Isothermal drying kinetics of municipal sewage sludge coupled with additives and freeze-thaw pretreatment.

The influences of five typical additives (coal fly ash, lignite, quick lime, potassium permanganate, dry sewage sludge), freeze-thaw pretreatment and temperatures (100-180 °C) on isothermal drying behavior of municipal sewage sludge were evaluated using a thermal analysis technique. The drying kinetics of the samples was addressed based on two falling rate stages. At the same adding dosage of 10%, the average drying rates for sewage sludge blending with coal fly ash, lignite, lime, dry sludge and potassium permanganate increased by 3.57, 2.81, 2.65, 3.05, 4.80% in comparison with the raw sewage sludge. The average drying rates for the sewage sludge after freeze-thaw pretreatment increased by 7.08%. Apparent activation energies for all sludge/additive blends and freeze-thaw sludge sample were less than those of the raw sewage sludge. Apparent activation energies of sludge/lime in two falling rate periods decreased with increasing the lime dosage from 10% up to 30%. Apparent activation energies of freeze-thaw sludge sample in two falling rate periods were the lowest in comparison with all sludge/additive blends. Coal fly ash, lignite, lime, potassium permanganate and back-mixing additives as well as freeze-thaw pretreatment were available for improving the thermal drying kinetics of the sewage sludge. [ABSTRACT FROM AUTHOR]