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The present study illustrates the electrocoagulation remediation of paper mill wastewater for multiple response optimization. Multiple response optimization can be combined into one desirability function. All variables and responses varied for a unique global solution. The effect of basic electrocoagulation process variables pH (3–10), conductivity (3.15–10 mS/cm), electrode distance (1–2.5 cm) and current density (5–20 mA/cm2) on four response parameters such as chemical oxygen demand, color, total dissolved solids and total organic carbon has been analyzed experimentally and statistically. The global solution for these variables and responses obtained by software over a hundred design points. For unit desirability function variables conditions were pH 7.49, Conductivity 8.34 mS/cm, electrode distance 2.06 cm and current density 9.32 mA/cm2. In these global variable conditions, responses were observed to be COD 70.19%, Color 75.03%, TDS 70.69% and TOC 71.93%, respectively.

The main objective of the present work was to understand the interactive behaviour of various operating parameters including concentration of pollutants during binary electrochemical mineralization of the two nitrogenous heterocyclic pollutants in the aqueous solution. Indole and pyrrole were selected as pollutants, whereas Pt/Ti was selected as anode and cathode. The effects of different operating parameters like current density, solution conductivity, initial concentration of the pollutants and time were studied. Taguchi method was used to optimize these operating parameters for obtaining the ultimate rate of degradation for the nitrogenous compounds. There were basically two responses, i.e. chemical oxygen demand (COD) degradation and specific energy consumption. These responses were maximized and minimized, respectively. At the optimum condition, removal efficiencies of pyrrole, indole and COD were found to be 46.1%, 62.4% and 61.4%, respectively. The optimum value of specific energy consumption was found to be 159.5 kWh per kg COD removed. Possible mineralization pathways are also proposed on the basis of the identified intermediates by gas chromatography coupled with mass spectroscopy. The operating cost was also calculated for the binary lab-scale treatment of the indole and pyrrole and compared with reported cost analysis for the electrochemical treatment.

The main objective of the present work was to understand the interactive behaviour of various operating parameters including concentration of pollutants during binary electrochemical mineralization of the two nitrogenous heterocyclic pollutants in the aqueous solution. Indole and pyrrole were selected as pollutants, whereas Pt/Ti was selected as anode and cathode. The effects of different operating parameters like current density, solution conductivity, initial concentration of the pollutants and time were studied. Taguchi method was used to optimize these operating parameters for obtaining the ultimate rate of degradation for the nitrogenous compounds. There were basically two responses, i.e. chemical oxygen demand (COD) degradation and specific energy consumption. These responses were maximized and minimized, respectively. At the optimum condition, removal efficiencies of pyrrole, indole and COD were found to be 46.1%, 62.4% and 61.4%, respectively. The optimum value of specific energy consumption was found to be 159.5 kWh per kg COD removed. Possible mineralization pathways are also proposed on the basis of the identified intermediates by gas chromatography coupled with mass spectroscopy. The operating cost was also calculated for the binary lab-scale treatment of the indole and pyrrole and compared with reported cost analysis for the electrochemical treatment.

Indole is a highly recalcitrant aromatic heterocyclic organic compound consisting of a five-membered nitrogen-containing pyrrole ring fused to a six-membered benzene ring. This study presents the results of the electro-chemical mineralization of indole in an aqueous solution using platinum-coated titanium (Pt/Ti) electrode. A central composite design was used to investigate the effect of four parameters namely initial pH (pHo), current density (j), conductivity (k) and treatment time (t) at 5 levels. Multiple responses namely chemical oxygen demand (COD) removal (Y 1) and specific energy consumption (Y 2) were simultaneously maximized and minimized, respectively, by optimizing the parameters affecting the mineralization of indole by using the desirability function approach. At the operating conditions of pH 8.6, j = 161 A/m2, k = 6.7 mS/cm and t = 150 min, 83.8% COD removal with specific energy consumption of 36.3 kWh/kg of COD removed was observed. Ultra performance liquid chromatography, UV–visible spectroscopy, Fourier transform infrared spectroscopy and cyclic voltammetry of the indole solution were performed at the optimum condition of the treatment so as to report a plausible mechanism of indole degradation. Field emission scanning electron microscopy analysis of electrodes before and after treatment was performed for determining the changes on anode surface during the treatment. Thermal analysis of the solid residue (scum) obtained was also performed for exploring its disposal prospects. Present study shows that electro-chemical oxidation can be used for mineralization of nitrogenous heterocyclic compounds such as indole.

The present paper assesses the adsorption capability of rice husk ash (RHA) to adsorb catechol (C) along with phenol (P) and resorcinol (R) individually and simultaneously from aqueous solution in both single and binary solutions using batch experiments. Equilibrium isotherm data were collected at 30°C by carrying out experimental runs for 24 h contact time with pre-optimized RHA dosage of 20 mg/L and initial concentration variation of individual components in the range of 50–500 mg/L. The equilibrium adsorption data for single component were fitted in three adsorption isotherm models, namely the Langmuir, the Freundlich and the Redlich–Peterson. Equilibrium adsorption data of binary aqueous solution of catechol–phenol, catechol–resorcinol and the parameter evaluated from single adsorption isotherm were fitted in various multi-component adsorption isotherm models. Extended Langmuir model which assumes overlapping of sites for different adsorbates better represented the binary isotherm data for bot...

Electrochemical oxidation of 4-chlorophenol (CP) was investigated (in terms of chemical oxygen demand (COD) and CP removal efficiencies) by using a dimensionally stable anode (DSA) namely ruthenium oxide coated titanium (Ti/RuO 2 ) electrode. Effect of process conditions such as current density ( j ), electrolyte concentration ( m ), initial pH (pH o ), time ( t ) and initial CP concentration ( C o ) has been studied. Current efficiency (CE) and specific energy consumption (SEC) were also measured. Gas chromatograph-mass spectrometry (GC/MS) analysis was used to understand the CP mineralization mechanism which has been established on the basis of intermediates identified such as benzoquinone, hydroquinone and organic acids. Reaction kinetics was expressed by pseudo-first order kinetic model. Maximum COD removal efficiency of 96.7% and CP removal efficiency of 97.2%, respectively, was observed at j = 222.22 A/m 2 , t = 180 min, pH o = 5.2 and m = 400 mg/l with SEC = 655 kWh/kg COD. Operating cost based on the studies performed on laboratory scale EC reactor has been calculated and compared with those reported for other pollutants degradation.

Present study investigates the direct and indirect electrochemical (EC) oxidation of malachite green (MG) dye in acidic and basic medium using RuO2–TiO2 and Pt coated Ti mesh electrodes (Ti/RuO2–TiO2 and Ti/Pt electrodes). The effects of process parameters such as current density (j), initial pH (pHo) and NaCl (electrolyte) concentration (m) during the EC oxidation were also examined. This study investigates the effect of dissolved chlorine, chlorate, chlorite, and chlorine dioxide formed during EC oxidation at different pH. Active sites of electrodes surface promote the production of OH radicals ( OH). Synergistic effect of active chlorine species and OH radicals significantly enhanced the indirect EC oxidation of MG dye solution with Ti/RuO2–TiO2 anode. Gas chromatography-mass spectrometry (GC–MS), high performance liquid chromatography (HPLC), color and chemical oxygen demand (COD) were used to identify the EC oxidative degradation mechanism with both electrodes. Acidic pH was found to promote the dye degradation. Under optimum condition, MG dye was completely decolorized and 98% COD removal was obtained after 140 min of EC treatment. Based on the intermediate and by-products identification, it seems that MG dye degradation occurred via N-methylation and conjugated structure destruction.

Many industrial aqueous streams contain nitrogenous aromatic compounds, which need to be removed by an adsorption process, for which it is essential to study the interactive affects of these compounds during their simultaneous adsorption. In the present study, granular activated carbon (GAC) was used for simultaneous adsorption of pyrrole and indole from aqueous solution. First, Taguchi's method (L27 orthogonal array) was applied to optimize various parameters, like initial adsorbate concentration, adsorbent dose, temperature and contact time for their simultaneous adsorption onto GAC. Adsorbent dose and the interaction between initial concentrations were found to be the most significant factors. Indole adsorption onto GAC was found to be higher than that of pyrrole. Thereafter, binary adsorption equilibrium data were generated and modeled by various multicomponent isotherm models. Extended-Langmuir isotherm best represented the isotherm data at 30 °C among various multicomponent isotherm models used in this study.

In this study, the electrochemical (EC) oxidation of a recalcitrant heterocyclic compound namely pyrrole has been reported using platinum coated titanium (Pt/Ti) electrodes. Response surface methodology (RSM) comprising of full factorial central composite design (CCD) with four factors and five levels has been used to examine the effects of different operating parameters such as current density (j), aqueous solution pH, conductivity (k) and treatment time (t) in an EC batch reactor. Pyrrole mineralization in aqueous solution was examined with multiple responses such as chemical oxygen demand (COD) (response, Y1) and specific energy consumption (SEC) in kWh/kg of COD removed (response, Y2). During multiple response optimization, the desirability function approach was employed to concurrently maximize Y1 and minimize Y2. At the optimum condition, 82.9% COD removal and 7.7 kWh/kg of COD removed were observed. Degradation mechanism of pyrrole in wastewater was elucidated at the optimum condition of treatment by using UV-visible spectroscopy, Fourier transformed infra-red spectroscopy (FTIR), cyclic voltammetry (CV), ion chromatography (IC), higher performance liquid chromatography (HPLC) and gas chromatography-mass spectroscopy (GC-MS). The degradation pathway of pyrrole was proposed on the basis of the various analysis.