Amongst the waste management strategies composting is gaining interest as a suitable method with economic and environmental profits. The mixture of wastes used in composting must be potentially biodegradable to favor biologically catalyzed breakdown of organic matter in aerobic conditions and drive the composting process into thermophilic temperatures required for pathogen reduction. Thus, this work aimed firstly to predict the biodegradability of an initial waste mixture and to investigate how this property determines the changes in organic matter characteristics during the composting process. A second objective for this work was to develop a dynamic mathematical model for aerobic composting process and its validation by fitting the experimental data.The initial mixtures tested were made from potato-peel industrial waste, grass clippings and sawdust in four different proportions. These blends were composted in self heating reactors (SHR) with 120 L of internal volume and well isolated. During composting, a data acquisition system for on-line monitoring of temperature and oxygen concentration was used, and feed air flow rate was measured with rotameters. The waste mixtures were sampled in pre-determined times along the period of composting. Biodegradability of each sample was assessed by measuring lignin content, by using the Klason method, which involves the gravimetric measurements after extracting the sample with sulphuric acid.Regarding the biodegradability of the mixtures the results indicated that independently of the initial mixture composition, there is an increase in lignin content that can be related to the decrease of the potential for biodegradation of the mixtures. The initial samples with the lower and higher lignin content showed a greater and smaller mass reduction, at the end of composting period, respectively. Therefore, higher lignin content of an initial mixture led to lower biodegradation. The mathematical model developed showed good fitting to experimental data, namely for temperature of substrate, organic matter conversion and water loss in the composting system. Thus, the proposed pseudohomogeneous model can be used for future prediction purpose.
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