Abundance of trace elements in demonstration biogas plants

Ten biogas plants across Europe were investigated for the concentrations of trace elements in their digestates. Many of these trace elements are important micro nutrients and act as microbial agents responsible for the anaerobic digestion of organic material. Great variations in concentrations from biogas plant to biogas plant were found covering a range of 1–2 orders of magnitude. No deficit of nutrients was detected in any of the biogas plants tested, but those plants with high inputs of energy crops and manure had lower values. Also biogas plants feeding high amounts of glycerol in addition to their agricultural feedstock generally showed low concentrations of micro nutrients. The highest concentrations of nutrients were detected at biogas plants fed by bleaching earth. Biogas plants fed with wastes like blood, kitchen and food waste also revealed higher concentrations of micro nutrients.