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

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

Treatment of dyeing and finishing waters using innovative photocatalysts

Waters coming from dyeing and finishing processes by leather industries produce serious problems because they contain dyes and other pollutants. Toxic and recalcitrant for the environmental, these pollutants are difficult to remove by conventional treatments. For this reason, the heterogeneous photocatalysis is a promising and efficient method to remove them. ZnO is an excellent and promising photocatalytic material to oxidize organic pollutants into CO2and H2O. In order to enhance the photocatalytic activity of ZnO, in this work, the doping of ZnO with praseodymium (Pr) has been realized and studied in the photocatalytic treatment of dyeing and finishing waters with a total organic carbon (TOC) values in the range 540-1200 mg·L-1. ZnO particles doped with Pr were prepared by a modified precipitation method and characterized by different techniques (XRD, Raman, UV-Vis DRS). The photocatalytic activities of the synthesized samples were investigated under UV light with a specifically photocatalytic apparatus designed for the experimental tests. Photocatalytic results showed a discoloration in the range 56-98% after 4 h of irradiation while TOC removal was about 40% after 3 h of UV irradiation for all the investigated dyeing and finishing waters. The obtained results evidenced the efficiency of the synthetized photocatalyst in the treatment of real dyeing and finishing water coming from leather industries