Removal of oil from produced water using electrochemical method

doi:10.21203/rs.3.rs-952455/v1

The produced water usually contains 1000 mg/litre of crude oil in dissolved, suspended and emulsion form. It is required to reduce the crude oil content to less than 40 mg/litre, to meet the latest discharge regulations. Current produced water technologies include centrifugation, compact floatation units, gravity settling, sand filtration, macroporous polymer extraction and ozonation. But their applications have certain disadvantages. This project is aimed to deal with the use of electrochemical methods for the removal of oil from produced water and thereby reducing the environmental impact of produced water. An experimental setup for electrocoagulation, containing a stainless-steel cathode and a mild steel anode is used in the present study. In the electrocoagulation process, the coagulant is generated in situ by electrolytic oxidation of anode material, which facilitates agglomeration or coagulation of oil droplets and suspended solids and resultant separation from the aqueous phase. The response surface methodology software has been used to determine the relation between oil removal performance of the system and operating parameters such as current density, time and initial pH.

Renewable Resources

Environmental Engineering

Produced water

Electrocoagulation

Response surface methodology

COD

Produced water is a term used in the oil industry to describe water that is produced along with oil and gas. Oil and gas reservoirs have a natural water layer (formation water) that lies under the hydrocarbons. Oil reservoirs frequently contain large volumes of water, while gas reservoirs tend to have smaller quantities. The produced water is brought to the surface along with oil or gas during the drilling process. To achieve maximum oil recovery additional water is often injected into the reservoirs to help force the oil to the surface. Both the formation water and the injection water are eventually produced along with the oil and therefore, as the field becomes depleted the produced water content of the oil increases. Large quantities of water are produced along with hydrocarbons in oil and gas fields all over the world. It is by far the largest volume byproduct or waste stream associated with oil and gas production [1].

Produced water is strongly contaminated because the water has been in contact with the hydrocarbon-bearing formation for centuries. It contains some of the chemical characteristics of the formation and the hydrocarbon itself. Produced water mainly contains oil in suspended, dissolved and emulsion forms. It also contains organic acids, traces of heavy metals, formation solids, various bacteria, etc. Dissolved hydrocarbons are found naturally in formation water and can be both toxic and bio-accumulative. Such water-soluble components, which are present in produced water are mainly BTEX (benzene, toluene, ethylbenzene, and xylene), polyaromatic hydrocarbons (PAH), and alkylphenols. These hydrocarbons together with heavy metals considered the most harmful contaminants in produced water.

The objectives of oil and gas produced water treatment include meeting discharge regulations (local, state, and federal), reusing treated produced water in oil and gas operations, developing agricultural water uses, rangeland restoration, cattle and animal drinking water, water for human consumption, and meeting water quality requirements for miscellaneous beneficial uses. Current produced water technologies include centrifugation, gravity settling, sand filtration, macroporous polymer extraction, adsorption and ozonation. But their applications have advantages and disadvantages [12]. The method used in the present study is the principle of electrocoagulation (EC).

Electro-coagulation is the process of destabilizing suspended, emulsified or dissolved contaminants in an aqueous medium by introducing an electrical current into the medium. The electrical current provides the electromotive force to drive the chemical reactions. When reactions are driven or forced, the elements or compounds will approach the most stable state. Generally, this stable state is a solid state that is either less colloidal, less emulsifiable, or less soluble than the element or compound at equilibrium values. As this occurs the contaminants form hydrophobic entities such as precipitates or phase separations, which can easily be removed by a number of secondary separation techniques.

The electrical current is introduced into the water via parallel electrodes constructed of various metals generally selected to optimize the removal process. The two most common electrode materials are Iron (Fe) and Aluminium (Al). By Faraday’s Law, metal ions will be split off or sacrificed into the liquid medium. This will form a nucleus, which will attract the contaminants into a precipitate that will be removed from the treated fluid. These metal ions tend to form metal oxide or hydroxide nuclei that are electro-coagulation attractants to the contaminants, which have been destabilized. The quantity of electrical current required varies with the liquid to be treated. It is necessary to provide sufficiently, but not excess electrical current to remove the unwanted contaminants.

The Electrocoagulation setup used for the present case consists of a pair of mild steel anode and a stainless-steel cathode. Using the principles of electrochemistry, the anode is oxidized (loses electrons), while the water is reduced (gains electrons), thereby making the wastewater better treated. When the anode electrode makes contact with the wastewater, the metal is emitted into the apparatus. When this happens, the particulates are neutralized by the formation of hydroxide complexes to form agglomerates. These agglomerates begin to form at the bottom of the tank and can be siphon out through filtration. However, when one considers an electrocoagulation-flotation apparatus, the particulates would float to the top of the tank using formed hydrogen bubbles that are created from the anode. The floated particulates can be skimmed from the top of the tank.

EC uses no chemicals as coagulating agents. These are generated during the electrolysis process by electro dissolution of a sacrificial anode made of aluminium or iron. Electrocoagulation has been successfully performed for decolorization treatment of dyes and remediation of dyehouse wastewater (Kobya et al., 2003; Akbal and Kuleyin, 2010), treatment of oil wastes (Adhoum and Monser 2004; Un et al., 2009), diary effluents (Tchamango et al., 2010), diesel and biodiesel wastewaters (Chavalparit and Ongwandee,2009; ElNaas et al., 2009), laundry wastewaters (Wang et al., 2009), slaughterhouse effluents(Asselin et al., 2008), arsenic or fluoride-containing waters (Hansen et al., 2007; Huet al., 2008) and heavy metal-bearing effluents (Kongsricharoern and Polprasert, 1996; Adhoum et al., 2004; Heidmann and Calmano 2008; Nouri et al., 2010). El-Naas et al. concluded that through batch experiments it was proven that the most effective treatment for petroleum refinery wastewater was using aluminium electrodes [14]. In vegetable oil refineries also, electrocoagulation is used for the treatment of wastewater [16]. This technique is also efficient in removing metallic pollutants, such as nickel, copper, zinc, and chromium from synthetic aqueous solutions and actual wastewater obtained from a local electroplating unit [17]. Electrocoagulation can also be a pre-treatment for other processes such as Reverse Osmosis, or a polish treatment for traditional treatment processes.

The mechanism of EC is highly dependent on the chemistry of the aqueous medium, especially conductivity. In addition, other characteristics such as pH, particle size, and chemical constituent concentrations will also influence the EC process. The mechanism of removal of ions by EC using iron electrodes is given below:

Iron upon oxidation in an electrolytic system produces iron hydroxide, Fe(OH)_n, where n = 2 or 3. Two mechanisms have been proposed for the production of Fe(OH)₃.

Mechanism I

Anode:

4 Fe_(s) → 4 Fe²⁺ _(aq) + 8e⁻

4 Fe²⁺_(aq) + 10 H₂O _(l) + O_{2 (g)} → 4 Fe(OH)_{3 (s)}

+ 8 H⁺ _(aq)

Cathode:

8H⁺ _(aq) + 8e⁻ → 4 H_{2 (g)}

Overall:

4 Fe_(s) + 10 H₂O _(l) + O_{2 (g)} → 4 Fe(OH)_{3 (s)}

+ 4H_{2 (g)}

Mechanism II

Anode:

Fe_(s) → Fe²⁺ _(aq) + 2e⁻

Fe²⁺ _(aq) + 2OH⁻ _(aq) → Fe(OH)_{2 (s)}

Cathode:

2 H₂O _(l) + 2e⁻ → H_{2 (g)} + 2OH⁻ _(aq)

Overall:

Fe _(s) + 2H₂O _(l) → Fe(OH)_{2 (s)} + H_{2 (g)}

The Fe(OH)n(s) formed remains in the aqueous stream as a gelatinous suspension, which can remove the pollutants from wastewater either by complexation or by electrostatic attraction, followed by coagulation. In the surface complexation mode, the pollutant acts as a ligand(L) to chemically bind hydrous iron:

L – H _(aq) (OH)OFe _(s) → L – OFe _(s) + H₂O _(l)

The pre-hydrolysis of Fe³⁺ cations also lead to the formation of reactive clusters for water treatment. Structural models for these oxy hydroxy iron cations have been extensively reported in the literature [4].

Chemicals:

Conc. Sulfuric acid, silver sulfate, potassium dichromate, Mercuric sulfate, and Ferrous ammonium sulfate are used for COD measurements. 0.1 N Sulfuric acid and 1N NaOH for pH adjustment. All the solutions are prepared with distilled water.

Experimental set-up:

Electrocoagulation is conducted in an undivided reactor of 350 ml volume. The overall experimental setup mainly consists of a cell unit, as shown in the figure 1. Mild steel and stainless steel are used as cathode and anode (radius: 3 cm) are arranged in parallel. The total effective electrode area is 26.002 cm ². The electrodes are connected to a DC power supply (0-30 V, 0-2 A) and all the experiments are to be made at room temperature. Electrolyses are carried out under current controlled conditions. Before the process, the raw produced water sample (350 ml) is filled in the electrolytic cell. The initial pH of the solution is adjusted with 0.1 N sulfuric acid/1 N NaOH. The ionic strength is maintained constant by adding 1.75 g NaCl/ 350 ml. The same procedure is repeated for different reaction times.

Analysis method

The most reliable technique for analyzing oil in produced water is finding the chemical oxygen demand (COD) of the treated sample and comparing it with the untreated sample. COD is an indication of the amount of oil present in the solution and here a standard method for COD determination is used for finding the oil removal.

Preparation of simulated produced water

For the simulation of the process, desalter water is using rather than the produced water, which is supposed to be used. This is because the characteristics and the components found in the desalted water are nearly the same as that of produced water. Desalted water is collected from the desalter of Bharat Petroleum Corporation Ltd. (Kochi refinery). This desalter water along with some crude oil is used as the sample solution, which is having a density of 0.8970 g/cc and COD ranging between 1100-1200.

Experimental procedure

Electrocoagulation of the produced water is carried out in a 500 ml beaker. Mild steel is used as anode and stainless steel is used as cathode. Filtered sample solution with 5 g/litre NaCl electrolyte dissolved in it, is taken in the beaker. The electrolyte is added to the solution to enhance the electrical conductivity of the solution. A magnetic stirrer is also introduced into the reactor to prevent the settling of coagulated particles. The initial pH of the solution is adjusted by using NaOH or HCl. Electrodes are then connected to the DC power supply unit and voltage is adjusted to attain the desired current density. After allowing sufficient reaction time, switch off the power supply. The amount of iron dissolution is found out by weighing the initial and final weight of electrodes and the quantity of sludge produced is calculated by filtering the treated solution using a rough filter paper.

RSM Software

To resolve this problem, response surface methodology (RSM) has been proposed to determine the influences of individual factors and their interactive influences. RSM evaluates the effects of several factors and searching for optimum conditions for desirable responses and reducing the number of experiments [9]. RSM uses an experimental design such as the Box Behnken design (BBD) or Central composite design (CCD) to fit a model by least squares technique [10] Adequacy of the proposed model is then revealed using the diagnostic checking tests provided by analysis of variance (ANOVA). The response surface plots can be employed to study the surfaces and locate the optimum. The present investigation aims at optimization of the current density, time, and initial pH to achieve the highest removal of COD from the produced water sample. The optimization is carried out via Box Behnken (BBD) RSM experimental design. The interaction between factors influencing COD removal is established and models describing the effect of the factors on COD removal are also described [11].

Electrocoagulation of the sample is done for known oil concentrations. Different sample runs are given by the RSM software. The operating parameters for the experiment are CD, time, initial pH, and concentration.

Experimental design and data analysis

As shown in Table 4, a Box Benkhen Design (BBD) in the form of 2³ full factorial design was used, in which three independent variables were converted to dimensionless ones (A, B, C), with the coded values at 3 levels: −1, 0, +1. The arrangement of BBD as shown in Table 2 was in such a way that allows the development of the appropriate empirical equations (second-order polynomial multiple regression equations).

y = constant + aA + bB + cC + aaA² + bbB² + ccC² + abAB + acAC + bcBC ……… (1)

The predicted response (y) was therefore correlated to the set of regression coefficients: the intercept (constant), linear (a, b, c), interaction (ab, ac, bc), and quadratic coefficients (aa, bb, cc). The Minitab (version 14) software is used for regression and graphical analyses of the obtained data. COD removal percent data is processed for Eq. (1). Minitab 14.0 program including ANOVA to obtain the interaction between the process variables and the response. The quality of the fit of the polynomial model was expressed by the coefficient of determination R² and R² adj, and statistical significance was checked by the F-test in the program. The desired goal is selected as maximum COD removal percent at minimum reaction time [10].

In the preliminary experiments, the best results obtained are for horizontal circular electrodes and so the same is used for further treatment of produced water. One pair of mild steel and stainless-steel electrodes having 3 cm. radius is used for secondary experiments. Best COD removal obtained during preliminary experiments is for a current density of 2 A/dm², initial pH of 7, and for a reaction time of 15 minutes, and so these parameters are selected as optimum parameters. Even though the COD removal is found to be increased with increasing NaCl concentration, optimum NaCl concentration is fixed at 5g/litre. This is because more than 5g/litre salt concentration will adversely affect COD determination due to the chloride ion effect. Optimum stirrer speed is selected as 50 rpm since more than 50 rpm stirrer speed has no effect on COD removal.

Table 3 shows COD removal percent and the current efficiency of the sample runs. Run 4 from the table specifically gives the best COD removal of 87.5%, which is obtained at a CD of 2A/dm², initial pH of 7, and for a reaction time of 15 minutes. Specific energy consumptions are also calculated for all the runs.

Evaluation of responses using Minitab 14.0 software:

The experimental results were evaluated by Minitab 14.0 software. The approximating function of COD removal percent(y1) obtained by Minitab 14.0 software is given in Equation (2).

y1 = -385.175 + 66.565A + 6.728B + 98.478C +

0.180D – 6.390A² – 0.099B² – 7.397C2

- 0.000D2 – 2.604AB + 0.523AC - 0.032AD

+ 0.022BC + 0.001BD + 0.010CD

……….(2)

Where, A, B, C & D are the independent variables CD, time, initial pH, and concentration respectively. The coefficients of the above equation will be directly given by Minitab software.

ANOVA results of the model are presented in Table 4, which indicates that the quadratic model could be used to navigate the design space. For Box Benkhen 3 factor design, the F value for regression for this case should be greater than 2.53. For this case, the F value of COD removal is 5.24, and this implies that the model is significant. The values of P less than 0.0500 indicate model terms are significant at a 95% confidence level. So, the regression model is significant at a 95% confidence level. But, the model for lack of fit is significant at a 92.7% confidence level, as its P-value is 0.073. Also, the F value for lack of fit should be less than19.41. Here the F value for lack of fit for COD removal is 13.09, which clearly states that the model is significant.

Statistical parameters obtained from the ANOVA for the reduced model of the responses are given in Table 4. The high R² value, close to 1, is desirable and must be in reasonable agreement with the adjustedR² for a significant model. The value of R² for COD removal is 0.8594. The value of the adjusted R² is 0.6953 is also a reasonable limit to advocate the significance of the model.

Effect of current density:

In any electrocoagulation process, current density (A/dm²) is an important operational parameter setting the ultimate removal and defining the electrical energy and power consumption so eventually the ultimate operating cost for the process. Some investigators have reported that in electrocoagulation, the current density can influence the treatment efficiency [28]. Khosla et al. (1991) reported that the applied current density determines the coagulant dosage rate, the bubble production rate and size, and the flocs growth resulting in faster removal of pollutants. In electrocoagulation, initially, the ferrous ions contribute to charge neutralization of the pollutant particles as the isoelectric point is attained. Here a sorption coagulation mechanism occurs resulting in the formation of loose aggregates. As time progresses, further ferrous ion addition results in ferrous hydroxide precipitation that promotes pollutant aggregation via a sweep coagulation mechanism. During the final stages, coagulated aggregates interact with bubbles and float to the surface or settle to the bottom of the reactor. Measurements were carried out at different current densities 1-2 A/dm², for an operating time of 15 minutes. It may be found that from table3, lower current density has a lesser effect on the COD removal, but removal is rapid with high current density. The highest removal for COD is achieved as 87.5% at a current density of 2A/dm², at 7 initial pH and 15 minutes reaction time. According to these results, as shown in Table 3, the removal rate of COD is increased, as expected, with increasing current density. This was attributed because at high current densities, the extent of anodic dissolution increased and the amount of hydroxo-cationic complexes resulted in an increase of the removal efficiency.

Figure 2 shows that the maximum COD removal of 80% is attained at CD values greater than 1.8 A/dm² for neutral initial pH. All the removal efficiencies reach a maximum level at CD 2 A/dm².

Effect of initial pH:

Generally, the pH of the medium changes during the process, as observed also by some investigators [24,25]. This change depends on the type of anode material and the initial pH value of the treated solution. For iron, the final pH is always higher than the initial pH. The increase of pH at initial pH lower than 7 is ascribed to the hydrogen evolution and the generation of OH- ions at the cathodes (Vik et al., 1984). In an alkaline medium (pH>7) the final pH does not change markedly because the generated OH- ions at the cathodes are consumed by the generated Fe³⁺ ions at the anode forming the needed Fe(OH)₃ flocs. These results suggest that electrocoagulation exhibits some pH buffering capacity, especially in an alkaline medium [24]. Experiments conducted at different initial pH values in the range 1-11 showed that the removal percent of COD is low at pH<7 (Table 3). It increases considerably at pH 7 and substantially decreases at pH>7. The decrease in removal efficiency at strong acidic and strong alkaline pH was described by other researchers (Adhoum et al., 2004; Vasudevan et al. 2009). It was ascribed to an amphoteric behavior of Fe(OH)₃which leads to soluble cations Fe³⁺, Fe(OH)²⁺, Fe(OH)²⁺ (at acidic pH), and monomeric anions Fe(OH)^4-, Fe(OH)^3- (at alkaline pH). It is well known that these species are not useful for water treatment and so pH 7 is selected as the best initial pH.

In the present study, initial pH has no considerable effect on the efficiency of the electrocoagulation process. The COD removal is found maximum at an initial pH of 7 and it is shown in figure 3. But, when comparing to other operating parameters like CD and time, the effect of initial pH on removal efficiency is low.

Effect of operating time:

The effluent treated with the iron electrode appeared yellowish first and then turned green and turbid. This green and yellow color may have resulted from Fe²⁺ and Fe³⁺ ions generated during the EC process. Fe²⁺ is the common ion generated in situ of electrolysis of iron electrode. It has relatively high solubility at acidic or neutral conditions and can be oxidized easily into Fe³⁺ by dissolved oxygen in water (Benefield et al., 1982; Babu et al., 2007). The effect of time was studied at a constant current density of 2 A/dm². Figure 4 illustrates the removal of COD as a function of operating time, which shows that EC time has a significant effect on pollutant removal. When the operating time increased from 3 to 15 minutes, the removal of COD increased from 70.83% to 87.5%. Also, from table 3, it can be noted that the current efficiency is very high for the less operating time and is small for high operating time. In this process, EC involves two stages which are destabilization and aggregation. The first stage is usually short and during this stage large quantity of ferrous ions going into the solution. But there is only a physical reaction that is taking place and chemical reaction is not predominant over this period- especially up to 3 minutes reaction time. So, the amount of iron dissolution is high when comparing to the extent of oil removal and this is the reason for high current efficiency. The second stage is relatively long, and in this stage, the chemical reaction is predominant over the physical reaction. So, the extent of oil removal is high when comparing to the amount of iron dissolution, and hence the current efficiency is low. The following figures show that better efficiency of the EC process was obtained at a treatment time higher than 12.5 minutes and it reaches a maximum at 15 minutes reaction time. Further increase in treatment time has an insignificant improvement in the removal efficiency for the studied parameters.

Cost estimation

The operating cost of the EC process includes energy cost, electrode material cost, and sludge management cost. Total operating cost is the sum of these three factors. For maximum COD removal, the operating cost is calculated as 14.027 Rs/kg COD. This result is in very good agreement with the results found in the literature [26,29]. Operating cost is calculated for different current densities and is graphically represented in figure 5. From the figure, it is clear that the cost increases with the current density. This increase in cost is steeper after 1.5A/dm²current density. So, 1.5 A/dm² is found to be the optimum current density, based on cost estimation parameters.

Produced water is the water that comes along with crude oil or natural gas during the drilling process, and it usually contains more than 1000 mg/litre oil in dissolved, suspended and emulsion form. After the drilling process, produced water is mainly discharged into the sea, which will adversely affect the marine environment due to its high oil content. This project aims to reduce the oil content to meet the latest discharge regulations. Here, the principle of electrocoagulation is applied for the treatment of produced water. Instead of using original produced water, the sample used here is desalter water along with some crude oil from Bharat petroleum Corporation Ltd. (Kochi Refinery), since it is difficult to get the original produced water. The electrochemical treatment of simulated produced water was studied using MS & SS electrodes in the presence of NaCl electrolyte in a batch electrochemical reactor. The literature data showed that the produced water was successfully simulated. The effect of operating parameters on COD removal was optimized using response surface methodology (RSM), and the approximating functions were obtained with satisfactory degrees of fit. The optimum conditions were found at 2 A/dm² current density, 7 initial pH, 50 rpm stirrer speed, and 5 g/L electrolyte concentration within 15 min reaction time. In the sample runs, the highest removal for COD is achieved as 87.5%. According to these results, the electrochemical method could be a strong alternative to conventional physicochemical methods for the treatment of produced water with further research.

1. Acknowledgements: Not applicable

2. Availability of data and materials: Not applicable

3. Funding : Not applicable

4. Competing interests : The authors declare that they have no competing interests

5. Author’s contributions :

Sumayya.V.M. – design, data collection, data analysis and interpretation, drafting the article

Dr.P.A.Soloman – conceptualization, design, critical revision of the article, supervision

6. Author’s info:

Sumayya.V.M. (Main author)

Department of Chemical Engineering

Government Engineering College, Thrissur

Kerala, India. Pin: 680009

Email : [email protected]

Phone : 00971 503133546

Dr.P.A.Soloman (Corresponding author)

Professor,

Department of Chemical Engineering

Government Engineering College, Thrissur

Kerala, India. Pin: 680009

Email : [email protected]

Phone : 00919447865261

Nature technology solution, Introduction to produced water treatment.
E.J. Sullivan (LANL), R.S. Bowman (New Mexico Tech), L. Katz (UT Austin), and K. Kinney (UT-Austin), Water treatment technology for oil and gas produced water.
Federal Regulations: U.S. Environmental Protection Agency, Produced Water Management Information System.
M. Yousuf A. Mollah, Robert Schennach, Jose R. Parga, David L. Cocke, Electrocoagulation science and applications, Journal of hazardous materials B84 (2001), Page no: 2941.
F. Falla Sotelo, P. Araujo Pantoja, J. López-Gejo, G. A. C. Le Roux, F. H. Quina, C. A. O. Nascimento, Application of fluorescence spectroscopy for spectral discrimination of crude oil samples, Brazilian Journal of Petroleum and Gas. v. 2, n. 2, p. 63–71, 2008.
R.H. Myers, D.C. Montgomery, Response Surface Methodology: Process and Product Optimization Using Designed Experiments, 2nd ed., John Wiley and Sons, USA, 2002.
D.C. Montgomery, Design and Analysis of Experiments, 4th ed., John Wiley and Sons, USA, 1996.
R.H. Myers, Response Surface Methodology, Allyn and Bacon, Boston, USA, 1971.
A.I. Khuri, J.A. Cornell, Response Surfaces, Design and Analyses, 2nd ed., Marcel Dekker Inc., New York, 1996.
D.C. Montgomery, Design and Analysis of Experiments, 5th ed., John Wiley and Sons, New York, 2001.
A.L. Ahmada, S.S. Wong a, T.T. Teng b, A. Zuhairi, Optimization of coagulation-flocculation process for pulp and paper mill effluent by response surface methodological analysis, Journal of Hazardous Materials 145 (2007) 162–168.
J. Daniel Arthur, P.E. Bruce, G.Langhus, ph.d., c.p.g., Chirag Patel, Technical summary of oil & gas produced water treatment technologies.
M. Ahmadi, F. Vahabzadeh, B. Bonakdarpour, E. Mofarrah, M. Mehranian, Application of the central composite design and response surface methodology to the advanced treatment of olive oil processing wastewater using Fenton’s peroxidation, Journal of Hazardous Materials B123 (2005) 187–195.
Shammas, N.K.; Pouet, M.; Grasmick, A. Wastewater Treatment by Electrocoagulation–Flotation. In Flotation Technology; Wang, L., Eds.; Springer: New York, NY, USA, 2010; pp. 99–124
Erick Butler 1,*, Yung-Tse Hung 1, Ruth Yu-Li Yeh 2 and Mohammed Suleiman Al Ahmad 1, Electrocoagulation in Wastewater Treatment, Water, ISSN 2073 – 4441.
Umran Tezcan, A Savas Koparal, Ulker Bakir, Electrocoagulation of vegetable oil refinery wastewater using aluminium electrodes, Science direct, Volume 90, Issue 1, January 2009.
Konstantinos Dermentzis, Achilleas Christoforidis, Evgenia Valsamidou, Removal of nickel, copper, zinc, and chromium from synthetic and industrial wastewater by electrocoagulation, International journal for environmental sciences, Volume 1, No 5, 2011.
Mohammed Y.A. Mollah, Paul Morkovsky, Jewel A.G. Gomes, Mehmet Kesmez, Jose Parga, David L. Cocke, Fundamentals, present and future perspectives of electrocoagulation, Journal of Hazardous Materials B114 (2004), Page no: 199210.
Parag R. Cogate, Anirudha B. Pandit, A review of imperative technologies for wastewater treatment I: oxidation technologies at ambient conditions, Advances in environmental research (2003).
J. Daniel Arthur, P.E., Bruce G. Langhus, Ph.D., C.P.G., Chirag Patel, Technical summary of oil & gas produced water treatment technologies.
Argonne national laboratory, John A. Veil, Markus G. Pudar, Deborah Elcock, Robert J. Redweik, A white paper describing produced water from the production of crude oil, natural gas, and coal bed methane.
Russell V. Lenth, Response-Surface Methods in R, Using RSM, Updated to version 1.40, 28 July 2010.
Raymond H. Myers, Douglas C. Montgomery, Christine M. Anderson-Cook, Response surface methodology: process and product optimization using designed experiments, Third edition, Wiley publications.
X. Chen, G. Chen, P.L. Yue, Separation of pollutants from restaurant wastewater by electrocoagulation, Sep. Purif. Technol. 19 (2000) 65–76.
E.A. Vik, D.A. Carlos, A.S. Eikum, E.T. Gjessing, Electrocoagulation of potable water, Water Res. 18 (1984) 1355–1360.
Mehmet Kobya, Orhan Taner Can, Mahmut Bayramoglu, Treatment of textile wastewaters by electrocoagulation using iron and aluminum electrodes, Journal of Hazardous Materials B100 (2003) 163–178.
Poü`et MF, Grasmick A, (1995), Urban wastewater treatment by electrocoagulation and flotation, Water Sci and Technol 31 (3-4): 275–283.
D.Ghosh, C.R.Medhi, H.Solanki, M.K.Purkait, Decolorization of crystal violet solution by electrocoagulation, Journal of environmental protection science (2008), vol. 2, pp. 25–35.
Soloman Poopana Antony, Balasubramanian Natesan, Optimization of the integrated electro-bio process for bleaching effluent treatment, Industrial engineering and chemistry research 2012, Vol. No. 51, Page No. 8211-8221.

Due to technical limitations, Tables 1 and 2 are only available as a download in the Supplemental Files section.

Table3: Responses for the sample runs

Run No.	Final pH	CE%	COD R%	SEC(kWh /kg COD)	SEC ( kWh /kg Fe dissolved)
1	8.84	125.52	30.21	1.345	1.606
2	9.49	107.06	70.83	1.584	2.60
3	11.0	87.13	78.13	1.733	1.542
4	10.74	95.98	87.5	7.296	3.30
5	8.97	85.32	46.67	7.760	2.925
6	10.06	83.68	30	13.464	3.326
7	9.26	86.96	40.85	4.467	3.422
8	9.30	73.83	32.39	3.815	2.73
9	9.25	91.06	46.67	3.781	2.003
10	9.64	100.9	66.67	7.243	2.473
11	9.39	93.52	66.67	1.165	2.361
12	10.46	98.45	80.28	3.226	3.218
13	8.45	49.22	35.42	2.048	4.875
14	10.41	79.74	50	8.415	3.491
15	9.46	113.21	26.04	2.340	1.78
16	10.64	89.59	41.67	6.616	2.036
17	9.33	68.91	41.67	2.089	2.089
18	9.61	81.22	62.5	5.757	3.664
19	9.19	54.15	37.5	4.024	4.609
20	9.71	84.91	60.42	5.379	3.165
21	8.64	123.06	73.33	1.646	2.028
22	9.97	40.36	75	8.667	6.659
23	8.66	73.83	70.42	0.919	4.29
24	10.74	86.63	74.65	2.891	2.438
25	9.88	95.16	78.13	2.229	2.017
26	9.88	95.16	71.87	2.422	2.017
27	9.88	95.16	75	2.321	2.017

Table4: ANOVA results of the quadratic models

Source

DF

F

P

COD removal % :

Regression

Residual error

Pure error

Lack of fit

14

12

2

10

5.24

13.09

0.003

0.073

R-Sq = 85.94% R-Sq(adj) = 69.53%

Tables1and2.docx

Removal of oil from produced water using electrochemical method

Status:

Version 1

Abstract

Figures

Introduction

Principle Of Electrocoagulation

Reactions Involved In The Ec Process

Mechanism I

Mechanism II

Materials And Methods

Results And Discussion

Conclusion

Declarations

References

Tables

Supplementary Files

Status:

Version 1