Enhancing the hydrolysis process in a dry anaerobic digestion process for the organic fraction of municipal solid waste

The potential of leachate recirculation and enzyme addition for increasing the conversion efficiency of a 2-stage dry anaerobic digestion process of OFMSW was studied and compared to a 1-stage setup. In the 2-stage reactor setup the methane yield increased from 31 to 227 ml-CH4/g-VS by lowering waste/percolate ratio from 6.5 to 2 (based on VS). Eventual pH increase and lower VFA release in the leachate indicated that methanogenesis occurred also in the first stage of the 2-stage system. The high waste/percolate ratio of 6.5 lead to overload of both 1- and 2-stage processes while lowering the waste/percolate ratio to 4 resulted in a methane yield of 268 ml-CH4/g-VS in the 1-stage reactor system. The higher water saturation of the waste led obviously to more homogenous process conditions. Addition of two different enzyme blends with cellulase and hemicellulase activity resulted in 19% increase of the methane potential.