Effects of full-scale substrate pretreatment with a cross-flow grinder on biogas production

Abstract

The enhancement of the degradation rate of energy crops, agricultural residues and manure by different lab scale pretreatment pathways is shown in previous studies.  In general, the pretreatments resulted in higher degradation efficiencies and an increase in methane yield for lignocellulosic and fibrous biomass.  The major drawback of most of the different pretreatment methods is that either they are not feasible for application in practice or the high energy demand makes them economically inefficient.  The aim of this study was to evaluate the effects of a full-scale mechanical pretreatment with a cross-flow grinder on commonly used energy crops (maize silage, grass silage and rye grain silage) and horse manure. Furthermore, the optimal treatment intensity for the highest energy output was estimated.  A grinding time of 15 s led to a significant increase in methane yield for horse manure (+ 9.2%) and a mixture of energy crops and horse manure (+ 9.7%).  However, only lower treatment intensities proved   to have a positive energy balance.  An increase in treatment intensity resulted in a further reduction of particle size but showed no effects on the degradation efficiency.  Hence, it can be concluded that the utilization of the mechanical treatment enables the digestion of lignocellulosic and fiber-rich substrates like residuals and organic wastes and therefore increases the environmental sustainability of energy production by anaerobic digestion.
Keywords: anaerobic digestion, biogas production, mechanical pretreatment, lignocellulosic materials, horse manure