Improvement of the Methane Generation Potential of the Anaerobic Digestion Solid Residue by Implementing a Biological Pretreatment With the Biomycete I. Lacteus at Various Conditions

Biological pretreatment of different digestates with Irpex lacteus was employed to investigate the potential of the fungal strain to exploit any digestible organic matter in the spent anaerobic digestion effluent in methane recovery. In all cases, pretreatment of sludge with the non-selective I. lacteus promoted methane generation. Incubation of I. lacteus in digestate for 20 days at 28 °C increased the residual methane generation potential of the sludge by 1.67-fold. Prolonging incubation time to 30 days led to an increment in methane yields (1.24-fold), however, the increase was lower than that accomplished at a shorter pretreatment period (20 days) due to a substantial loss of fermentable organics, especially cellulose. Regardless the digestate type, inoculation with I. lacteus enhanced the digestibility of sludge by at least 1.6-fold. The degree of improvement was depended on the amount of lipids and proteins supplied by the fungus when the modified sludge contained a small carbohydrate proportion and on the available for digestion cellulose when the pretreated digestate was rich in carbohydrates.