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Treatment of tannery liming drum wastewater by electrocoagulation

Abstract The removal of COD, suphide and oil–grease from tannery liming drum wastewater was experimentally investigated using direct current (DC electrocoagulation (EC. In the EC of the wastewater, the effects of initial pH, electrolysis time and current density were examined. The COD, sulphide and oil–grease in the aqueous phase were effectively removed when mild steel electrodes were used as sacrificial anode. The optimum operating range for each operating variable was experimentally determined. The experimental results show that COD, sulphide and oil–grease was removed effectively. The overall COD, sulphide and oil–grease removal efficiencies reached 82%, 90% and 96%, respectively. The optimum current density for removal of COD, sulphide and oil–grease in the tannery liming drum wastewater were 35 mA/cm, 35 mA/cm and 3.5 mA/cm at 10 min electrolysis time and pH 3, respectively. Mean energy consumptions were 5.768 kWh/m of COD, 0.524 kWh/m of sulphide and 0.00015 kWh/m of oil–grease. Results show that the pseudo-second-order rate equation provides the best correlation for the removal rate of the parameters. 333222Keywords: Tannery wastewater; Liming drum wastewater; Electrocoagulation; Mild steel electrodes Article Outline 1. Introduction 2.
Experimental
2.1. Wastewater samples 2.2. Experimental device 2.3. Experimental procedure 2.3.1. Iron electrodes 2.3.2. Aluminum electrodes 3.

Results and discussion
3.1. Effect of electrode materials 3.2. Effect of initial pH 3.3. Effect of current density 3.4. Effect of electrolysis time 3.5. Electric Energy Consumption
4.
Conclusions References
1. Introduction The leather industry is well known as a high consumer of water. Variety of chemicals at significant quantities are employed for leather processing. Major chemicals used for leather manufacturing are lime, sodium and ammonium salts, fatliquors, bacterial- and fungicides, tannins, dyes, etc. Wastewater from the leather industry is known to be heavily contaminated with inorganic and organic pollutants. It can create heavy pollution from effluents containing high levels of salinity, organic loading, inorganic matter, dissolved and suspended solids, ammonia, organic nitrogen and specific pollutants (sulphide, chromium and other toxic metal salt residues [1], [2] and [3]. It was reported that the total global quantity of bovine hides, sheep, goat and pigskins was nearly 8 × 10 t as wet salted weight a year and tanning workshop worldwide used 4 × 10 t of chemicals, produced over 3 × 10 t of wastewater and about 8 × 10 t of solid waste and dewatered sludge [4].
There are many processes for the treatment of tannery wastewater such as chemical coagulation [5], [6] and [7], reverse osmosis membrane [2] and [8], nanofiltration [9], Fenton and H2O2/UV [10] and [11], biodegradation [6], [12], [13], [14] and [15]. Although biodegradation process is cheaper than other methods, it is less effective because of the toxicity of the tannery wastewater that affects the development of the bacteria [16]. Due to the limitations of the primary and biological wastewater treatment processes, alternative processes have been pursued. Amongst them, electrochemical processes 6866

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