Electrochemical oxidation for the treatment of textile industry wastewater

Current trends in textile wastewater treatment-bibliometric review

A bibliometric study using 1992 to 2021 database of the Science Citation Index Expanded was carried out to identify which are the current trends in textile wastewater treatment research. The study aimed to analyze the performance of scholarly scientific communications in terms of yearly publications/citations, total citations, scientific journals, and their categories in the Web of Sciences, top institutions/countries and research trends. The annual publication of scientific articles fluctuated in the first ten years, with a steady decrease for the last twenty years. An analysis of the most common terms used in the authors' keywords, publications' titles, and KeyWords Plus was carried out to predict future trends and current research priorities. Adsorbent nanomaterials would be the future of wastewater treatment for decoloration of the residual dyes in the wastewater. Membranes and electrolysis are important to demineralize textile effluent for reusing wastewater. Modern filtration techniques such as ultrafiltration and nanofiltration are advanced membrane filtration applications.

Electrochemical Removal of Nitrogen Compounds from a Simulated Saline Wastewater

In the last few years, many industrial sectors have generated and discharged large volumes of saline wastewater into the environment. In the present work, the electrochemical removal of nitrogen compounds from synthetic saline wastewater was investigated through a lab-scale experimental reactor. Experiments were carried out to examine the impacts of the operational parameters, such as electrolyte composition and concentration, applied current intensity, and initial ammoniacal nitrogen concentration, on the total nitrogen removal efficiency. Using NaCl as an electrolyte, the N_TOT removal was higher than Na₂SO₄ and NaClO₄; however, increasing the initial NaCl concentration over 250 mg·L^-1 resulted in no benefits for the N_TOT removal efficiency. A rise in the current intensity from 0.05 A to 0.15 A resulted in an improvement in N_TOT removal. Nevertheless, a further increase to 0.25 A led to basically no enhancement of the efficiency. A lower initial ammoniacal nitrogen concentration resulted in higher removal efficiency. The highest N_TOT removal (about 75%) was achieved after 90 min of treatment operating with a NaCl concentration of 250 mg·L^-1 at an applied current intensity of 0.15 A and with an initial ammoniacal nitrogen concentration of 13 mg·L^-1. The nitrogen degradation mechanism proposed assumes a series-parallel reaction system, with a first step in which NH₄⁺ is in equilibrium with NH₃. Moreover, the nitrogen molar balance showed that the main product of nitrogen oxidation was N₂, but NO₃^- was also detected. Collectively, electrochemical treatment is a promising approach for the removal of nitrogen compounds from impacted saline wastewater.

A Review of Hybrid Process Development Based on Electrochemical and Advanced Oxidation Processes for the Treatment of Industrial Wastewater

Nowadays, increased human activity, industrialization, and urbanization result in the production of enormous quantities of wastewater. Generally, physicochemical and biological methods are employed to treat industrial effluent and wastewater and have demonstrated high efficacy in removing pollutants. However, some industrial effluent and wastewater contain contaminants that are extremely difficult to remove using standard physicochemical and biological processes. Previously, electrochemical and hybrid advanced oxidation processes (AOP) were considered a viable and promising alternative for achieving an adequate effluent treatment strategy in such instances. These processes rely on the production of hydroxyl radicals, which are highly reactive oxidants that efficiently break down contaminants found in wastewater and industrial effluent. This review focuses on the removal of contaminants from industrial effluents and wastewater through the integration of electrochemical and advanced oxidation techniques. These processes include electrooxidation, electrocoagulation/electroflocculation, electroflotation, photo-Fenton, ozone-photo-Fenton, sono-photo-Fenton, photo-electro-Fenton, ozone/electrocoagulation, sono-electrocoagulation, and peroxi/photo/electrocoagulation. The data acquired from over 150 published articles, most of which were laboratory experiments, demonstrated that the hybrid process is more effective in removing contaminants from industrial effluent and wastewater than standalone processes.

Performance Optimization and Toxicity Effects of the Electrochemical Oxidation of Octogen

Octogen (HMX) is widely used as a high explosive and constituent in plastic explosives, nuclear devices, and rocket fuel. The direct discharge of wastewater generated during HMX production threatens the environment. In this study, we used the electrochemical oxidation (EO) method with a PbO2-based anode to treat HMX wastewater and investigated its degradation performance, mechanism, and toxicity evolution under different conditions. The results showed that HMX treated by EO could achieve a removal efficiency of 81.2% within 180 min at a current density of 70 mA/cm2, Na2SO4 concentration of 0.25 mol/L, interelectrode distance of 1.0 cm, and pH of 5.0. The degradation followed pseudo-first-order kinetics (R2 > 0.93). The degradation pathways of HMX in the EO system have been proposed, including cathode reduction and indirect oxidation by •OH radicals. The molecular toxicity level (expressed as the transcriptional effect level index) of HMX wastewater first increased to 1.81 and then decreased to a non-toxic level during the degradation process. Protein and oxidative stress were the dominant stress categories, possibly because of the intermediates that evolved during HMX degradation. This study provides new insights into the electrochemical degradation mechanisms and molecular-level toxicity evolution during HMX degradation. It also serves as initial evidence for the potential of the EO-enabled method as an alternative for explosive wastewater treatment with high removal performance, low cost, and low environmental impact.

Sono-degradation of Reactive Blue 19 in aqueous solution and synthetic textile industry wastewater by nanoscale zero-valent aluminum

Reactive dyes, which are commonly used in the textile industry, are toxic and carcinogenic for the ecosystem and human health. The objective of this study was to investigate the removal of Reactive Blue 19 (RB19) from aqueous solution and synthetic textile industry wastewater using nanoscale zero-valent aluminum (nZVAl), ultrasonic bath (US-40 kHz), and combined US/nZVAl through the consideration of varying experimental parameters such as pH, nZVAl dosage, contact time, and initial RB19 dye concentration. The acidic pH value was an effective parameter to degrade RB19. As the nZVAl dosage and contact time increased, the degradation of RB19 dye from aqueous solution and synthetic textile industry wastewater increased using combined US/nZVAl process. A similar result was obtained for RB19 removal with combined US/nZVAl using 0.10 g dosage at 30 min, whereas it was obtained with nZVAl alone using 0.20 g dosage at 60 min. The sono-degradation process activated the nZVAl surface depending on US cavitation effect and shock waves, and increased RB19 dye uptake capacity with a shorter contact time and lower nZVAl dosage. Increasing the initial dye concentration decreased the removal efficiency for RB19. According to the obtained reusability results, nZVAl particles could be reused for four and two consecutive cycles of combined US/nZVAl and nZVAl alone, respectively.

Electroconductive moving bed membrane bioreactor (EcMB-MBR) for single-step decentralized wastewater treatment: Performance, mechanisms, and cost

Membrane bioreactor (MBR) is an advantageous technology for wastewater treatment. However, efficient nutrient removal and membrane fouling mitigation remain major challenges in its applications. In this study, an electroconductive moving bed membrane bioreactor (EcMB-MBR) was proposed for simultaneous removal of organics and nutrients from domestic wastewater. The EcMB-MBR was composed of a submerged MBR, filled with electrodes and free-floating conductive media. Conductive media were introduced to reduce energy consumption in an electrochemical MBR, to improve nitrogen removal, and to mitigate membrane fouling. The results showed that COD, total nitrogen, and total phosphorus removal was up to 97.1 ± 1.4%, 88.8 ± 4.2%, and 99.0 ± 0.9%, respectively, in comparison with those of 93.4 ± 1.5%, 65.2 ± 5.3%, and 20.4 ± 11.3% in a conventional submerged MBR. Meanwhile, a total membrane resistance reduction of 26.7% was obtained in the EcMB-MBR. The optimized operating condition was determined at an intermittent electricity exposure time of 10 min-ON/10 min-OFF, and a direct current density of 15 A/m². The interactions between electric current and conductive media were explored to understand the working mechanism in this proposed system. The conductive media reduced 21% of the electrical resistivity in the mixed liquor at a selected packing density of 0.20 (v/v). The combination of electrochemical process and conductive media specially enhanced the reduction of nitrate-nitrogen (NO₃^--N) through hybrid bio-electrochemical denitrification processes. These mechanisms involved with electrochemically assisted autotrophic denitrification by autotrophic denitrifying bacteria. As a result, 5.2% of NO₃^--N remained in the effluent of EcMB-MBR in comparison with that of 29.5% in the MBR. Membrane fouling was minimized via both mechanical scouring and electrochemical decomposition/precipitation of organic/particulate foulants. Furthermore, a preliminary cost analysis indicated that an additional operating cost of 0.081 USD/m³, accounting for 10 - 30% increment of the operating cost of a conventional MBR, was needed to enhance the nitrogen and phosphorus removal correspondingly in the EcMB-MBR.

Real textile effluents treatment using coagulation/flocculation followed by electrochemical oxidation process and ecotoxicological assessment

As it is well known, the textile industry generates a large amount of wastewater with varied composition that need to be treated. In particular, the Sergipe state, in Brazil, is a region that requires attention due the presence of several local textile industries. In this study, the efficiency of electrochemical oxidation (EO) process applied in the samples of Brazilian textile industry effluents previously treated by physical-chemical process coagulation-flocculation (CF) was evaluated by the reduction in TOC parameter and by the ecotoxicity using Lactuca sativa and Raphidocelis subcapitata bioassays. The optimized experiments achieved for the CF ([Al₂(SO₄)₃]₀ = 1.5 mg L^-1, pH = 6.0, alkalinity = 0.675 mg L^-1, [flocculating agent] = 61 mg L^-1, rapid mixing = 100 rpm for 1 min, slow stage = 20-60 rpm for 20 min) a reduction of 20% on TOC. The best results obtained for EO was using the DSA electrode (I = 300 mA) reaching a TOC removal efficiency of 82% after an electrolysis time of 180 min. The ecotoxicity experiments indicated that the proposed treatment (CF + EO, I = 300 mA) was effective to decrease the dissolved pollutants presented in the treated samples. In comparison with raw samples, the treatment achieved a reduction of 52% for IC50_72h value using R. subcapitata as bioindicator, and a 98% reduction of LC₅₀ (Lactuca sativa).

Electrochemical Oxidation of Resorcinol in Aqueous Medium Using Boron-Doped Diamond Anode: Reaction Kinetics and Process Optimization with Response Surface Methodology

Electrochemical oxidation of resorcinol in aqueous medium using boron-doped diamond anode (BDD) was investigated in a batch electrochemical reactor in the presence of Na₂SO₄ supporting electrolyte. The effect of process parameters such as resorcinol concentration (100–500 g/L), current density (2–10 mA/cm²), Na₂SO₄ concentration (0–20 g/L), and reaction temperature (25–45°C) was analyzed on electrochemical oxidation using response surface methodology (RSM). The optimum operating conditions were determined as 300 mg/L resorcinol concentration, 8 mA/cm² current density, 12 g/L Na₂SO₄ concentration, and 34°C reaction temperature. One hundred percent of resorcinol removal and 89% COD removal were obtained in 120 min reaction time at response surface optimized conditions. These results confirmed that the electrochemical mineralization of resorcinol was successfully accomplished using BDD anode depending on the process conditions, however the formation of intermediates and by-products were further oxidized at much lower rate. The reaction kinetics were evaluated at optimum conditions and the reaction order of electrochemical oxidation of resorcinol in aqueous medium using BDD anode was determined as 1 based on COD concentration with the activation energy of 5.32 kJ/mol that was supported a diffusion-controlled reaction.

Decolorization of synthetic textile wastewater using electrochemical cell divided by cellulosic separator

BACKGROUND

Annually, large quantities of dyes are produced and consumed in different industries. The discharge of highly colored textile effluents to the aquatic environments causes serious health problems in living organisms. This paper investigates the performance of each of the electro-oxidation and electro-reduction pathways in the removal of reactive red 120 (RR120) from synthetic textile effluents using a novel electrochemical reactor.

METHODS

In the current study, a two-compartment reactor divided by cellulosic separator was applied in batch mode using graphite anodes and stainless steel cathodes. Central Composite Design was used to design the experiments and find the optimal conditions. The operational parameters were initial dye concentration (100-500 mg L^-1), sodium chloride concentration (2500-12,500 mg L^-1), electrolysis time (7.5-37.5 min), and current intensity (0.06-0.3 A).

RESULTS

The results showed that electro-oxidation was much more efficient than electro-reduction in the removal of RR120. According to the developed models, current intensity was the most effective factor on the electro-oxidation of RR120 as well as in power consumption (Coefficients of 12.06 and 0.73, respectively). With regard to the dye removal through electro-reduction, electrolysis time (coefficient of 8.05) was the most influential factor. Under optimal conditions (RR120 = 200 mg.L^-1, NaCl = 7914.29 mg.L^-1, current intensity = 0.12 A, and reaction time = 30 min), the dye was removed as 99.44 and 32.38% via electro-oxidation and electro-reduction mechanisms, respectively, with consuming only 1.21 kwhm^-3 of electrical energy.

CONCLUSIONS

According to the results, electro-oxidation using graphite anodes in a cell divided by cellulosic separator is very efficient, compared to electro-reduction, in the removal of RR120 from aqueous solutions.

Boron-doped diamond electrode: Preparation, characterization and application for electrocatalytic degradation of m-dinitrobenzene

Boron-doped diamond (BDD) electrode was successfully prepared via microwave plasma chemical vapor deposition method and it was used in electrocatalytic degradation of m-dinitrobenzene (m-DNB). The electrocatalytic degradation efficiency of m-DNB was evaluated under different experimental parameters including current density, temperature, pH, Na₂SO₄ concentration and initial m-DNB concentration. Under optimal parameters, degradation efficiency of m-DNB reached up to 82.7% after 150min. The degradation process of m-DNB was fitted well with pseudo first-order kinetics. Moreover, UV and HPLC analyses implied that m-DNB was totally destroyed and mineralized after 240min degradation, and the proposed mechanism during the electrocatalytic degradation process was analyzed. All these results demonstrated that BDD electrode possessed excellent electrocatalytic property and showed a great potential application in wastewater treatment.

Photocatalytic discoloration of Acid Red 14 aqueous solution using titania nanoparticles immobilized on graphene oxide fabricated plate

Textile industry consumes remarkable amounts of water during various operations. A significant portion of the water discharge to environment is in the form of colored contaminant. The present research reports the photocatalytic degradation of anionic dye effluent using immobilized TiO2 nanoparticle on graphene oxide (GO) fabricated carbon electrodes. Acid Red 14 (AR 14) was used as model compound. Graphene oxide nanosheets were synthesized from graphite powder using modified Hummer's method. The nanosheets were characterized with field emission scanning electron microscope (FESEM) images, X-ray diffraction (XRD) and FTIR spectrum. The GO nanoparticles were deposited on carbon electrode (GO-CE) by electrochemical deposition (ECD) method and used as catalyst bed. TiO2 nanoparticles were fixed on the bed (GO-CE- TiO2) with thermal process. Photocatalytic processes were carried out using a 500 ml solution containing dye in batch mode. Each photocatalytic treatment were carried out for 120 min. Effect of dye concentration (mg/L), pH of solution, time (min) and TiO2 content (g/L) on the photocatalytic decolorization was investigated.

Treatment of industrial effluents by electrochemical generation of H2O2 using an RVC cathode in a parallel plate reactor

Electrochemical techniques have been used for the discolouration of synthetic textile industrial wastewater by Fenton's process using a parallel plate reactor with a reticulated vitreous carbon (RVC) cathode. It has been shown that RVC is capable of electro-generating and activating H2O2 in the presence of Fe(2+) added as catalyst and using a stainless steel mesh as anode material. A catholyte comprising 0.05 M Na2SO4, 0.001 M FeSO4.7H2O, 0.01 M H2SO4 and fed with oxygen was used to activate H2O2.The anolyte contained only 0.8 M H2SO4. The operating experimental conditions were 170 mA (2.0 V < ΔECell < 3.0 V) to generate 5.3 mM H2O2. Synthetic effluents containing various concentrations (millimolar - mM) of three different dyes, Blue Basic 9 (BB9), Reactive Black 5 (RB5) and Acid Orange 7 (AO7), were evaluated for discolouration using the electro-assisted Fenton reaction. Water discolouration was measured by UV-VIS absorbance reduction. Dye removal by electrolysis was a function of time: 90% discolouration of 0.08, 0.04 and 0.02 mM BB9 was obtained at 14, 10 and 6 min, respectively. In the same way, 90% discolouration of 0.063, 0.031 and 0.016 mM RB5 was achieved at 90, 60 and 30 min, respectively. Finally, 90% discolouration of 0.14, 0.07 and 0.035 mM AO7 was achieved at 70, 40 and 20 min, respectively. The experimental results confirmed the effectiveness of electro-assisted Fenton reaction as a strong oxidizing process in water discolouration and the ability of RVC cathode to electro-generate and activate H2O2 in situ.

Treatment of textile wastewater by submerged membrane bioreactor: In vitro bioassays for the assessment of stress response elicited by raw and reclaimed wastewater

The performance of a pilot-scale membrane bioreactor (MBR) system for the treatment of textile wastewater was investigated. The MBR was continuously operated for 7 months. Very high treatment efficiencies were achieved (color, 100%; chemical oxygen demand (COD), 98%; biochemical oxygen demand (BOD5), 96%; suspended solids (SS), 100%). Furthermore, the MBR treatment efficiency was analyzed from a toxicological-risk assessment point of view, via different In vitro bioassays using Caco-2 cells, a widely used cell model in toxicological studies. Results showed that MBR treatment significantly reduced the raw textile wastewater (RTWW) cytotoxicity on Caco-2 cells by 53% for a hydraulic retention time (HRT) of 2 days. Additionally, the RTWW-induced disruption in the barrier function (BF) of the Caco-2 cell monolayer was also significantly reduced after MBR treatment under a HRT of 2 days (no disruption of BF was observed). Moreover, the effect of RTWW and treated wastewater on stress response was investigated using different stress genes: AHSA1, HSPD1, HSPA1A, HSPA5 and HSPA8. The cell exposure to RTWW significantly increased the expression of all used stress genes; interestingly, the treated wastewater (HRT 2 days) did not show any significant modulation of the stress genes.

Anodic oxidation of textile wastewaters on boron-doped diamond electrodes

The objective of this study is to investigate the potential application of the anodic oxidation (AO) on two electrolytic cells (monopolar (Cell 1) and bipolar (Cell 2)) containing boron-doped diamond electrodes on the treatment of real textile effluents to study the reuse possibility of treated wastewater in the textile industry process. AO is applied in the flocculation coagulation pretreatment of both upstream (BH) and downstream (BS) effluents. The chemical oxygen demand (COD) results show that the final COD removal obtained for the BH effluent in the case of Cell 1 and Cell 2 is 800 and 150 mg O₂L⁻¹ after 5 and 6 h of electrolysis, respectively. The treatments of the BS effluent allow for obtaining a final COD of 76 mg L⁻¹ for Cell 1 and a total mineralization for Cell 2. The obtained results demonstrate that the apparent mineralization kinetics of both effluents when using Cell 2 are about four times faster than the one obtained by Cell 1 and highlight the important contribution of the bipolar cell. Besides, the energy consumption values show that the treatment of the BH effluent by Cell 1 consumes 865 kWh kg COD⁻¹ against 411 kWh kg COD(-1) by Cell 2. Therefore, the use of Cell 2 decreases the energy cost by 2.1-6.65 times when compared to Cell 1 in the case of the BH and BS effluent treatment, respectively.

Hydrophilic hollow carbon nanocapsules for high-capacity adsorptive removal of cationic dyes in aqueous systems

The hollow carbon nanocapsules prepared from Ni₃C nanoparticles show a high adsorption rate and a high maximum adsorption capacity to organic dyes in water solutions.

Advanced treatment of cephalosporin pharmaceutical wastewater by nano-coated electrode and perforated electrode

The objective of this study was to investigate the degradation of nonbiodegradable organic pollutants in biologically cephalosporin pharmaceutical wastewater using different electrodes such as non-nano-scale electrode (traditional coated), nano-scale (nano-coated) electrode, and perforated electrode after biotreatment. The traditional coated electrode plate, nano-coated electrode plate, and two different perforated titanium dioxide (TiO2) electrode plates with an average pore size of 10 μm and 20 μm were chosen as the anode. The results demonstrated that traditional coated electrode, nano-scale electrode, and perforated electrode could effectively remove nonbiodegradable organic pollutants from pharmaceutical wastewater. The perforated electrode with an average pore size of 10 μm exhibited the best degradation effect with a 90 % decrease in the chemical oxygen demand (COD) (COD content reduced from 320 mg L(-1) to 32 mg L(-1)). During catalytic degradation, the electrical conductivity of pharmaceutical wastewater increased and the pH increased and finally reached equilibrium. It was also found that the perforated TiO2 electrode produced relatively large amounts of dissolved oxygen during the catalytic oxidation process, reaching above 4 mg L(-1), whereas the nano-coated electrode produced little dissolved oxygen. The biotoxicities of all wastewater samples increased firstly then decreased slightly during the electrical catalytic oxidation, but the final biotoxicities were all higher than initial ones.

Effect of electric current on adsorption effectiveness on chitin and chitosan

The objective of this study was to determine the effect of an electric current on the effectiveness of reactive dye Reactive Black 5 (RB 5) adsorption onto two adsorbents: chitin and chitosan. The current density applied in the experiment was 50 A/m2. The experiment was carried out using electrodes made of stainless steel. At the first stage of the experiment - without the flow of electric current - the effectiveness of RB 5 dye adsorption onto chitin was determined at pH 3.0 and 5.0, whereas onto chitosan it was at pH 5.0. In the second stage, the effectiveness of RB 5 dye adsorption was determined onto chitin and chitosan with a simultaneous flow of direct current. In the case of both adsorbents, the pH value of the solution was 5.0. Results achieved in the study proved that the electric current had a positive effect on adsorption effectiveness onto chitin, as it contributed to an increase in the quantity of removed RB 5 dye to 440 mg/g d.m. from the initial 270 mg/g d.m. when assayed at the optimal pH 3.0 and from 135 mg/g d.m. when assayed at pH 5.0.

Textiles wastewater treatment using anoxic filter bed and biological wriggle bed-ozone biological aerated filter

In this study, the performance of the anoxic filter bed and biological wriggle bed-ozone biological aerated filter (AFB-BWB-O(3)-BAF) process treating real textile dyeing wastewater was investigated. After more than 2 month process operation, the average effluent COD concentration of the AFB, BWB, O(3)-BAF were 704.8 mg/L, 294.6 mg/L and 128.8 mg/L, with HRT being 8.1-7.7h, 9.2h and 5.45 h, respectively. Results showed that the effluent COD concentration of the AFB decreased with new carriers added and the average removal COD efficiency was 20.2%. During operation conditions, HRT of the BWB and O(3)-BAF was increased, resulting in a decrease in the effluent COD concentration. However, on increasing the HRT, the COD reduction capability expressed by the unit carrier COD removal loading of the BWB reactor increased, while that of the O(3)-BAF reactor decreased. This study is a beneficial attempt to utilize the AFB-BWB-O(3)-BAF combine process for textile wastewater treatment.

Electrochemical oxidation of tannic acid contaminated wastewater by RuO2/IrO2/TaO2-coated titanium and graphite anodes

The electrochemical oxidation of tannic acid contaminated wastewater by RuO2/IrO2/TaO2-coated titanium and graphite anodes has been investigated. The effect of the process variables, such as initial pH, current density, processing time, concentration of the electrolyte and anode materials, on the degradation of tannic acid was studied. During the various stages of electrolysis, parameters such as COD, chloride ion concentration and UV-Vis spectra were examined and discussed. The maximum chemical oxygen demand (COD) removal efficiency of 94% was achieved at pH 5, operated at the current density of 8.10 mA/cm2, electrolyte (NaCl) concentration of 0.1 M and at 60 min of electrolysis using graphite anodes. The experimental results showed that the electrochemical oxidation process could effectively reduce the COD from the tannic acid contaminated wastewater. An acidic pH showed the maximum reduction of COD compared with neutral and alkaline pH. Increase in current density, process time and electrolyte (NaCl) concentration with the increase in COD removal. Graphite anodes showed maximum removal of COD and better tannic acid degradation when compared with RuO2/IrO2/TaO2-coated titanium anodes.

Removal of acid green dye 50 from wastewater by anodic oxidation and electrocoagulation--a comparative study

The present work represents a comparative study for removing acid green dye 50 by anodic oxidation and electrocoagulation using a new batch self gas stirred electrochemical cell. The effect of operating parameters such as current density, initial dye concentration, NaCl concentration and pH on the efficiency of colour removal has been examined. The chemical oxygen demand (COD) reduction under suitable operating conditions was also calculated and found to be reduced by 68% and 87% in case of electrochemical oxidation and electrocoagulation methods, respectively. The results indicate that electrocoagulation is more economic than anodic oxidation, energy consumption ranged from 2.8 to 12.8 kWh/kg dye removed in case of electrocoagulation while in case of anodic oxidation it ranged from 3.31 to 16.97 kWh/kg dye removed. Although the mechanisms of electrocoagulation and anodic oxidation are different, results show that the first-order rate equation provides the best correlation for the decolourization rate of acid green 50 by the two methods.

A new type of chitosan hydrogel sorbent generated by anionic surfactant gelation

A new type of chitosan hydrogel beads (CSB) with a core-shell membrane structure was generated by sodium dodecyl sulfate (SDS) gelation process. CSB exhibited higher mechanical strength and acid stability than chitosan hydrogel beads (CB) formed by alkali gelation. The effect of SDS concentration variation during gelation on the adsorption capacity of CSB for congo red (CR) as a model anionic dye showed that CSB formed by 4gl(-1) SDS gelation had the highest adsorption capacity. The maximum adsorption capacity of CSB (208.3mgg(-1)) obtained from the Sips model was found slightly higher than that of CB (200.0mgg(-1)). Membrane materials of CSB obtained after squeezing core water from the beads showed approximately 25 times higher volumetric adsorption capacity than CB.