Trace element supplementation in the biogas production from wheat stillage – Optimization of metal dosing

• Optimal dosing of trace elements was determined by a depletion approach in CSTRs.
• Trace elements have to be augmented for the AD of wheat stillage at high OLR.
• Dosing of these elements can be reduced compared to recommendations in literature.
• Deficiency of Fe caused an increase of propionic but not of acetic acid.
• Deficiency of Ni resulted in accumulation of both acids at similar levels.

A trace element dosing strategy for the anaerobic digestion of wheat stillage was developed in this study. Mesophilic CSTR reactors were operated with the sulfuric substrate wheat stillage in some cases under trace element deficiency. After supplementing trace elements during the start-up, one of the elements of Fe, Ni, Co, Mo, and W were depleted in one digester while still augmenting the other elements to determine minimum requirements for each element. The depletion of Fe and Ni resulted in a rapid accumulation of volatile fatty acids while Co and W seem to have a long-term effect. Based on the results it was possible to reduce the dosing of trace elements, which is positive with reference to economic and environmental aspects.