Wet Oxidation of Crude Manure and Manure Fibers: Substrate Characteristics Influencing the Pretreatment Efficiency for Increasing the Biogas Yield of Manure

The biogas yield of manure is typically lower than 25 m3/t due to its low dry matter content and its high ratio of lignocellulosic fibers that are recalcitrant towards anaerobic digestion. A new pre-treatment method – wet oxidation – has been tested for disruption of the lignocellulosic fiber structure with subsequent higher degradation efficiencies and methane yields. A screening of crude manure and the separated fiber fraction shows that wet oxidation is more adequate for treatment of high concentrated solid fraction than for crude manure and an increase of 35% in biogas yield can be gained from wet oxidation of digested fibers. The wet oxidation treatment of the manure fiber fraction has to be carefully adjusted in order to achieve the highest increase in biogas yield for the manure fiber fraction under low production of inhibiting compounds and low losses of valuable organic matter.