Methods for increasing the biogas potential from the recalcitrant organic matter contained in manure

The biogas potential of manure could be significantly increased by treatment of the recalcitrant organic matter (biofibers) contained in the manure. Several treatment methods were tested. Mechanical maceration resulted in an average increase of the biogas potential of approximately 17% as shown by the continuous stirred reactor experiment. In general the smaller the fibers the higher the biogas potential was. The best results showed an approximately 20% increase of the biogas potential with fibers smaller than 0.35 mm as measured by batch experiments. The increase was approximately 16% with fibers of size 2 mm. Chemical treatment of the fibers with bases such as NaOH, NH4OH or a combination of bases also resulted in an increased methane potential. However, combination of maceration and chemical treatment did not result in a further increase of the methane potential. There was not any significant difference of the biogas potential from fibers in the range 5–20 mm. Treatment of the fibers with hemicellulolytic or cellulolytic enzymes did not result in any significant increase of the methane potential. However, biological treatment of the fibers of the manure with the hemicellulose degrading bacterium B4 resulted in a significant increase of the biogas potential of manure. An increase of approximately 30 % in methane potential was achieved compared to controls.