Performance analysis of a continuous serpentine flow reactor for electrochemical oxidation of synthetic and real textile wastewater: Energy consumption, mass transfer coefficient and economic analysis.

A continuous flow electrochemical reactor was developed, and its application was tested for the treatment of textile wastewater. A parallel plate configuration with serpentine flow was chosen for the continuous flow reactor. Uniparameter optimization was carried out for electrochemical oxidation of synthetic and real textile wastewater (collected from the inlet of the effluent treatment plant). Chemical Oxygen Demand (COD) removal efficiency of 90% was achieved for synthetic textile wastewater (initial COD - 780 mg L-1) at a flow rate of 500 mL h-1 (retention time of 6 h) and a current density of 1.15 mA cm-2 and the energy consumption for the degradation was 9.2 kWh (kg COD)-1. The complete degradation of real textile wastewater (initial COD of 368 mg L-1) was obtained at a current density of 1.15 mA cm-2, NaCl concentration of 1 g L-1 and retention time of 6 h. Energy consumption and mass transfer coefficient of the reactions were calculated. The continuous flow reactor performed better than batch reactor with reference to energy consumption and economy. The overall treatment cost for complete COD removal of real textile wastewater was 5.83 USD m-3.

Multivariate optimization for electrochemical oxidation of methyl orange: Pathway identification and toxicity analysis.

Electrochemical oxidation of methyl orange (Sodium 4-[(4-dimethylamino) phenyldiazenyl] benzenesulfonate) with lead dioxide coated on mild steel was modelled using response surface methodology (RSM) to analyze the influence of pH, NaCl dose and current on color and chemical oxygen demand (COD) removal. Higher current, acidic pH and 0.8-1.2 g L(-1) NaCl dose had an enhancing effect on the removal efficiencies. Interaction effect of the variables highlights the action of (•)OH and HOCl in the oxidation of methyl orange, where HOCl has effect at lower current range. More than 90% COD removal efficiency and ∼100% color removal efficiency was obtained in 5 h at optimum conditions for an initial concentration of 50 mg L(-1). High performance liquid chromatography-mass spectroscopy (HPLC-MS) analysis carried out to identify degradation intermediates revealed the absence of chlorinated intermediates, which was further verified with Fourier transform infrared spectroscopy (FTIR) analysis. The postulated pathway of degradation indicated breakdown through dealkylation, deamination, desulfonation and cleavage of an azo bond and benzene ring. The degradation of methyl orange to smaller compounds was also confirmed by Ion Chromatography (IC). Cytotoxicity analysis on HaCaT cells revealed the intermediates to be more cytotoxic than the dye, possibly due to the aromatic amines and diazines formed during the degradation process.

Investigation onto feasibility of an adsorbent for chromium abatement with its extended application for real mine drainage water.

The feasibilities of the adsorbents ferrous modified calcined bauxite (FEMCB) and ferric modified calcined bauxite (FRMCB) in the abatement of Cr(VI) was investigated in the present study. The adsorbents were characterized by scanning electron micrographs (SEM), electro diffraction spectra (EDS), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectra. Parameter optimization of both adsorbents was done and performance efficiencies in the removal of Cr(VI) were compared. Although pH and temperature seemed to have no significant role in the removal efficiency of FEMCB, sorption by FRMCB was found to be depending on both. The optimum pH and temperature was found to be 5 ± 0.2, and 30°C, respectively. At optimum conditions, both adsorbents demonstrated removal efficiencies of >99% for a concentration of 5 mg L(-1). Sorption of Cr(VI) by FEMCB followed Freundlich isotherm model, while that of FRMCB fitted well with Langmuir isotherm model. The isotherm parameters were optimized by minimizing the error functions. The kinetics of sorption by FEMCB followed a pseudo-second-order model confirming chemisorptive mechanism, while FRMCB followed pseudo-first-order. Thermodynamic study revealed that sorption process was spontaneous and that the rate limiting step was governed by film diffusion. Both the adsorbents showed removal efficiencies of >99% in removing Cr(VI) from real sample of mine drainage water of concentration 1.86 mg L(-1) at optimum conditions.

Heterogeneous photocatalysis of real textile wastewater: evaluation of reaction kinetics and characterization.

Real textile wastewater collected from the cotton dyeing bath of a fabric dyeing and finishing plant was subjected to heterogeneous photocatalysis using Ag(+) doped TiO(2) under UV irradiation in a batch reactor. The photocatalysts were characterized by FESEM, XRD, EDS, FTIR, DRS and BET analyses. The kinetics of the reaction was also evaluated. Colour removal was more than 88%, 94% and 99%, respectively for undiluted, 2 times diluted and 5 times diluted wastewater with Ag(+) doped TiO(2) (2.5 g/L) after UV irradiation for 360 minutes. The COD removal for undiluted, 2 times diluted and 5 times diluted wastewater was 47%, 70% and 92%, respectively under similar conditions. The reaction followed Langmuir-Hinshelwood pseudo first order kinetic model and the data fitted well to polynomial regression analysis.