Abstract
Different methods were tested to evaluate the performance of a pretreatment before anaerobic digestion. Besides conventional biochemical parameters, such as the biochemical methane potential (BMP), the methane production rate, or the extent of solubilization of organic compounds, methods for physical characterization were also developed in the present work. Criteria, such as the particle size distribution, the water retention capacity, and the rheological properties, were thus measured. These methods were tested on samples taken in two full-scale digesters operating with cattle manure as a substrate and using hammer mills. The comparison of samples taken before and after the pretreatment unit showed no significant improvement in the methane potential. However, the methane production rate increased by 15% and 26% for the two hammer mills, respectively. A relevant improvement of the rheological properties was also observed. This feature is likely correlated with the average reduction in particle size during the pretreatment operation, but these results needs confirmation in a wider range of systems.
Highlights
In the field of anaerobic digestion, a vast number of reviews have been published in the last twenty years about substrate conditioning and pretreatments of organic biowaste [1,2,3], or on different products such as municipal wastewater sludge [4], municipal organic solid wastes [5,6,7,8], lignocellulosic biomass [9,10,11,12], and agricultural wastes [13]
Biomass pretreatment extends to the types of feedstocks usable in anaerobic digestion The reduction in particle size leads to an increment in the accessible surface area and may increase methane production, either by increasing the methane yield or by increasing the methane production rate [18]
For versus volatile solids (VS) (%total solids (TS)), a higher amount was found for Site I
Summary
In the field of anaerobic digestion, a vast number of reviews have been published in the last twenty years about substrate conditioning and pretreatments of organic biowaste [1,2,3], or on different products such as municipal wastewater sludge [4], municipal organic solid wastes [5,6,7,8], lignocellulosic biomass [9,10,11,12], and agricultural wastes [13]. Knife and hammer mills were cited as the most suitable techniques for dry matter comminution, while extruders are more suitable for wet matter They point out that particle size reduction will depend on the feeding system and the equipment operation (e.g., rotational rate). Further research on the influence of mechanical pretreatments at the industrial scale on the rheological behavior of untreated and treated substrates with high TS and long-sized fiber contents is important in order to evaluate their performance. In addition to biochemical parameters, physical parameters, such as size reduction, rheological properties, and water retention capacity, were evaluated This method was tested on two anaerobic digesters using two different hammer mills as pretreatments
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