Electrochemical degradation of malachite green: Multivariate optimization, pathway identification and toxicity analysis

• Published in: Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering Vol. 51; no. 13; pp. 1091 - 1099
• Main Authors: Sasidharan Pillai, Indu M., Gupta, Ashok K.
• Format: Journal Article
• Language: English
• Published: England Taylor & Francis 09-11-2016; Taylor & Francis Ltd
• Subjects: Biological Oxygen Demand Analysis; Box-behnken design; Chemical oxygen demand; Current density; Degradation; degradation intermediates; Efficiency; Electrochemical Techniques; Electrodes; Escherichia coli; Hydrogen-Ion Concentration; Industrial Waste; Malachite green; Multivariate Analysis; Optimization; Oxidation; Oxidation-Reduction; photocatalysis; photoelectrocatalysis; Rosaniline Dyes - chemistry; Rosaniline Dyes - toxicity; Sodium Chloride - analysis; Toxicity Tests; Waste Disposal, Fluid; Waste Water - chemistry; zone of inhibition; Box–behnken design; photoelectrocatalysis; photocatalysis; degradation intermediates; zone of inhibition
• ISSN: 1093-4529; 1532-4117
• DOI: 10.1080/10934529.2016.1199640

Application of a newly developed electrode material, PbO
2
coated on mild steel plate (MS-PbO
2
), for the degradation of malachite green (MG) by photocatalytic oxidation (PCO), electrochemical oxidation (ECO) and photoelectrochemical oxidation (PEC) was explored. PEC performed marginally better at lower current density. However, the performances of PEC and ECO were equally good at higher current densities. One variable at a time optimization was carried out to identify the major parameters influencing ECO. Multivariate optimization was carried out with NaCl concentration, current density and pH as the variables and chemical oxygen demand (COD) removal efficiency and current efficiency (CE) as the responses. Increasing the current density aided the COD removal efficiency, but decreased the CE. Low NaCl concentration and acidic pH were beneficial for both. The optimum condition for maximizing the COD removal efficiency and CE of MG (50 mg L
−1
) was obtained as NaCl concentration of 1.56 g L
−1
, a current density of 1.91 mA cm
−2
and pH 5. The maximum predicted and experimental COD removal efficiencies were 89.41% and 90.8%, and CEs were 21.52% and 21.1%, respectively. Degradation intermediates were identified and a possible pathway of degradation was proposed. Disc inhibition study showed that the degraded samples are non-toxic. The efficacy of the method was tested for treating wastewater collected from dyebath having a COD of about 2000 mg L
−1
. COD removal efficiency of greater than 90% was achieved within 12 h at a current density of 7.2 mA cm
−2
.