Analysis of the outcome of shredding pretreatment on the anaerobic biodegradability of paper and cardboard materials

Paper and cardboard stand for the major biodegradable organic fraction of most of municipal solid waste (MSW). This article aims at discussing the possible positive impact of a thin shredding of this fraction on its biodegradability under mesophilic anaerobic conditions, either for landfilling or for digestion in industrial reactors. For that purpose, BMP tests were performed on two types of paper and cardboard mixtures: one sorted from a complex landfill French MSW income, one built from source separated papers and cardboards. For both of these substrates, comparison was made between assays on large pieces of waste and assays on tiny shredded waste (powder particles of less than 1 mm diameter). For the second substrate, assays at two different inoculation levels were performed. All results are discussed both in terms of maximal methane conversion yields and in terms of kinetic rates. The main conclusion is that shredding does not improve methane potential of paper and cardboard, neither the biogas production rates. This leads the authors to put forward the hypothesis that shredding does not significantly either increase enzyme accessibility to cellulose nor favor the surface bacterial colonization, although it strongly affects the macrostructure of the waste.