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

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-Na₂ 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-Na₂ 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 H₂S content. The exchangeable fraction of specific TE (Mo) in H₂/CO₂ 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.