1、Thermal analysis and FTIR studies of sewage sludge produced in treatment plants. The case of sludge in the city of Uberlndia-MG, BrazilJader de Oliveira Silva a,b , Guimes Rodrigues Filho a, , Carla da Silva Meireles a , Sabrina Dias Ribeiro a , Jlia Graciele Vieira a , Cleuzilene Vieira da Silva c
2、, Daniel Alves Cerqueira da Instituto de Qumica da Universidade Federal de Uberlndia, Av. Joo Naves de vila, 2121, CEP 38400-902, Cx. Postal 593, Uberlndia - Minas Gerais, Brazil b Departamento Municipal de gua e Esgoto de Uberlndia (DMAE), Brazilc Faculdade de Engenharia Qumica da Universidade Fede
3、ral de Uberlndia, Brazild Instituto de Cincias Ambientais e Desenvolvimento Sustentvel da Universidade Federal da Bahia, Brazila r t i c l e i n f oArticle history:Received 26 August 2011Received in revised form 4 November 2011 Accepted 8 November 2011Available online 19 November 2011Keywords:UASB s
4、ludgeCalorific powerThermal analysesPyrolysisOrganic materiala b s t r a c tThe operation of anaerobic reactors in Brazil creates a by-product, sewage sludge, for which adequate treatment is necessary to obtain a solid and stable material. The burning of sewage sludge may be an effective alternative
5、 for its management, and looking to enhance its energy potential, an environmentally friendly method of disposal is necessary. As the quantity of sludge generated has increased over the past few years, the physical chemical characterization of this waste is the first stage for its utilization as raw
6、 material. The material was characterized by thermal analyses (Thermogravimetry (TG)/Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) and Infrared Analysis (FTIR) in order to determine the main organic groups present in sludge. The calorific power of the anaerobically
7、digested sludge of Uberlndia-MG, Brazil was measured, and an energy content equal to 16.2 MJ kg1 was found, which is within the range of values reported in the literature. 2011 Elsevier B.V. All rights reserved.1. IntroductionDuring the last few years, a veritable revolution of technolo-gies and con
8、cepts has emerged concerning domestic wastewater treatment on the world stage 1. It is within this framework that the growth and development of sewage treatment technologies allowed the applicability of collective anaerobic systems, especially those involved in Anaerobic Sludge Blanket Reactors, kno
9、wn inter-nationally as UASB reactors Upflow Anaerobic Sludge Blanket reactors 2, which utilization opened new paths in the area of sewage treatment in Brazil, as well as facilitated the expansion and enhancement of the applicability of this process 3.Because the sludge is a solid by-product with pol
10、lutant charac-teristics, as much at the pathogen level as in the unwanted nutrient content, its final destination is a necessary and complex opera-tion since it involves technical, economic, environmental and legal aspects which usually surpass those of Sewage Treatments Station (STS) 4.In Uberlndia
11、, a city in the southwest of Brazil, a system of UASB reactors has been adopted, followed by a physicalchemical post treatment, which involves stages of coagulation and flotation. InCorresponding author. Tel.: +55 34 3239 4174x201; fax: +55 34 3239 4208. E-mail addresses: guimesufu.br, (G.R. Filho)
12、.addition to the UASB sludge generated in the biological stage of treatment, chemical sludge is produced in the physicalchemical treatment system. In each case, it is necessary to discard sludge, i.e., remove it from the liquid phase.There are several studies involving sewage sludge, as for exam-ple
13、: the production of bio-oil from sewage sludge, co-incineration with coal for thermal drying, kinetic modeling of sewage sludge, characterization of pyrolysis products and investigation of its pyrol-ysis mechanism 5, as well as the application of frying processes for energy recovery in the incinerat
14、ion of sewage sludge 6,7, and the utilization of sludge in the biosorption of heavy metals 8 and in agriculture 9.Thus, the object of this study was to thermally characterize the UASB sludge, using Differential Scanning Calorimetry (DSC), Thermogravimetry (TG) and Differential Thermal Analysis (DTA)
15、, therefore obtaining data regarding the sludge stability by means of the decomposition process, measuring the energetic content of the same sludge generated in the municipal treatment plant using bomb calorimetry, and providing its characterization by FTIR.2. Experimental proceduresSamples of dehyd
16、rated sludge originating from the Uberabinha STS and disposed at the landfill in Uberlndia, Minas Gerais, Brazil, have been collected.0040-6031/$ see front matter 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2011.11.010J. de Oliveira Silva et al. / Thermochimica Acta 528 (2012) 7275 73T
17、he domestic sewage treatment plant is composed of grating and grit chamber (preliminary treatment), upflow anaerobic reactors (UASB), a dissolved air flotation system (coagulationflotation), centrifuge and geotextile systems, both for dewatering sludge generated in the process, with an estimated mon
18、thly production of 264.23 tons of dehydrated sludge, which is consistent with that presented by Aisse et al. 10, which estimates an average production rate of sludge generated in a UASB reactor of 16 g STS hab1 d1 .The collected sample was obtained by dewatering sludge in a centrifuge system (UASB s
19、ludge), generating a matrix which was subjected to characterization by thermal analyses (TGA, DTA and DSC), in order to monitor the thermal phenomena of the material and determine its energy potential. This sludge has a solid con-tent of 20%, (13% volatile solids), determined using a drying oven (No
20、va tica) model 400/4 ND, muffle furnace (Hydrosan) model HY-200F/DM and an analytical balance (GEHAKA) model AG 200, to carry out the procedures according to the 2540 G method, as described by APHA 11.Before thermal analyses and FTIR characterization, the sample was sterilized in an a Prismatec CS v
21、ertical autoclave at 121 C for 15 min.TG and DTA experiments were carried out using a Shimadzu DTG-60 H thermo analyzer from room temperature to 600 C with a heating rate of 10 C min1 , under a nitrogen flowing rate of 50 mL min1 . The sample masses ranged around 5.00 mg.The superior calorific value
22、 (SCV) of the sludge was determined in an IKA C 2000 digital bomb calorimeter, with an IKA KV 600 water refrigeration system. The bomb calorimeter was calibrated with benzoic acid (thermochemical standard) with an average mass of 1.0300 g. The solid sludge sample was compressed into a tablet, yieldi
23、ng an average mass of 1.0438 g. As for the standard, the sample to be analyzed was weighed using a Shimadzu AW 220 balance. A crucible containing the sample was placed in the calorimetric reac-tor, which worked in the isoperibolic mode at 25 C. The system was pressurized at 30 bar with oxygen (99.95
24、%) and refrigerated in a thermostatic bath at 20 C. The measurements, which were duplicated, and calculations of the SCV are compliant with the stan-dards DIN 51900, ISO 1928, ASTM D240, ASTM D1989 and ASTM E711.The second scan of the DSC thermogram was obtained in a TA DSC Q-20 differential scannin
25、g calorimeter. Before the second scan, the material was heated to 200 C to eliminate any water present in the material, and afterwards the sample was heated in an alu-minum crucible at 10 C min1 from 25 to 500 C under a nitrogen flowing rate of 50 mL min1 .For FTIR analysis, a tablet was made with 1
26、% (w/w) of the sample dispersed in KBr. The spectra were obtained using a Shimadzu IR Prestige-21 spectrometer. Thirty-two scans were performed with a resolution of 4 cm1 .3. Results and discussion3.1. Thermal analysisTGA and DTA thermograms for the UASB sludge are shown in Fig. 1.In the TGDTA curve
27、s, three distinct regions are identified. As the sludge sample was not initially dry, there was a mass loss of 72% on the TG curve with a corresponding endotherm around 70 C, which is due to the release of water from the material, on the DTA curve.According to Francioso et al. 12, the thermal decomp
28、osition of thermolabile components of organic material (proteins and car-boxyl groups) produces very significant exothermic reactions at453C 601004080302C 2060 0MassDTA% -2040-4020-6070C0 -800 100 200 300 400 500 600Temperature (C)Fig. 1. TGDTA curves of dewatered sludge (UASB sludge).approximately
29、300 C, while exothermic reactions at higher tem-peratures ( 450 C) originate from the decomposition of carbon refractories, such as aromatic rings, N-alkyl long chain structures and saturated aliphatic chains. Unlike the methanogenic sludge DTA curve studied by that author, the UASB sludge DTA curve
30、 of our study presented an exothermic reaction accentuated at 453 C with a mass loss of 10%, and an exothermic reaction less accen-tuated at 302 C, losing about 11% of mass. These two exothermic peaks on the DTA curve of the UASB sludge sample shown in Fig. 1 differed from the experimental data pres
31、ented at the literature 12 because the digestion and settling of the UASB sludge take place in a single reactor with the acetogenic and methanogenic phases and not with the two phases separated, as occurred in the thermal characterization presented by the cited authors.For UASB sludge, SCV determine
32、d by the bomb calorimeter was 16.2 MJ kg1 , on a dry basis. After the combustion of the material, a reddish residue was observed in the reactor that contained the sample, probably a result of the mineral material contained in the sludge. This SCV value is 24% higher than the reported by Andreoli et
33、al. 4, who obtained an energy content between 6 and 13 MJ kg1 for digested sludge produced in an anaerobic digester used for the treatment of sludge with high content of unstable organic mate-rial. Differences were expected since the data are related to sludge from anaerobic reactors, intended only
34、for stabilization of the solid waste and not generating it inside, all of which occurs in the UASB reactors.According to Dweck et al., SCV for sludge ranging from 9.50 to 18.57 MJ kg1 have been related, even though the calorific power depends on the specific origin and composition of the sludge 5. T
35、herefore, 16.2 MJ kg1 on dry basis obtained in the present work confirms that the sludge of Uberlndias treatment stations is among those with higher calorific power.Fig. 2 shows the curve obtained from the DSC, second scan, of the UASB sludge, where it is observed the decomposition process, with its
36、 respective enthalpies.As shown in Fig. 2, a first event with an exothermic H of 4.59 J g1 and a transition temperature of 291 C, followed by sec-ond exothermic event ( H = 11.02 J g1 ) with a peak temperature at 413 C. The absence of a thermal event on the DSC curve with endothermic characteristic
37、close to 100 C indicates that there was not a loss of humidity in the sample, due to the pre-heating stage of the sample in the DSC equipment. These results corroborate those of TG/DTA and show that the enthalpy value related to the second exothermic event is 2.4 times higher than that of the first
38、exother-mic event. This result is characteristic of the material produced by the UASB treatment.74 J. de Oliveira Silva et al. / Thermochimica Acta 528 (2012) 72750,40,2 413CFlow (W/g) 0,0291C 11,02 J/gHeatexo-0,2 4,59 J/gendo -0,4100 150 200 250 300 350 400 450Temperature (C)Fig. 2. DSC thermogram,
39、 second scan, for the UASB sludge.3.2. Characterization of the sludge by FTIRFTIR spectra of the UASB sludge from the Uberabinha STS is shown in Fig. 3.It is seen in Fig. 3, several absorption bands in the region from 3600 cm1 to 3000 cm1 , with the region between 3400 cm1 and 3000 cm1 being attribu
40、ted to the OH stretching of groups present in acids and alcohols. Also in this first region of the spectra, in 3440 cm1 there is an absorption band related to the stretching of the NH bond of organic compounds 12,13. These compounds also present characteristic bands in 1545 cm1 and 1655 cm1 related
41、to C O vibration of primary amides 12,14. In 3040 cm1 , there is small shoulder that according to Francioso et al. is attributed to the stretching of the CH bond for cis-alkenes 12.Other absorption bands in the region from 3000 to 2800 cm1 are attributed to the presence of hydrocarbon chains 9 prese
42、nt on the organic material of the sludge sample, as inferred by thermal analysis. Bands in 2963 cm1 and 2920 cm1 are attributed to the asymmetrical stretching of CH bonds from mehyl and methylene groups, respectively. The band in 2851 cm1 is related to the sym-metrical stretching of CH from methylen
43、e groups and the band in 1460 cm1 is attributed to CH2 rocking. The region next to 738 cm1 is attributed to the scissoring deformation of CH2 .-1,2-1,43440 2920 16551545 1032-1,6Absorbance 29632851 14601234-1,8738-2,03500 3000 2500 2000 1500 1000 500Wavenumber (cm-1)Fig. 3. FTIR spectrum for UASB sl
44、udge.The region between 1170 and 1000 cm1 , with an intense band around 1032 cm1 is attributed to OH vibration of mineral com-pounds present in the sludge 12, but hydrocarbon and silicate compounds also absorb in this region 15.The results of the FTIR analyses are consistent with the literature and
45、confirm the attributes given to the two main exothermic events which appeared in the TG/DTA analyses. However, the exotherm in 453 C in DTA curve corresponds mainly to the presence of long N-alkyl chains and to aliphatic saturated, present in the decom-position stage of refractory carbon since it wa
46、s not inferred the presence of the characteristic bands of aromatic rings.4. ConclusionsFTIR results show that the main groups in the studied sludge are aliphatic chains with double bonds, as well as carbonyl, hydroxyl and NH groups in organic compounds. The results of the thermal analyses (TG/DTA/D
47、SC) showed that the material from the Uber-abinha STS presents an exothermic event around 450 C (where the decomposition of carbon refractory predominate, such as N-alkyl long chain structures, and saturated aliphatic chains) with a calorific content about 2.4 times greater than that which is locate
48、d around 300 C (referring to the thermal decomposition of ther-molabile components of organic material (proteins and carboxyl groups).This study showed that it is possible use UASB sludge for generation of energy once the material presents a significant biodegradable portion of 65%, and a superior c
49、alorific value of 16.2 MJ kg1 .Thus, taking into account the increasing disposal of waste at landfills over time and the problem of finding permissible disposal sites, which is more and more difficult in big cities, the immediate allocation of a larger proportion of sludge for burning is possible and becomes a good alternative to avoid its submission to landfills, considering its potential energy, as well
