Electrochemical process employing scrap metal waste as electrodes for dye removal

An economical electrocoagulation process of a hazardous anionic azo dye wastewater with the combination of recycled electrodes and solar energy

The energy and electrode costs are the restrictions of applying electrocoagulation (EC) in wastewater treatment and many attempts have been made to decrease these costs. In this study, an economical EC was investigated to treat a hazardous anionic azo dye wastewater (DW) that threatens the environment and human health. Firstly, an electrode for EC process was produced from recycled aluminum cans (RACs) by remelting in an induction melting furnace. The performance of the RAC electrodes in the EC was evaluated for COD, color removal, and the EC operating parameters such as initial pH, current density (CD), and electrolysis time. Response surface methodology which is based on central composite design (RSM-CCD) was used for the optimization of the process parameters which were found to be pH 3.96, CD 15 mA/cm², and electrolysis time 45 min. The maximum COD and color removal values were determined as 98.87% and 99.07%, respectively. The characterization of electrodes and the EC sludge was conducted by XRD, SEM, and EDS analyses for the optimum variables. In addition, the corrosion test was conducted to determine the theoretical lifetime of the electrodes. The results showed that the RAC electrodes show an extended lifetime as compared to their counterparts. Secondly, the energy cost required to treat DW in the EC was aimed to decrease by using solar panels (PV), and the optimum number of PV for the EC was determined by the MATLAB/Simulink. Consequently, the EC with low treatment cost was proposed for the treatment of DW. An economical and efficient EC process for waste management and energy policies was investigated in the present study which will be instrumental in the emergence of new understandings.

Efficient removal of norfloxacin from water using batch airlift-electrocoagulation reactor: optimization and mechanisms analysis

In this study, we developed an airlift-electrocoagulation (AL-EC) reactor to remove norfloxacin (NOR) from water. Six parameters influencing NOR removal were investigated, and the possible removal mechanism was proposed based on flocs characterization and intermediates analysis. The performances for treating different antibiotics and removing NOR from 3 types of water were also evaluated. The best NOR removal efficiency was obtained with the iron anode and aluminum cathode combination, a current density of 2 mA cm-2, an initial pH of 7, a treatment time of 32 minutes and an air flow rate of 200 mL min-1, the supporting electrolyte type was NaCl, and the initial NOR concentration was 10 mg L-1. Flocs adsorption and electrochemical oxidation were the main ways to remove NOR from water. The average removal efficiency of the AL-EC reactor exceeded 60% of the different antibiotic concentrations in artificial and real water. The highest NOR removal rate reached 93.48% with an operating cost of 0.153 USD m-3. The present work offers a strategy for NOR removal from water with high efficiency and low cost, showing a huge potential for the application of the AL-EC in antibiotic contaminated water treatment.

Evaluation of scrap metallic waste electrode materials for the application in electrocoagulation treatment of wastewater

The constant need for sacrificial electrodes is one of the limitations of applying the EC in wastewater treatment. Accordingly, this study proposes a sustainable alternative in reusing scrap metallic wastes as electrode materials. Four different types of metallic wastes (beverage cans, used aluminum (Al) foil, scrap iron, and scrap mild steel) are proposed as sacrificial electrodes for grey water (GW) treatment using the EC technique. At electrical current densities (CD) ranging between 5 and 20 mA/cm², the treatment performance was evaluated for a reaction time of 10 min in terms of the removal efficiency of some key parameters such as color, turbidity, chemical oxygen demand (COD), and electrical conductivity, energy and material consumption, and metal contamination of GW from electrodes. The results demonstrated that using metallic wastes as sacrificial electrodes can achieve a considerable reduction in color, turbidity, COD, and electric conductivity of about 97.2%, 99%, 88%, and 89%, respectively. However, their reuse as electrodes revealed some important concerns. Al foil undergoes quick and substantial perforation and loss of surface area during electrolysis. The scrap iron and scrap mild steel were found to cause metal contamination by increasing Fe ions in the treated GW. Generally, metal scrap wastes can serve effectively as alternative sustainable electrodes. However, further research is recommended regarding the operating costs, which are considered crucial aspects of the EC process in terms of energy consumption and the most efficient method of fabricating the metallic wastes into a form suitable for reuse in the EC technique.

Variation of current density with time as a novel method for efficient electrochemical treatment of real dyeing wastewater with energy savings

Electro-oxidation is a promising technology for wastewater treatment with biorefractory organic and nitrogen pollutants; however, the high energy demand hinders its wide application. In this study, a novel method by regulating significant parameter during the electro-oxidation process in a timely manner for real dyeing wastewater treatment with energy savings was studied. Operating factors (i.e., flow rate, initial pH value, electrode distance, and current density) were investigated for chemical oxygen demand (COD) and ammonia removal, and the results indicated that current density was the key factor that obviously influenced the electrochemical performance. Indirect oxidation by active chlorine was then confirmed as the main reaction pathway for pollutant oxidation, and the relationship between the current density and the generation of active chlorine was established, suggesting that a large part of the generated active chlorine was not utilized effectively. Subsequently, a novel method of varying the current density in a timely manner based on the reaction mechanism was proposed; the results indicated that, with similar pollutant removal efficiencies, energy consumption could be reduced from 31.6 to 20.5 kWh/m3. Additionally, the novel system was further optimized by Box-Behnken design: The COD removal efficiency could reach 71.8%, and the energy demand could be reduced by 45.6%.

Pollutants removals and energy consumption in electrochemical cell for pulping processes wastewater treatment: Artificial neural network, response surface methodology and kinetic studies

Response surface methodology (RSM) and artificial neural network (ANN) were used for modelling the electrocoagulation removal of pollutants from wastewater from pulping processes. The Design of Experiment based on central composite design was used to investigate the combine effects of pH (5.4-9.0), time (10-45 min) and current density (j) (9-39 mA/m²), on the removal efficiency of the Chemical Oxygen Demand (COD), Total Dissolve Solids (TDS) as well as Turbidity while Energy consumption (EC) was estimated per kg [COD] removed. The kinetics of the process was modelled with pseudo first and second order models. The removability of the COD, TDS and Turbidity were found to be 76.4, 57.0 and 97.13% with Energy consumption of 2.72 kWh/kg_[COD] at optimal pH 6.83, current density of 22.06 mA/m², and reaction time of 45 min. The ANN model gave a better fitting of the electrocoagulation process than the RSM, considering the R² of 0.999 and MSE of 0.00753 obtained for the former. The pseudo first order model gave a better analysis of the kinetic data. The characterization of the sludge produced showed the potential of its use as adsorbent for organic or mineral contaminants and recovery of aluminium and other metals. Thus, electrocoagulation with monopolar aluminium electrodes displayed effective and a viable alternative for the pollutants removal from pulp processing wastewater.