Photocatalytic treatment of spent caustic wastewater in petrochemical industries

Document Type : Research Paper


Faculty of Chemical, Gas and Petroleum Engineering, Semnan University, Semnan, Iran


In this study, the photocatalytic method was used for treating the spent caustic in the wastewater of Olefin units used in petrochemical industries which contain large amounts of total dissolved solids (TDS). By using the synthetic photocatalyst of suspended titanium dioxide and measuring the chemical oxygen demand (COD) which was reduced in the photocatalyst (lbc) process, the values of COD were modeled and evaluated by means of the Box-Behnken (BBD) and the artificial neural network (ANN) using experimental tests in a double-cylindrical-shell photo reactor. According to the applied calculations, it was found that the artificial neural network was a more suitable method than the experimental design in modeling and forecasting the amount of COD removal. The modeling employed in this research showed that increasing the concentration of the photocatalyst in a state of neutral pH enhanced the COD removal up to the optimal amount of 1.31 g/L without restrictions and 2 g/L with restrictions at the rate of 81% and 79%, respectively. In addition, the study of the parameter effects including oxidizer amount, aeration rate, pH, and the amount of loaded catalyst indicated that all factors except pH  had a positive effect on the model; furthermore, if the interactions were neglected, the COD removal efficiency would increase by increasing each of these factors (except pH). In addition, there was no interaction between the aeration and the concentration of the photocatalyst, and the acidic pH was more suitable at low concentrations of the photocatalyst. Besides that, by increasing the pH, the efficiency of removal was reduced when the oxidant was at its low level. The results showed that photolysis and adsorption adoptions had a very small effect on the efficiency of the removal of COD compared to the photocatalyst adoptions, and it was insignificant. In addition, the photocatalytic method had an acceptable capacity for removing the phenol in the wastewater sample, whereas it was inefficient in reducing the sulfide solution in the wastewater. 


Main Subjects

[1] De Graaff, M., Bijmans, M. F., Abbas, B., Euverink, G. J., Muyzer, G., Janssen, A. J. (2011). Biological treatment of refinery spent caustics under halo-alkaline conditions. Bioresource technology, 102(15), 7257-7264.
[2] Kumfer, B., Felch, C., Maugans, C. (2010, March). Wet air oxidation treatment of spent caustic in petroleum refineries. In national petroleum refiners association conference, Phoenix, Arizona state (Vol. 23).
[3] Carlos, T. M. S., Maugans, C. B. (2000, September). Wet air oxidation of refinery spent caustic: a refinery case study. In NPRA conference, San Antonio, TX.
[4] Sheu, S. H., Weng, H. S. (2001). Treatment of olefin plant spent caustic by combination of neutralization and Fenton reaction. Water research, 35(8), 2017-2021.
[5] Rodriguez, N., Hansen, H. K., Nunez, P., Guzman, J. (2008). Spent caustic oxidation using electro-generated Fenton's reagent in a batch reactor. Journal of environmental science and health Part A, 43(8), 952-960.
[6] Nunez, P., Hansen, H. K., Rodriguez, N., Guzman, J., Gutierrez, C. (2009). Electrochemical generation of Fenton's reagent to treat spent caustic wastewater. Separation science and technology, 44(10), 2223-2233.
[7] Yu, Z. Z., Sun, D. Z., Li, C. H., Shi, P. F., Duan, X. D., Sun, G. R., Liu, J. X. (2003). UV-catalytic treatment of spent caustic from ethene plant with hydrogen peroxide and ozone oxidation. Journal of environmental sciences (China), 16(2), 272-275.
[8] Hawari, A., Ramadan, H., Abu-Reesh, I., Ouederni, M. (2015). A comparative study of the treatment of ethylene plant spent caustic by neutralization and classical and advanced oxidation. Journal of environmental management, 151, 105-112.
[9] Abdulah, S. S., Hassan, M. A., Noor, Z. Z., Aris, A. (2011, September). Optimization of photo-Fenton oxidation of sulfidic spent caustic by using response surface methodology. In national postgraduate conference (NPC), 2011 (pp. 1-7). IEEE.
[10] Chen, C. (2013). Wet air oxidation and catalytic wet air oxidation for refinery spent caustics degradation. Journal of the chemical Ssociety of Pakistan, 35(2), 244-250.
[11] Alaiezadeh,M.(2015).Spent caustic wastewater treatment with electrical coagulation method. The 1st international conference oil, gas, petrochemical and power plant.
[12] Montgomery,D.(2012).Design and Analysis of Experiments.6th ed.,John Wiley and Sons.
[13] Haykin,S.(2008).Neural Networks: A Comprehensive Foundation.4th ed.,Prentice Hall PTR.
[14] Rehman, S., Ullah, R., Butt, A. M., Gohar, N. D. (2009). Strategies of making TiO2 and ZnO visible light active. Journal of hazardous materials, 170(2), 560-569.
[15] Rivera‐Utrilla, J., Bautista‐Toledo, I., Ferro‐García, M. A., Moreno‐Castilla, C. (2001). Activated carbon surface modifications by adsorption of bacteria and their effect on aqueous lead adsorption. Journal of chemical technology and biotechnology, 76(12), 1209-1215.
[16] Standard methods for the examination of water and wastewater. (2005). in American Public Health Association (APHA):Washington, DC, USA, W.E. Federation and A.P.H. Association,Editors.
[17] Gaya, U. I., Abdullah, A. H. (2008). Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: a review of fundamentals, progress and problems. Journal of photochemistry and photobiology C: Photochemistry reviews, 9(1), 1-12.
[18] Nelofer, R., Ramanan, R. N., Rahman, R. N. Z. R. A., Basri, M., Ariff, A. B. (2012). Comparison of the estimation capabilities of response surface methodology and artificial neural network for the optimization of recombinant lipase production by E. coli BL21. Journal of industrial microbiology and biotechnology, 39(2), 243-254.