Making lignin accessible for anaerobic digestion by wet-explosion pretreatment

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 10L reactor at 170°C for 25min using 4bars 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±36L/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.