Enhanced Thermal Treatment of Tannery Sewage Sludge

Thermal conversion of sewage sludge presents several advantages, such as the reduction of mass and volume of solid waste and energy recovery from the organic sludge fraction, resulting in lower disposal costs with respect to landfilling. In this work, the combustion behaviour of a dried tannery sewage sludge was compared in the absence and in the presence of a catalyst, investigating the role of catalyst loading. The catalyst mixed with the dried sludge improves either the selectivity of the sludge combustion process, reducing the emission of cyclic and aromatic substances, either the combustion peak temperature, yielding a higher oxidation rate of the sludge organic fraction. By adding the catalysts in the step of sludge formation, i.e. immediately after the addition of flocculant into the coagulation-flocculation step of tannery wastewater, the combustion peak of the sludge organic fraction occurred at about 300 K lower than in the absence of catalyst (about 798 K), pointing out to a significant improvement of the oxidation process due to the catalytic material.