Performance of tio2 in photodegradation seafood wastewater - Luu Cam Luc

Journal of Science and Technology 54 (4B) (2016) 80-87 PERFORMANCE OF TiO2 IN PHOTODEGRADATION SEAFOOD WASTEWATER Luu Cam Loc1,2, Ha Cam Anh2, Nguyen Tri1, Nguyen Thi Thuy Van1, Ho Linh Da2, Hoang Chi Phu2, Vo Tan Luc2, Hoang Tien Cuong1, * 1Institute of Chemical Technology (VAST), 01 Mac Dinh Chi, Ho Chi Minh City 2HCMC University of Technology (VNU-HCM), 268 Ly Thuong Kiet, Ho Chi Minh City *Email: info@cte.com.vn Received: 15th August 2016; Accepted for publication: 10th November 2016 ABSTRACT In this work, photocatalysts TiO2-HT prepared by hydrothermal method and TiO2-P25 Degussa were characterized by Energy Dispersive X-Ray analysis (EDX), X-ray powder diffraction analysis (XRD), Raman Spectroscopy, BET surface area measurements, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and UV-Vis absorption spectroscopy and tested in degradation of recalcitrant organic pollutants in bio-treated seafood wastewater (COD > 80 mg/L). After 9 hours of photodegradation under UV-A irradiation, COD removal efficiency reached 85.6 % and 48.9 % on TiO2-P25 and TiO2 catalysts, respectively. COD values of seafood wastewater treated by photocatalysis met the standard discharge requirement - QCVN 11:2008 – level A (COD ≤ 50 mg/L). Keywords: photocatalysis, TiO2-HT, TiO2-P25 Degussa, seafood wastewater. 1. INTRODUCTION Nowadays, seafood processing has developed to become the major economic activity which contributes to integrate the local economy into the global one. According to the report of Vietnam Association of Seafood Exporters and Producers in 2015 [1], the robust growth of seafood processing not only forced the economic restructuring, poverty reduction, but also created the work for over 4 million employees. Furthermore, it plays an important role in national defence on marine area. From 2001 to 2015, products of seafood processing, which were distributed at local area, increased continuously from 277 thousands of tons (2001) to 680 thousands of tons (2010) with the rate of 10.5 %/year. Beside that, the exportation also developed both quality and quantity. At 2015, the export value reached 6.57 billion USD, the seafood products exported to 164 countries, in which, EU, America and Japan accounted for over 54 % proportion. Up to 2012, Vietnam had 568 seafood processing facilities. However, the development of seafood processing also harms the environment by discharging a large amount of wastewater. Performance of TiO2 in photodegradation of seafood wastewater 81 Seafood wastewater contains not only organic proteins and degradable lipids, but also an amount of surfactant which is used in the rinsing process of equipment and factory. According to our investigation, the major surfactant in wastewater is n-lauryl diethanol amine with its concentration of 35–300 μg/L. Hence, the wastewater discharge did not meet level B (COD ≤ 80 mg/L) QCVN 11:2008 if it only treated by biological method as many factories applying. Up to now, there are many methods being used to treat the polluted water such as adsorption, sedimentation, filtration, membrane, disinfection with clorua, etc. [2]. However, they do not eliminate effectively recalcitrant organic pollutants, badly, they may create the secondary toxic contaminants. While the other solutions have the tough weaknesses, the demand of a best treatment wastewater technology is necessary, so that, Advanced Oxidation Processes (AOPs) are attractive measures, in which, photocatalysis based on TiO2 is an outstanding candidate [2,3]. TiO2 can be synthesized by many methods such as chloride, sulfate, sol-gel method or hydrothermal treatment method, etc.[5-8], the last is one of the best ways to produce pure TiO2 with suitable particle size from the raw cheap TiO2 precursor, moreover, the particle size can be controlled by changing the reaction conditions such as the temperature, reactants, and the reaction procedure. On the other hand, for the ready to use photocatalyst, TiO2-P25 Dugussa, with the mixture of anatase and rutile, is evaluated as a good commercial catalyst which has high photocativity in photodegradation of recalcitrant organic compounds [4]. However, the previous literature just reported the performance of TiO2-P25 in model wastewater systems. To apply the photocatalyst in the real wastewater treatment, in this work, TiO2 synthesized by the hydrothermal treatment method from the raw cheap material was tested in photodegradation of recalcitrant organic contaminants in bio-treated wastewater from seafood processing factory to obtain reusable water. This will contribute to the sustainable development of seafood processing. Beside that, in comparison with commercial TiO2-P25, the relationship between the characterization of catalysts and their activity was emphasized. 2. EXPERIMENTAL In this work, the catalysts TiO2-P25 (Degussa, Merck) and TiO2 synthesized by hydrothermal treatment method (TiO2-HT) were investigated. The synthesis of TiO2-HT catalyst, which used the precursors TiO2.nH2O (Xilong, > 98 %), H2SO4 (Merck, 98 %), isopropanol (Merck, 99.8 %) and distilled two times water, was carried out with the following proceduce. 6 grams of TiO2.nH2O was dissolved in 300 mL of solution of H2SO4 and isopropanol (ratio of 1:2) at 40 oC with stirring for 12 hours. Then the obtained mixture was transfered into an autoclave to carry out the hydrothermal treatment at 250 oC for 5 hours without stirring. After that, the resulting powder was collected by filtraton and thoroughly washed with water and drying at room temperature. Finally, it was calcined at 450 oC for 2 hours (with the rate of 2 oC/min) to receive TiO2-HT. Furthermore, prior to using in reaction, both catalysts TiO2-HT and TiO2-P25 (Ti-P25) were calcined at 450 oC for 2 hours in air with the flowrate of 3 L/h. The physicochemical characteristics of catalysts (XRD, FTIR, BET, UV-Vis, SEM and TEM) were determined by methods described in our previous work [7]. The photoactivity of catalysts were tested for treatment wastewater sample of seafood processing factory (bio-treated, COD > 80 mg/L) with catalyst concentration of 1 g/L under UV- A irradiation with λ = 365 nm. The reaction system is decribled in Figure 1. The reaction was conducted with 250 mL wastewater sample/ batch, the conditions of reaction were inherited Lưu Cẩm Lộc et al 82 from the optimum condition of model wastewater in the previous work [9] as follows: stirring speed of 250 rpm, the temperature of 25 oC, initial pH of 7 and dissolved oxygen of 7.6 mg/L. Figure 1. Photocatalytic reaction system. 1-Circulation pump; 2-Cooling water tank; 3-Water pipeline; 4-Magnetic stirrer; 5-Reactor; 6-Thermometer; 7-Air pump; 8-Valve; 9-Flow meter; 10 -Air pipeline; 11-UV-LED lamps system; 12-UV-LED lamps controller (PC adaptable); 13-Liquid Cooling system; 14-Liquid coolant pipeline; 15-Electrical wire; 16-Sampling holes. The COD values of water sample before and after reaction were determined by bicrommat method according to ISO 6060:1989/TCVN 6491:1999 standard. 3. RESULTS AND DICUSSIONS 3.1. Physicochemical characterization IR spectra of both catalysts TiO2-HT and TiO2-P25 (Figure 2) indicates characteristic peaks at 3418–3420 cm-1 (stretching modes) referring to OH vibration of Ti-OH groups and 1635 cm-1 (bending modes) reflecting the hydroxyl groups of adsorbed water molecules on TiO2 surface. These peaks of sample TiO2-P25 exhibit a higher intensity in comparison with ones belonging to TiO2-HT demonstrating the higher OH-groups on surface of TiO2-P25 than that of TiO2-HT. Additionally, IR spectra also contains the peaks at 400–700 cm-1 that may be attributed to the vibration of Ti-O, specially, separated two individual peak in TiO2-HT spectra showing the vibration of Ti-O (ν = 490 cm-1) and Ti-O-Ti (ν = 700 cm-1) [10]. Figure 2. IR spectra of TiO2-HT (dashed line) and TiO2-P25 (full line). Figure 3. XRD patterns of TiO2-HT (a) and TiO2-P25 (b). Figure 4. Raman spectra of TiO2-HT (dashed line) and TiO2-P25 (full line). Performance of TiO2 in photodegradation of seafood wastewater 83 XRD spectra (Figure 3) shows that TiO2-HT and TiO2-P25 samples consisted anatase phase with main characteristic peak at 2θ = 25.3o; 38.3o; 49o; 54.3o; 55.7o and 62.6o; there is only characteristic peak of rutile (2θ = 27.5 o; 36.7o and 41.7o) in TiO2-P25 spectra that is no existence in TiO2-HT spectra. The difference can be explained that commercial catalyst P25 included both of anatase and rutile phase, whereas TiO2-HT catalyst contained only anatase phase. That result is consistent with Raman spectra (Figure 4). Particularly, the Raman characteristic peaks represent for the anatase phase at: 144, 398, 516 and 640 cm-1 in both spectra of TiO2-HT and TiO2-P25. While the peaks at 144 and 640 cm-1 are generated by the stretching vibration, the peaks at 398 and 516 cm-1 are related to the bending vibration of O-Ti-O. Furthermore, there is a appearance of additional peak referring to rutile phase in TiO2-P25 at 450 cm-1. Consequently, photocatalyst TiO2 prepared by hydrothermal method was activated under condition at 450 oC in 2 hours including only anatase phase. There are same conclusions in many works [7, 8]. The ratio of phase composition (anatase/rurile) and crystallite size were shown in Table 1. Table 1. Anatase/rutile ratio (A/R), crystallite size (d), pore size (dpor), pore volume (Vpor), BET surface area (SBET), light wavelength threshold (λ) and band gap energy (Eg) of TiO2-HTand TiO2-P25 catalysts. Catalyst A/R d, nm dpor, Å Vpor, m³/g SBET, m2/g λ, nm Eg, eV TiO2-HT 100 43.7 10.3 0.010 14.0 390 3.17 TiO2-P25 80/20 23.0 33.5 0.037 43.6 390 3.17 According to Table 1, the pore size and volume of TiO2-HT catalyst are smaller than those of Degussa TiO2-P25 sample, on the contrary, the crystallite size of TiO2-HT is higher. The morphologies of TiO2-HT and TiO2-P25 are illustrated by SEM images (Figure 5), the distribution of TiO2-P25 particles, which range from 30 to 40 nm, is more uniform than TiO2-HT (range from 30 − 200 nm) in particular. Besides, TEM images also show the shape and crystallite size of TiO2-HT samples with higher spherical particles and smaller porosity compared with another catalyst. As a consequence, TiO2-P25 has more than 3.1 times the specific surface area of TiO2-HT (Table 1). a) b) Figure 5. SEM images of TiO2-HT (a) and TiO2-P25 (b) samples. Lưu Cẩm Lộc et al 84 a) b) Figure 6. TEM images of TiO2-HT (a) and TiO2-P25 (b) catalysts. The curve on UV-Vis spectrum of TiO2- HT photocatalyst has a greater slope than that of TiO2-P25 (Figure 7) due to the different ratio of phase composition with both anatase and rurile (A/R = 80/20) or only anatase phase in TiO2-P25 and TiO2-HT catalysts respectively. Nevertheless, the bending point of the curve of two catalysts is similar to each other and approximately 390 nm leading to the band gap energy of 3.17 eV (Table 1) photoactivited under UV-A irradiation. This result proves again that the successful preparation of photocatalyst TiO2 by hydrothermal method achieves nanoparticles along with the properties of light wavelength threshold and band gap energy closed to that of commercial Degussa TiO2-P25. Figure 7. UV–Vis reflectance of TiO2-HT (dashed line) and TiO2-P25 (full line). 3.2. Evaluating the degradation efficiency of authentic wastewater by using photocatalysts The quality parameters of seafood wastewater before and after bio-treating were analyzed and show in Table 2. As can be seen from the table, after using mechanical, physicochemical and biological wastewater treatment methods, industrial wastewater discharge reached virtually level B, but COD value and coliform did not stable and unqualified. For coliform, it can be treated to qualified threshold via disinfection, but the process cannot eliminate the recalcitrant organic compounds in wastewater. If these contaminants accumulate in the environment, they can harm the health of living thing, even human, through the food chain. Therefore, using the traditional treating methods did not degrade effectively recalcitrant organic pollutants. So that, AOPs is promising solution to handle the problem by deep treating wastewater to obtain level A product. Performance of TiO2 in photodegradation of seafood wastewater 85 Table 2. Water quality parameters of industrial effluent. Parameter Unit Untreated water Bio-treated water QCVN 11:2008/ BTNMT (B) Method TSS mg/L 150 – 400 30 – 95 100 SMEWW 2540 D:2012 COD(*) mg/L 400 – 1800 40 – 120 80 TCVN 6491:1999 BOD5 mg/L 550 – 1200 10 – 50 50 SMEWW 5210 B:2012 Total nitrogen mg/L 40 – 70 15 – 30 60 TCVN 6624-2:2000 Total phosphorus mg/L 9-20 2 – 4 6 SMEWW 4500-P B&E:2012 Total oil and grease mg/L 3– 42.5 n.d. 20 SMEWW 5520 D:2012 N-NH4+ mg/L 26 – 31 5 – 20 20 SMEWW 4500 B&C:2012 Coliforms MPN/ 100mL 106– 109 10 – 105 5000 TCVN 6187-2:1996 Cl⁻ mg/L n.d. n.d. 2 TCVN 6194:1996 pH - 6.9 6.5 – 7.5 5.5 – 9.0 TCVN 6492:2011 n-LDEA μg/L 35 – 300 51 – 100 - HPLC n.d.: Not detected; (*)COD value depends on sampling time. In this work, the degradation efficiency of authentic seafood wastewater was evaluated by COD value. According to Table 3, COD value after alone photolysis process (in the absence of photocatalyst) decreased slightly from 90.5 mg/L to 87.8 mg/L (only 3 %), this result pointed out the presence of recalcitrant organic pollutants and the indispensable role of the catalyst in photocatalytic wastewater treatment. In additional, solution COD in adsorption process without UV illumination reached equilibrium at 40 minutes and stayed nearly unchanged thereafter demonstrating the significant role of UV irradiation to activate photocatalyst. As a result, there was 40 minutes pre-adsorption without UV illumination to start photocatalytic reaction. Table 3. COD degradation of authentic seafood wastewater during the adsorption (Cxt = 1 g/L, T = 25 oC, pH = 7, DO = 7.6 m/L) and photolysis process (λ = 365 nm, T = 25 oC, pH = 7, DO = 7.6 m/L). Process Reaction time (min) 0 10 15 20 40 50 60 Photolysis 90.5 90.4 89.4 90.1 88.4 87.9 87.8 Adsorption TiO2-HT 94.8 105.4 99.3 99.3 100.9 115.9 95.5 TiO2- P25 91.8 104.6 83.4 94.0 91 81.9 97.0 Lưu Cẩm Lộc et al 86 Figure 8. COD degradation of authentic seafood wastewater using TiO2-HT and TiO2-P25 photocatalysts (Cxt = 1 g/L, λ = 365 nm, T = 25 oC, pH = 7, DO = 7.6 m/L). The degradation efficiency of authentic seafood wastewater increased according to the rise of reaction time but this increasing became not considerable after 7 hours of reaction (Figure 8). After 7 hours of treatment, COD value of wastewater reached level A of the standard discharge requirement (COD < 50 mg/L) using TiO2-HT catalyst. Moreover, COD removal efficiency on TiO2-P25 and TiO2-HT catalysts attained 85.6 % and 48.9 % respectively after 12 hours reaction. Compared with TiO2-HT, photocatalyst TiO2-P25 showed higher COD degradation efficiency which can be explained by intrinsic properties of photocatalyst such as a higher surface area, smaller crystallite size and higher amount of OH-groups on catalyst surface (according to result above). On the other hand, TiO2-P25 sample contained a relevant phase content (anatase/rurile = 80/20) that rutile phase play a important role in to prevent electron-hole recombination, according to Anna et al [11]. However, TiO2-HT catalyst was synthesized from raw cheap material TiO2.nH2O for economic aspect and still employed completed decomposition of organic contaminants. 4. CONCLUSIONS TiO2 synthesized by hydrothermal treatment method from raw cheap precursor TiO2.nH2O had nanosize, moreover, its band gap energy was equivalent to TiO2-P25 that leads to the same light wavelength threshold. Under irradiation of UV-A light source, TiO2-P25 exhibited the higher photoactivity than TiO2-HT due to its larger surface area, smaller particle size, more number of OH groups on the catalyst’s surface and its suitable phase content. However, after 7 hours of treatment with TiO2-HT, the quality of wastewater discharge also met level A, QCVN 11:2008/ BTNMT and could be reusable. Acknowledgement. This work was supported by 7 FP -the main supporter for the project “Photo-catalytic materials for the destruction of recalcitrant organic industrial waste”. REFERENCES 1. 2. Chong M. N., Jin B., Chow C. W. K., and Saint C. - Recent developments in photocatalytic water treatment technology: a review, Water Research 44 (2010) 2997- 3027. Performance of TiO2 in photodegradation of seafood wastewater 87 3. Ana R. Ribeiro, Olga C. Nunes, Manuel F.R. Pereira, Adrián M.T. Silva - An overview on the advanced oxidation processes applied for the treatment of water pollutants defined in the recently launched Directive 2013/39/EU, Environment International 75 (2015) 33-51. 4. Ohtani B., Mahaney O. O. P., Li D., and Abe R. - What is Degussa (Evonik) P25? Crystalline composition analysis, reconstruction from isolated pure particles and photocatalytic activity test, Journal of photochemistry and photobiology A: Chemistry 216 (2010) 179–182. 5. Kneko M., Okura I. - Photocatalysis: Science and Technology, Springer Berlin Heidelberg, 2002. 6. Nguyen Quoc Tuan - Advanced oxidation of p-xylene by modified TiO2, Doctoral Dissertation, Institute Of Chemistry, 2010 (in Vietnamese). 7. Cam Loc Luu, Quoc Tuan Nguyen, Si Thoang Ho, Tri Nguyen - Characterization of the thin layer photocatalysts TiO2 and V2O5- and Fe2O3- doped TiO2 prepared by the sol–gel method, Advances in Natural Sciences: Nanoscience and Nanotechnology 4 (2013) 035003. 8. Calza P., Pelizzetti E., Mogyorosi K., Kun R., and Dekany I. - Size dependent photocatalytic activity of hydrothermally crystallized titania nanoparticles on poorly adsorbing phenol in absence and presence of flouride ion, Applied Catalysis B: Environmental 72 (2007) 314-321. 9. Do Tran Thien Loc - Treatment seafood waste water by using TiO2 photocatalyst, Master's Thesis, University of Science, 2016 (in Vietnamese). 10. Wang G., Xu L., Zhang J., Yin T., and Han D.- Enhanced photocatalytic activity of TiO2 powders (P25) via calcination treatment, International Journal of Photoenergy 50 (2012) 1-9. 11. Anna D., Hurum D. C., Agrios A. G., and Gray K. A. - Explaining the enhanced photocatalytic activity of degussa P25 mixed-phase TiO2 using EPR, J. Phys. Chem. B 107 (2012) 4545-4549.