Nutrient augmentation enhances biogas production from sorghum mono-digestion.

• Mono-digestion of sorghum was conducted for more than 420 days. • Nutrients deficiencies of sulfur and cobalt were confirmed. • Bioavailability of micronutrients was analyzed in sorghum digestion. • Sulfur was confirmed as a key factor affecting bioavailability of micronutrients. • Methane yield of 223 mL-CH 4 /g-VS was achieved through nutrients augmentation. This study investigated the effects of the addition of micro- (Fe, Co, Ni, and Mo) and macro-(Sulfur) nutrients on mono-digestion of sorghum under mesophilic conditions. A continuous stirred-tank reactor was operated for more than 420 days under seven different experimental conditions. The experimental results showed poor performance for methane production and process stability without nutrient supplementation. Serious deficiencies in Co and S were confirmed by nutrient analysis of dry sorghum and digestate. Nutrient augmentation efficiently enhanced methane production and volatile fatty acid (VFA) removal. Methane production reached 223 mL-CH 4 /g-VS, almost matching the yield predicted by biochemical methane potential (BMP) test. S was demonstrated to have a critical effect on metal availability in the digester. Consequently, to maintain stable methane fermentation, suitable supplementations of S and Co are recommended for anaerobic sorghum mono-digestion. [ABSTRACT FROM AUTHOR]