(2cl) Experimental and Theoretical Investigations on Electrochemical Removal of Reactive Black 5 Dye from Wastewater

Background

The pollution created by dyes wastewater after dyeing and finishing processes from textile industry has shown a critical environmental problem for many years. Among different types of dyes, reactive dyes have more affinity to react with textile fibers with more demand in textile industries but having difficulties in removal/treatment due to their complex molecular structures. The electrochemical based electrocoagulation (EC), a green process has shown the capability of treating a multiple pollutants of wastewater, including suspended solids, dyes, pulp and paper wastewater, metal processing industries, urban wastewater, etc. In the present investigation, the batch electro-coagulation (BEC) process is employed to remove Reactive Black 5 (RB5) dye from simulated waste water based on textile industries.

Experimental

All investigations were carried out with 500 ml dye solution in an electrochemical reactor, (14.5x12x12.5) cm³ having two pairs of iron electrodes with each electrode area, 48 cm² at room temperature of 25±1 ^oC. A LABINDIA/UV3000+ UV/VIS Spectrophotometer at the wavelength 597 nm was used to find out the percentage removal of dye. The percentage removal (% R) of dye is given by Eq. 1

(1)

where, C_o (mg/L) and C (mg/L) are initial and final concentrations of dye, respectively.

Theoretical

Different adsorption isotherm models such as Langmuir, Freundlich, Tempkin, Redlich and Peterson (R-P) and Sips in nonlinear fit are used to describe the experimental equilibrium results and different kinetics models such as pseudo-first order, pseudo-second-order, Avrami and Elovich models are performed to get insights of reaction mechanism.

Results and Discussion

Various experimental parameters such as current density (0.47-2.78 mA/cm²), electrode gap (0.5-2.5 cm), operating time (5-30 mins), initial dye concentration (100-300 mg/L) and pH (3-10) are used to examine the effects on removal efficiency of the dye. Due to the formation of iron hydroxide at higher pH which adsorb the dye molecules at the surface, the removal efficiency increases. The removal efficiency is increased up to 99.53 % by increasing the current density. Then the maximum dye-removal efficiency is reached up to 99.53 % with the 1.0 cm gap between the two electrodes. The dye removal efficiencies are found to be decreased from 99.59 % to 69.4 % with the increase in initial dye concentration from 100 mg/L to 300 mg/L. The dye removal efficiency also depends upon the time till as equilibrium. In the present study, electrical energy consumption is calculated and found 2.1 kWh/m³ using optimum process parameters (pH 8, concentration 100 mg/L, electrode gap 1.0 cm, time 30 mins and current density 2.78 mA/cm²).

The experimental data are found to be most fitted with Sips isotherm with the highest R² (0.98) followed by R-P isotherm (R² =0.97) and Tempkin isotherm (R² =0.97). Among all the kinetic models used in this study, Pseudo first order and Elovich models are found to be better based on R² values (0.99) as given in Table 1. However, Pseudo first order has shown close agreement of produced and experimental value of Q_e.

Conclusion

The maximum removal percentage of dye, 99.53 % is achieved under investigated optimum conditions such as pH of 8.0, electrode gap of 1cm, current density of 2.78 mA/cm², EC time of 30 mins and Initial dye concentration of 100 mg/L. Moreover, electrical energy consumption is also found to be 2.1 kWh/m³. At optimized equilibrium conditions of EC experiment, Sips equilibrium isotherm and pseudo first order kinetic model are best fit.

Research Interests

My research is aligned with the current areas of research specialization of chemical engineering such as Process intensification, bio-separations, wastewater treatment, and biofuels/biopolymers. My current research projects, which are going on at current Institution, MNNIT Allahabad (India) are: (i) Recovery of Bioactive Compounds from Fruit/Plant Wastes; (ii) Integrated/hybrid technology for sustainable treatment of industrial wastewater; (iii) Intensified approaches in extractions: Reactive extraction and micro-extraction using green solvents; (iv) Biodiesel production

Teaching Interests

Based on my work experience at Birla Institute of Technology and Science, Pilani (India) and Motilal Nehru National Institute of Technology Allahabad (India), I am contributing in quality teaching and research in the various areas of chemical engineering. More than fifteen years, I have been involved in active teaching of major chemical engineering subjects of undergraduate and post graduate level such as Thermodynamics, Chemical Engineering Thermodynamics, Process Intensification, Mass Transfer, Environmental Pollution and Control, Process Dynamics and Control, Mechanical Operations, Chemical Reaction Engineering-I, Polymer Science and Technology, Biochemical Engineering, etc.