Chemical Oxygen Demand Elimination Research Articles

Production of Methane and Hydrogen from Mild-Strength Industrial Wastewater

Over the past two decades, fossil fuel reserves have sharply shrunk, which has resulted in a global fall in energy sources. Alternative carbon-neutral renewable energy sources have caught the interest of experts due to the erratic nature of energy prices and their severe ecological effects. The treatment plant’s mild-strength effluent from an equalization tank at an industrial factory was used in this study to generate hydrogen and methane. This mild-strength effluent had a chemical oxygen demand (COD) content of 2.8 ± 1.0 g COD/L. A double stage anaerobic digestion system’s hydrogen-generating digester was run at a hydraulic retention time of 8 h while the methane-generating digester was run at a hydraulic retention time of 24 h. The highest methane production rate (MPR), methane yield (MY), methane content and COD elimination were, in order, 71 ± 30 mL/L-d, 57 ± 10 mL/g COD, 90 ± 1% and 77%, respectively. In this experiment, energy efficiency was assessed using the following criteria: Maximum heating was at a value of 2.1 × 108 kcal/y. Utilizing energy-equivalent coal, natural gas, or fuel reduced annual carbon emissions by 8.7 × 104 kg CO2/y, 5.1 × 104 kg CO2/y and 7.1 × 104 kg CO2/y, respectively.

Optimization of operational parameters using central composite design in the peroxi‐alternating current‐electrocoagulation process for the pollutant removal with determination of power consumption from industrial wastewater

AbstractThe utilization of electrochemical and advanced oxidation technologies for industrial wastewater (IW) treatment has grown in popularity during the last two decades. The effectiveness of several methods for treating IW, including hydrogen peroxide (H2O2), direct‐current (DC) and alternating‐current (AC)‐electrocoagulation (EC), and the combination of H2O2 with DC/AC‐EC (H2O2‐DC/AC‐EC) processes were all investigated. In comparison to the H2O2, DC/AC‐EC, and H2O2‐DC/AC‐EC technologies, the results showed that the H2O2‐AC‐EC process produced 100% total colour and 100% chemical oxygen demand (COD) removal efficiency with a low power consumption of 4.4 kWhm−3. The H2O2/AC‐EC technology was optimized for treating IW using a response surface methodology approach based on a central composite design using a five‐factor level. Utilizing statistical and mathematical techniques, the optimum parameters were determined to minimize consumption of power (1.02 kWhm−3) and maximum COD elimination (75%). The experimental parameters comprised the following: H2O2 of 600 mg/L, current of 0.65 Amp, pH of 7.6, COD of 1600 mg/L, and treatment time (TT) of 1.26 h. When using a Fe/Fe electrode combination with the wastewater pH of 7, the COD removal efficiency was shown to be enhanced by increasing the TT, current and H2O2, and decreasing the COD concentration. The synergistic impact, quantified as the combined efficiency of eliminating % COD utilizing the H2O2, AC‐EC, and H2O2/AC‐EC procedures, was found to be 15.75%. Therefore, employing a hybrid H2O2‐AC‐EC approach is considerably more effective in treating IW.

Development of data-driven models for the optimal design of multilayer sand filters for on-site treatment of greywater

Greywater, with limited content of pathogens, makes up more than half of the produced wastewater in urban areas. Given the high cost of wastewater management and treatment, it causes sense to collect greywater separately at the source and employ an on-site treatment system to increase opportunities for on-site water reuse. For this purpose, this paper aims to propose a multilayer granular filter as an inexpensive and simple on-site treatment method for greywater reuse. Furthermore, as determining the optimal structure of multilayer filters is a serious challenge, a simulation-optimization model is developed for determining the best filter configuration. An Artificial Neural Network (ANN) is trained based on experimental results to simulate the filter performance with different combinations of layers and the Genetic Algorithm (GA) is used to find the optimal thickness of different layers based on ANN simulation results. The proposed filter in this paper for greywater treatment consists of silica sand (in three different gradings) and activated carbon (with fixed grading) and treatment measures for evaluation of filter performance are considered as Chemical Oxygen Demand (COD) and Electrical Conductivity (EC). Due to difficulties in collecting, transferring, and storing the real greywater, synthetic greywater was used in this study. 49 experiments with different combinations of filter media thicknesses were performed and the performance of the filter was analyzed. Generally, three-layer filters perform better in COD and EC reduction, however, the average COD and EC elimination equals 36.3% and 15.1%, respectively, which indicates more efficiency of filter in COD reduction in comparison with EC. Based on the optimization-simulation model and experimental results, a filter consisting of 33 cm of fine sand, 20 cm of activated carbon, and 7 cm of medium sand results in the maximum efficiency and can reduce the COD and EC of greywater by 72% and 30%, simultaneously. According to the optimization outputs, the ideal filter can treat greywater up to having EC of 1000 μS/cm and COD of 321 mg/L, which is generally suitable for irrigation purposes.

Doxycycline Removal by Solar Photo-Fenton on a Pilot-Scale Composite Parabolic Collector (CPC) Reactor

In this study, the solar photo-Fenton (SPF) process was investigated for the degradation of doxycycline (DOX) using a solar compound parabolic collector (CPC) reactor and a borosilicate serpentine tube with an irradiated volume of 1.8 L. The influence of the operating parameters, such as H2O2, Fe2+ dosage, and DOX concentration, was investigated. The optimum H2O2, Fe2+ dosage, and DOX concentration were found to be 4, 0.1, and 0.06 mM, respectively. The results of photo-Fenton experiments fitted the pseudo-first-order kinetic equation (R2 = 0.99). The efficiency of the treatment under optimized conditions was analyzed by an HPLC analysis of the samples, chemical oxygen demand (COD), and total organic carbon (TOC). The results obtained showed that the solar photo-Fenton process achieved a DOX degradation of 95.07%, a COD elimination of 81.43%, and a TOC elimination of 73.05%. The phytotoxicity tests revealed a 73.32% decrease in the germination index of watercress seeds, demonstrating that the SPF process minimizes the toxicity of the chemical and did not have any negative impact on plant growth. Overall, the results of this study suggest that SPF is a promising technology for the removal of doxycycline from wastewater.

Raw fruit juice processing wastewater treatment using electrochemical coagulation followed by synthesis of CuO Nano sorbents using leaf extract

Stainless steel and aluminium electrode was utilized inside batch electro chemicals coagulations (BECCs) using current densities (CD) for the treatment of fruit juice processing wastewater (FJPW). During ECC, ~65-70% color removal and COD removal of ~55-60% was observed for CD 260 A/m2 at 75 min electrolysis time for both 4SS (four stainless steel) and 4Al (four aluminium) electrodes. In general, 4SS and 4Al electrodes had less influence on FJPW for all CDs. Therefore, to improve the quality of treatment of leftover color and COD by BECC treatment, the batch adsorption studies were conducted as secondary treatment by synthesis of CuO nanoparticles using Carica papaya, Centella asiatica (CA), Ocimum sanctum and 1:1:1 mixture of leaves. An effect of several operating parameters like adsorbent dose, pH, and contact duration on leftover color and COD removal was studied for optimal conditions to treat FJPW. The results showed that ~70% color and ~65% Chemical Oxygen Demand elimination at an optimal condition for adsorbent dosages 0.60 g/L, at pH 8.0 to 8.5 and contact time 40 min for CA and 1:1:1 mixture of leaves. Altogether, BECC - nanosorption, a dual treatment, effectively treated FJPW wastewater with clean water reclamations of up to 90%.

Characteristics of Biogas Production and Synergistic Effect of Primary Sludge and Food Waste Co-Digestion.

The online version contains supplementary material available at 10.1007/s12155-023-10620-8.

Treatment of Petroleum Refinery Wastewater by Sono Fenton Process Utilizing the in-Situ Generated Hydrogen Peroxide

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 concentration. Additionally, the results revealed that the concentration of 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 externally, classical Fenton and sonolysis processes showed that the combined process of sono-Fenton is better than individual processes and the external addition of .

Optimized photodegradation of palm oil agroindustry waste effluent using multivalent manganese-modified black titanium dioxide.

This article presents a methodological approach to use manganese (Mn3+Mn7+)-modified black titanium dioxide (Mn/BTiO2) as a photocatalyst to optimize and improve visible-light-driven photodegradation of treated agro-industrial effluent (TPOME). A modified wet chemical process was used to prepare BTiO2. The BTiO2 was then wet impregnated with Mn and calcined at 300 °C for 1 h to produce Mn/BTiO2. The activity of Mn/BTiO2 was investigated in terms of photo-assisted elimination of chemical oxygen demand (COD), phenolic compounds (PCs), color, and total organic carbon (TOC). Using the design of experiments (DOE), the conditions of the photocatalytic process, including photocatalyst loading, Mn concentration, hydrogen peroxide (H2O2) dose, and irradiation time, were optimized. Under the optimum conditions (0.85 g/L photocatalyst loading, 0.048 mol/L H2O2 dose, 0.301 wt.% Mn concentration, and 204 min irradiation time) COD, PCs, color, and TOC removal efficiencies of 88.87%, 86.04%, 62.8%, and 84.66%, respectively, were obtained. Statistical analysis showed that the response variable's removal from TPOME estimation had high R2and low RMSE, MSE, MAD, MAE, and MAPE values, indicating high reliability. This study demonstrated the significant potential of the developed photocatalytic system for the treatment of waste effluent generated by the palm oil industry and other agro-industries, with the ability to simultaneously reduce a number of organic pollution indicators (OPIs).

Removal of COD from real oily wastewater by electrocoagulation using a new configuration of electrodes.

In order to bring the chemical oxygen demand (COD) concentration down to safe levels for widespread use, this study plans to use a state-of-the-art electrocoagulation reactor (ECR) to treat real oily wastewater discharged from the Al-Muthanna petroleum refinery. A one-side finned (1SF) cathode tube was positioned between two tubular anodes in the continuous ECR, where the active area of the cathode was much more than its submerged volume. Each of these electrodes was made of aluminum and joined in a monopolar parallel to a DC power supply. On COD elimination efficiency, the impacts of operational parameters such as electrolysis time (4-60min), current density (0.630-5.000mA/cm2), and flow rate (50-150ml/min) were explored. In conclusion, Increasing current density and electrolysis duration increases COD removal efficiency, whereas increasing flow rate reduces it. COD removal efficiencies were 82% at optimal electrolysis times of 60 (min), 5 (mA/cm2) current density, and 50 (ml/min) flow rate, with energy consumption of 4.787 (kWh/kg COD) and electrode consumption of 0.544 (g). The investigation results demonstrated that the new reactor could treat oily wastewater within the specified operational limits. It might be used before other, more conventional treatments.

Factorial Design Statistical Analysis and Optimization of the Adsorptive Removal of COD from Olive Mill Wastewater Using Sugarcane Bagasse as a Low-Cost Adsorbent

This work highlights the elimination of chemical oxygen demand (COD) from olive mill wastewater using sugarcane bagasse. A 25−1 fractional factorial design of experiments was used to obtain the optimum conditions for each parameter that influence the adsorption process. The influence of the concentration of sugarcane bagasse, solution pH, reaction time, temperature, and agitation speed on the percent of COD removal were considered. The design experiment describes a highly significant second-order quadratic model that provided a high removal rate of 55.07% by employing optimized factors, i.e., a temperature of 60 °C, an adsorbent dose of 10 g/L, a pH of 12, a contact time of 1 h, and a stirring speed of 80 rpm. The experimental data acquired at optimal conditions were confirmed using several isotherms and kinetic models to assess the solute interaction behavior and kind of adsorption. The results indicated that the experimental data were properly fitted with the pseudo-first-order kinetic model, whereas the Langmuir model was the best model for explaining the adsorption equilibrium.

Chemical Oxygen Demand (COD) and Total Suspended Solid (TSS) Removal from Rubber Wastewater Factory Using Electrocoagulation Technique

Rubber industrial wastewater is obtained during washing, shredding, grinding, crumbbing, drying, and pressing bokar. The wastewater produced can be an environmental pollutant because it contains relatively large amounts of organic matter. One alternative to treating rubber wastewater is to use the electrocoagulation process, which is a combination of the coagulation and electrolysis processes. This electrocoagulation process has several advantages in the form of simple equipment, short time, produces odorless wastewater, does not require large areas of land, and can remove various contaminants in water. In this study, rubber wastewater was treated by electrocoagulation using a batch system with variations in the contact time used, namely 20, 40, 60, 80, and 100 minutes. This type of research is experimental research, and descriptive analysis is carried out. Rubber wastewater is physically gray-black before treatment and chemically contains large organic matter. The results of this study showed that the content of chemical oxygen demand (COD) and total suspended solids (TSS) before processing had values of 691 mg/L and 317 mg/L. Optimum conditions for the elimination of COD and TSS contents were achieved within 80 minutes with the percentage of elimination being 89% and 85%.

Combining Constructed Wetlands and UV Photolysis for the Advanced Removal of Organic Matter, Nitrogen, and Emerging Pollutants from Wastewater

This study reports the performance of a three-step lab-scale system including a hybrid digester (HD), a vertical flow (VF) constructed wetland, and a photodegradation (PD) lamp, with two different arrangements regarding the position of the recirculation point. In addition to total suspended solids (TSS), chemical oxygen demand (COD), and nitrogen compounds, removal of the following pollutants was investigated: paracetamol (ACE), ofloxacin (OFL), caffeine (CAF), ketoprofen (KET), ibuprofen (IBU), clofibric acid (ACB), bisphenol A (BPA), and sotalol (SOT). An excellent performance of HD was achieved on the elimination of TSS (82.2 ± 18.5% on average) and COD (63.9 ± 4.1%). TSS and COD removal increased to 91.2 ± 0.4% and 83.4 ± 2.9%, respectively, for the combined HD–VF system. Ammonia removal was 57.0 ± 7.8% in the VF unit while significant denitrification occurred in the HD. The overall HD–VF–PD system achieved mean removals of 100% for OFL, KET, SOT, and IBU, 98 ± 2% for ACE, 87 ± 8% for CAF, 81 ± 38% for ACB and 26 ± 9% for BPA. The removal of ACE, OFL, CAF, and IBU was mostly by biodegradation in the HD and VF units while the PD unit was responsible for the removal of KET, ACB, and SOT.

Implementation of FeSO4·H2O as an Eco-Friendly Coagulant for the Elimination of Organic Pollutants from Tertiary Palm Oil Mill Effluent: Process Optimization, Kinetics, and Thermodynamics Studies

The biologically treated palm oil mill effluent (POME) urges further treatment to minimize the residual pollutant concentration for safe discharge in the nearest watercourse. In the present study, the post-treatment of biologically treated POME was conducted using ferrous sulfate monohydrate (FeSO4·H2O) as a coagulant. The influence of the FeSO4·H2O coagulation of POME was determined on the elimination of biochemical oxygen demand (BOD), suspended solids (SS), and chemical oxygen demand (COD) with varying flocculation time (min), slow mixing speed (rpm), coagulant doses (g/L) and pH. The FeSO4·H2O coagulation–flocculation experimental conditions were designed following the central composite design (CCD) of experiments and optimized by employing response surface methodology (RSM) based on the optimal SS, COD, and BOD elimination from POME. The maximum BOD, SS, and COD elimination achieved were about 96%, 97%, and 98%, respectively, at the optimized experimental condition. The surface morphology and elemental composition analyses of raw FeSO4·H2O and sludge generated after coagulation revealed that the FeSO4·H2O effectively removed the colloidal and suspended particles from POME. The well-fitted kinetic model equation was the pseudo-second-order kinetic equation to describe the FeSO4·H2O coagulation–flocculation behavior. The thermodynamics properties analyses revealed that the FeSO4·H2O coagulation of POME was non-spontaneous and endothermic. The residual SS, COD, and BOD in treated POME were determined to be 28.27 ± 5 mg/L, 147 ± 3 mg/L, and 6.36 ± 0.5 mg/L, respectively, lower the recommended discharged limits as reported by the Department of Environment (DoE), Malaysia.

Pollutant removal from cheese processing effluent using effective indigenous natural scavengers.

The goal of this study was to come up with an efficient method for treating cheese production wastewater. Because the effluent has a higher concentration of organic and inorganic materials, the indigenous microbial treatment process was used to effectively remove total dissolved solids (TDS), chemical oxygen demand (COD), and color without the addition of any nutrients. The indigenous microorganisms were tested for color, TDS, and COD elimination by growing them in "nutrient broth medium" loaded with different amounts of cheese effluent. The isolates were identified by 16S rRNA sequencing, and the results revealed that strain 1 was Enterobacter cloacae, strain 2 was Lactococcus garvieae, and strains 3 and 4 were Bacillus cereus and Bacillus mycoides, respectively. After 36h of incubation, the data were evaluated. Among all the microbes, E. cloacae reduced TDS and COD from the effluent the most (80 ± 0.2% and 87 ± 0.4% COD, respectively). When compared to individual species, consortia were more efficient (86 ± 0.2% TDS and 90 ± 0.3% COD). On treatment, the correlation coefficient "r" for TDS and COD elimination was found to be 1, resulting in a positive linear connection. The current study suggests that microbial therapies are both effective and environmentally beneficial.

Treatment of petroleum refinery wastewater by adsorption using activated carbon fixed bed column with batch recirculation mode

Water pollution and the lack of access to clean water are general global problems that result from the expansion of industrial and agricultural activities. Petroleum refinery wastewaters consider as a major challenge to the environment and their treatment is mandatory. The present work concerns with the removal of chemical oxygen demand (COD) from petroleum refinery wastewater taken from Iraq's Al-Diwaniyah petroleum refinery plant by using an activated carb fixed-bed column operated at a batch recirculation mode. The fixed bed column used in this work was composed of three sections: upper, central, and bottom compartments. The bottom compartment serves as a feeding chamber to the central adsorption chamber while the upper compartment serves as a collecting effluent chamber. By adopting response surface methodology (RSM), in the pacts of various operational parameters such as packing level, pH, and time on the COD removal efficiency were investigated. The optimal conditions were an activated carbon packing level of 80%, pH of 5.7, and adsorption time of 73 min approximately, which resulted in a COD removal efficiency of 96.70%. The results indicated that the packing level of activated carbon had a major effect on COD elimination followed by pH, while time had a minor effect. The model equation's adequacy was demonstrated by its strong R2 value (0.975). The present study demonstrates that the adsorption system by activated carbon is an effective method for removingcondomODom Al-Diwaniyah petroleum refinery wastewaters.

Removal of chemical oxygen demand (COD) from hospital wastewater by electro fenton process using graphite–graphite electrochemical system

Removal of COD from hospital wastewater generated from Al- Diwaniyah hospital located in Iraq was achieved using graphite–graphite electro-Fenton (EF) system. The effect of various operational parameters on the COD removal efficiency was investigated based on response surface methodology (RSM). Optimal conditions were the current density of 20mA/cm2, FeSO4 concentration of, and time of It achieved a COD elimination efficiency of 97.964 % at a specific energy consumption of 10.78 kWh/kg. The results indicated that time had the least effect on the efficiency with which chemical oxygen demand is eliminated, however, the share of current density had the greatest effect, followed by the FeSO4 concentration. The adequacy of the model equation was confirmed by its high R2 value (99.62%). The present study shows that the graphite–graphite EF system was an efficient tool for removing COD from hospital wastewaters.

Facile isotherms of iron oxide nanoparticles for the effectively removing organic and inorganic pollutants from landfill leachate: Isotherms, kinetics, and thermodynamics modelling

Landfill leachate is obstinate wastewater due to the presence of various organic and inorganic pollutants. In this study, iron oxide (Fe2O3) nanoparticles were isolated from iron ore for use as adsorbents to eliminate chemical oxygen demand (COD), color, and ammoniacal nitrogen (NH3–N) from landfill leachate. The efficiency of this process was determined by varying the pH, adsorbent dosage (g/L), contact time (min), and heat level (°C). The results showed that the Fe2O3 nanoparticles could effectively remove more than 70% of COD, 60% of NH3–N, and an estimated 98% of color from landfill leachate. The Langmuir and Freundlich isotherm models were employed to determine the adsorption equilibrium behavior of Fe2O3 nanoparticles for eliminating COD, color, and NH3-N. The Langmuir isotherm model was found to be the most effective for the aforementioned process. Kinetic studies indicated that the elimination of COD, NH3–N, and color fitted well with the pseudo-second-order kinetic model. The thermodynamic properties were determined through analysis, indicating that the removal of COD, NH3–N and color from landfill leachate using the Fe2O3 nanoparticles occurred spontaneously and endothermically. This research indicates that Fe2O3 nanoparticles can be utilized as adsorbents for effectively removing both organic and inorganic pollutants from landfill leachate.

A hybrid process for leachate wastewater treatment: Evaporation and reverse osmosis/sequencing batch reactor.

In this study, a hybrid process for leachate wastewater treatment including evaporation and reverse osmosis (RO) membrane or biological treatment systems was suggested. Experiments were performed on a real landfill leachate wastewater. The leachate was subjected to evaporation; as a result, a distillate was obtained containing less organic matter and less substantial amounts of other pollutants, as ammonium salts and total phenols were removed. Tests were carried out at different evaporation temperatures and times. The initial leachate pH was adjusted and optimized. For optimum conditions, each of chemical oxygen demand (COD), total phenol, and ammonium salt concentrations were reduced to 99.99%, 95.00%, and 83.00%, respectively. The distillate of the first stage of the proposed process was then exposed to RO membrane system, as a first study, under different transmembrane pressure of 20, 30, and 40 bar and at different pH values of 7, 8, and 9. As a second suggested treatment system, the distillate was subjected to a biological treatment process for 30 days as a retention time, pH = 6, and room temperature 25°C ± 1°C. At the end of the research study, a comparison was conducted between results obtained with RO membrane separation and biological treatment system as two distinct treatment systems proposed for leachate landfill wastewater treatment. Although both systems were effective for landfill leachate wastewater treatment, however, with the RO membrane separation system, COD removal efficiency reached 99.99%. In the other hand, with biological treatment process, COD elimination was as much as 90.00%. Certainly, evaporation and RO are not novel ways of landfill leachate treatment; however, few studies have attempted to use similar combined system for landfill leachate wastewater treatment and attained effective results of treated water. PRACTITIONER POINTS: A hybrid process of evaporation and RO membrane or biological treatment systems was suggested for leachate wastewater treatment. For optimum conditions, COD, total phenols, and ammonium salt reductions were achieved to 99.99%, 95%, and 83%, respectively, after the first evaporation stage. The distillate of the first stage of the proposed process was then exposed to RO membrane system and biological treatment system. Different transmembrane pressure and different pH values were optimized for RO.

The role of saline-related species in the electrochemical treatment of produced water using Ti/IrO2-Ta2O5 anode

Large volumes of produced water (PW) are daily generated at oil and gas exploration plants, and it has to be efficiently treated before final disposal, avoiding the sending of recalcitrant organic and inorganic constituents to the ecosystem. Anodic oxidation (AO) was employed in the treatment of a PW using a Ti/IrO2-Ta2O5 dimensionally stable anode (DSA). The role of the high concentration of chloride (13 g L-1) and sulfate (0.8 g L-1) in the effluent was investigated regarding the quantification of oxidizing species, chemical oxygen demand (COD) removal, different applied current densities (j), total current efficiency (TCE), and a partial costs analysis. The better efficiency, in terms of organic removal (79% of COD elimination), was achieved by applying 30 mA cm−2 during 240 min of electrolysis, at room temperature, without pH adjustment before or after the treatment. Under these conditions, lower concentrations of undesirable chlorinated species were produced, as well as lower energy requirements were also achieved regarding those achieved at 60 and 90 mA cm−2, and consequently, reduced costs were estimated. It seems that no significant influence on the oxidation of the organic matter was observed due to the higher dissolved sulfate concentration in the effluent. Conversely, the high concentration of chloride in the effluent plays an important role to favor the electrochemical production of oxidant species which act in the bulk of the solution to remove the organic matter as well as the chloride ions help in the maintenance of the conductivity.

Removal of chemical oxygen demand (COD) from hospital wastewater by electro fenton process using graphite–graphite electrochemical system

Removal of COD from hospital wastewater generated from Al- Diwaniyah hospital located in Iraq was achieved using graphite–graphite electro-Fenton (EF) system. The effect of various operational parameters on the COD removal efficiency was investigated based on response surface methodology (RSM). Optimal conditions were current density of 20mA/cm2, FeSO4 concentration of 0.697 mM and time of 48.687 min. At these conditions COD elimination efficiency of 97.964 % was achieved at a specific energy consumption of 10.78 kWh/kg. The results indicated that time had the least effect on the COD removal efficiency, while the impact of current density had the greatest effect, followed by the FeSO4 concentration. The adequacy of the model equation was confirmed by its high R2 value (99.62%). The present study shows that graphite–graphite EF system was an efficient tool for removing of COD from hospital wastewaters.