In this paper the experiments carried out in a 3 m3 reactor using mechanically sorted organic fractions of municipal solid waste as substrate are described. The influence of operating parameters such as hydraulic retention time (HRT), organic loading rate (OLR) and temperature are examined. Even at the critical levels of OLR and HRT used (6 days and 20 kg TVS/m3d, respectively) the stability parameters have values which can be considered safe. A kinetic study is also carried out using the first order and step diffusional models, based on the biogas production profiles obtained after feeding the digester. The most relevant fact is the appearance of a “plateau” in these profiles. The larger the overload, the larger the plateau formed after feeding the digester. This approach could be used to control the digester stress.

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