Oil refinery wastewater treatment using physicochemical, Fenton and Photo-Fenton oxidation processes

This art icle was downloaded by: [ Maha A. Tony] On: 10 February 2012, At : 06: 24 Publisher: Taylor & Francis I nform a Lt d Regist ered in England and Wales Regist ered Num ber: 1072954 Regist ered office: Mort im er House, 37- 41 Mort im er St reet , London W1T 3JH, UK Journal of Environmental Science and Health, Part A: Toxic/ Hazardous Substances and Environmental Engineering Publicat ion det ails, including inst ruct ions f or aut hors and subscript ion inf ormat ion: ht t p: / / www. t andf online. com/ loi/ lesa20 Oil refinery wastewater treatment using physicochemical, Fenton and Photo-Fenton oxidation processes Maha A. Tony a , Pat rick J. Purcell b & Yaqian Zhao b a Basic Engineering Science Depart ment , Facult y of Engineering, Shbin El-Koum, Minouf iya Universit y, Minouf iya, Egypt b Cent re f or Wat er Resources Research, School of Civil, St ruct ural and Environment al Engineering, Universit y College Dublin, Newst ead, Belf ield, Dublin, Ireland Available online: 09 Feb 2012 To cite this article: Maha A. Tony, Pat rick J. Purcell & Yaqian Zhao (2012): Oil ref inery wast ewat er t reat ment using physicochemical, Fent on and Phot o-Fent on oxidat ion processes, Journal of Environment al Science and Healt h, Part A: Toxic/ Hazardous Subst ances and Environment al Engineering, 47: 3, 435-440 To link to this article: ht t p: / / dx. doi. org/ 10. 1080/ 10934529. 2012. 646136 PLEASE SCROLL DOWN FOR ARTI CLE Full t erm s and condit ions of use: ht t p: / / www.t andfonline.com / page/ t erm s- and- condit ions This art icle m ay be used for research, t eaching, and privat e st udy purposes. Any subst ant ial or syst em at ic reproduct ion, redist ribut ion, reselling, loan, sub- licensing, syst em at ic supply, or dist ribut ion in any form t o anyone is expressly forbidden. The publisher does not give any warrant y express or im plied or m ake any represent at ion t hat t he cont ent s will be com plet e or accurat e or up t o dat e. The accuracy of any inst ruct ions, form ulae, and drug doses should be independent ly verified wit h prim ary sources. The publisher shall not be liable for any loss, act ions, claim s, proceedings, dem and, or cost s or dam ages what soever or howsoever caused arising direct ly or indirect ly in connect ion wit h or arising out of t he use of t his m at erial. Journal of Environmental Science and Health, Part A (2012) 47, 435–440 C Taylor & Francis Group, LLC Copyright
ISSN: 1093-4529 (Print); 1532-4117 (Online) DOI: 10.1080/10934529.2012.646136 Oil refinery wastewater treatment using physicochemical, Fenton and Photo-Fenton oxidation processes MAHA A. TONY1, PATRICK J. PURCELL2 and YAQIAN ZHAO2 1 Basic Engineering Science Department, Faculty of Engineering, Shbin El-Koum, Minoufiya University, Minoufiya, Egypt Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin, Newstead, Belfield, Dublin, Ireland Downloaded by [Maha A. Tony] at 06:24 10 February 2012 2 The objective of this study was to investigate the application of advanced oxidation processes (AOPs) to the treatment of wastewaters contaminated with hydrocarbon oil. Three different oil-contaminated wastewaters were examined and compared: (i) a ‘real’ hydrocarbon wastewater collected from an oil refinery (Conoco-Phillips Whitegate refinery, County Cork, Ireland); (ii) a ‘real’ hydrocarbon wastewater collected from a car-wash facility located at a petroleum filling station; and (iii) a ‘synthetic’ hydrocarbon wastewater generated by emulsifying diesel oil and water. The AOPs investigated were Fe2+/H2 O2 (Fenton’s reagent), Fe2+/H2 O2 /UV (PhotoFenton’s reagent) which may be used as an alternative to, or in conjunction with, conventional treatment techniques. Laboratory-scale batch and continuous-flow experiments were undertaken. The photo-Fenton parametric concentrations to maximize COD removal were optimized: pH = 3, H2 O2 = 400 mg/L, and Fe2+ = 40 mg/L. In the case of the oil-refinery wastewater, photo-Fenton treatment achieved approximately 50% COD removal and, when preceded by physicochemical treatment, the percentage removal increased to approximately 75%. Keywords: Oil refinery wastewater, hydrocarbons degradation, photocatalysis, Fenton’s reagent, Chemical oxygen demand (COD). Introduction Crude oil is transformed into petroleum and other useful by-products through refining processes. During those processes large quantities of water are consumed and there is therefore a corresponding quantity of wastewater produced which consists of cooling water, process water, storm water, and sewage. This wastewater may, however, contain some oil because of the origin of the wastewater.[1] The fraction of oil entrained in the wastewater depends on the oil processing undertaken. Coelho et al.[2] reported that the quantity of water used in the oil refinery processing industry ranges from 0.4 to 1.6 times the volume of processed oil and this wastewater may, if untreated, cause serious damage to the environment. The development of treatment processes appropriate to wastewaters contaminated with oil is clearly very important. Typically, wastewaters generated in refinery processes are treated on-site and then discharged to publicly owned treatment works or discharged to an adjacent receiving water. [3] Address correspondence to Maha A. Tony, Basic Engineering Science Department, Faculty of Engineering, Shbin El-Koum, Minoufiya University, Minoufiya, Egypt; E-mail: maha tony1 @yahoo.com Received May 31, 2011. Conventional chemical and physical treatment methods can be applied for treating these kinds of wastewaters. Petroleum refineries typically utilize primary and secondary wastewater treatment. Primary wastewater treatment consists of oil-water separation using physical methods which include the use of sedimentation or dissolved air flotation. Chemicals, such as ferric hydroxide or aluminum hydroxide, can be used to coagulate impurities into sludge which can be more easily removed.[1,3] However, these processes result in concentrated sludges which require further processing and disposal. In addition, conventional treatment processes have difficulty in fully removing emulsified oil or small oil droplets. [1, 4–7 ] Advanced oxidation processes (AOPs) have been investigated for the oil-contaminated wastewater treatment as an alternative to conventional treatment techniques. AOPs are characterized by the use of highly reactive intermediates, hydroxyl radicals (·OH), which attack the organic pollutants in the wastewater and mineralize them.[8–12] Such processes include UV [2]; O3 /H2 O2 [1]; O3 /UV [1, 2]; TiO2 photo-catalysis[13–15] and Fenton and photo-Fenton processes [16]. In the present investigation, UV-light and Fenton’s reagent were used to treat an oil process wastewater at an oil refinery. The photo-Fenton kinetics were investigated and the process was compared with conventional 436 Tony et al. Table 1. Properties of wastewaters used in this study. Parameter Oil-refinery wastewater Oil-water emulsion Car-wash wastewater ∗ ∗ ∗∗ COD (mg-COD/L) SS (mg/L) pH Turbidity (NTU) Colour (Pt Co) 364 1500 82 105 — 55 7.6 8.0 8.2 42 49 12 946 987 271 Chemical Oxygen Demand, ∗∗ Suspended Solids. treatment methods. In addition, the treatment performance of two different types of oil-contaminated wastewaters with Fenton’s reagent was compared with that of oil refinery wastewater. Downloaded by [Maha A. Tony] at 06:24 10 February 2012 Materials and methods Materials Samples of the raw wastewater were collected from a petroleum refinery at Whitegate, County Cork, Ireland. For the purpose of comparison with the refinery wastewater, two other kinds of wastewaters were compared: a synthetic oil-water emulsion and car-wash wastewater sourced from a petroleum filling station. The synthetic model oil-water emulsion was prepared using commercial automotive diesel oil and chemical emulsifier mixed in distilled water and the resulting mixture was stirred as described in our previous work. [6] The principal parameters for these wastewaters are listed in Table 1. A solution of Fe2+ (prepared from ferrous chloride tetrahydrate (FeCl2 .4H2 O)) and hydrogen peroxide (30%, by weight) was used in the experiments as the Fenton’s reagent for hydroxyl radical generation. Sulfuric acid and sodium hydroxide were used to adjust the pH to the desired values. Procedures A schematic of the experimental setup is illustrated in Figure 1. A 200 mL aliquot of the wastewater sample was subjected to magnetic stirring, following the addition of Fig. 1. Schematic diagram of the experimental setup. Fenton’s reagent. The UV light was provided by a high intensity 254 nm UV grid lamp, manufactured by UVP Inc. (model R-52). The physicochemical treatment of the oil refinery wastewater undertaken in this laboratory study includes conventional physical separation processes in conjunction with the Fenton and photo-Fenton processes. Following the addition of Fenton’s reagent, the wastewater was subjected to 10 minutes of rapid mixing followed by 30 minutes of slow mixing to promote reaction coagulation and flocculation, respectively. Analytical determinations The wastewater substrate concentration was measured by its Chemical Oxygen Demand (COD) using a HACH analyser (model HACH DR-2400) following the standard procedure of sample digestion.[17] In addition, the suspended solids (SS) and the colour were determined for the raw wastewater using the HACH analyser. The turbidity of the wastewater was also measured using a HACH 2100N IS Turbidimeter (USA). The pH of the wastewater was measured using a digital pH-meter (model PHM62 Radiometer, Copenhagen). Results and discussion Effect of reaction time To find the reaction time required to reach a steady state, experiments were performed over a 160 minute period for two different treatments: (a) Fenton’s reagent and (b) photoFenton reagent at the following operating parameters pH = 7.6; [H2 O2 ]o = 400 mg/L; [Fe2+]o = 40 mg/L. The COD of the wastewater was monitored continuously during the course of the reaction. COD removal efficiency increased with increasing reaction time, as illustrated in Figure 2, but after about 80 minutes, the rate of COD removal significantly diminished. Kim et al.[18]; Moraes, et al.[19]; Galavo et al.[16] and Tony et al.[6] recorded a similar result. These findings may be explained by the production of highly reactive intermediates (hydroxyl radicals) which primarily influence the reaction kinetics during the first phase of the reaction. Thereafter, the reaction rate diminished as the hydrogen peroxide, which is the primary source for the generation of the hydroxyl radicals, was consumed. Examination of Figure 2 shows that UV light in conjunction with Fenton’s reagent (photo-Fenton) is clearly more 437 Oil refinery wastewater treatment Figure 3, the COD removal increased as the H2 O2 concentration increased from 100 to 400 mg/L and decreased thereafter. Clearly, the H2 O2 concentration is a key factor that significantly influences the reaction kinetics since the number of OH radicals generated in the photo-Fenton reaction is directly related to the H2 O2 concentration. However, when the concentration of H2 O2 exceeds the optimum value, the reaction rates decreased as a result of the socalled scavenging effect of excess of H2 O2 reacting with .OH, thereby decreasing the .OH available to degrade the wastewater organics. [20–22]. 1.05 1 0.95 COD/CODo 0.9 0.85 0.8 0.75 0.7 Fenton 0.65 photo-Fenton 0 20 40 60 80 100 Time (minutes) 120 140 Effect of Fe2+ 160 Fig. 2. Effect of reaction time for Fenton and photo-Fenton treatment (operating parameter: pH = 7.6; [H2 O2 ]o = 400 mg/L; [Fe2+]o = 40 mg/L). effective in the COD degradation than Fenton’s reagent on its own. This observation implies that the UV photolysis generated more reaction hydroxyl intermediates, which resulted in enhanced degradation of the pollutants. Based on these results, further experiments were performed to examine the effects of the Fenton’s reagent operating parameters, as will be described hereunder. Effect of H2 O2 To determine the optimum H2 O2 concentration to treat the oil refinery wastewater using Fenton process, the H2 O2 dose was varied from 100 to 800 mg/L. As illustrated in To determine the optimum Fe2+ concentration for the mineralization of the refinery wastewater, the wastewater was dosed with Fe2+ concentration in the range of 10 to 80 mg/L, the H2 O2 concentration kept at the optimum value of 400 mg/L. As illustrated in Figure 4, the optimum Fe2+ concentration was found to be 40 mg/L which resulted in 15% removal after approximately 2 hours’ reaction time. Increasing the Fe2+ concentration above the optimal value adversely impacted on the reaction kinetics and resulted in additional iron precipitation, one of the disadvantages of the Fenton process. Similar observations were made in earlier studies by Kositzi et al. [14] and Tony et al. [6]. Effect of pH The pH significantly affects the Fenton process since the process has a preferred pH range for optimal performance. The pH affects the activity of both the speciation of iron, and hydrogen peroxide decomposition. Figure 5 shows the effect of pH on the COD removal efficiencies. Examination 1.02 1 1.05 100 mg/L 400 mg/L 10 mg/L 20 mg/L 40 mg/L 80 mg/L 0.98 200 mg/L 800 mg/L 0.96 COD/CODo 1 COD/CODo Downloaded by [Maha A. Tony] at 06:24 10 February 2012 0.6 0.95 0.9 0.94 0.92 0.9 0.88 0.86 0.85 0.84 0.8 0 20 40 60 80 100 Time (minutes) 120 140 0 20 40 60 80 100 Time (minutes) 120 140 160 160 Fig. 3. Effect of hydrogen peroxide (operating parameter: pH = 7.6; [Fe2+]o = 40 mg/L). Fig. 4. Effect of Fe2+ (operating parameter: pH = 7.6; [H2 O2 ]o = 400 mg/L). 438 Tony et al. are shown in Figure 6. Examination of Figure 6 shows that, as expected, COD removal efficiency improved with increasing HRT. The percentage COD removal was in the range of 35–45% at steady state, as shown in Figure 6. COD removals greater than 45% were attained (steady-state values) when HRT exceeded 1000 minutes. The results presented above are in accordance with the published findings of Coelho et al. [2], who investigated the photo-Fenton treatment of sour wastewater. A reactor design with better flow-though characteristics, coupled with a more efficient UV radiation system, are likely to improve the process performance, and, thus, higher hydrocarbon removal rates. 1.2 1 COD/CODo 0.8 0.6 0.4 0.2 3 5 7.6 0 20 40 60 80 100 Time (minutes) 120 140 160 Effect of Fenton’s reagent on different wastewater effluents Fig. 5. Effect of pH (operating parameters: [H2 O2 ]o = 400 mg/L; [Fe2+]o = 40 mg/L). of the figure shows that the removal efficiency increases with decreasing pH, the optimal pH being 3.0. These observations are in accordance with those reported by Paterlini and Nogueira [23] and Kang and Hwang [24] who found that an acidic pH (2.5–4) was optimum for the photo-Fenton process. Hence, the optimal pH for the treatment of the oil refinery wastewater is 3.0, at which OH radical production is maximized, resulting in a reduction in the wastewater COD by approximately 50%. Effect of continuous-flow To access the COD removal efficiencies under continuous flow operating conditions, the wastewater was pumped through the bench-scale reactor shown in Figure 1. The COD removal efficiencies, from start-up until steady state was reached for various hydraulic residence times (HRT) In this part of the study, experiments were undertaken to compare the performance of the photo-Fenton’s reagent in respect of three types of wastewater polluted with hydrocarbons: (a) car-wash wastewater; (b) car-wash wastewater augmented with 100 mL/L diesel oil; (c) synthetic oil-water emulsion wastewater. The experimental conditions are based on earlier work by the authors, in which the effect of the main process variables was examined.[6, 7] The results of these earlier studies were used as a guide for the choice of the H2 O2 and Fe2+ concentration to be adopted in the present study for the treatment of a car-wash wastewater and a synthetic oil wastewater emulsion. The photo-Fenton experiments were performed simultaneously on each of the wastewaters. During the experiments, the COD removal increased with reaction time, as illustrated in Figure 7. Removal rates 1.4 1.1 1 HRT 40 min 80 min 200 min 1000 min Oil refinery wastewater car-wash wastewater car-wash wastewater augmented with diesel oil synthetic oil water emulsion wastewater 1.2 1 COD/CODo 0.9 COD/COD o Downloaded by [Maha A. Tony] at 06:24 10 February 2012 0 0.8 0.7 0.8 0.6 0.6 0.4 0.5 0.2 0.4 0 50 100 150 200 Time (minutes) 250 300 350 Fig. 6. COD removal against time for continuous flow operation at different hydraulic residence times (HRT): Experimental conditions pH = 3; [H2 O2 ]o = 400 mg/L; [Fe2+]o = 40 mg/L. 0 0 20 40 60 80 100 Time (minutes) 120 140 160 Fig. 7. Effect of photo-Fenton’s reagent on different types of wastewater effluent: Experimental conditions (operating parameters: pH = 3; [H2 O2 ]o = 400 mg/L; [Fe2+]o = 40 mg/L). 439 Oil refinery wastewater treatment of about 66% for the car-wash wastewater, 50% for the car-wash wastewater augmented with diesel oil and 43% for the synthetic oil-water emulsion were recorded in the experiments undertaken. The synthetic oil-water was the most difficult wastewater to degrade and this finding is most likely attributable to the difficulty in degrading the emulsion contained in the wastewater. Clearly, the concentration and the type of organic compounds contained in the wastewater have a significant effect on the reaction kinetics. These results are in accordance with previous observations concerning the degradation rate of organic contaminants by photo-Fenton processes. [25, 26] Downloaded by [Maha A. Tony] at 06:24 10 February 2012 Effect of combined physicochemical treatment The investigation of pre-treating the wastewaters prior to the application of the photo-Fenton reagent is described next. The two-stage process consists of physicochemical pre-treatment of oil refinery wastewater followed by photoFenton treatment for hydroxyl radical production. The purpose of combined physical and chemical treatment is to maximize process performance at minimum cost. A schematic of the laboratory-scale treatment sequence is presented in Figure 8. As illustrated in the figure, the process sequence consists of coagulation, flocculation, sedimentation, filtration and photo-Fenton treatment. Following pretreatment, the wastewater was subjected to photo-Fenton treatment. Physical treatment processes merely transfer pollutants from one phase to another without mineralizing them. Physicochemical processes can eliminate both suspended and dissolved solids. Therefore, better removal rates can be obtained with physical separation followed by the Fenton treatment than treatment with Fenton’s reagent alone. Figure 9 illustrates the COD removal efficiencies for the oil-refinery wastewater for two different pre-treatments: (a) coagulation, flocculation, sedimentation; (b) coagulation, flocculation, sedimentation and filtration. In the former case, a 61% COD removal efficiency was achieved while in the latter case a 69% COD removal efficiency was achieved after 160 minutes. In the oxidation process, the contaminants are treated with a combination of hydrogen peroxide and ferrous chloride (Fenton’s reagent) and artificially irradiated with ultraviolet light. Optimal conditions for Fenton’s reagent were established and the pH was adjusted to 3. The highest percentage COD removal achieved was 75%, which occurred with pre-treatment including filtration followed by Fenton treatment. When the waste was treated with Fenton’s reagent alone, only 50% COD removal was achieved and when preceded by physicochemical treatment without filtration 64% COD was removed. Hydrogen peroxide Ferrous chloride pH adjusting agent pH Influent wastewater Solid liquid separation tank Coagulation Flocculation Filtration Magnetic stirrers Fenton process U.V. lamp Effluent wastewater Settling (1 hr) Magnetic stirrer Photo oxidation Fig. 8. Schematic laboratory physicochemical treatment sequence for oil refinery wastewater. 440 Tony et al. 1.2 (a) without filtration (b) with filtration 1 Physical treatment Fenton oxidation COD/CODo 0.8 0.6 0.4 0.2 0 0 100 200 300 400 500 600 700 800 Downloaded by [Maha A. Tony] at 06:24 10 February 2012 Time (minutes) Fig. 9. Effect of physiochemical treatment processes followed by Fenton oxidation. Conclusions Two industrial wastewaters containing hydrocarbons (an oil-refinery wastewater and a car-wash wastewater) were subjected to laboratory studies to investigate photo-Fenton treatment of the wastewaters. Because the degradation rate by Fenton’s reagent depends on the concentration of Fe2+, H2 O2 and pH, the optimal conditions were applied to maximize COD removal. The laboratory-scale experimental results show that photo-Fenton oxidation is an effective treatment process for industrial wastewater containing hydrocarbons. The results show that approximately 50% of the COD of the wastewater was degraded in a reaction time of 1.5 hours. When the photo-Fenton treatment was combined with physicochemical pre-treatment, the percentage COD removal was increased to approximately 75%. Acknowledgment The authors wish to acknowledge the co-operation of the ConocoPhillips Whitegate Refinery Ltd., Whitegate, County Cork, Ireland for providing wastewater samples. 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