Packed microcosms, consisting of 0.6 L-flask filled with tire chips (TC, a non-cost-recyclable non-biodegradable material) or ceramic cubes, were employed in the wet batch mesophilic anaerobic codigestion of a mechanically sorted organic fraction of a municipal solid waste with cattle manure. Two different waste mixtures were digested within four successive batch experiments, performed by collecting the digested waste and by refilling each microcosm with the same experimental mixture. Methane production yields related to the first experiment were comparable to those of non-packed identically developed microcosms, while they significantly grew during all the following experiences. No CH4-production lag-phase was observed since the second batch experiment. Similar results were obtained for both packing materials: however, the highest methane yields were achieved within bioreactors packed with TC in the presence of a mixture in which the volatile suspended solids (VSS) provided by the municipal waste represented the 55% of the total ones. Under such condition, a methane yield corresponding to the biochemical methane potential (BMP) calculated through a 6-month experiment with non-packed microcosms (176 ml/gVS) was attained in about 1/4 of the time. Importantly, the BMP can significantly grow up as a consequence of the approach described in this study.

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