Optimization of anaerobic digestion for mechanically pretreated waste paper

The accessibility of microorganisms to the fermentable components in anaerobic digestion is restricted by the complex structure of the lignocellulosic materials, such as paper wastes. In order to reduce the biomass particle size and to increase the feedstock’ specific surface area available to the microorganisms, and therefore improve the methane yield, a beating pre-treatment with a Hollander beater was assessed. The mechanical pretreatment has been applied to a batch of office paper previously shredded and inoculated with sludge from a biogas production plant. The methane yield decreased with increased ratio F/I for all pretreatment times. The methane yield decreased by 5.24% when the paper waste was beated for 30 min and increased by 20.60% for 60 min. A response surface methodology (RSM) was used in order to evaluate the effect of the operational parameters on the methane production. The optimal methane yield of 245.37ml/gVS from the numerical optimisation was found at BT= 55 min and F/I ratio= 0.3, allowing 17% extra methane when compared to the maximum methane production for untreated paper.