Monitoring of a Composting Process: Thermal Stability of Raw Materials and Products
In the following chapter, thermal methods of thermogravimetry (TG) and differential scanning calorimetry (DSC) were utilised on agro-industrial raw materials and on samples collected during a 5-month composting period. The main objective was to investigat
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Introduction Chemical composition and structure of raw materials used in the composting process are important factors in determining the potential degradation of organic wastes. The amount of lignocellulosic substrates and nitrogen are fundamental in determining the optimal starting conditions for microbial activity, when process parameters such as temperature, oxygen and water availability are not limiting factors to microbial growth. On a gross scale, the carbon to nitrogen ratio of raw materials is in practice considered one of the key parameters, even if no information on fibre components can be deduced. Furthermore, the wet chemical methods for determining the composition of lignocelluloses are complex and timeconsuming (Sharma 1995), and few direct methods on whole samples are available so far. In this context, thermal methods of thermogravimetry (TG) and differential scanning calorimetry (DSC) provided estimation of lignin and fibre components (Sharma 1990, 1991, 1995; Kaloustian et al. 1997). On the basis of these TG and DSC applications, thermal techniques have also been successfully used for IIstituto Sperimentale per la Nutrizione delle Piante, Via della Navicella 2, 00184 Roma, Italy; e-mail: [email protected]
H. Insam, N. Riddech, S. Klammer (Eds.) Microbiology of Composting © Springer-Verlag Berlin Heidelberg 2002
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maturity assessment in compost, as a comparative method in evaluating organic matter (OM) transformation of lignocellulose-based materials during the composting process (Blanco and Almendros 1994, 1997; Dell'Abate et al. 1998, 2000). While the most widespread chemical methods for characterisation of compost organic matter require extraction and fractionation procedures of C compound classes, the application of TG and DSC on whole compost samples allows the analysis of thermal stability in organic matter within the mineral matrix to which it is closely associated. In the present study such a thermo analytical approach to compost characterisation was used. It was aimed to investigate the energetic status of different raw materials with respect to that of compost samples at different stages of the composting process, in order to obtain a process monitoring and to verify the possible influence of the starting organic substrates on the compost thermal patterns. Samples from two different piles, obtained using citrus industrial processing wastes as input materials, were studied in the framework of a wider investigation carried out on the possible utilisation of citrus industrial process wastes for compost production. In particular, the aspects related to C turnover and humification were described in Tittarelli et al. (2002) and those regarding the microbial dynamics in Pinzari et al. (2002).
Materials and Methods Raw Materials The main typologies of wastes produced by the citrus industrial process are and sludge. Pastazzo, a mixture of citrus pulp and skins, represents almost 60% of the initial fruit weight, while sludge, the final product of fruit purification treat
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