Simultaneous decolorization and desalination of dye wastewater through electrochemical process

Unravelling the potential of combined electrodialysis/electrocoagulation for boosted dye removal and membrane anti-fouling activity

Membrane fouling is the major technology issue facing the wide application of electrodialysis (ED) for water purification in real world cases. The fouling of membrane in ED leads to reduce the removal rate, increase in membrane damage, and it requires continuous costly maintenance. Herein, a successful dual process combining ED and electrocoagulation (EC) was designed to combat anionic membrane (AMX) fouling and to boost organic dye pollutant (methyl orange, (MO)) removal efficiency. Electrodialysis-electrocoagulation (ED-EC) was constructed via the use of cheap aluminum anode. In such a combined system, coagulation synergistically accumulates and eliminates MO species, and meanwhile, the separation of mineral (Na+ and Cl-) occurs by ED mechanism. A performance comparison between single ED and ED-EC demonstrates technological, economic, and efficiency benefits of combined ED-EC process as compared to single ED. The MO removal rate was improved from 20.72 to 96.92%, the electrical resistance of the ED cell (EREDC) was reduced by 40%, and the amount of Cl- ions transferred was boosted by twice. Membrane surface characterization proved that AMX membrane fouling was very intense in single ED due to MO fixation and accumulation on the membrane pores, which in turn makes the process unable to function effectively and continuously. On the contrary, ED-EC exhibits excellent mass transfer and boosted continuous removal without any observed increase in the electrical resistance of the dual cell. To further understand synergistic performance of dual ED-EC, experiments were carried out under different operating conditions including variation in current density, variation in MO concentration, and changes in pH and NaCl electrolyte dose. Highest efficiency using dual system was recorded at pH close to neutral, while the removal at alkaline or acidic solutions. The final sludge obtained after the treatment was characterized via SEM-EDS, XRD, and FTIR techniques. Overall, this study proves the correlation between ED and EC to build a dual process allowing highly efficiency and continuous processing which are the crucial factors that are wanted at real-world application.

Treatment of dye-containing wastewater using discarded animal blood-derived hemoglobin crystals

Ever-expanding industrial and agricultural production has satisfied human needs but unfortunately causes serious environmental pollution. Pollutants such as dye-containing wastewater from the dye industry and animal blood waste from the meat industry impose heavy burdens on the environment and are difficult to treat. Here we demonstrate that hemoglobin crystals prepared from animal blood waste can effectively and selectively adsorb and remove organic pollutants from dye-containing wastewater. This approach simultaneously mitigates two types of environmental pollutants: wastewater dye and animal waste. The absorption properties of low-cost and stable cross-linked hemoglobin crystals (CLHCs) prepared from discarded chicken blood were experimentally tested on various dyes (methylene blue, malachite green, methyl orange and Congo red). The CLHCs adsorbed all dyes in a pH-dependent manner, achieving controllable selective adsorption. Adsorption of anionic dyes was especially effective, with an adsorption capacity of 184.18 mg/g for methylene blue. Unexpectedly, the CLHCs also exhibited degradative activity against methylene blue and malachite green. Mechanistic studies showed that the crystals removed methylene blue mainly by multi-layer physical adsorption and malachite green mainly by chemical degradation. Finally, we evaluated whether CLHCs can remove dyes from actual wastewater to promote the germination of contaminated rice seeds. Our results confirm that hemoglobin crystals can effectively treat dye-containing wastewater in practical scenarios.

Bibliometric analysis of electrochemical disinfection: current status and development trend from 2002 to 2022

The removal of waterborne pathogens from water is critical in preventing the spread of waterborne diseases. Electrochemical methods have been extensively researched and implemented for disinfection, primarily owing to their simplicity, efficiency, and eco-friendliness. Thus, it is essential to conduct a review about the research progress and hotspots on this promising technique. In this paper, we provided a comprehensive bibliometric analysis to systematically study and analyze the current status, hotspots, and trends in electrochemical disinfection research from 2002 to 2022. This study analyzed literature related to electrochemical disinfection or electrochemical sterilization published in the Web of Science database from 2002 to 2022 using CiteSpace and Biblioshiny R language software packages. The analysis focused on the visualization and assessment of annual publication volume, discipline and journal distribution, collaborative networks, highly cited papers, and keywords to systematically understand the current status and trends of electrochemical disinfection. The results showed that between 2002 and 2022, 1171 publications related to electrochemical disinfection were published, with an exponential increase in the cumulative number of publications (y=17.518e0.2147x, R2= 0.9788). The publications covered 76 disciplines with many articles published in high-impact journals. However, the research power was characterized by a large number of scattered research efforts and insufficient cooperation, indicating the need for further innovative collaboration. The citation analysis and keyword analysis suggest that future development in this field may focus on optimizing electrode materials, investigating the disinfection performance of ·OH based systems, optimizing conditions for actual wastewater treatment, and reducing energy consumption to promote practical applications.

Preparation of polyethyleneimine-modified chitosan/Ce-UIO-66 composite hydrogel for the adsorption of methyl orange

In this work, a polyethyleneimine-modified chitosan/Ce-UIO-66 composite hydrogel (PEI-CS/Ce-UIO-66) was prepared using the ex-situ blend method. The synthesized composite hydrogel was characterized by SEM, EDS, XRD, FTIR, BET, XPS, and TG techniques, while the zeta potential was recorded for sample analysis. The adsorbent performance was studied by conducting adsorption experiments using methyl orange (MO), which showed that PEI-CS/Ce-UIO-66 exhibited excellent MO adsorption properties (900.5 ± 19.09 mg/g). The adsorption kinetics of PEI-CS/Ce-UIO-66 could be explained by the pseudo-second-order kinetic model, and its isothermal adsorption followed the Langmuir model. Thermodynamics showed that the adsorption was spontaneous and exothermic at low temperatures. MO could interact with PEI-CS/Ce-UIO-66 via electrostatic interaction, π-π stacking, and hydrogen bonding. The results indicated that the PEI-CS/Ce-UIO-66 composite hydrogel could potentially be used for the adsorption of anionic dyes.

Synthesis, characterization, and dye degradation photocatalytic activity of the nano-size copper iron binary oxide

Magnetic nano-size copper iron binary oxide is synthesized via a sol-gel method using copper and iron nitrates as precursors and citric acid, chicken egg white, and starch as stabilizers followed by annealing at 400 °C and 800 °C in air. The TG-DTG, XRD, FESEM, EDX, VSM, and FT-IR and UV-Vis DRS spectroscopy methods are used for thermal, structural, magnetic, and optoelectronic characterizations. Depending on the stabilizer and annealing temperature, pure CuFe₂O₄, (CuFe₂O₄,CuO) or (CuFe₂O₄,CuO,Fe₂O₃) phases are formed with nano-size particles of 20-65 nm, having optical band gaps in the range of 2.15-2.60 eV (577-477 nm). Photocatalytic activities of the synthesized nano-size copper iron binary oxide samples are examined for degradation of Nile Blue textile dye displayed first-cycle removal (from water solution) efficiencies of 86.7-93.3%. Considering usage of non-toxic metals and low-cost green stabilizers, good degradation performances, and easy/efficient (magnetic) recyclability, this nano-size catalyst is suggested for further optimization studies for industrial applications.

Investigation of indole biodegradation by Cupriavidus sp. strain IDO with emphases on downstream biotransformation and indigo production

Indole, as a typical N-heterocyclic aromatic pollutant, poses risks to living things; however, indole-biotransformation mechanisms remain under-discussed, especially those related to its downstream biotransformation. Here, we systematically investigated the characteristics of indole degradation by strain Cupriavidus sp. IDO. We found that Cupriavidus sp. IDO could utilize 25 to 150 mg/L indole within 40 h and identified three intermediates (2-oxindole, indigo, and isatin). Additionally, integrated genomics and proteomics analysis of the indole biotransformation mechanism in strain IDO revealed 317 proteins showing significant changes (262 upregulated and 55 downregulated) in the presence of indole. Among these, three clusters containing indole oxidoreductase, CoA-thioester ligase, and gentisate 1,2-oxidoreductase were identified as potentially responsible for upstream and downstream indole metabolism. Moreover, HPLC-MS and -omics analysis offered insight into the indole-degradation pathway in strain IDO. Furthermore, the indole oxidoreductase IndAB, which initiates indole degradation, was heterologously expressed in Escherichia coli BL21(DE3). Optimization by the response surface methodology resulted in a maximal production of 135.0 mg/L indigo by the recombination strains in tryptophan medium. This work enriches our understanding of the indole-biodegradation process and provides new insights into multiple indole-degradation pathways in natural environments.

Electrochemical oxidation of aniline using Ti/RuO2-SnO2 and Ti/RuO2-IrO2 as anode

Electrocatalytic properties of anode and the electrolyte composition are important parameters influence the degradation efficiency for aniline wastewater. Ti/RuO₂-SnO₂ and Ti/RuO₂-IrO₂ have been fabricated using thermal decomposition method and experiments in electrolyte containing 0.05 M Na₂SO₄, 0.05 M NaCl and 0.05 M Na₂SO₄+0.005 M FeSO₄ at different current density were conducted to study the influence on aniline degradation. Linear sweep voltammetry (LSV) showed that Ti/RuO₂-SnO₂ had higher oxygen evolution potential and degrade aniline through electrochemical transformation and electrochemical combustion while Ti/RuO₂-IrO₂ degrade aniline mainly through electrochemical transformation. The study showed that Ti/RuO₂-SnO₂ had higher electrocatalytic activity towards the degradation of aniline than Ti/RuO₂-IrO₂ anode in 0.05 M Na₂SO₄ and in 0.05 M NaCl electrolyte. The maximum TOC removal efficiency for Ti/RuO₂-SnO₂ was 64.2% at 40 mA cm^-2 in Na₂SO₄ electrolyte while the average MCE was 1.6% and the average EC_TOC was 1.51 kWh (g TOC)^-1. On the contrary, the maximum TOC removal efficiency for Ti/RuO₂-IrO₂ was 63.1% at 40 mA cm^-2 in NaCl electrolyte while the average MCE was 1.6% and the average EC_TOC was 1.95 kWh (g TOC)^-1. The presence of Fe²⁺ in Na₂SO₄ electrolyte would decrease the TOC removal efficiency except at low current density (20 mA cm^-2) for Ti/RuO₂-SnO₂. These results indicated that Ti/RuO₂-SnO₂ and Ti/RuO₂-IrO₂ anode were suitable in Na₂SO₄ and NaCl electrolyte, respectively, while the presence of Fe²⁺ would inhibit aniline degradation.

Silicalite-1 zeolite membrane: Synthesis by seed method and application in organics removal

Silicalite-1 (S-1) zeolite membrane synthesized by seed method with superior features attracts intensive attentions, while the influences of key parameters during synthesis process and its applications for organics removal require further investigation. This study revealed the morphology and the structure of the prepared membranes under different crystallization temperatures and seed concentrations by using a suite of characterization methods. The as-prepared membrane under optimal condition (crystallization temperature of 175 °C and seed concentration of 1.0 wt. %) possessed high membrane integrity, with ideal separation factor of 4.0. It also exhibited outstanding performance for organics removal, with dyes retention of 99.9% and 99.2% for 500 mg L^-1 neutral red and 500 mg L^-1 methyl blue, respectively. Excellent antifouling property of the synthesized membrane was also proved. Results of this work can guide the characteristic improvement of the S-1 zeolite membrane by adjusting key parameters and broaden its applications in dye wastewater treatment.

Removal of indigo carmine dye by electrocoagulation using magnesium anodes with polarity change

The aim of this study was to evaluate the performance of high purity magnesium and the magnesium-aluminum-zinc alloy AZ31 as sacrificial anodes in an electrocoagulation process with polarity change for the treatment of synthetic indigo carmine solution. It was studied the effect of the main parameters such as temperature, anodic material, current density, initial dye concentration, and agitation speed on the diminishing of indigo carmine concentration and non-purgeable organic carbon. Also, image analysis was used in conjunction with zeta potential measurements to understand the mechanism of flocs formation. The best results were 80% and 96% removal for non-purgeable organic carbon and dye content respectively at room temperature, by using turbulent regime, initial dye concentration of 100 mg L^-1 and 50 A m^-2 as current density with AZ31 alloy as electrodes. Particularly, high purity magnesium reached 75% in non-purgeable organic carbon removal and 86% in dye removal at the conditions described above. Finally, an additional improvement of 43% in the diminishing of the organic carbon content was observed when polarity change was used, a phenomenon that was attributed to the distribution of the oxidation reaction between electrodes, avoiding the saturation of the surface with oxide and hydroxide layers. Major areas and major fractal dimension were obtained by using a polarity change.

Electrochemical degradation of Mordant Blue 13 azo dye using boron-doped diamond and dimensionally stable anodes: influence of experimental parameters and water matrix

In this work, the electrooxidation as environmentally clean technology has been studied to the degradation of Mordant Blue 13 azo dye (MB13) using boron-doped diamond (p-Si/BDD) and oxide ruthenium titanium (Ti/Ru_0.3Ti_0.7O₂ (DSA)) anodes in various water matrices: distilled water (DW), hot tap water (HTW), and simulated wastewaters with (SWS) and without surfactant (SW). The influence of experimental parameters, such as current density, initial dye concentration, electrolysis time/specific charge, and pH on the MB13 degradation rate, current efficiency, and energy consumption, has been determined. The enhanced rate of both color and chemical oxygen demand (COD) removal in sulfate aqueous solutions with BDD was observed, which indicates that sulfate (SO₄^-•) radicals along with ^•OH ones might be responsible for the degradation process. The MB13 decolorization process obeyed a pseudo-first-order reaction kinetics with the apparent rate constant from 7.36 × 10^-2 min^-1 to 4.39 × 10^-1 min^-1 for BDD and from 9.2 × 10^-3 min^-1 to 2.11 × 10^-2 min^-1 for DSA depending on the electrolysis conditions. The effect of water matrix on the decolorization and COD removal efficiency has been evaluated. Inorganic ions, mordant salt, and surfactant contained in simulated effluents decelerated the COD decay compared to DW and HTW for the both anodes; meanwhile, they differently affected the discoloration process. A comparison of the specific energy consumption for each electrocatalytic material under different experiment conditions has been made. The BDD electrode was more efficient than the DSA to oxidize the MB13 dye in all kinds of water.