A thermogravimetric study on tannery sewage sludges

Two different tannery sewage sludges (Sludge 1 and Sludge 2) have been characterized by thermal anal. coupled with mass spectrometry of evolved gases (TG-DSC-MS), inductively coupled plasma-at. emission spectrometry (ICP-AES), Gas chromatog. - mass spectrometry (GC-MS), Purge and trap GC-MS. Four main temp. ranges of wt. loss were individually examd. in air flow TG-DSC-MS expts. on Sludge 1. The first, below 200C, coupled to an endothermic signal, is related to water release. Between 200 and 350C, an exothermic signal accompanies the loss of sulfate as evolved SO2 org. substances, aroms. and satd. cyclic compds. In the latter range, development of CO2 was also obsd., this becomes prevalent in the range 350-600C. From 600 to 700C carbon dioxide from carbonate decompn. was obsd. In Sludge 2, three main temp. ranges of wt. loss are present, below 150C, between 150 and 350C and from 350 to 600C, attributed, resp., to water, sulfate, CO2 plus arom. and carbonyl compd. releases. A larger amt. of Cr and Al was found by ICP-AES in Sludge 2. The differences between the samples evidence the influence of the compn. of the parent wastewater and of the depuration process. The influence of additives on combustion profiles has been also evaluated. Catalyst addn. to the sludge results to reduce the emission of cyclic and arom. substances, to lower temp. and to increase the oxidn. rate of org. fraction combustion