The rheology of pre-composted and fresh organic fractions of municipal solid wastes (OFMSW) anaerobically digested in thermophilic range of temperature and different operative conditions is presented. Rheological properties are strongly influenced by feed characteristics and the biodEgradation achieved. The metabolization of complex substrates has been invoked to explain different behaviours. A semiempirical model of plastic viscosity with total volatile solids, organic loading rate removed and specific gas production before feeding is proposed. The fluid behaviour of OFMSW sludges where complex substrates exert a determinant role, is outlined by thixotropy and temperature effect.
Paper mill sludge is often incinerated for heat recovering and also for an important volume reduction. In Italy about 6x10 5 tons of paper sludge is yearly produced giving 60kg of paper ash per ton. In this project, the ash coming from burning of paper mill sludge from primary mechanical separation process, fired as single fuel, was studied in order to evaluate its use as supplementary cementitious material in concrete manufacturing. On the basis of the data collected it can be concluded that the paper mill sludge ash, if replaced by 5 to 10% of Portland cement, show a positive effect on the mechanical performance of the concrete. On the other hand, due to its high fineness and consequently high water absorption, it requires a higher dosage of water, so that the use of paper ash should not be higher than 10% by weight of cement.
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