Decolourization of melanoidins by a electrocoagulation process using aluminium electrodes

Abstract

The decolourization ofmelanoidins was studied with a batch electrocoagulation (EC) process using aluminium electrodes. The effects of conductivity (K = 500-3000 microS/cm), initial pHi (4.2-8.2), current density (j = 2.5-7.5 A/m2), initial melanoidin concentration (C0 = 100-800 mg/L) and operating time (tEC = 0-60 min) were investigated on the decolourization efficiency. The results obtained from the EC process were extremely efficient and able to achieve a decolourization efficiency of > 98% at pHi = 4.2, j = 5 A/m2, K = 2500 microS/cm, C0 = 100 mg/L and tEC = 10 min. The decolourization performance was dependent on pHi value since the lower pH values led to faster reactions and higher decolourization efficiency. Melanoidins in the EC process were removed by precipitation and charge neutralization at pH < 6.5, and both adsorption and sweep coagulation by amorphous Al(OH)3(s) occurred at pH > 6.5. The operating cost was calculated as 0.0096 Euro/m3

Treatment of textile dyeing wastewater by electrocoagulation using Fe and Al electrodes: optimisation of operating parameters using central composite design

“…pH i is also one of the most important parameters influencing the production of metal species at the anode, the production of hydroxyl ions at the cathode, and the chemical structure of the wastewater . When an Al electrode was used, monomeric species such as Al(OH) 2+ , , , and Al(OH) 4− and polymeric species such as , , , , and were formed during the EC process .…”

“…In this study, the pH of the wastewater was increased during the EC process and the maximum removal efficiencies occurred at pH i 4–6 (Figures and ). These results are consistent with literature studies in which coprecipitation and adsorption were suggested as two significant interaction mechanisms during the process. The pH ranges of wastewater were found to be effective for both mechanisms.…”

“…The initially formed colloidal precipitate in the pH range was positively charged and stable, which suggested that coprecipitation played a significant role for Fe and Al electrodes in the process. The formed amorphous Al(OH) 3(s) and Fe(OH) 3(s) flocs (sweep flocs) had minimum solubility within the pH 6.5–7.8 range and a large specific surface area that could absorb some soluble organic compounds onto its surface . When pH i was greater than 8, the monomeric anion concentration was increased according to Eqn 15 and reduced the significance of solid Al(OH) 3(s) .…”

“…The increasing amount of sludge increased the removal efficiencies through sweep coagulation. pH i is also one of the most important parameters influencing the production of metal species at the anode, the production of hydroxyl ions at the cathode, and the chemical structure of the wastewater [29]. When an Al electrode was used, monomeric species such as Al(OH) 2+ , AlðOHÞ þ 2 , Al 2 ðOHÞ 4þ 2 , and Al(OH) 4À [31].…”

Optimization and Modelling Using the Response Surface Methodology for Methylene Blue Removal by Electrocoagulation/Hazelnut Shell Adsorption Coupling in a Batch System

“…Al 3+ ion generation occurs at the anode surface, whereas hydrogen gas transpires at the cathode surface. Flocs of Al(III) hydroxides and polyhydroxy species formed during coagulation, and the organic pollutants are removed from the aqueous phase via charge neutralisation, adsorption and sweep flocculation [16]. The flocs can then be separated by sedimentation or/and flotation [12].…”