Homogeneous solar Fenton and alternative processes in a pilot-scale rotatable reactor for the treatment of petroleum refinery wastewater

Journal Pre-proof Homogeneous solar Fenton and alternative processes in a pilot-scale rotatable reactor for the treatment of petroleum refinery wastewater Omid Pourehie, Javad Saien

PII:

S0957-5820(19)32232-3

DOI:

https://doi.org/10.1016/j.psep.2020.01.006

Reference:

PSEP 2064

To appear in:

Process Safety and Environmental Protection

Received Date:

7 November 2019

Revised Date:

5 January 2020

Accepted Date:

7 January 2020

Please cite this article as: Pourehie O, Saien J, Homogeneous solar Fenton and alternative processes in a pilot-scale rotatable reactor for the treatment of petroleum refinery wastewater, Process Safety and Environmental Protection (2020), doi: https://doi.org/10.1016/j.psep.2020.01.006

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Homogeneous solar Fenton and alternative processes in a pilot-scale rotatable reactor for the treatment of petroleum refinery wastewater Omid Pourehie, Javad Saien Department of Applied Chemistry, Bu-Ali Sina University, Hamedan, 65174, Iran

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Highlights

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Graphical abstract



The solar Fenton process has an excellent capability to treat the refinery wastewater.



Effects of various parameters were studied and the optimum values were determined.

 Organic pollutants were identified before and after treatment, showing significant removal. The solar Fenton process was compared with the alternative processes.



Cost estimations revealed the preference of the employed method.

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

ABSTRACT

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Corresponding author. Email address: [email protected] (J. Saien)

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Applicability of the solar Fenton process for the treatment of a real refinery wastewater was investigated. A novel solar-reactor was used with the capability of automatic rotating against the sun, enabling maximum utilization of direct and single reflective sunlight beams. The COD and TOC criteria were measured to follow the pollutants removal. Results revealed optimal operating conditions of 694.7 mg/L hydrogen peroxide, 67.3 mg/L ferrous salt and solution pH of 3.2. Under these conditions, COD and TOC were, respectively, decreased to 79.6 and 73.2% after 180 min

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2+ 2+ sunlight envision. For comparison, alternative H2 O2 /Fe2+ , S2 O2− 8 /Fe , NaOCl /Fe , NaOCl,

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S2 O2− 8 and H2 O2 processes, all activated with sunlight, were performed. The present pollutants were identified by means of the GC/MS headspace technique, showing significant removal of the

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majority of petroleum aliphatic and aromatic hydrocarbons and that biodegradability was feasible

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since BOD5/COD reached from 0.36 to 0.62. The process performance was compared with the previously reported similar processes for treating specified pollutants and wastewaters. High

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preference of the employed process using the particular solar-reactor was probed based on different criteria. Meanwhile, the total operating costs was estimated to be quite low, compared to other

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processes.

Keywords: Solar Fenton; Solar-reactor; Refinery wastewater; Biodegradability; Operating costs

1. Introduction

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Considering the huge water consumption in petroleum refineries, it is important to find methods

for easier and economy treatment and reusing the wastewaters. Refinery wastewaters contain different hazardous compounds from crude oil, products, lubricants and petrochemical intermediates that are a major source of environmental pollution (Coelho et al., 2006; Wake, 2005). Discharge of these pollutants into environment affects the human health and aquatic ecosystems.

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Thus, increasing global energy demand requires greater exploration and exploitation of these wastewaters (Diya’uddeen et al., 2011). In this regard, advanced oxidation processes (AOPs) have been highly studied in the treatment of petroleum refinery wastewaters to reduce the level of pollutants as well as the odor and/or color (Tony et al., 2012). In a well-known mild and environmental friendly AOP, Fenton process, the simultaneous presence of hydrogen peroxide and ferrous salt can generate hydroxyl radicals for

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degrading organic pollutants (Cuzzola et al., 2002). Meanwhile, the homogeneous Fenton process

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has the advantage of no need to separate the solid catalysts for reusing. However, a major disadvantage is the sludge formation through flocculation of the reagents with the pollutants (Tao

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et al., 2019). Instead, when this process is performed under UV, visible and/or sunlight, sludge

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formation will not be the case (Cuzzola et al., 2002; Malato et al., 2002). In the photo-Fenton process, hydroxyl radicals are produced by oxidation/reduction reactions.

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First, ferrous ions are oxidized by hydrogen peroxide, producing hydroxyl radicals, and then are regenerated to the initial oxidation state via a photochemical reaction. Hydroxyl radicals are

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additionally produced as long as hydrogen peroxide is available. The resulted hydroxyl radicals have the reduction-oxidation potential, 𝐸0 , of 2.8 V vs. NHE (Hassanshahi and Karimi-Jashni, 2018):

Fe2+ + H2 O2 → Fe3+ + OH − + HO• h𝑣

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Fe3+ + H2 O →

(1)

Fe2+ + H + + HO•

(2)

In addition to UV light, sunlight could also generate the hydroxyl radicals in the “solar Fenton”

process, which is known as an energy saving and environmental friendly process for treatment of wastewaters particularly at large scales (Nogueira et al., 2012; Patil et al., 2019). The homogeneous

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Fenton processes have the advantage of easily handling of one phase and that low amount of iron sulfate salt is required as an environmentally low impact reagent. The novelty of this investigation relies on the removal of organic pollutants from a real refinery wastewater using the environmental friendly homogeneous solar Fenton process, for the first time, utilizing a novel rotatable pilot-scale solar-reactor. Alternative homogenous processes of

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2+ 2+ H2 O2 /Fe2+ , S2 O2− 8 /Fe , NaOCl /Fe , NaOCl, all under the sunlight, are considered. The effects

of hydrogen peroxide and ferrous salt concentrations as well as media pH are important. These as

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well as the extent of pollutant degradation for different involved hydrocarbons are considered. In order to evaluate the performance; alternative processes are investigated, under similar conditions,

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by utilizing the solar-reactor. This study helps to implement the solar Fenton process as a

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complementary operation in the treatment of petroleum refinery wastewater. To the best of our knowledge, no work has been reported dealing with the treatment of real refinery wastewater by

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2. Experimental

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different homogeneous solar processes.

2.1. Materials

The refinery wastewater samples were collected from the stream leaving of the dissolved air flotation (DAF) unit and while entering the biological treatment lagoon in the Arak petroleum

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refinery plant. Chemical oxygen demand (COD) of this stream was within the range of 210 - 280 mg/L, TOC of 60 - 65 mg/L and biochemical oxygen demand (BOD5) of 70 - 95 mg/L. Other specifications were pH: 7 - 8 and total dissolved solids: 420 - 750 mg/L. Hydrogen peroxide (35%) and potassium persulfate (99%), used as oxidants; ferrous sulfate heptahydrate (99.5%), for supplying ferrous ions; sulfuric acid (98%) and sodium hydroxide (98%), for adjusting pH of

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samples, were all Merck products. Sodium hypochlorite (15%) as an oxidant in the alternative solar/NaOCl process was the product of Chlorpars Company.

2.2. The solar-reactor and procedure There are mainly two types of solar-reactors for wastewater treatment, depending on the area and number of light collectors as well as the capacity of wastewater handling. The most

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conventional classification is concentrating and non-concentrating solar-reactors. Both of these

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reactor types have a number of advantages and disadvantages. Concentrating solar-reactors are rather used in energy generation due to their high sunlight absorption capacity. Non-concentrating

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reactors are rather used in wastewater treatments and those equipped with compound parabolic

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collectors (CPCs) are the most common type. These are static systems with usually no solar tracking facility and hence, a disadvantage of CPC reactors is that a remarkable percentage of

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incident lights reaches the receiver tube after double reflection when inclined sunlight irradiation is corresponding. However, their advantage is simplicity and low capital investment (Davididou

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et al., 2019; Tanveer and Guyer, 2013).

Based on the above points, in this work, a novel pilot scale solar-reactor was used to perform solar Fenton and alternative processes. The set-up consisted of parabolic collectors which concentrate lights on the perimeter of conducting tubes and lights could be received with single

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reflection as well as direct lights. Fig. 1a illustrates a schematic of the used solar-reactor that consisted of a series of five quartz tubes with 2.5 cm diameter and 150 cm length, each mounted on a parabolic full glazy aluminum sheet (Fig. 1b). The whole collector surface was equipped with a sunlight-sensitive sensor to provide automatic rotation clockwise from east to west to be in front of the sun. Thus, sunlight utilization was available both in direct and diffuse lights with the

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parabolic collectors. The set-up was installed on the roof of applied chemistry department, Bu-Ali Sina University, Hamedan, Iran (latitude 34º 47', longitude 48º 29'). The reactor was connected from inlet and outlet to a tank containing the wastewater which also provided the homogeneity of the feedstock as well as supplying oxygen from air by recycling under flow rate of 1 L/min via a centrifugal pump. The total capacity of the system was 10 L. The surface latitude angle could also be adjusted depending on the month/season orbit of the sun. The

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incident sunlight covered the entire length of tubes.

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“Fig. 1 (a and b)”

Solar radiation was measured by a UV Radiometer (Solarmeter, model 4.2-UV). The incident

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radiation could be evaluated as a function of time. Accordingly, the accumulated UV energy per

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̅̅̅̅, in unit volume, 𝑄UV,𝑛 in kJ/L, can be obtained from the average solar ultraviolet radiation, UV W/m2, measured at time intervals of ∆𝑡𝑛 = 𝑡𝑛 − 𝑡𝑛−1 of 1800 s, as the following equation (Cabrera-

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Reina et al., 2019; Malato et al., 2002). 𝑆

̅̅̅̅ 𝑄UV,𝑛 = 𝑄UV,𝑛−1 + ∆𝑡𝑛 UV 𝑉

𝑡

(3)

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where 𝑆 is the illuminated reactor surface area (2.625 m2 in this case) and 𝑉𝑡 is the total reactor capacity volume (10 L). During the considered experimental times, ̅̅̅̅ UV intensity was ranged within

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20 - 33 W/m2 and the corresponding accumulated UV energy, 𝑄UV, within 0 - 75 kJ/L.

2.3. Analytical methods and operating procedure Degradation of pollutants in the samples was followed by measuring the COD and total organic

carbon (TOC) values. The COD measurements were performed by the standard closed reflux and colorimetric method (Eaton et al., 1995) using a COD reactor (HACH, DRB200) with a spectrophotometer (HACH, DR/2800) and the corresponding standard reagent. The biochemical 6

oxygen demand was followed by BOD5 tests, where the dissolved oxygen content was determined after 5 days of incubation (APHA, 2005). For a proper analysis, the TOC of samples was also measured by means of a TOC analyzer (Shimadzu, VCSH model). Analysis of the organic content was performed by means of the headspace technique, coupled to a GC/FID system (HS 2000, Thermo Quest), equipped with a 50 m/0.32 mm CP-Sil 5 CB column. The separation conditions were similar to those applied by Stepnowski et al. (2002) and

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our previous investigation (Saien and Nejati, 2007), working on a real petroleum refinery

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wastewater.

The solar-reactor was fed with the wastewater and the pH was adjusted by dilute solutions of

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either sulfuric acid or sodium hydroxide. Then the specified amounts of H2 O2 and FeSO4 . 7H2 O

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were added. The run time was 180 min usually within 10:30 am - 3 pm. The wastewater was continuously circulated through the system in the closed cycle. A sample of 50 mL was taken every

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30 min from the outlet of the reactor for analyzing.

Data at different conditions were obtained and analyzed using the COD removal criterion as: [COD]0 −[COD]𝑡 [COD]0

× 100

(5)

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COD removal (%) =

where [COD]0 and [COD]𝑡 are the initial and at any time (t) measured COD values. Similar efficiency could be attributed to the TOC values.

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2.4. Design of the experiments

There are a number of influencing factors and interactions involved in AOPs. A conventionally

used method is the response surface methodology (RSM) (using Design-Expert software, version 7), which can determine the contribution of operational factors and construct a descriptive mathematical model for the provided data (Dutta et al., 2011). The H2 O2 and FeSO4 . 7H2 O 7

concentrations as well as pH variables were considered in the solar Fenton process and COD removal efficiency was the response factor. The level of parameters were determined based on a number of preliminary experiments and each of the variables was studied in different levels (−α, −1, 0, +1, +α). Table 1 lists the level and the range of the considered parameters as well as the designed CCD matrix, which consists of three experimental point types of cubic, axial and center points. The number of required experiments is determined as 𝑁 = 2𝑚 + 2𝑚 + 𝑁0 , where 𝑚 is

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the number of parameters, 2𝑚 and 2𝑚 and 𝑁0 are the cubic, axial and center point runs,

parameters.

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“Table 1”

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respectively. Distinction between the axial and center points depends on the number of involved

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3. Results and discussion

3.1. Effects of the involved parameters and evaluations

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Effects of different operating parameters are usually presented by 3-D graphs where one parameter is maintained constant and the effect of other parameters are presented. Accordingly,

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the initial concentration of hydrogen peroxide and ferrous salt were considered as the more important parameters in the process (Ahmed et al., 2011; Dbira et al., 2014). Fig. 2 shows the variation of COD removal versus these parameters in the solar Fenton process. It is observed that a maximum COD removal was corresponding to the initial H2 O2 concentrations of 694.6 mg/L.

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Accordingly, The ratio of this amount of H2 O2 to the average initial COD and TOC (in mg/L) are, respectively, 2.8 and 10.7. Low levels of H2 O2 reagent, give no enough hydroxyl radical and removal efficiency would be limited (Ahmed et al., 2009). On the other hand, when H2 O2 concentration exceeds the optimum value, COD removal decreases due to scavenging HO• radicals with excess H2 O2 (Eqs. 5 and 6) leading a limited degradation of pollutants. Additionally, the auto

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decomposition of H2 O2 into H2 O and O2 , and regeneration of H2 O2 (Eq. 7) leads to diminishing the amount of HO• radicals (Daneshvar and Khataee, 2006; Zheng et al., 2007). H2 O2 + HO• → H2 O + HO•2

(5)

HO•2 + HO• → H2 O + O2

(6)

HO• + HO• → H2 O2

(7)

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As another involved parameter, increasing ferrous sulfate dosage up to 67.3 mg/L gives higher COD removal, implying that the used amounts of this salt were not sufficient to supply proper

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hydroxyl radicals. Further, it has been reported that high amounts of Fe2+ can lead to the selfinhibition of HO• radicals by this ion (Dbira et al., 2014). Thus, the optimum FeSO4 . 7H2 O

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“Fig. 2”

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concentration of 67.3 mg/L was utilized in the subsequent solar Fenton process.

Generally, the Fenton process gives a better performance under acidic conditions under which

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higher oxidation power of HO• radicals is appropriate (Clarizia et al., 2017; Li et al., 2009). Here, as it is possible to observe in Fig. 3, acidic pHs provided reasonably a higher degradation of

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pollutants in the solar Fenton process, and a rather high COD removal was achieved at pH 3.2. The oxidation of pollutants decreases at elevated pHs due to low rate of H2 O2 degradation (Clarizia et al., 2017). In this regard, addition of the alkaline solutions like NaOH, can lead to consumption of iron ions into iron hydroxides and inhibits the process activity (Elmolla and Chaudhuri 2009;

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Guerra et al., 2019). Similar findings have been reported in the previous studies for degradation of different type pollutants by the Fenton and photo-Fenton processes (Guerra et al., 2019; Yang et al., 2009).

“Fig. 3”

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COD and TOC removal versus accumulated solar energy, 𝑄UV, is depicted in Fig. 4; indicating a reasonable ascending variation versus accumulated solar energy and tending to higher efficiencies when 𝑄UV increases, after 180 min treatment. The corresponding COD and TOC at this time were, respectively, 79.6 and 73.2%. In view of practical applications, the rate of COD removal for the solar Fenton treating of the refinery wastewater under the optimum conditions was investigated. As is indicated in the inset

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Fig. 4, the overall pseudo first order COD removal, as ln[COD]0 /[COD]𝑡 = 𝑘𝑡, can be attributed

constant of 0.089 min1.

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“Fig. 4”

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to the COD removal rate. The coefficient of determination (R2) was 0.992, relevant to the rate

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3.2. Modeling of experimental data

The provided data for solar Fenton process can be represented with a quadratic equation based

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on regression analysis, developed by the Design-Expert software, as: COD removal (%) = 81.60 − 2.83 pH + 5.17 [H2 O2 ] + 1.45 [FeSO4 . 7H2 O] + 1.70 [H2 O2 ] × (8)

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[FeSO4 . 7H2 O] − 2.19 pH 2 − 20.82 [H2 O2 ]2 − 12.48 [FeSO4 . 7H2 O]2

Table 2 lists the statistical criteria based on the provided experimental data and this model. “Prob > F” values less than 0.05, indicate that the model is significant for the response and a value greater than 0.10 imply a non-significant model. The model F-value of 318.02 and the p-value of

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less than 0.0001, in this work, confirm that the model is significant and a “Lack-of-Fit of F-value” of 0.44 is corresponding. Further, the coefficient of determination (R2) value of 0.994 indicates that the model fits the data satisfactorily. Apart from these, the model feature, presented in Fig. 5, confirms a good agreement between experimental and predicted values. From Eq. (8) a maximum COD removal of 82.9% is resulted under optimum conditions.

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“Table 2” and “Fig. 5” 3.3. Identification of wastewater pollutants Fig. 6 presents chromatograms of the wastewater samples before and after treatment with solar Fenton process under the optimum conditions. The peaks are labeled with the corresponding hydrocarbon name according to the GC/MS identification data base. The majority of the peaks correspond to aliphatic hydrocarbons (n-branched and cycloalkanes, up to C12). Trace amounts of

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aromatic compounds, toluene, benzene and ethylbenzene, were also present. The heavy poly-

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aromatic hydrocarbons could be eliminated during the mechanical and physiochemical pretreatments of the refinery wastewater (Saien and Nejati, 2007). Comparison of two chromatograms

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in Fig. 6 and the results of TOC analysis in Fig. 4 shows that most organic pollutants have been

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effectively degraded into harmless inorganic substances i.e. CO2 and H2 O in the presence of oxygen as can be represented in the following symbolic equation (Zyoud et al., 2017; Malato et

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al., 2016). Oxygen was injected into the tank during the homogeneity of the feedstock with the airmixed recycle flow or from decomposition of H2 O2 into H2 O and O2 . O2

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C x Hy Oz(here z= 0, 1) + HO• → → → CO2 + H2 O

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“Fig. 6”

3.4. Comparison with alternative processes

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For evaluation of the efficiency of the solar Fenton process, alternative conventional available processes were investigated under similar conditions, all by utilizing the solar-reactor. As a remarkable attempt, due to rather safe storage and low price of sodium hypochlorite, NaOCl, this oxidant has been used in the Fenton process for treating aromatic compounds, and an efficiency close to homogenous Fenton process has been reported (Behin et al., 2017). Moreover, the

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performance of UV/persulfate process has been investigated and the results have revealed that this method was effective for the treatment of refinery wastewater (Pourehie and Saien, 2019). Here, in addition to solar Fenton, treatment with sodium hypochlorite, solar/NaOCl/Fe2+ , and its alternatives were conducted under conditions identical to optimum conditions of solar Fenton. Based on the obtained results, presented in Fig. 7, the solar processes were efficient in the order 2+ of: H2 O2 /Fe2+ > NaOCl /Fe2+ > S2 O2− > NaOCl > S2 O2− 8 /Fe 8 > H2 O2 > only solar. The

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solar/H2O2/Fe2+ process is more efficient than others. It can be explained by redox potential of

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hydrogen peroxide (1.78 V) which is more than sodium hypochlorite (1.49 V) (Rodriguez et al. 2008). On the other hand, sunlight alone, with no oxidant, had no sensible influence. It was while

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by using oxidants, the efficiency was improved and that further assisting by the ferrous catalyst

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gave significant enhancement in the efficiency. Similar results have been reported by Kałużna et al. (2010), Behin et al. (2017) and Dhir et al. (2012). Regarding S2 O2− 8 , it has to mention that

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despite a higher redox potential (2.1 V), a much lower molar concentration (with the same weight percent) has been consumed; thus a lower efficiency is expected. Furthermore, hydroxyl radicals,

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generated from H2 O2 are non-selective species in degradation whereas sulfate anion radicals, 2− SO•− 4 , originated from S2 O8 affect rather selective.

Use of different solar-reactors in photochemical and photocatalytic degradation of specified pollutants and wastewaters was also considered for comparison and summarized in Table 3.

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Details of operational parameters and process efficiencies are listed. As indicated, the efficiency of the employed solar-Fenton process, based on COD and TOC removal efficiencies, are significantly more than similar reported homogeneous and heterogeneous processes. “Fig. 7” and “Table 3”

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3.5. Biodegradability improvement Due to the presence of a variety of aromatic and aliphatic compounds, biological processes may not solely treat the refinery wastewater to a desired extent. On the other hand, AOPs could be expensive when used for one step wastewaters treatment. Thus, they have been introduced as pretreating operations before biological step (Babaei and Ghanbari, 2016). It has been reported that wastewaters can be biologically further treated if BOD5/COD ratio becomesw greater than 0.4

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(Estrada et al., 2012). Here, the BOD5/COD ratio of the wastewater before treatments was 0.36;

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however, as shown in Fig. 8, utilizing the solar Fenton process improved the biodegradability to 0.62 after 180 min.

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For proper evaluation, different alternative processes were investigated under identical

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conditions. In the cases of just solar, solar/H2 O2 and solar/S2 O2− 8 processes, biodegradability was not meaningfully changed, and reached to less than 0.50, which can be attributed to the levels of

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COD and BOD5 decrease (Estrada et al., 2012). It was while, BOD5/COD ratio reached to more 2+ than 0.58 with solar Fenton and solar/S2 O2− processes. The results indicate that 8 /Fe

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2+ biodegradability capability of the studied processes follows the order of: H2 O2 /Fe2+ > S2 O2− 8 /Fe

> NaOCl /Fe2+ > S2 O2− 8 > H2 O2 > NaOCl > solar. Obviously, sunlight alone, with no additive, had no significant effect. It was while using oxidants, the biodegradability was slightly increased, and

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that further assisting by ferrous ions significantly improved the process performance. “Fig. 8”

3.6. Cost effectiveness analysis Cost effectiveness is essential for selecting or evaluating a wastewater treating process.

Accordingly, the total operating costs was considered as the sum of the major imposed costs of electrical energy for the pump and the electromotor for rotating the reactor surface, as well as the

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used chemicals. The required energy for the pump (250 W), during 180 min operation and the electromotor for rotation of the solar-reactor surface (500 W, 3 s on use every 10 min intervals) was totally obtained as 75.8 kWh for each cubic meter wastewater. Given the electrical energy cost in U.S. market as US$0.133/kWh in 2019 (US Energy Information, 2019), the energy cost is obtained as $10.1/m3 for the used process. By adding the price of the required chemicals, i.e. H2 O2 ($0.5/kg) and FeSO4.7H2O ($0.2/kg) (www.alibaba.com, 2019) to the electrical energy costs, the

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total operating costs was obtained as $10.4/m3. Our previous investigation (Saien and Nejati, 2007)

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indicated a much higher energy cost for treatment of real refinery wastewater by UV/TiO2 heterogeneous process. In other work by Fenoll et al. (2012) total operating costs were estimated

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as $30.74/m3 and $178.04/m3 respectively, for solar/ZnO/S2 O2− and solar/TiO2/S2 O2− 8 8

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heterogeneous photodegradation of eight miscellaneous pesticides in drinking water. Babaei and Ghanbari (2016) evaluations indicate a $17.4/m3 total operating costs for COD removal of

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2+ petrochemical wastewater with UV/S2 O2− process. Recently, degradation of furfural in 8 /Fe

aqueous solutions by UV/potassium periodate was investigated and total cost in this work was

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$72.79/m3 (Saien et al. 2017).

Bearing in mind that the solar energy is highly received per each square meter with many clear sunny days in many parts of the world (Najafi et al., 2015), it can easily be accepted that the solar Fenton process enhances the cost efficiency of the refinery wastewater treatment at large-scale and

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looking on a possible coupling with a biological treatment.

4. Conclusions

Solar Fenton treatment of real refinery wastewater was feasible using an automatic rotatable solar-reactor. Results revealed optimal operating conditions of low hydrogen peroxide and very

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trace ferrous salt concentrations at acidic pH, under which the chemical oxygen demand and total organic carbon of solutions were highly decreased during 180 min. The COD removal efficiency could be presented with a quadratic equation and that variations under established optimum conditions well fitted with a pseudo-first order kinetic model. Quantitative analysis revealed that the identified major pollutants were effectively degraded in this process and the biodegradability was improved. Meanwhile, comparing the performance of the employed method with the

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previously reported solar-treatment investigations revealed the highly preference of the employed

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method based on different criteria including the operating costs. The results of this work indicate possibility of implementation of solar Fenton process as an efficient and cost effective treatment

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Declaration of competing interest

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step for real petroleum wastewater.

The authors declare that they have no known competing financial interests or personal

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relationships that could have appeared in this paper.

Acknowledgments

This study was supported by the Arak Petroleum Refinery Company. The authorities are

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acknowledged.

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miscellaneous pesticides in drinking water after treatment with semiconductor materials under sunlight at pilot plant scale. Chem. Eng. J. 204, 54-64.

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Mat. Sol. C. 168, 30-37.

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Table 1. The range and levels of the parameters and CCD matrix of the experiments. levels and ranges -α 61.37

low (-1) 300

middle (0) 650

high (+1) 1000

+α 1238.63

[FeSO4 . 7H2 O] (mg/L)

6.13

30

65

100

123.86

pH

2.65

3

3.5

4

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4.34

pH

COD removal (%)

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65 65 30 65 123.86 65 65 65 100 65 65 65 30 100 100 6.14 30 30 100 65

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61.37 650 1000 650 650 650 650 650 1000 650 650 1238.63 1000 300 300 650 300 300 1000 650

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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Run

Design Matrix [H2 O2 ] (mg/L) [FeSO4 . 7H2 O] (mg/L)

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Parameter [H2 O2 ] (mg/L)

3.5 3.5 4 3 3.5 2.66 4.34 3.5 4 3.5 3.5 3.5 3 4 3 3.5 4 3 3 3.5

12.94 83.75 45.39 80.79 50.18 80.36 70.18 81.9 50.16 79.16 84.87 32.19 51.63 39.18 41.84 42.12 39.36 45.34 56.78 79.18

Table 2. Statistical criteria, ANOVA and lack-of-fit tests for the response quadratic Eq. (7). Degree of freedom

Mean square

F value

Prob > F

Remarks

8362.66 365.12

7 1

1194.67 365.12

318.02 97.19

< 0.0001 < 0.0001

significant

[𝐅𝐞𝐒𝐎𝟒 . 𝟕𝐇𝟐 𝐎]

28.69

1

28.69

7.64

𝐩𝐇 [𝐇𝟐 𝐎𝟐 ] × [𝐅𝐞𝐒𝐎𝟒 . 𝟕𝐇𝟐 𝐎]

109.22

1

109.22

29.07

23.12

1

23.12

[𝐇𝟐 𝐎𝟐 ]𝟐

6247.72

1

6247.72

2245.58

1

𝐩𝐇𝟐

68.95

1

45.08 17.21 27.87 8407.74

12 7 5 19

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Residual Lack of Fit Pure Error Cor Total

22

0.0172

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0.0002

6.15

0.0289

1663.13

< 0.0001

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[𝐅𝐞𝐒𝐎𝟒 . 𝟕𝐇𝟐

𝐎]𝟐

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Sum of squares

2245.58

597.77

< 0.0001

68.95

18.35

0.0011

3.76 2.46 5.57

0.44

0.8422

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Source Model [𝐇𝟐 𝐎𝟐 ]

Non-significant

Table 3. Overview of the recent works performed with solar-reactor.

phenol

-

TiO2/AC

1.2 g/L

heterogeneous

-

-

bench scale

150

80% degradation

(Gar Alalm et al., 2016)

miscellaneous pesticides in drinking water

-

ZnO, TiO2, WO3, ZnS

200 mg/L

heterogeneous

S2 O2− 8

150 mg/L

pilot scale

240

90% removal

(Fenoll et al., 2012a)

100

Fe+2

0.5 g/L

homogenous

H2O2

1.5 g/L

bench scale

120

95% average removal

(Alalm et al., 2015)

reactive dye

-

TiO2

0.5 - 1 g/L

heterogeneous

winery wastewater

-

TiO2

200 mg/L

heterogeneous

gasoline in water and of oil-field- Water

-

Fe+2

1 mM

20–200

petroleum wastewater

-

refinery wastewater

-

Oxidant

Oxidant conc.

TiO2-G/ZnOG

1.2 g/L

heterogeneous

-

-

Solar reactor scale Lab scale

homogenous

Time (min)

Efficiency

Ref.

60

100% degradation

(Malekshoar et al., 2014)

re

-p

ro

Process

-

-

bench scale

300360

90–98% removal

(Damodar et al., 2007)

H2O2, S2 O2− 8

10 mM

pilot scale

400

TiO2, TiO2/H2O2 and TiO2/S2 O2− 8 , originating TOC 10%, 11% and 25% degradation in different cases

(Lucas et al., 2009)

H2O2

300 mM

bench scale

270

60% average degradation

(Moraes et al., 2004)

TiO2

0.1–1 g/L

heterogeneous

-

-

bench scale

720

50% TOC removals

(MendezArriaga et al., 2009)

ZnO, TiO2

0.5, 0.54 g/L

heterogeneous

-

-

bench scale

180

48.5% COD and 15.5% TOC removals

(Palaniandy et al., 2015)

Fe+2

67 mg/L

homogenous

H2O2

694 mg/L

pilot scale

180

79.6% COD and 73.2% TOC removals

This work

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ibuprofen

Catalyst conc.

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pharmaceuticals wastewater

Catalyst type

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phenol

Pollutant conc. (mg/L) 40

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Pollutant type

23

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(a)

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(b)

Fig. 1(a). The used solar photo reactor setup; 1: surface of solar-reactor, 2: light sensor, 3: recycle pump, 4: electromotor for rotation, 5: flow meter, 6: flow recycle valves, 7: storage tank, 8: dynamic Jack. (b). Surface of the solar-reactor; 1: quartz tubes, 2: parabolic polished aluminum reflector sheets, 3: Wind crossing paths, 4: light sensor.

24

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Fig. 2. Variation of COD removal as a function of H2 O2 and FeSO4 . 7H2 O concentrations; pH 3.2.

Fig. 3. Variation of COD removal as a function of H2 O2 concentration and pH; [FeSO4 . 7H2 O] = 67.3 mg/L.

25

90 80

COD TOC

70

50

20 10

R² = 0.9922

of

30

1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0

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40 ln(COD0/COD)

removal efficiency (%)

60

30

60

90

120

150

180

-p

t (min)

0 0

10

20

30

40 QUV (kJ/L)

50

60

70

80

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Fig. 4. Removal efficiency based on COD and TOC versus accumulated solar energy and kinetic diagram based on COD for solar-Fenton process under optimum conditions; [H2 O2 ] = 694.7 mg/L, [FeSO4 . 7H2 O] = 67.3 mg/L and pH 3.2. 100 90

2

R = 0.994

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80

COD removal (%) (Predicted)

70 60 50 40 30

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20 10

0 0

20

40

60

80

100

COD removal (%) (Exprimental)

Fig. 5. The model predicted COD removal versus its experimental values for solar Fenton process.

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Fig. 6. GC/MS headspace chromatograms before (A) and after (B) solar Fenton process under optimum conditions; [H2 O2 ] = 694.7 mg/L, [FeSO4 . 7H2 O] = 67.3 mg/L and pH 3.2.

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90 80

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60 50 40 30

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COD removal (%)

70

20 10 0

H2O2/Fe2+

NaOCl/Fe2+ S2O82-/Fe2+

NaOCl

S2O82-

H2O2

Only solar

Fig. 7. COD removal efficiency for different processes under similar optimum conditions by solar-reactor.

27

0.7

0.6

BOD5/COD

0.5

0.4

0.3

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0.2

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0.1

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0

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Fig. 8. The BOD5/COD values for different processes under similar optimum conditions by solar-reactor.

28