Humic Acid-Like and Fulvic Acid-Like Inhibition on the Hydrolysis of Cellulose and Tributyrin

Enzymatic hydrolysis of complex wastes is a critical step for efficient biogas production in anaerobic digesters. Inhibition of this hydrolytic step was studied by addition of humic acid-like (HAL) and fulvic acid-like (FAL) substances, extracted from maize silage and fresh cow manure, to batch tests with cellulose and cellulases from Aspergillus niger and tributyrin and lipases from Candida rugosa. To confirm the inhibition results, microbially catalysed hydrolysis trials were performed, where Fibrobacter succinogenes was grown exclusively on cellulose. Hydrolysis products, as glucose, glycerol and butyric acid, were measured to determine the hydrolysis efficiency and its rate. Cellulose hydrolysis was inhibited by 0.5 to 5.0 g l(-1) of HAL and FAL substances extracted from maize and cow manure, which are relevant concentrations for manure and maize digestion. Tributyrin hydrolysis, on the other hand, was only inhibited by 0.5 to 5.0 g l(-1) of HAL substances extracted from maize and cow manure and not by FAL substances.