Comparison of efficiecy of two solar-catalytic sytems treatment of textile dyes and washing out reagents

Transcription

1 Proceedings of International Symposium on Environmental Pollution Control and Waste Management 7- January 02, Tunis (EPCOWM 02), p Comparison of efficiecy of two solar-catalytic sytems treatment of textile dyes and washing out reagents GHOZZI K.*, ZAYANI G, BOUSSELMI L., GHRABI A. INRST, Laboratoire Eau & Environnement, Tunisia S.U. GEISSEN, A, WEIDEMEYER, A. VOGELPOHL Institut für Thermische Verfahrenstechnik, Technical University of Clausthal, Germany ABSTRACT Several systems are used in photocatalytic degradation, two of them are experimented in the treatment of textile dyes and washing out reagents. The Thin Fixed Film Bed Reactor (TFFBR) and Aerated Cascade photocatalytic reactor ACP models developed to investigate photocatalytic degradation of organic compounds. For the first one the catalyst is fixed while, for the second one the catalyst is hanging in the solutions. The efficiency of the two systems are tested for the solar catalytic treatment of commercial dyes and washing out reagents.the degradation of the black, red, blue and golden dyes shows that the black had the highest TOC dgradation than others. Moreover the ACP sytem was more efficient than TFFBR. The treatment of the washing out reagents in suspended solutions and TFFBR reactor gives a high TOC degradation with the last system comparing to the first one. KEYWORDS Photocatalytic, reactor, Dyes, washing out reagent I - Introduction : Wastewaters from textile process contain many types of polluants such as dyes, detergents, fungicides, grease and oils, sulfide compounds, solvents, heavy metals and inorganic salts and fibers (Balanosky et al, 1999). The commonly used method for the treatment of textile wastewater is the combination of bilogical oxidation and physical-chemical treatment. However these processes are quiete ineffective in decolorization of wastewater (Idil arslan et al, 00). Photocatalytic degradation technique has been developed to oxidize wastewater containing dyes and has attracted much attention (Chunmei Zhu et al, 1999). ). While there have been many successful solar pilot scale studies using TiO 2 suspensions for treating contaminated water solutions but the catalyst separation can limit the use of this method (Feitz et al, 00). Solar fixed bed photocatalysis overcomes any need for the separation and is receiving increasing interest as low energy alternative with the recent development of a number of innovative pilot scale reactors (bahneman et al, 1996). The aim of the present study is to compare the photocatalytic degradation efficiency of the both systems (suspended and fixed) for dyes solutions and washing out reagents. II- Experimental conditions : II-1 Reactors II-1-1 The Thin Film Fixed Bed Reactor :TFFBR The main part of TFFBR reactor is a glass pane (0,7 m 1,4 m) coated with the catalyst TiO 2 DEGUSSA P25 as a thin layer by spraying. The distribution system is a tube at the top of the pane (Length = 700 mm ; diameter = 6 mm). The inclination of the glass pane is equal to 30, so that the thickness and the retention time are depended only on the flow rate. The treated volume used is 5 liters, the flow is 1 l/h. The main advantage of fixed system is its simplicity and no separation of catalyst from the treated wastewater is necessary. II-1-2 Aerated Cascade Photo reactor : ACP It consists of a double skin sheet channeling system made of UV- transparent acrylic glass (Plexiglas) (Weimin Xi et all,00). The ACP system is composed by : 683

2 Ghozzi et al. - A Plexiglas pane (57cm 137 cm) with 1,5 cm thickness placed on metallic support and moved round horizontal axe. Nine Comminuted compartments compose the pane. - A cylindrical tank (90 cm high, 19 cm diameter) allows the mixture between wastewater and catalyst using agitator. - A pump supplys the reactor with the mixture at the flow rate of 5 l/h - An aeration system injects air in to the 9 compartments at a pressure of 1 bar and flow rate of 85 l/h - A settling tank allows the separation of catalyst The ACP system uses the same catalyst but mixed with wastewater. The mixture is pumped to the reactor divided in 9 compartments. The solution is aerated by using air source. After treatment, the wastewater is settled to separate TiO 2. Twenty liters of wastewater are used for this treatment at a catalyst concentration (TiO 2 Degussa P25) equal to 1g/l. II-2- Dyes : Reactive dyes used by textile factory are presented under the commercial names. Table 2 gives the commercial names, initial concentration, TOC, IC and ph of solution dyes. Table 2 : Commercial names, initial concentration,toc, IC and ph of dyes solutions Color Commercial Name Concentration TOC mg/l IC mg/l ph (mg/l) Golden Levafix goldgelb E-RA CLg Blue Bleu Cibacrone FN-R CB ciba Black Everzol Black B CEB Red Rouge Cibacrone FN-R CR ciba The TOC comparison of the solution dyes shows that the golden and the red dyes have almost the same TOC concentration. The black dye is purely organic. While the three dyes golden, blue and red have nearly the same inorganic carbon. II-3- Washing out reagents: Washing out process is characterized by high water consumption. Different steps taken place using detergents and chemical reagents (table 3). Chemicals commercial names Table 3 : Washing out chemicals steps Concentration ph TOC mg/l IC mg/l Croscour RDT Damping Erpazyme FD1 Stone wash (enzyme) CroscoulorTRP Stone wash (enzyme) Anticx 0 Soaping ACX-BL (softening) Softening All compoundes except ACX-BL shows a high organic pollution. 684

3 Photocatalytic degradation II-4- The UV-A intensity : 25 UV-A (w/m2) Figure 1 : Exemple of UV-A variation during the experimentation The solar UV-A intensity varied during the treatment, the maximum reached the 25 w/m 2 between 12h and 13h. The minimum values are obtained at the morning (11 h) and at the end of experiment (5 h). III- Results and discussion : III-1-Dyes III-1-1 TFFBR reactor : The solar catalytic degradation of TOC and IC present a zero order kinetic. The highest TOC degradation rate is obtained with the black dye (table 4). The blue and the red have almost the similar TOC degradation and the golden the lowest one. However the IC degradation rate for this dye is the higher. The IC and TOC removal are equivalent for the blue and the red dyes. The black and the blue dyes have equal linearisation coefficient (K) the same results was obtained for both golden and the red dyes. Table 4 : Degradation parameters of dyes solutions TFFBR Black Blue Golden Red Dye Concentration ( mg/l) TOC 0 ( mg.l -1 ) TOC K (.h -1 ) r mg. m -2.h IC 0 ( mg.l -1 ) IC K (mg.l -1.h -1 ) r mg. m -2.h , 40 1,00 Everzol black IC (m g/l) 30 TOC/TOC0 0,80 0,60 Bleu cibacrone Rouge cibacrone 0,40 Levafix goldegelb , Figure 2 : TOC and IC degradation with TFFBR system 685

4 Ghozzi et al. II-1-2- ACP reactor : The ACP treatment leads to a highest TOC degradation rate with the black dye then the red and the golden, no TOC degradation of the blue dye is shown. Concerning the IC removal the higher rate is obtained for the red then the blue and the golden. Previous adsorption study, demonstrated that adsorption is favored by suspended system than fixed one which can increase. Table 5 : Degradation parameters of dyes solutions ACP Black Blue Golden Red Dye Concentration ( mg/l) TOC 0 ( mg.l -1 ) TOC K (mg.l -1.h -1 ) r mg. m -2.h IC 0 ( mg.l -1 ) IC K (mg.l -1.h -1 ) r mg. m -2.h IC (mg/l) TOC (mg/l) Everzol black Bleu cibacrone Levafix goldgelb Rouge cibacrone 0 0,5 1 1, ,5 1 1,5 2 Figure 3: TOC and IC degradation with ACP reactor Comparing the two systems, the TOC degradation rate is higher for the ACP than the TFFBR, except for the blue dye. The same results is obtained with the IC removal ACP reactor is more efficient than the TFFBR. the results show a great influence of initial inorganic concentration on the degradation of organic compounds but less on the TFFBR than the ACP system. This is can be explained by the occupation of the active sites by inorganic compounds which are degraded firstly. III-2- Washing out reagents : The degradation of these chemicals are tested by two systems TFFBR and suspended. Samples were taken, the ph,toc, COD and EC were measured. The table 6 summarizes the results of reagent solar catalytic treatment. 686

5 Photocatalytic degradation Table 6: recapitulative results of washing out reagent treatment Chemicals Adsorption mgtoc/gtio 2 (TFFBR) (suspended) mg TOC m -2.h -1 mg TOC m -2.h -1 Croscour RDT Erpazyme FD Croscoulor TRP Anticx ACX-BL If we compare the results for the two photocatalytic reactor, we can remarks that the high TOC removal with suspended system was obtained for the detergent reagent Anticx0. However, for the TFFBR reactor the treatment shows an important TOC degradation for the enzyme used in the stone step of washing out process (Crouscoulor TRP).However the experiments shows that the most important adsorption rate was obtained for the damping reagent (Crouscour RDT). 4 -Conclusion : To choose the photocatalytic reactor is very important for photocatalytic treatment. The results reported above have shown that, decolorisation rates are more important with ACP reactor for all dyes only the blue color that shows a higher TOC degradation with TFFBR system. The washing out reagent have different behavior with the two photcatalytic systems dependent on the initial composition and reaction parameters. Acknowledgment : This work is realized in the frame of the Tunisian -German project DFG/BMZ, N 3 / REFERENCES Balanosky. E, Herrera.F, Lopez. A and kiwi. J (1999),oxidative degradation of textile wastewater. Modeling reactor performance. Wat.Res.Vol.34. No Chunmei Zhu, Liangyan Wang, Linren Kong, Xi Yang, Liansheng Wang, Shaojian Zheng, Feili Chen, Feng Maizhi, Huang Zong (00). Photocatalytic degradation of AZO dyes supported TiO2 +UV in aqueous solution, (chemosphere Idil arslan, Isil Akmehmet Balcioglu, Detlef W.Bahnemann (00), Heterogenous photocatalytic treatment of simulated dyehouse effluents using novel TiO 2 -photocatalysts, Applied catalysis B : Environmental Feitz.A.J, Boyden.B.H and Waite.T.D (00), Evaluation of two solar pilot scale fixed bed photocatalytic reactors, Wat. Res.Vol 34. No Weimin Xi, Sven-Uwe Geissen and Alfons Vogelphol (00), Solar water detoxification with a novel photocatalytic reactor aerated cascade photoreactor (ACP), international conference on wastewater treatment and reuse adapted to mediterranean area (25-28 october 00, Tunisie). 687