Studies on electrochemical treatment of dairy wastewater using aluminum electrode

Treatment of biologically treated distillery spent wash employing electrocoagulation and reverse-osmosis treatment train

In the present study, electro-coagulation (EC) with stainless steel (SS) electrodes has been used as a pretreatment process before the reverse osmosis (RO) for the biologically treated distillery spent wash. The optimized operating parameters (pH, time, current, and electrode distance) for the EC process were obtained from the previous study. EC treated wastewater was further used as a feed for the RO system. RO membrane system operating parameters (pH, temperature, and trans-membrane pressure) were optimized by employing response surface methodology. Optimized conditions for the RO process were found to be: pH (pH_o): 6.12; temperature (T): 20°C and trans-membrane pressure (TMP): 45.7 bar. The combined (EC-RO) process showed 98%, 99.2%, and 98.5% of COD, color, and TDS removal, respectively, with permeate flux of 40.5 L/m²/h (EC-RO). Experimental results indicated that EC followed by RO could be used as an additional step for biologically treated spent wash treatment to improve the treated effluent quality and membrane life. Results also revealed that the techno-economic performance of combined (EC-RO) treatment in terms of total annual water production is more efficient and economical than RO alone.

Membrane and Electrochemical Based Technologies for the Decontamination of Exploitable Streams Produced by Thermochemical Processing of Contaminated Biomass

Phytoremediation is an emerging concept for contaminated soil restoration via the use of resilient plants that can absorb soil contaminants. The harvested contaminated biomass can be thermochemically converted to energy carriers/chemicals, linking soil decontamination with biomass-to-energy and aligning with circular economy principles. Two thermochemical conversion steps of contaminated biomass, both used for contaminated biomass treatment/exploitation, are considered: Supercritical Water Gasification and Fast Pyrolysis. For the former, the vast majority of contaminants are transferred into liquid and gaseous effluents, and thus the application of purification steps is necessary prior to further processing. In Fast Pyrolysis, contaminants are mainly retained in the solid phase, but a part appears in the liquid phase due to fine solids entrainment. Contaminants include heavy metals, particulate matter, and hydrogen sulfide. The purified streams allow the in-process re-use of water for the Super Critical Water Gasification, the sulfur-free catalytic conversion of the fuel-rich gaseous stream of the same process into liquid fuels and recovery of an exploitable bio-oil rich stream from the Fast Pyrolysis. Considering the fundamental importance of purification/decontamination to exploit the aforementioned streams in an integrated context, a review of available such technologies is conducted, and options are shortlisted. Technologies of choice include polymeric-based membrane gas absorption for desulfurization, electrooxidation/electrocoagulation for the liquid product of Supercritical Water Gasification and microfiltration via ceramic membranes for fine solids removal from the Fast Pyrolysis bio-oil. Challenges, risks, and suitable strategies to implement these options in the context of biomass-to-energy conversion are discussed and recommendations are made.

Binary electrochemical mineralization of heterocyclic nitrogenous compounds: parametric optimization using Taguchi method and mineralization mechanism

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.

Ofloxacin adsorptive interaction with rice husk ash: Parametric and exhausted adsorbent disposability study

The present study investigates the adsorptive interaction of rice husk ash (RHA) with Ofloxacin (OFL) antibiotic. The OFL loaded RHA was studied for its disposability by solidification to find its possible use as a building material. Further, toxicity analysis of leachate from the solidified RHA was also studied for probable leaching of OFL. The effects of adsorption parameters such as initial pH, the dosage of RHA (m), initial OFL concentration (C₀), and contact time (t) on the responses % OFL removal (X₁) and adsorption capacity (mg/g) (X₂) were evaluated using the central composite design (CCD) based on response surface method (RSM). Kinetic and thermodynamic studies were performed at optimized parameters, and adsorption equilibrium data were illustrated by using Langmuir, Redlich-Peterson (R-P), and Tempkin isotherm models. Optimum condition was found as m = 7.94 g/L, t = 430 min and pH = 6, and at this actual responses X₁ and X₂ were evaluated as 79.71% and 6.28 mg/g, respectively. Pseudo-first-order kinetic fitted best for the adsorption kinetic data. Toxicity analysis of leachate from solidified RHA indicated that most of the OFL was encapsulated inside the cement and the OFL present in leachate is not sufficient to eradicate the growth of E.coli and Bacillus subtilis.

Mechanistic insight into ultrasound-induced enhancement of electrochemical oxidation of ofloxacin: Multi-response optimization and cost analysis

In this paper, a hybrid advanced oxidation process of sonoelectrochemical, in which ultrasound and electrochemical are applied simultaneously, has been used for the degradation of ofloxacin (bio-recalcitrant pharmaceutical pollutant). Response surface methodology based central composite design was applied to understand the parametric effects of ultrasonic power, current density, initial pH, and electrolyte dose. Enhanced ofloxacin degradation was obtained using sonoelectrochemical (≈95%) process in comparison to the electrochemical (≈60.6%) and sonolysis alone (≈7.2%) after 120 min treatment time. Multi-response optimization was used so as to maximize COD removal (70.12%) and minimize specific energy consumption (11.92 kWh (g COD removed)^-1)at the optimized parametric condition of pH = 6.3 (natural pH), ultrasonic power = 54 W, current density = 213 A m^-2, and Na₂SO₄ electrolyte dose = 2.0 g L^-1. It was revealed that ^•OH radicals contribute major to the ofloxacin degradation reaction among the other oxidizing agents. Degradation of the ofloxacin followed pseudo-first-order kinetics with a higher reaction rate, which confirmed the synergistic effect of 34% between ultrasound and electrochemical approaches. The degradation pathway of ofloxacin removal was elucidated at optimum condition by the temporal evolution of the intermediate compounds and final products using gas chromatography coupled with mass spectroscopy (GC-MS), liquid chromatography-mass spectroscopy (LC-MS), high-resolution mass spectroscopy (HR-MS), and Fourier transform infrared spectroscopy (FTIR). Atomic force microscopy (AFM) and field emission scanning electron microscope (FE-SEM) coupled with energy dispersed X-ray (EDX) were used to determine the morphology of electrodes. Operational cost analysis was done based on the reactor employed in the present study.

Transformation products and degradation pathway of textile industry wastewater pollutants in Electro-Fenton process

In this study, pollutants from textile industry wastewater were transformed/oxidized using Ti/RuO₂ electrode by Electro-Fenton (EF) method in a continuous reactor. The performance was evaluated in terms of % COD removal, % color removal and energy consumed. Electrolysis time, retention time, current, and ferrous sulphate concentration as Fenton catalyst were selected as EF process parameters. To determine the optimum operating conditions multiple response optimization with desirability approach based on central composite design under response surface methodology was used. Spectrophotometric and GC-MS analysis were performed to identify the degraded/transformation compounds, and on this basis degradation mechanism during EF process as well as disposability of treated wastewater was analyzed. Further, bioassay test of treated textile wastewater was conducted for toxicity analysis in view of its disposal quality. Results showed that all the components of textile wastewater were totally eliminated/transformed in lower molecular weight compounds after EF treatment of textile effluent. Further, bioassay test analysis confirmed the nontoxic nature of treated wastewater.

Electrocatalytic oxidative treatment of real textile wastewater in continuous reactor: Degradation pathway and disposability study

Electrocatalytic treatment of real textile wastewater was investigated in continuous electrochemical reactor using dimensionally stable Ti/RuO₂ anode. Effects of various parameters such as: elapsed time, current, pH, retention time on the COD removal, color removal and specific energy consumed were evaluated. Central Composite Design under RSM was used for experimental design, data analysis, optimization, interaction analysis between the various electrochemical parameters and steady state time analysis. GC-MS and UV spectrophotometric analysis of the untreated and treated wastewater were conducted to identify the oxidized and transformed/degraded compounds during the oxidation process, and a suitable degradation mechanism was proposed. Treated wastewater may contain toxic chlorinated compounds due to mediated oxidation by various hydrolyzed chlorine species. Therefore, disposability of treated wastewater was assessed by conducting toxicity bioassay test. The optimal set of operating parameters were found to be elapsed time = 124 min, current = 1.37 A, pH = 5.54 and retention time = 157.6 min to simultaneously achieve COD removal, color removal and specific energy consumed as 86.22%, 94.74% and 0.012 kW h, respectively. GC-MS analysis showed presence of chlorinated compounds in the treated wastewater. The toxicity bioassay test resulted acute toxicity with 100% mortality rate within one minute and one hour exposure with untreated and treated textile wastewater, respectively.

Continuous electrocoagulation treatment of pulp and paper mill wastewater: operating cost and sludge study

Schematic view of continuous electrocoagulation set up.

Modeling and evaluation of electro-oxidation of dye wastewater using artificial neural networks

Treatment of CBSOL LE red wool dye containing wastewater by an electro-oxidation (EO) method was investigated using a Ti/RuO₂ electrode.

Continuous electrocoagulation of cheese whey wastewater: an application of Response Surface Methodology

In this study, treatment of cheese whey wastewater was performed using a uniquely-designed continuous electrocoagulation reactor, not previously encountered in the literature. An iron horizontal rotating screw type anode was used in the continuous mode. An empirical model, in terms of effective operational factors, such as current density (40, 50, 60 mA/cm(2)), pH (3, 5, 7) and retention time (20, 40, 60 min), was developed through Response Surface Methodology. An optimal region characterized by low values of Chemical Oxygen Demand (COD) was determined. As a result of experiments, a linear effect in the removal efficiency of COD was obtained for current density and retention time, while the initial pH of the wastewater was found to have a quadratic effect in the removal efficiency of COD. The best fit nonlinear mathematical model, with a coefficient of determination value (R(2)) of 85%, was defined. An initial COD concentration of 15.500 mg/L was reduced to 2112 mg/L with a removal efficiency of 86.4%. In conclusion, it can be said that electrocoagulation was successfully applied for the treatment of cheese whey wastewater.

Electrochemical oxidation of textile industry wastewater by graphite electrodes

In the present article, studies have been performed on the electrochemical (EC) oxidation of actual textile industry wastewater by graphite electrodes. Multi-response optimization of four independent parameters namely initial pH (pHo): 4-10, current density (j): 27.78-138.89 A/m(2), NaCl concentration (w): 0-2 g/L and electrolysis time (t): 10-130 min have been performed using Box-Behnken (BB) experimental design. It was aimed to simultaneously maximize the chemical oxygen demand (COD) and color removal efficiencies and minimize specific energy consumption using desirability function approach. Pareto analysis of variance (ANOVA) showed a high coefficient of determination value for COD (R(2) = 0.8418), color (R(2) = 0.7010) and specific energy (R(2) = 0.9125) between the experimental values and the predicted values by a second-order regression model. Maximum COD and color removal and minimum specific energy consumed was 90.78%, 96.27% and 23.58 kWh/kg COD removed, respectively, were observed at optimum conditions. The wastewater, sludge and scum obtained after treatment at optimum condition have been characterized by various techniques. UV-visible study showed that all azo bonds of the dyes present in the wastewater were totally broken and most of the aromatic rings were mineralized during EC oxidation with graphite electrode. Carbon balance showed that out of the total carbon eroded from the graphite electrodes, 27-29.2% goes to the scum, 71.1-73.3% goes into the sludge and rest goes to the treated wastewater. Thermogravimetric analysis showed that the generated sludge and scum can be dried and used as a fuel in the boilers/incinerators.

Multistep Optimization and Residue Disposal Study for Electrochemical Treatment of Textile Wastewater Using Aluminum Electrode

This paper reports multistep optimization studies on electrochemical (EC) treatment of textile wastewater containing three dyes namely basic orange 30, basic violet 16 and basic green 4 using an aluminum electrode. Chemical oxygen demand (COD) and color removal efficiencies were maximized in a batch EC experimental reactor. In first step, Plackett–Burman (PB) design was used to sort most effective factors amongst the various factors namely current density (j), time (t), electrode gap (g), temperature (T), initial pH (pHo) and NaCl salt concentration (m) that affected the removal efficiency. In the next step, steepest accent/descent method and Box–Behnken (BB) design methods were utilized to evaluate the optimum electrochemical conditions. In BB design, three operational parameters, namely j: 117.64–196.07 A/m2; t: 150–210 min and pHo: 3.5–5.5 were taken as input parameter whereas COD removal (Y1) and color removal (Y2) were taken as responses of the system. At the optimum operating conditions of j = 185.30 A/m2, t190 min and pHo 5, more than 70.5% COD and 98.2% color removal efficiencies were observed. Field emission scanning electron microscopy of aluminum electrodes, scum and sludge has been carried out to understand the EC mechanism.