Production of Biofuels from Animal Bedding: Biogas or Bioethanol? Influence of Feedstock Composition on the Process Layout

Abstract

The design of biorefineries based on farmyard manure remains unknown, because various groups have obtained disparate results. These differences have been attributed to the composition of the material—an explanation that this study intends to develop. Several biorefinery layouts were tested in the laboratory for animal beddings with various manure contents, and the same result was obtained in all cases: fractionating the material and recycling part of the fiber, after pretreatment, to the anaerobic digester delivered the highest conversion efficiencies (540 N mL CH4 g–1 VS). This result proves that the processing of animal bedding does not depend on the manure content of the material or, probably, on any other aspect of the composition. The process being unaffected by the composition of the material was attributed to fractionation of the material, because the output of this step was constant even though the feedstock differed. This result implies that fractionating animal bedding allows this material always to be processed through the same technique. This is because fractionation increases the conversion efficiencies compared with designs that lack this step (e.g., 15% higher ethanol yield), as it enables to unlock synergies between biogas and bioethanol production from this feedstock.