The concentration of organic matter present in PW represented by COD demonstrated a reduction from 3790 mg/L to 2849 mg/L over a 30 min period of EC, translating to a 25% removal (see Figure 9). To put this into perspective, the initial COD levels reported in the used PW are considerably higher than those reported for other PW from different oil fields, such as the 1560 mg/L found in Malaysian oil fields. Ezechi et al. reported a 52% COD removal efficiency using EC in treating PW with an initial COD of 1560 mg/L [30]. Another study showed that a subsequent biological treatment could achieve up to 97% COD removal efficiency from PW with an initial COD concentration of 600 mg/L [39]. Notably, the EC and biological treatment efficiencies reduced to 39% when applied to PW with high initial COD, indicating that while biological treatment is highly effective in certain conditions, its efficacy is contingent upon the concentration of pollutants. This suggests the necessity of tailoring treatment systems to the specific characteristics of the PW.

The EC exhibited a substantial reduction in TOC from an initial concentration of 1320.30 mg/L to 490.25 mg/L at its lowest point over 30 min, as shown in Figure 10. This corresponds to a peak removal efficiency of nearly 60%. Such results confirm the efficacy of EC in removing TOC from PW, aligning with other treatments like photo-Fenton oxidation, which also reports TOC removal efficiencies of around 60%. The obtained TOC removal via simple EC configuration confirms the suitability of this process in treating PW. Other studies reported TOC removal of 60% from PW using photo-Fenton oxidation. The utilization of a heterogeneous catalyst was pointed out to be instrumental in enhancing the TOC removal efficiency, particularly by optimizing hydrogen peroxide use. It is noteworthy, however, that over time, the removal rate tends to decline, attributed to the decomposition of hydrogen peroxide into less reactive oxygen, thus slowing down the reaction rate [40]. The investigation further identifies the LaFeO₃ catalyst structure as particularly effective, exhibiting a 60% removal efficiency for TOC, underscoring the significant role that tailored catalyst structures can play in improving PW treatment outcomes. This suggests a promising area for further research and optimization in the field of water treatment technologies, aiming to achieve high efficiency in TOC removal from PW.

Figure 11 presents the reduction in O&G levels in PW during EC tests. The O&G was markedly reduced from 44 mg/L to 2.0 mg/L via EC, achieving a removal efficiency of 99.6%. This signifies that EC is an exceptionally effective method for the elimination of O&G. Fine-tuning controllable parameters is essential to further decrease pollutant levels to target concentrations. In their 2020 study, Manilal et al. examined O&G removal in synthetically prepared PW using an EC system. They discovered that increasing current density and salt content in the water improved removal efficiency due to the oxidative mechanisms involved. They reported a maximum removal efficiency of 96.4% with an optimal pH of 7 and a current density of 0.8 A/dm² [41]. In contrast, experiments conducted in this study employed a higher current density of 2.0 A/dm² and achieved a slightly elevated pH of just over 10. The discrepancy in O&G removal efficiency between these studies is attributed to the differences in the initial O&G concentration in the PW.

Chloride ions (Cl⁻) are a significant concern in PW, with implications for the corrosion of steel structures; the corrosion mechanisms intensify as the chloride concentration increases. The data presented in Figure 12 reflect the variable behavior of chloride concentration during a 30 min EC treatment process. The initial chloride concentration was approximately 9360 mg/L, with a minor removal observed throughout the treatment, reaching a low of 7835.62 mg/L. The apparent inconsistency in chloride reduction could be due to several factors, including the complex nature of EC and its interactions with various contaminants in PW. It is essential to recognize that chloride levels in PW can be significantly higher than in freshwater, sometimes up to fourteen times the concentration found in seawater. The removal of chloride ions from PW can be approached through various methods such as adsorption, membrane separation [42], advanced oxidation, and chemical precipitation [43]. A comparative study by Olajire et al. on PW from a Chinese shale gas field evaluated the effectiveness of the RO process [2]. This study reported a dramatic reduction in chloride concentration from 11,000 mg/L to 97 mg/L, corresponding to a chloride removal efficiency of 99.1%. Such high efficiency proposes the RO for the treatment of high-chloride PW. The variance observed in the EC treatment process points to potential limitations when dealing with ionic contaminants such as chloride. It suggests that while EC is effective for certain types of contaminants, it might require optimization or combination with other treatment processes, like RO, for comprehensive decontamination. To enhance the removal efficiency of chloride and other ions from PW, it is imperative to continue investigating the interaction of EC with ionic species and to explore integrated treatment systems that combine EC with other established methods. Such integrative approaches could offer a more robust solution for the treatment of PW, ensuring the mitigation of corrosion risks and the protection of infrastructure.

Figure 13 and Figure 14 reveal the effectiveness of the EC process in the removal of diluted concentrations of hydrocarbons, specifically BTEX, from PW. At the outset, benzene exhibited the highest initial concentration at 2801.0 µg/L, followed by toluene at 1674 µg/L, xylenes at 811 µg/L, and ethyl benzene at the lowest with 101 µg/L. After undergoing EC treatment, substantial reductions were observed, resulting in concentrations of 1024 µg/L for benzene, 432 µg/L for toluene, 129 µg/L for xylenes, and 11.0 µg/L for ethyl benzene.

Another set of EC experiments was carried out with the original BTEX concentration from PW. Untreated PW has alarmingly high levels of toluene at 36,000 µg/L and benzene at 72,000 µg/L. These constituents were significantly reduced through the EC treatment process, with removal efficiencies exceeding 99%, illustrating EC’s capability to drastically reduce BTEX concentrations in PW. Silvia Jiménez et al. underscored the rapid removal of BTEX using AOP in PW treatment [18], Olajire et al. highlighted that microalgae could achieve 100% benzene removal from PW [2], regardless of concentration by Alsarayreh et al. [44].

Fenton oxidation was also mentioned as favorable for benzene removal due to its higher reaction rate [19]. However, all these processes are expensive and complicated. On the other hand, the EC process particularly showed a remarkable removal efficiency for xylenes, with reductions from 13,400 µg/L to 130 µg/L. Yet, to achieve complete BTEX removal, EC likely needs to be combined with advanced polishing systems [45]. Fakhru’l-Razi et al. reported a 54% removal efficiency for xylenes using membrane filtration (MF and UF), which also nearly completely removed heavy metals [46]. While EC experiments have shown that heavy metals are not effectively removed by EC, this aligns with theoretical expectations. Consequently, combining EC with membrane processes is recommended for comprehensive heavy metal removal [31]. Conventional adsorption differs from EC by generating adsorbent particles for colloidal removal but is less effective for heavy metal ions. AOPs have been efficacious in degrading heavy metal complexes, Du et al. have documented [47], with various AOPs achieving between 60 and 90% efficiency for heavy metal removal. In conclusion, EC demonstrates promise for BTEX removal in PW. However, to optimize its effectiveness, further investigation into the process’s degradation efficiency and electrode longevity is warranted, particularly at higher BTEX concentrations. Integrating EC with advanced oxidation and membrane technologies appears to be the most effective approach for holistic PW treatment, efficiently addressing both organic compounds like BTEX and inorganic constituents such as heavy metals.

Figure 15 illustrates the progression of various ions throughout EC tests. The initial potassium concentration is 208.322 mg/L and exhibits a gradual decline over time, reaching a final value of 193.000 mg/L after 30 min of EC. This suggests that potassium ions may be consumed or removed during the electrochemical process. The initial sodium concentration is 2768.980 mg/L, reaches its highest point at 15 min (3159.960 mg/L), and subsequently drops gradually, reaching a final value of 2664.160 mg/L. The EC reactions may entail the participation of sodium ions, and their oscillations can be attributed to a range of variables, including the production and dissolution of compounds. The concentration of silica exhibits significant fluctuations, with a decrease from 4.922 to 3.234 mg/L after 25 min. The iron concentrations exhibit a notable increase subsequent to the initial test, potentially suggesting the deposition of iron on the electrodes as a component of the electrochemical therapy.

PW is a complex wastewater that contains many constituents as well as a mixture of organic and inorganic components [48]. Table 2 provides a comprehensive analysis of various contaminants in untreated PW and the corresponding reductions achieved at incremental time intervals through EC treatment. The COD was initially at 3790 mg/L. EC treatment progressively decreased this parameter, reaching 2525 mg/L at the 30 min mark, reflecting a modern purification effect that required further treatment to reuse that water for industrial purposes. Similarly, TOC levels saw a substantial decline from 1320.3 mg/L to 619.0 mg/L, indicating the breakdown of organic compounds and the potential for further reuse after EC treatment. For specific inorganic ions like bromide, chloride, sulfate, and heavy metals such as chromium, potassium, and sodium, the variations in concentration after EC treatment depict a complex behavior. Notably, while bromide levels reduced to 60.3 mg/L, chloride saw an unusual peak at the 20 min mark before settling at 9426.00 mg/L, hinting at ion-specific interactions within the EC process. The EC method also proved highly effective in reducing O&G content to less than 10 mg/L, significantly decreasing the environmental impact and enhancing the feasibility of water reuse. Remarkably, the EC process showed impressive efficacy in reducing BTEX concentrations. For instance, toluene was reduced from 36,330.0 µg/L to 432.0 µg/L, and benzene from 72,272.0 µg/L to 1024.0 µg/L, showcasing the potential of EC in mitigating these harmful organic compounds. Despite these positive outcomes, the variable results for heavy metals suggest that while EC can significantly purify PW, it may not be uniformly effective across all contaminants. Metals like cadmium, copper, and mercury remained below detection limits, while iron and lead showed decreased concentrations after treatment. This indicates that EC, while capable of treating certain metal contaminants, might require a supplementary treatment process for others to achieve comprehensive water reuse standards.

According to the study of EC technique for processing wastewater treatment reported by [27], CD and hydrolysis time are the most effective parameters for EC efficiency. Therefore, the link between the coagulant dissolved load and EC process intensity from the anode can be explained by using Faraday’s law of electrolysis (Formula (6)) [28]:
where w is the total amount of metal dissolved (g). M is the molecular weight (g/mol). I is the current applied from the power supply (A). t is the hydrolysis time (s). n refers to the number of electrons involved in the reaction. F represents Faraday’s law constant (96,500 C/mol).

The first experiment (Table 2) showed a slight improvement in terms of pollutant removal by increasing the hydrolysis time and maintaining the current at 1.35 amps (CD = 630 A/m²). The first possible reason for lower efficiency refers to the increment of pH from 4 to 10 with extended hydrolysis time and the possibility of other reactions that took place than the electrons released from the anode. The change in Ph could be attributed to the CO₂ stripping off due to hydrogen gas production at the cathode [26]. It also strongly depends on the carbonate concentration in PW [49]. The second possible contribution could be connected to the ion exchange by chloride and sulfate ions into flocs Fe(OH)₃ [49]. The third possible reason is the limitation of the released iron due to the fouling of the electrode, which was clearly observed after the experiment.

Operating time is proportional to the electrode consumption. Figure 16 shows the electrode consumption for different electrical currents applied to the EC process almost steadily for every minute. The weight of the iron electrode decreased by 0.8 and 1.5 g when applied current at 0.75 and 1.87 amps, respectively. This indicates that the higher current or extended electrolysis time can increase the removal rate of pollutants. Nevertheless, it was observed that the quantity of flocs is more when supplying a high current. The result indicates that the dry solids are 2.41% and 2.62% when applied 0.75 and 1.87 amps, respectively. Furthermore, in Faraday’s law, the calculated amount of metal dissolved (Formula (6)) was found to be 0.3 and 0.8 g for the 0.75 and 1.87 amps tests, respectively. The deviation is observed between the experimental and theoretical dissolution rates. According to the literature review, Sasson et al. described the gap and highlighted the correction factors, such as Faradic yield and current efficiency, that were not predicted in Faraday’s law since it was approved at the beginning of the 20th century. The theoretical values of dissolution rate are valid only when all electrons participate in the metal dissolution reaction at the anode and should not react with any other reaction, such as OER near the anode [28]. The applied current controls the amount of dissolved ions and hydroxyl production [50].