Influence of trace elements on methane formation from a synthetic model substrate for maize silage

The effect of a well-defined trace element solution and the elements nickel, cobalt and molybdenum on anaerobic digestion of a synthetic model substrate for maize silage was studied in batch reactor experiments at 35 °C. The defined substrate (dS) consisted of xylan and starch as the main carbon source, urea as nitrogen source and phosphorus from a 0.1 M potassium phosphate buffer. Batch reactors were operated for 30 days with 1.5% organic dry matter (ODM) of inoculum sludge from a mono-maize biogas plant and 1% ODM of the defined substrate. Results showed an increase of methane yield of up to 30% upon addition of the trace element solution. With an addition of nickel at 10.6 μM, a final yield of 407 l kg−1 ODM was reached and an enhanced methane production by 25% at day 25 of operation was observed. Total elimination of nickel from the trace element solution highly decreased methane formation and process stability. Cobalt in a concentration range of 0.4 up to 2.0 μM increased the methane production by 10% approximately. Interestingly, addition of molybdenum did not significantly effect methane production.