Making lignin accessible for anaerobic digestion by wet-explosion pretreatment

•The pretreatment of feedlot manure was performed using 4 bars oxygen.•Oxygen assisted wet-explosion pretreatment promotes lignin solubility.•4.5 times higher methane yield observed as a result of the pretreatment.•44.4% lignin in pretreated material was actually converted in the AD process.•Aliphatic compounds formed in the pretreatment were utilized by microbes.

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.