This is an open access article under the CC BY license: Al-Khwarizmi Engineering Journal Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, June, (2023) P. P. 52- 67 Treatment of Petroleum Refinery Wastewater by Sono Fenton Process Utilizing the in-Situ Generated Hydrogen Peroxide Marwa M. Jiad* Ali H. Abbar** *,**Department of Biochemical Engineering/ Al-Khwarizmi College of Engineering/ University of Baghdad/ Baghdad/ Iraq *Email: Marwa.jeyad2205m@kecbu.uobaghdad.edu.iq **Email: ali.abbar@kecbu.uobaghdad.edu.iq (Received 30 January 2022; accepted 26 April 2023) https://doi.org/10.22153/kej.2023.04.002 Abstract Combining ultrasonic irradiation and the Fenton process as a sono-Fenton process, the chemical oxygen demand (COD) in refinery wastewater was successfully eliminated using response surface methodology (RSM) with central composite design (CCD). The impact of two main influential operational parameters (iron dosage and reaction time) on the COD removal from wastewater generated by an Iraqi petroleum refinery facility was explored. Removal of 85.81% was attained under the optimal conditions of 21 minutes and 0.289 mM of Fe2+ concentration. Additionally, the results revealed that the concentration of Fe2+ has the highest effect on the COD elimination, followed by reaction time. The high R2 value (96.40%) validated the strong fit of the model equation and the successful adopting RSM in the treatment of wastewaters from petroleum refineries. Furthermore, a comparison among sono-Fenton, sono-Fenton with addition of 𝐻2𝑂2 externally, classical Fenton and sonolysis processes showed that the combined process of sono-Fenton is better than individual processes and the external addition of 𝐻2𝑂2 . Keywords: COD removal, Hybrid processes, Petroleum refinery wastewater, Hybrid processes, Sono-Fenton; Sonolysis, Response surface methodology. 1. Introduction Water is vital to life because it is a necessity for all species. The rapid economic and industrial expansion has facilitated rapid population growth and development [1]. The world is experiencing industry expansion and growth using different industrial methods [2]. Continuously producing massive volumes of wastewater at high rates is an environmental issue. These are often discarded without effective management and treatment [3, 4]. From an economic growth standpoint, petroleum refineries and industries are massively important [5]. Between 2010 and 2017, OPEC liquids rose to an average of 1.9 to 1.8 mb/d, with a significant contribution from Iraq (millions of barrels daily) [6]. There are more than 15 refineries in Iraq, including the refineries in the Kurdistan province, and the refining total amounts to more than 1 million barrels per day [6]. How to dispose of this wastewater poses a challenge for petroleum refineries. Petroleum industry wastewater comprises several organic and inorganic pollutants, sulfides, and heavy metals [7]. Petroleum industry activities, such as oil production, oil refining, transportation, and storage, generate vast quantities of environmental and human health dangerous compounds [6]. Various physical, chemical, and biological techniques were utilized to treat wastewater the petroleum sector creates [8]. However, the bulk of these techniques are not mailto:Marwa.jeyad2205m@kecbu.uobaghdad.edu.iq mailto:ali.abbar@kecbu.uobaghdad.edu.iq https://doi.org/10.22153/kej.2023.04.002 Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 53 suggested for separating the various groups of chemicals and are best suited to meet the specific treatment needs of each application [9]. Consequently, there is an immediate need to develop effective and environmentally friendly technologies for cleaning contaminated waters from petroleum refineries and decreasing or eliminating contaminants. In the 1980s, advanced oxidation processes (AOPs) were first found for the treatment of drinking water by Glaze et al. (1987) and were later extensively studied for the treatment of various wastewaters [10]. During the AOP treatment of wastewater, adequate hydroxyl radicals (OH•) or sulfate radicals (S𝑂4•) are generated to remove refractory organic matters, trace organic contaminants, or certain inorganic pollutants or to increase wastewater bio- degradability as a pre-treatment prior to a subsequent biological treatment [11, 12]. Multiple types of AOPs rely on the in-situ formation of OH• radicals via chemical, photo-chemical, sono- chemical, or electro-chemical reactions. Ultrasound is a superior method of AOPs, in which water molecules break up and release OH• due to high-frequency acoustic cavitation. After the generation of OH•, the hydroxyl radicals attack the organic pollutant to degrade it (Eq.1 and Eq.2) [13]. Over the last few years, ultrasound has been widely used to remove/degrade organic pollutants from water/wastewater [13]. H2O+ ))) → OH • + H • … (1) Organic pollutant + OH • → CO2 + H2O …(2) Where:- ))) denotes to the ultrasound waves. Sono-lysis creates acoustic cavitation, which involves producing and developing high-energy microbubbles when subjected to periodic pressure. When these bubbles rupture, an increase in temperature (5000 K) and pressure (500 bar) accelerates the dissociation of hazardous chemicals [14]. However, water sono-lysis has several drawbacks, including insufficient OH• production, which results in a lower degradation efficiency of organic pollutants [15]. Consequently, several studies have been conducted to combine sono- lysis with other AOPs to improve the overall efficacy of organic pollutant degradation [15-18]. The Fenton method, which uses a mixture of soluble iron (II) salt and hydrogen peroxide (Fenton's reagent) to degrade and eliminate refractory organic contaminants, is the oldest and most common chemical AOP (Eq. 3) [19]. Fe2+ + H2O2 → Fe 3+ + OH− + OH • …(3) The Fenton method is favoured among AOPs because it is user-friendly, has a short reaction time, and runs at room temperature and pressure, making it more cost-effective. In addition, it had other disadvantages, including a narrow pH range and an excessive amount of iron sludge [20]. To overcome classical Fenton's limitations, many researchers combine the Fenton process with other AOPs, such as sono-lysis [21, 22]. It is generally known that ultrasonic irradiation of water produces hydrogen peroxide (Eq. (1) and Eq. (4)) [23, 24, 25]. However, only a few researchers depend on the amount of H2O2 produced by the sonication of water because it is minimal [26]. 2 OH • → H2O2 ...(4) It is worth noting that all local works done in sono-Fenton, were done by adding H2O2 externally, and only a few global works were done depending on the in-situ sono-generated H2O2. This study focuses on the combined application of ultrasound and the Fenton process for treating natural petroleum refinery wastewater from the Al-Diwaniya refinery plant located in Iraq. The effect of two crucial operating parameters (Fe dosage and reaction time) on the chemical oxygen demand (COD) removal rate was investigated by adopting response surface methodology (RSM). 2. Materials and Methods 2.1 Properties of actual refinery wastewater In this investigation, the chosen pollutant was resistant organic COD from the Iraqi Al- Diewanya refinery. Prior to the biological treatment stage, 15L of effluents were been obtained from the storage tank and refrigerated at 4⁰C until use. Table 1 displays the sample properties submitted by the refinery administration before treatment and after treatment. Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 54 Table. 1. Properties of refinery plant wastewater Characteristic Initial Final Unit pH 6.6 7.3 Temperature 25 22 ºC TDS 5566 4898 ppm Phenol 18.5 0.05 ppm COD 550 102 ppm BOD 180 20 ppm Oil 25.2 11.6 mg/L Turbidity 33 7.29 NTU PO4 3- 0.12 0.8 Ppm Cl- 900 450 Ppm 2.2 Chemicals Ferrous sulfate (FeS𝑂4.7H2O; 99% pure) and hydrogen peroxide (H2O2,35%) were used as Fenton’s reagents and the pH of solution was adjusted using sulfuric acid (1M) and sodium hydroxide (1M). Potassium Permanganate (KMnO4) employed in a titration to estimate the concentration of H2O2 produced in situ. All substances were diluted with deionized water to reach the desired concentrations and the used chemicals were purchased from Sigma-Aldrich Co. (Japan). 2.3 Sono-Fenton system and procedure Ultrasonic bath from (ISOLAB Laborgerger GmbH, Germany) was used for ultrasound irradiation. In which constant ultrasonic power was obtained (60 W) and constant frequency (40 KHz). Before start any experiment, the ultrasonic bath was switch on and setting the temperature on 25 o C for a period of 15min. A 250 ml of wastewater was put in 500 ml conical flask the pH was adjusted to 3 using 1M 𝐻2 𝑆𝑂4 , and the suitable amount of ferrous sulfate was added. After that, the conical flask was closed from top by rubber stopper and placed inside the ultrasonic bath. The flask was fixed by a stand and the ultrasonic bath was covered with a plastic black plate to prevent effect of sun lights. The temperature in all experiments was fixed at 25±3 o C by the ultrasonic bath controller. Figure 1 shows the Fenton-Sonication system. Fig. 1. Fenton-Sonication system. 2.4 Analytical method 2.4.1 Chemical oxygen demand (COD) COD is the amount of a particular oxidant that reacts with existing pollutants in a sample under controlled conditions. The concentration of chemical oxygen demand (COD) in the effluent was used to quantify the amount of organic compounds in the polluted stream. 2 ml of treated wastewater was digested with 𝐾2 𝐶𝑟2𝑂7 as an oxidizing agent for 2 hours at 150 °C in a thermal reactor (Lovibond, RD125) to ascertain the COD value. The COD concentration was measured using a spectrophotometer, after bringing the digested sample to ambient temperature, The pH of an electrolyte was determined using a digital pH meter (ISOLAB Laborgerger GmbH, Germany). The effectiveness of COD removal was determined using (Equation 5) [27]: RE% = CODi −CODf CODi × 100 ...(5( RE% is the removal efficacy, CODi is the initial COD (mg/L), and CODf is the final COD (mg/L). Energy consumption was calculated by (Eq. 6) [28]: Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 55 𝐸 𝐶 = 𝑃𝑒𝑙×𝑡×1000 𝑉60log ( 𝐶𝑂𝐷𝑖 𝐶𝑂𝐷𝑓 ) ...(6) EC is the energy consumption (kWh/m 3 ), 𝑃𝑒𝑙 denotes ultrasound power rates in (kW), t denotes time in (min), and V is the solution volume in (L). 2.4.2 The concentration of 𝐇𝟐𝐎𝟐 generated in-situ by sonication Using deionized water, experiments were done in the absence of the pollutant of interest to determine the amount of 𝐻2 𝑂2 generated in-situ by sonication. A conical vessel containing 250 ml of pH- adjusted deionized water was immersed in an ultrasonic bath for 45 minutes. Throughout the experiment, samples were taken every fifteen minutes and analyzed using a titration with an aqueous potassium permanganate solution until a subtle pink shade was obtained. The chemical interaction is represented by the equation (Eq. 7) [29]: 2MnO4 − + 5H2O2 + 6H + → Mn2+ + 5O2 + 8H2O …(7) The H202 concentration was calculated using (Eq. 8) [29]: [𝐻2 𝑂2] (mg/lit) = 5 2 × 𝑁𝑘𝑚𝑛𝑜4 ×𝑉𝑘𝑚𝑛𝑜4 𝑉𝐻2𝑂2 × 34 × 1000 … (8) Where 𝑁𝑘𝑚𝑛𝑜4 is the molar concentration of 𝑘𝑚𝑛𝑜4 solution (mol/L) and 𝑉𝑘𝑚𝑛𝑜4 and 𝑉𝐻2𝑂2 are the volumes of 𝑘𝑚𝑛𝑜4 and the sample, respectively. 2.5 Experimental design The central composite design (CCD) is the most prevalent design in the response surface methodology (RSM) method. The CCD is a fractional factorial design with five levels that is most commonly used to create second-order response surface models. This design consists of three types of points: cube points obtained from a factorial design, axial points, and the center point. N can be determined using the formula N = k 2 +2k + n, where k is the number of parameters and n is a number of repetitions [30]. The selected parameters in the current study were the 𝐹𝑒2+ dosage (X1), reaction time (X2) as the factors and COD removal rate (RE%) value as the response. The process component scales have been identified as high (+1), median (0), and low (-1). Table 2 depicts the selected values for the process variables. As shown in Table 3, the Minitab-17 software was used to design the array of experiments for this investigation based on CCD. Table 2, Factors of the process in the refinery plant (coded and real levels). Process factors Range in CCD Coded levels -α Low (-1) Middle (0) High (+1) +α 𝐹𝑒2+ dosage mM, (X1) 0.0586 0.1 0.2 0.3 0.3414 Reaction Time min, (X2) 5.8579 10 20 30 34.142 Table 3, CCD design experimental array Run Order Blocks Coded Values Real values x1 x2 𝑭𝒆𝟐+ dosage (mM),X1 Reaction Time (min),X2 1 1 +1 -1 0.3000 10.000 2 1 0 0 0.2000 20.000 3 1 0 0 0.2000 20.000 4 1 0 +α 0.2000 34.142 5 1 +1 +1 0.3000 30.000 6 1 -1 -1 0.1000 10.000 7 1 0 0 0.2000 20.000 8 1 +α 0 0.3414 20.000 9 1 0 -α 0.2000 5.8579 10 1 -1 +1 0.1000 30.000 11 1 -α 0 0.0586 20.000 12 1 0 0 0.2000 20.000 13 1 0 0 0.2000 20.000 Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 56 Response surface model or methodology describes the empirical model expressed as Y = F(x1 + x2 +... + xk). The first or second order polynomial models are utilized to develop a suitable approximation for F and are represented below. Regarding the 1st order model (Eq. 9): Y = β° + ∑ βjxj + ε k j=1 … (9) And for the 2nd order model (Eq. 10): Y = β° + ∑ βjxj + ∑ βjjxj 2 +kj=1 k j=1 ∑ ∑ βjixjxi + εi k i=2 k−1 j=1 …(10) Y is the predicted response, β° is the constant, x1 , x2 , x3 , x4 and x5 are the operating variables, j, ji (j = 1, 2,..., k; I = 1, 2,..., k) and jj represent the regression coefficients of linear, interaction, and quadratic terms, respectively, and ε is the error. Typically, the quadratic model is suitable for RSM in the majority of instances. Therefore, models of the first or second order are sometimes refers to a regression models. In addition, fitting an acceptable response surface model involves statistical concepts, regression analysis methodologies, and optimization criteria [31]. 3. Results and Discussion 3.1 Preliminary experiments for determination of in-situ generated 𝐇𝟐𝐎𝟐 by Sonication Ultrasonic irradiation of an aqueous solution generates OH• radicals and H radicals by cavitation (Eq. 1). The hydroxyl radical has a high oxidation potential and can directly oxidize organic substrates, leading to their decomposition or mineralization (Eq. 2) [32-33-34]. Nevertheless, hydroxyl radicals have a very limited lifetime and tend to bind to generate H2O2 (Eq. 4) [35, 36]. The production of hydrogen peroxide by ultrasonic irradiation at different time intervals and at fixed intensity and pH value of 3 is shown in Figure 2. It can be seen from Fig. 2 that the concentration of H2O2 is increased linearly with time. This result is predicted since many previous studies has demonstrated that, during sonication at constant intensity, the rate of hydroxyl radical formation may be considered to be constant, with hydrogen peroxide being a main result of sonication (Eq. 4 and Eq. 11) accumulating linearly in solution and serving as an OH• scavenger under ultrasonic irradiation [37-39]. Consequently, at the current study the rate of H2O2 generation is considered constant since ultrasonic intensity is also constant. 2 OOH → H2O2 + O2 … (11) Fig. 2. H2O2 in-situ generation by sonication. 3.2 Statistical Analysis of the Sono-Fenton results Thirteen runs were performed in accordance with the CCD in order to find out and optimize the effects of process operating parameters on COD removal efficacy (RE%). Table 4 shows the number of runs, the experimental circumstances, the actual and estimated COD removal efficiency RE%. Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 57 Table 4, CCD results Run Order Blocks Fe dosage(mM) Time (min) RE%Actual RE% Predicted 1 1 0.3000 10.000 80.78 81.9626 2 1 0.2000 20.000 86.89 85.4780 3 1 0.2000 20.000 85.00 85.4780 4 1 0.2000 34.142 75.98 75.0894 5 1 0.3000 30.000 82.31 84.4162 6 1 0.1000 10.000 70.00 68.3688 7 1 0.2000 20.000 83.00 85.4780 8 1 0.3414 20.000 90.00 87.7728 9 1 0.2000 5.8579 73.00 73.4156 10 1 0.1000 30.000 68.99 68.2824 11 1 0.0586 20.000 65.00 66.7522 12 1 0.2000 20.000 88.00 85.4780 13 1 0.2000 20.000 84.50 85.4780 Results in Table 4 showed that RE% is ranged between 65-90%. A comparison between run 8 and run 11 at the mid value of time (20 min) displays that Fe2+ dosage has the higher effect on COD removal with a maximum difference of 25% while at the mid value of 𝐹𝑒2+ dosage (0.2mM) effect of time is the lower with a maximum deference of 3% (runs 4 and 9). However, the real effect of each variable could be observed by ANOVA analysis. The quadratic model regression was obtained by Minitab-17 software in terms of actual values (Eq. 12): RE% =33.09 + 225.9 X1 + 2.177 X2 - 410.8 𝑋1 2 - 0.05613 𝑋2 2+ 0.64 X1*X2 …(12) Where X1*X2 describe the interaction influence of model parameters and the double influences of model parameters (X1) 2 and (X2) 2 were utilized to determine the magnitude of their impact. The negative and positive coefficients in the model represent the negative and positive influence of experimental factors on COD elimination, respectively. As stated in Equation (12), the maximum coefficient belonged to (X1*X1) factor, implying that the double effect of 𝐹𝑒2+ dosage has the highest effect on the removal of COD during sono-Fenton process when compared to the other independent variables. In contrast, a low coefficient showed that double effect of reaction time (X2*X2) had the minimal effect on the response. By graphing the anticipated versus actual data and the normal probability plot of the standardized residuals, the attractiveness and sufficiency of the model were also confirmed in Figure 3. It is evident from Figure 3 that there is a strong correlation between the experimental and estimated values, showing that the model was well-fitted and had a good ability to predict the COD removal rate RE%. No scattering with no definite pattern was observed, respecting the residuals revealing the significance of the model. This may be interpreted as below [40]: a) No Outliers exist in the data with respect to normal probability plot. This states that data are normally distributed and the RE% is affected by 𝐹𝑒2+ dosage and time. b) A non-linear relationship was observed with respect to the plot of residuals versus fitted values plot confirming the variance is constant. c) No skewing nor outliers were existed in Histogram. d) An organized effects were observed in the data plot on residuals versus order due to time or data collection order. Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 58 Fig. 3. Residual plots of COD removal rate by sono-Fenton. In addition, the model's sufficiency and significance were evaluated using analysis of variance (ANOVA), and the results are shown in Table 6. The Model 𝑅2 and 𝑅2 𝑎𝑑𝑗𝑢𝑠𝑡𝑒𝑑 values of 96.40% and 92.20%, respectively was relatively high, which indicates that the model obtained was able to give a convincingly good estimate of response in the studied range [41]. Furthermore, ANOVA table reveals that the present of contribution of the model was 95.68% and the linear term Contr.% is 57.03 in which 𝐹𝑒2+ dosage (X1) Contr.% of 56.67 which represents the majority of the linear term with very week contribution of reaction time (X2) 0.36%.the week contribution of time could be results from nonlinear its behavior with RE%. The double (square) effect term contributes in the model was 38.45% while the interaction term was 0.21% only which is very insignificant. According to the ANOVA table, the model was extremely significant as the Fisher F test (F value) was determined to be 31.02 with a very low probability value (P value 0.0001), indicating that there was only a 0.01% chance that such a model could have been caused by noise [42]. Table 6. Analysis of Variance results Source DF Seq SS Contr. % Adj SS Adj MS F-Value P-Value Model 5 746.075 95.68 746.075 149.215 31.02 0.000 Linear 2 444.669 57.03 444.669 222.334 46.22 0.000 X1 1 441.867 56.67 441.867 441.867 91.86 0.000 X2 1 2.808 0.36 2.802 2.802 0.58 0.470 Square 2 299.793 38.45 299.793 149.896 31.16 0.000 X1*X1 1 80.642 10.34 117.382 117.382 24.40 0.002 X2*X2 1 219.151 28.11 219.151 219.151 45.56 0.000 2-Way Interaction 1 1.613 0.21 1.613 1.613 0.34 0.581 X1*X2 1 1.613 0.21 1.613 1.613 0.34 0.581 Error 7 33.672 4.32 33.672 4.810 Lack of Fit 3 17.993 2.31 17.993 5.998 1.53 0.337 Pure error 4 15.680 2.01 15.680 3.920 Total 12 779.747 100.00 Model Summary R2 R2(adj.) R2(pred.) 96.40% 92.20% 80.45% Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 59 3.3 Effect of operating factors on the sono- Fenton process The surface plot combined with the contour plot was used to investigate the effect of Fe dosage and time on the COD removal efficiency, as shown in Figure 4 - a, b. It was clear that increasing Fe dosage results in increasing RE% to an optimum Fe dosage beyond which no further increase of RE% could occur. This behaviour occurs at any time. This can be interpreted as increasing the Fe2+ dosage results in increase the COD removal rate due to Fe2+ reaction with the in-situ generated hydrogen peroxide according to (Eq. 3) [43]. Pang and his coauthors [44] stated that increasing Fe2+ dosage would also increase the sono-Fenton process’s efficiency. Nevertheless, with increasing the Fe2+ dosage more than the optimum value, self-quenching of •OH to produce Fe3+ through (Eq. 13) could occur Fe2+ + OH • → Fe3+ +OH− … (13) Then, the resulting Fe3+ can further react with H2O2 to form a complex intermediate (Fe (HO2 ) 2+) (Eq. 14). Although (Fe (HO2) 2+ ) can be spontaneously decomposed to Fe2+ and •OOH, the decomposition rate was much lower. The decomposition rate of (Fe (HO2) 2+) can be greatly enhanced under ultrasonic irradiation (Eq. 15). A cycle mechanism is established once the isolated Fe2+ further reacts with H2O2 to produce •OH (Eq. 3) [45, 46]. Fe3+ + H2O2 → Fe − O2H 2+ + H+ … (14) Fe − O2H 2++ ))) → Fe2+ + OOH • …(15) Several studies had investigated the effect of iron dosage on the sono-Fenton process, and the majority of researchers have concluded that the degradation of pollutants by the sono-Fenton process increased significantly with the addition of Fe2+ [47-50]. On the whole, the addition of Fe2+ is generally beneficial for the acceleration of organic compound degradation; however, an excessive dosage of Fe2+ will decrease treatment efficiency due to the reduction of OH• caused by the addition of excessive Fe2+ (Eq. 13) [50-52]. Consequently, higher iron dosages are only advantageous under specific conditions. According to previous studies, reaction time is one of the most crucial parameters affecting hybrid wastewater treatment systems [53, 54]. Based on Figure 4-a, the RE% increases with increasing time up to 20 min then starts to decrease. According to data concerning the effect of reaction time, as the time climbed from 20 to 34.14 min at constant Fe2+ dosage 0.2 mM, the rate of removal decreased by 9.02%. This is probably because the in-situ generated hydrogen peroxide by sonication was partially consumed [55]. This behavior was happen at any value of Fe dosage. In the majority of previous literature reviews, it was found that the COD removal rate increased as the reaction time increased. This behaviour is expected due to the increased production of hydroxyl radicals OH• during sonication [31, 14, 56-58]. In contrast, in the current study, increasing the reaction time beyond 20 minutes will decrease the COD removal rate, which is an unpredicted result consistent with a small number of previous findings [59-61]. Yosofi and Mousavi [62] attributed that the decrease of RB5 removal rate happened when the concentration of H2O2 elevated to 400 mg/l due to the consumption of OH• radicals by extra hydrogen peroxide at high concentration instead of reacting with RB5 Eqs. (16, 17, 18) [62]. OH • + H2O2 → HO2 • + H2O ...(16) HO2 • + OH • → H2O + O2 … (17) H • + H2O2 → HO2 • + H2 .. (18) However, the rate of H2O2 generation at the current study was considered constant, authors suggests that the OH• radicals instead of attacking the organic pollutant, it will continue producing H2O2 overtime and hence accumulating it in the solution which results in consuming OH• (Eq. 16, 17, 18) in the same behavior of [62] when authors increased the concentration of H2O2. In addition, the accumulated hydrogen peroxide may function as a hydroxyl radical scavenger, resulting in the production of hydro-peroxy radicals that are less reactive than hydroxyl radicals (Eq. 19) [61]. H2O2 + OH • → HO2 • + H2O … (19) Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 60 (a) (b) Fig. 4. The interaction effect of Fe dosage and time on the COD removal. a)surface plot, b) contour plot. The contour plot is significant to detect the reign of optimum values. As shown in Figure 4-b, the higher removal rate with RE% higher than 85% could be attained only at Fe dosage greater than 0.2 mM and time in the range (15-25min), hence the optimization results should be lied with this scope. 3.4 Optimization The primary objective of CCD-based RSM was to identify the ideal operating parameters for maximizing the percent of COD removal efficiency in the treatment of petroleum refinery wastewater by the hybrid process (sono-Fenton). Minitab-17 software was used to maximize the COD RE%, taking into account the variety of examined parameters and their responses as shown in Tables 2 and 5, respectively. Within these constraints and parameters, the optimization technique was carried out, and the results are displayed in Table 7 and Figure 5. For confirmation, an experiment was conducted utilizing the improved parameters. Besides, for comparing the efficiency of combining ultrasound irradiation with Fenton reaction, three more experiments were done (sonolysis, classical Fenton, and sono-Fenton with addition of H2O2 externally). Table 8 provides the results. After approximately 21 minutes of the sono-Fenton process, the COD removal efficiency at pH=3 was 85.81% (in the range of the optimal value determined by optimization analysis with a DF of 1) (Table 6). Consequently, employing CCD in conjunction with DF is effective and efficient for maximizing COD elimination using sono-Fenton hybrid advanced oxidation method. Based on the present method, the final COD concentration was (65ppm) which is lower than the value of the effluent discharge from the 10 02 60 70 80 1.0 03 .0 0.2 .0 3 80 09 %ER )Mm( egasod eF )nim( emiT Time (min) F e d o sa g e ( m M ) 3025201510 0.30 0.25 0.20 0.15 0.10 > – – – – – < 60 60 65 65 70 70 75 75 80 80 85 85 RE% Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 61 biological unit (102 ppm) used in the Al- Diewanya refinery plant and is in agreements with the standard level for discharging of wastewaters globally. External addition of H2O2 to sono-Fenton was found to decrease the COD removal rate to be 57.68% and a dark yellow color of the solution after treatment was observed. This could be due to the reaction between excessive H2O2 and OH• according to (Eq. 19), which results in the creation of HO2 •, which has insignificant oxidative strength in comparison to hydroxyl free radicals [63, 64]. At greater concentrations of hydrogen peroxide, 𝐻2 𝑂2 served as an interfering agent and reacted with hydroxyl radicals OH• in the aqueous medium, thereby limiting their attack on contaminant molecules [64]. In addition, sonolysis alone and classical Fenton process give removal efficiency of 64.84% and 56% ,respectively which is also lower than the hybrid sono-Fenton process removal. This is because of the increased number of hydroxyl radicals generated by sono-Fenton, therefore, the rate of breakdown and oxidation of organic matter will also increase. Since the number of radicals derived from 𝐻2 𝑂2 in the hybrid system is greater than in an isolated sonication system, the rate of oxidation will be greater in the hybrid system [65]. Table 7. Response Optimization: RE% Response Target Lower Upper Weight Importance RE (%) Max 65 90 1 1 Parameters Fe 2+ (mM) Time (min) Fit SE Fit 95% CI 95% PI 0.29 21 88.90 1.06 86.38-91.41 83.14-94.66 Fig. 5. Optimization plot Table 8. Confirmative run with comparison with related processes Run Case Fe 2+ (mM) Time (min) H2O2 COD (ppm) RE% initial final 1 Sono-Fenton 0.29 21 458 65 85.81 2 Sono-Fenton with addition of 𝐻2𝑂2 externally 0.29 21 2.9mM 458 193 57.86 3 Sonolysis only - 21 458 161 64.84 4 Classical Fenton process 0.29 21 458 199 56.55 Marwa M. Jiad Al-Khwarizmi Engineering Journal, Vol. 19, No. 2, P.P. 52- 67 (2023) 62 3.5 Comparison with previous works The results of the current study were compared to prior research in the same field in Table 9. It demonstrates that the current results are favorable in terms of the high removal rate in a brief amount of time, approximately 20 minutes, the lack of energy consumed, and the low cost, which encourages the adoption of the current method for treating polluted water from sources other than oil refineries, such as textile and cosmetics factories. Table 9. Comparison with previous works Reference optimum Conditions process [22] RE%=58.2 =30 mg/l, 2+200mg/l, Fel Pheno =800mg/l, 2O2H pH=3,time=60min temperature =30º C Degradation of phenol in aqueous solution by fenton, sono‐fenton and sono‐photo‐fenton methods [66] For US/ 2O2/H 2+Fe RE%=40 EC=216kWh 3m/ =30mM2+Fe pH=7,time=180 min temperature =30º C Ozone (O3) and sono (US) based advanced oxidation processes for the removal of color, COD for landfill leachate [67] RE%=84.25 =102+/Fe2O2H pH=3, time=10 min Treatment of petroleum effluents using the combined ultrasound and Fenton oxidation process [25] RE%=95.3 =0.2mM2+Fe pH=3,time=10 min temperature =30C The production of sono-Fenton System by Trace ferrous ion addition in sono-degradation Dimethoate Present study RE%=85.81 EC=90.57k 3Wh/m =0.289 mM2+Fe pH=3,time=21 min temperature =30C Petroleum refinery wastewater /sonofenton 4. Conclusion In this research, combining of ultrasound irradiation and Fenton as a hybrid process was investigated to treat real petroleum refinery wastewater. The optimum operation variables were found by response surface methodology (RSM) with central composite design (CCD). A maximum concentration of H2O2 that generated in-situ by sonication was found to be 8.5 mg/l at 45min and its rate was constant throughout all experiments. The optimal RE% for sono-Fenton process was 85.81% obtained at 21 minutes and Fe2+ dosage of 0.289. Analysis of variance (ANOVA) showed that the model R2 is 96.40% and the Fe2+ dosage is the main factor that greatly affects the treatment process. The results revealed that the efficiency of the individual classical Fenton process and sonolysis process were low. In contrast, when Fenton is combined with sonication, the removal efficiency is considerably enhanced. Adding external H2O2 has an adverse effect on the COD removal which decreased by 27.95%. 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(2023) 52-67، صفحة 2، العدد19مجلة الخوارزمي الهندسية المجلد مروة محسن جياد 67 ثمارمعالجة المياه العادمة الخارجة من مصافي النفط بأعتماد عملية السونوفنتون وبأست بيروكسيد الهيدروجين المتولد آنيًا من الموجات الفوق الصوتية **علي حسين عبار *مروة محسن جياد جامعة بغداد كلية الهندسة الخوارزمي/ قسم الهندسة الكيميائية االحيائية/**,* Marwa.jeyad2205m@kecbu.uobaghdad.edu.iqالبريد األلكتروني: * ali.abbar@kecbu.uobaghdad.edu.iq:البريد األلكتروني ** الخالصة طريقة جديدة لمعالجة المياه العادمة الخارجة من المصافي النفطية من خالل الجمع بين الموجات فوق الصوتية وعملية الفنتون كعملية الدراسةتقدم هذه تمت دراسة اثنين من العوامل المؤثرة الرئيسية على العملية . (%RE)كدالة هدف (COD) لألوكسجينتم اختيار ازالة الطلب الكيميائي . فنتون-سونو (CCD) مع اعتماد التصميم المركب المركزي Respone surface methodology (RSM)البرنامج االحصائي منهجية سطح االستجابة باستخدام Central Composite design . تم الحصول على أعلى نسبة ازالة REملي موالر من 0.289دقيقة و 21ظروف المثالية لمدة في ال ٪85.81 ٪ وهي 2R أثبتت قيمة . ، يليه وقت التفاعل COD له أعلى تأثير على التخلص من +Fe2 باإلضافة إلى ذلك ، أوضحت النتائج أن تركيز +Fe2 الحديد عالوة على ذلك ، .في معالجة المياه العادمة من مصافي البترول RSM صحة التوافق القوي لمعادلة النموذج واالعتماد الناجح لـ( ٪96.40)المرتفعة فنتون التي تم اجرائها باالعتماد على الكمية المتولدة داخليا من بيروكسيد الهيدروجين عن طريق الموجات فوق الصوتية -أظهرت مقارنة بين عملية سونو عملية Sonolysis الكالسيكية و الفنتون الخارجية لبيروكسيد الهيدروجين وايضا عمليةفنتون أخرى تم اجراءها عن طريق االضافة -وبين عملية سونو التي تم اجراءها بدون اضافة فنتون-هي العملية المشتركة السونو لإلزالةأفضل عملية أن الصوتنة االعتيادية بدون اضافة الحديد وبيروكسيد الهيدروجين .بيروكسيد الهيدروجين خارجيا وان هذه العملية افضل من العمليات الفردية الكالسيكية كالفنتون فقط او الصوتنة فقط mailto:Marwa.jeyad2205m@kecbu.uobaghdad.edu.iq mailto:ali.abbar@kecbu.uobaghdad.edu.iq