Solar Photocatalytic Oxidation (PCO) Process with a Flat-plate Reactor

Transcription

1 Solar Photocatalytic Oxidation (PCO) Process with a Flat-plate Reactor Y., L. Zou and E. Hu School of Engineering and Technology Deain University Geelong, Victoria 317 Australia yuncang@deain.edu.au Abstract An experimental rig with a flat-plate solar reactor was built to study the effectiveness of radation using the reactive methylene blue as sensitive objective. The factors that affect the radation performance, such as dosages of photocatalyst ( ), initial concentration of reactive methylene blue, flow rate through the flat-plate reactor, solar UV radiation intensity and decolourising efficiency of the solution, have been investigated. The results showed that the solar PCO process with a Flat-plate Reactor could rade the methylene blue and decolour in methylene blue solution efficiently. 1. NTRODUCTON Dyes are an abundant class of coloured organic compounds that represent an increasing environmental ris. Dyeing effluent with intensive colour and toxicity can be discharged into aquatic system in dye production and textile manufacturing processes. A single dyeing operation can use a number of dyes from different chemical classes. t maes the composition of dyeing effluent varies with the textile produced, have highly varying chemical characteristics and is a very complex wastewater. Conventional biological treatment methods are ineffective for decolour and radation since the large ree of aromatics presents in the molecules and the stability of modern dyes (X. Z. 1996; Y. M. Sloar 1998; Wang ). This had led to the study of other methods. Use of solar radiation for photocatalytic oxidation for treatment of wastewater is a very fascinating and fast-developing area (Goswami 1997; Ajona and Vidal ; Danielle Roche ). This is a high-added value application of solar energy. Solar non-concentrating reactors mae use of both direct and diffuse components of solar UV radiation and have the potential for low cost development and more efficient. The diffuse component of solar UV radiation in some climatic regions can be as much as, or in some cases even greater than, the direct component. The objective of this investigation is to explore the feasibility of using low cost non-concentrating reactors for treating dye effluent by solar photocatalytic oxidation process. An experimental rig with a flat-plate solar reactor was built to study the effectiveness of radation using the reactive methylene blue as indicator. The factors that affect the radation performance, such as dosages of photocatalyst ( ), initial concentration of reactive methylene blue, flow rate through the flat-plate reactor, solar UV radiation intensity and the decolour efficiency of the solution, have been investigated.. EXPERMENTS.1. Experimental Rig An experimental rig with a flat-plate solar reactor used for this investigation is shown schematically in Figure 1 and Figure. The methylene blue solution to be treated was prepared and stored in a tan. The outlet of the tan fed the suction side of a pump. A LZB flowmeter with a stainless float was used to record the system flow rate. From the outlet of the flowmeter, fluid was pumped into the reactor where it tricled through a spray tube which a number of holes with the diameter of 1mm and the gap of 5mm between holes were drilled on along its length. After the solution was treated, it was gravitated bac to the tan. SES 1 Solar World Congress 1855

2 n our investigation, two experimental systems, system 1 and system, were built. The reactor areas and the tan volumes in system 1 and system were.18m.8m(m ) and 1.15m..55m(m ), 5L and 1L respectively. Three UV lambs of 15Watt each and the central wavelength of 365nm were used as UV light source in system 1 for indoor experiments. Solar radiation was the light source for system in outdoor experiments. UV intensity was measured by an UV irradiance meter (model UV-A, the ranger of 3-nm, made in photoelectric instrument factory of Beijing Normal University). UV spectrophotometer (PE Company, US) was used to measure the absorbency of solution at the maximum absorbent wavelength of 66.3nm and then determine the solution concentration of Methylene Blue by using the curve of standard absorbency-mass concentration. UV Radiation Tricle Reactor Mixer Flow Meter Stainless Reactor Tan Circulating Pump Figure 1 Schematic diagram of a solar PCO facility with the flat-plate reactor Figure Schematic diagram of a flat-plate reactor with the tricled spray tube.. Experimental Methods powder (made in Beijing Yili fine chemical Ltd Company) had been separated by ultrasonic for ten minutes. Deionized water and a certain amount of Methylene Blue (made in Shanghai third reagent factory) were mixed to produce the treated solution of certain concentration. The solution was stored in the tan and then TiO powder was added according to the needs of tests. The reactor was tilted at a desired angle from the horizontal. With an opaque cover placed over the reactor, the solution was circulated through the rig and the throttling valve was adjusted until the desired flow rate was achieved. After twenty minutes the fluid flow stage became stable, the cover was removed from the reactor and the test begun. mmediately the first sample was taen. At specified time intervals, typically ten minutes or twenty minutes, a 15ml sample of the test solution is drawn from the tan using a syringe. Sample were analysed after centrifugation (18rpm for 1 minutes) and filtration by a.5µm syringe filter. t has been experimentally observed that first-order inetics, i.e., C = Ce (where C and C are the solute concentration and the initial solute concentration respectively, t is the reaction time, and is the reaction rate constant), are sufficient for characterizing the PCO process (P.Wyness 199; Goswami 1995; Goswami 1997). The constant can be determined for experimental data as using the regress analysis method. t 3. NDOOR EXPERMENTAL RESULTS AND DSCUSSON The indoor tests on system 1 were carried out in the different conditions and the results are shown in Figure 3-6 and Table 1. The effects of the different solute concentration Ct of is shown in Figure 3 at the test condition of the flow rate =8, the reactor titled angel =5, the initial solute concentration of Methylene Blue C =5m, UV intensity =13.5W/m and ph=7. The reaction rate increases with the solute concentration of going up. However, when Ct is over certain value the increasing reaction rate becomes insignificant and there is an optimum Ct of 1. in the test. This is because the lower Ct reduces the formation of hydroxyl radicals and the higher Ct increases the UV light scatter by grains to decreases the photo-efficiency. The initial solute concentration of methylene blue in the treated solution also is a ey parameter for PCO process (Figure, =8, =5, ph=7, =13.5W/m and Ct=1.). The higher initial solute concentration the lower decomposition rate is. Otherwise, the lower initial solute concentration would be treated at a higher SES 1 Solar World Congress 1856

3 reaction speed. But the decomposition amount is less actually. n the practicing application the suitable initial solute concentration would be selected depend on the technique and economics. Concentration fo Methlene Blue(m ,=.19/min 1.,=.616/min 1.5,=.655/min.,=.673/min 3.,=.695/min 6 8 Concentration of Methylene Blue(m =.77/min =.616/min =.575/min =.9/min 6 8 Figure 3 PCO process with the different concentration of Figure PCO process with the different initial concentration of methylene blue Concentration of Methylene Blue(m ,=.557/min 65,=.58/min 8,=.616/min 95,=.635/min 6 8 Figure 5 PCO process with the different flow rate Concentrationg Methylene Blue(m ,=.635/min 15,=.63/min 5,=.616/min,=.595/min 6 8 Figure 6 PCO process with the different titled angle of reactor There are not significant effects for the flow rate and the angle in the test conditions (Figure 5-6, other test conditions were same as above). This is because the flow rate in the test is a quite low and fewer variables. But the reaction rate increases with the flow rate up and the angle down. f the flow rate is high the effects will be significant. The test for the effect of different initial solute ph was done at =8, =5, C =5m, =13.5W/m and the concentration of Ct=1.. The reaction rate was accelerated when the solute ph increased (Table 1). Table 1. Effects on PCO process with different initial ph of solution nitial ph (1-3 /min) SES 1 Solar World Congress 1857

4 . OUTDOOR EXPERMENTAL RESULTS AND DSCUSSON n order to study the performance of solar PCO process system an experimental rig (system ) was tested under the sunlight. The results are shown in Table -5. The methylene blue was decomposed much quicly with the increasing of sunlight intensity (Table ). This means that the higher UV intensity the more hydroxyl radicals are produced in the reaction. The same effect for the different solute concentration of as the indoor test was observed (Table 3). The reaction rate increases with the solute concentration of going up. The higher initial solute concentration of methylene blue resulted in the lower decomposition rate (Table ). The reaction rate increases with the flow rate up and the angle down (Table 5). These results agreed with that in the indoor experiments. Table. Solar PCO process with the flat plate reactor at the different solar intensity m Table 3. Solar PCO process with the flat plate reactor at the different concentration of m Table. Solar PCO process with the flat plate reactor at the different initial solute concentration of methylene blue m Table 5. Solar PCO process with the flat plate reactor at the different flow rate and the angle m CONCLUSON Solar photocatalytic oxidation (PCO) process with a Flat-plate Reactor for decolour was investigated in this study. The parameters that affect the radation performance, such as dosages of photocatalyst, initial concentration of reactive methylene blue, flow rate through the flat-plate reactor, solar UV radiation intensity and decolour efficiency of the solution have been investigated. The results showed that the solar PCO process with a Flat-plate Reactor can raded the methylene blue and decolour in methylene blue solution efficiently. Over long term, it could be a valuable tool in dealing with the hazardous waste problem. SES 1 Solar World Congress 1858

5 REFERENCES Ajona, J.. and A. Vidal (). The use of CPC collectors for detoxification of contaminated water: design, construction and preliminary results, Solar Energy 68, 19-. Danielle Roche and K. B. (). A preliminary investigation of colour removal from dyeing operation wastewater, WaterTECH conference, 9-13 April,, Sydney. Goswami, D. Y. (1995). Engineering of Solar Photocatalytic Detoxification and Disinfection Processes, Advances in Solar Energy, 1, Goswami, D. Y. (1997). A review of engineering developments of aqueous phase solar photocatalytic detoxification and disinfection processes. Journal of Solar Energy Engineering, 119, P.Wyness, J. F. K., D.Y. and Goswami (199). Performance of Non-concentrating solar photocatalytic oxidation reactors, Part : flat-plate configuration, Journal of Solar Energy Engineering, 116, -7. Wang, Y. (). Solar photocatalytic radation of eight commercial dyes in suspension, Water Research, 3(3), X. Z. (1996). Decolorization and bioradability of dyeing wastewater treatment by a -sensitized photooxidation process, water science and technology, 3(9), Y. M. Sloar and A. Majcen Le Marechal. (1998). Methods of Decoloration of Textile Wastewaters, Dyes and Pigments, 37, SES 1 Solar World Congress 1859

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