Making lignin accessible for anaerobic digestion by wet-explosion pretreatment

Abstract

Lignin is a major part of the recalcitrant fraction of lignocellulose and in nature its degradation occurs through oxidative enzymes along with microbes mediated oxidative chemical actions. Oxygen assisted wet-explosion pretreatment promotes lignin solubility and leads to an increase biodegradation of lignin during anaerobic digestion processes. The pretreatment of feedlot manure was performed in a 10. L reactor at 170. °C for 25. min using 4. bars oxygen and the material was fed to a continuous stirred tank reactor operated at 55. °C for anaerobic digestion. Methane yield of untreated and pretreated material was 70 ± 27 and 320 ± 36. L/kg-VS/Day, respectively, or 4.5 times higher yield as a result of the pretreatment. Aliphatic acids formed during the pretreatment were utilized by microbes. 44.4% lignin in pretreated material was actually converted in the anaerobic digestion process compared to 12.6% for untreated material indicating the oxygen assisted explosion promoted lignin degradation.