COD removal from leachate by electrocoagulation process: treatment with monopolar electrodes in parallel connection

Comprehensive understanding of electrochemical treatment systems combined with biological processes for wastewater remediation

The presence of toxic pollutants in wastewater discharge can affect the environment negatively due to presence of the organic and inorganic contaminants. The application of the electrochemical process in wastewater treatment is promising, specifically in treating these harmful pollutants from the aquatic environment. This review focused on recent applications of the electrochemical process for the remediation of such harmful pollutants from aquatic environments. Furthermore, the process conditions that affect the electrochemical process performance are evaluated, and the appropriate treatment processes are suggested according to the presence of organic and inorganic contaminants. Electrocoagulation, electrooxidation, and electro-Fenton applications in wastewater have shown effective performance with high removal rates. The disadvantages of these processes are the formation of toxic intermediate metabolites, high energy consumption, and sludge generation. To overcome such disadvantages combined ecotechnologies can be applied in large-scale wastewater pollutants removal. The combination of electrochemical and biological treatment has gained importance, increased removal performance remarkably, and decreased operational costs. The critical discussion with depth information in this review could be beneficial for wastewater treatment plant operators throughout the world.

Leachate post-treatment by electrocoagulation process: Effect of polarity switching and anode-to-cathode surface area

In the electrocoagulation process, passivation or corrosion of the electrodes is one of the biggest challenges that cause a drop in treatment effectiveness. In this study, the effect of polarity switching was investigated, for the first time, in an attempt to enhance electrocoagulation treatment's ability to remove chemical oxygen demand (COD) and color from pretreated landfill leachate. Moreover, the ratio of the anode to cathode surface area and rotating electrode were examined in light of experimental results. The effect of different parameters, including the stirring speed, initial leachate pH, electrical current density, anode to cathode surface area ratio, and polarity switching time on system efficiency, was evaluated using the one-factor-at-a-time (OFAT) classical method. According to the results, polarity switching resulted in an almost 18% increase in COD removal, 14% increase in color removal, 13% decrease in electrical energy consumption (EEC), 51% decrease in the specific sludge production (TSS/COD), and improved electrode performance compared to non-polarity switching mode. The findings of this research showed the highest COD and color removal efficiencies, which were 34% and 67%, respectively, in a 120 min period, a stirring speed of 135 rpm, the initial leachate pH of 9, the current density of 14.4 mA/cm², the anode/cathode surface ratio of 0.35, and the polarity switching time of 300 s.

Coupling of electrocoagulation and powder activated carbon for the treatment of sustainable wastewater

The present research work is based on an electrochemical technique in combination with powdered activated carbon (PAC) for the removal of micropollutants by adsorption as an advanced stage purification step from effluents of pilot plant wastewater treatment plants (WWTP). The effluents of sedimentation tank comprised of wastewater plus PAC (WWPAC). The pilot plant mainly consists of two parts: the first one consists of electrocoagulation (EC) reactor, and the second consists of electrophoretic deposition (EPD) discs and electroflotation (EF) setup. The electrocoagulation (EC) reactor consisted of the electrode material (Al and Fe). Both types of electrodes have been tested with the outflow of sedimentation tank. The outflow from the sedimentation tank has been entered into the EC reactor for the determination of EC reactor efficacy for the successful accomplishment of EC process at the designed pilot plant for WW treatment. The effect of different operational parameters, PAC dosage (20 mg), electrode nature (Fe and Al) and current density (0.34-2.02 A/m²), has been studied to find out the optimum conditions. Sludge volume index (SVI) of the sludge, thermogravimetric (TG), differential thermal analyses (DTA) and particle size distribution (PSD) of the flocs generated after the EC process has also been studied. The turbidity, pH and conductivity of effluents before and after EC treatment have also been carried out. The research work performed detailed analysis of the wastewater effluents at pilot plant scale and gave promising results for future work in advance wastewater treatment direction.

Electrochemical activation of peroxides for treatment of contaminated water with landfill leachate: Efficacy, toxicity and biodegradability evaluation

Contaminated water with landfill leachate (CWLL) with high salinity and high organic content (total organic carbon (TOC) = 649 mg/L and Chemical Oxygen Demand (COD) = 1175 mg/L) is a toxic and non-biodegradable effluent. The present research aimed to assess the treatment effectiveness of CWLL by electrocoagulation (EC)/oxidant process. The ferrous ions generated during the process were employed as coagulant and catalyst for the activation of different oxidants such as peroxymonosulfate (PMS), peroxydisulfate (PDS), hydrogen peroxide (HP), and percarbonate (PC) to decrease TOC in CWLL. Removal of ammonia, color, phosphorous, and chemical oxygen demand (COD) from CWLL effluent was explored at various processes. EC/HP had the best performance (∼73%) in mineralization of organic pollutants compared to others under the condition of pH 6.8, applied current of 200 mA, oxidant dosage of 6 mM, and time of 80 min. The oxidation priority was to follow this order: EC/HP > EC/PMS > EC/PDS > EC/PC. These processes enhanced the biodegradability of CWLL based on the average oxidation state and biochemical oxygen demand (BOD)/COD ratio. SUVA₂₅₄ and E₂/E₃ indices were also investigated on obtained effluents. The phytotoxicity evaluation was carried out based on the germination index, indicating that the electro-activated oxidant was an effective system to reduce the toxicity of polluted waters. EC/HP showed supremacy compared to others in terms of efficiency, cost, and detoxification. Therefore, the electro-activated oxidant system is a good means for removing organic pollutants from real wastewater.

Techno-economical optimization using Box-Behnken (BB) design for chemical oxygen demand and chloride reduction from hospital wastewater by electro-coagulation

The study examines the optimum condition of an electro-coagulation (EC) unit for treatment of hospital wastewater (HWW) using iron (Fe) electrodes. The impact of factors such as pH, current, and electrolysis time on COD, chloride, and anode dissolution was investigated. For this purpose, Box-Behnken (BB) design based on the response surface methodology (RSM) was used to design and analyze the results. The predicted value of chemical oxygen demand (COD) and chloride removal at optimum conditions (pH: 7.41, current: 2.64 A and electrolysis time: 41.31 min) were 92.81% and 71.23%, respectively. At same optimum conditions, the value of energy and electrode consumption per kg of COD was 0.06376 kWh/kg COD and 1.362 kg/kg COD, respectively. High value of R² (i.e., R²  > 99%) for all three responses (Y₁ , Y₂ , and Y₃ ) obtained from ANOVA confirms that the proposed model is valid, accurate, and acceptable. The kinetic study shows linear relationship and follows pseudo-first-order kinetics. Pareto graph shows that the percentage impact of current factor on COD and chloride removal was maximum, that is, 54.984% and 66.79%, respectively. Lastly, the total cost of EC treatment was calculated in terms of COD removal and was found to be 55.47 ₹/kg COD. PRACTITIONER POINTS: Using Fe electrode results in 92.81% COD and 71.23% Chloride removal, respectively. High value of R²  > 99% for all three responses from ANOVA confirms the proposed model is valid. Pareto analysis shows current factor has maximum percentage impact on pollutant removal. Kinetic study shows linear relationship and follows pseudo-first-order kinetics.

Optimization and economical study of electro-coagulation unit using CCD to treat real graywater and its reuse potential

The reclamation of graywater for non-potable purposes has attained utmost importance, particularly in developing nations. The present research aimed to evaluate the optimal condition of electro-coagulation system in treatment of graywater and its reuse. Moreover, the study also evaluates the impact of major operating parameters on pollutant removal and anode dissolution. To achieve this, two-factor (voltage potential and time) and 5-level (- 1, - 0.5, 0, + 0.5, and + 1) full factorial design, based on response surface methodology (RSM) has been executed for the actual design. The data were acquired after conducting 20 experiments, as suggested by RSM (response surface methodology). Design Expert 12.0.8.0 software has been used to design mathematical model to obtain optimum condition (14 V and 47 min) at pH of 7.35, which provides experimental removal efficiency (75.6% chemical oxygen demand, 78.7% total dissolved solids, 93.4% turbidity, and 63.2% chloride) with minimal electrode consumption of 1.38 mg L^-1. Adequacy of the model developed has been verified by ANOVA. The operating cost of treating graywater at the optimized condition obtained as 0.7 US$/kg COD.