure (CM) leachate to investigate this research gap. The results showed relatively low bioavailability of Fe, Mn, and Zn. The bioavailability of all TEs remained stable along with a gradual increase in total ammonia nitrogen concentration. Both TE and EDTA-Na supplementation improved the bioavailability of TEs, but TEs supplementation also gave a high proportion of soluble TEs. Adding TEs improved methane production efficiency (+38.3%) and decreased the HS content. The exchangeable fraction of specific TE (Mo) in H/CO pathway was higher in the TEs treatment. TEs bioavailability and absolute concentrations of available TEs are critical aspects that need to be scrutinized to assess the risk of TEs deficiency.