A novel technique of COD removal from electroplating wastewater by Fenton-alternating current electrocoagulation

Approaches for electroplating sludge treatment and disposal technology: Reduction, pretreatment and reuse

Electroplating sludge (ES) has become an obstacle to the sustainable development of the electroplating industry. Electroplating sludge has a large storage capacity, with a high concentration of soluble pollutants (heavy metals), which has great potential to harm the local ecosystems and human health. Although much research has been done in this area, there seems to be no mature and stable solution. Therefore, the latest technologies for the reduction, pretreatment and reuse of electroplating sludge are emphatically introduced based on the analysis of the characteristics of electroplating sludge and its impact on the ecological environment. The factors hindering the treatment and disposal of electroplating sludge are pointed out, and reasonable and feasible suggestions to solve this problem are proposed. The solidification and removal mechanism of heavy metals in electroplating sludge is emphatically analyzed. The physicochemical and separation processes of heavy metals, as well as thermal treatment technique are discussed. Finally, it is proposed to establish a database of the physicochemical properties and elemental content of electroplating sludge to achieve its systematic treatment and digestion. We hope that this paper can help solve the problem of electroplating sludge and promote the sustainable development of the electroplating industry.

Electrochemical treatment of electroplating wastewater using synthesized GO/TiO2 nanotube electrode

The graphene oxide (GO) deposited TiO₂ nanotube (GO/TiO₂) electrode on a titania plate was prepared using a simple anodization method. The morphological and structural properties of TiO₂ and GO/TiO₂ electrodes have been studied using field emission scanning electron microscopy energy dispersive spectroscopy (FESEM-EDS), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Raman spectroscopy, Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectroscopy (XPS). FESEM-EDS analysis confirmed that the 13.56% wt of GO nanoparticles was formed over the TiO₂ substrate, with the thickness of the wall to be ∼300 nm. The crystallite size of GO/TiO₂, i.e., 19.53 nm, was confirmed by XRD analysis. Analysis of the UV-DRS spectrum showed the bandgap of the synthesized GO/TIO₂ nanotube electrode to be 3.052 eV. Box-Behnken design (BBD) under response surface methodology (RSM) was used to design the experiments. The effect of operating input parameters like pH, current (i), and degradation time (t) on % COD degradation (X₁) and energy consumed (X₂) were also examined. At optimum process parameters, the value of X₁ and X₂ were 57.61% and 15.00 kWh/m³, respectively. Possible intermediates were identified based on the GC-MS data analysis. Scavenger tests showed that •OH radical plays a major role in electroplating effluents degradation. Based on the results, the EO process using GO/TiO₂ electrodes could be considered a promising technique for electroplating effluent degradation due to high degradation efficiency.

Nickel removal from wastewater using electrocoagulation process with zinc electrodes under various operating conditions: performance investigation, mechanism exploration, and cost analysis

Economically feasible approaches are needed for wastewater treatment. Electrocoagulation (EC) is an electrochemical treatment method that removes various pollutants from wastewater. It has grown in popularity over conventional treatment methods, especially in industrial wastewater, due to its high performance and the ability to remove toxic compounds. However, it is crucial to reduce the costs associated with EC for widespread implementation. It is also important to decrease nickel (Ni) concentrations in wastewater to prevent potential health and environmental problems. Therefore, this study investigates Ni removal from synthetic and real wastewater using electrocoagulation. Zinc, as a novel electrode, was used as the sacrificial anode. Several operating conditions were assessed, including current density, initial pH, electrolysis time, and spacing between electrodes. The maximum Ni removal efficiency, after 90 min, reached 99.9% at a current density of 10 mA/cm2 when the pH was 9.2 and the gap distance was 4 cm. The Ni removal rate reached 94.4% and 94.9% at a 2- and 6-cm spacing, respectively, after 90 min. Anode morphology, kinetic modeling, electrical energy consumption, and cost analysis were also investigated. The type of corrosion was uniform, which is easily predicted compared to pitting corrosion. The comparison between chemical coagulation and electrocoagulation was also reported. Experimental results indicated that the maximum Ni removal rates reached 99.89% after 90 min. The optimum spacing between electrodes was 4 cm, and the optimum current density was 10 mA/cm2. Additionally, the kinetic data were best represented through the second-order Lagergren model. The results demonstrated that the electrocoagulation performance was better than that of chemical coagulation for Ni removal. The maximum electrical energy consumption was 23.79 KWh/m3 for Ni removal.

The role of the current waveform in mitigating passivation and enhancing electrocoagulation performance: A critical review

Electrocoagulation (EC) can be an efficient alternative to existing water and wastewater treatment methods due to its eco-friendly nature, low footprint, and facile operation. However, the electrodes applied in the EC process suffer from passivation or fouling, an issue resulting from the buildup of poorly conducting materials on the electrode surface. Indeed, such passivation gives rise to various operational problems and restricts the practical implementation of EC on a large scale. Therefore, it has been suggested that using pulsed direct current (PDC), alternating pulse current (APC), and sinusoidal alternating current (AC) waveforms in EC as alternatives to conventional direct current (DC) can help mitigate passivation and alleviate its associated detrimental effects. This paper presents a critical review of the impact of the current waveform on the EC process towards the capabilities of the PDC, APC, and AC waveforms in de-passivation and performance enhancement while comparing them to the conventional DC. Additionally, current waveform parameters influencing the surface passivation of electrodes and process efficiency are elaborately discussed. Meanwhile, the performance of the EC process is evaluated under different current waveforms based on pollutant removal efficiency, energy consumption, electrode usage, sludge production, and operating cost. The proper current waveforms for treating various water and wastewater matrices are also explained. Finally, concluding remarks and outlooks for future research are provided.

Effective removal of Sb(V) from aqueous solutions by electrocoagulation with composite scrap iron-manganese as an anode

Improving the removal rate of pentavalent antimony (Sb(V)) by electrocoagulation (EC) is of great significance to the environment. In this paper, the EC with composite scrap iron and manganese filings as an anode (Fe-Mn EC) was investigated for the high-efficiency elimination of Sb(V). The results showed that Fe-Mn EC can enhance the removal of Sb(V) by 11.18-17.36% compared with the traditional iron electrocoagulation (Fe EC). Meanwhile, Sb(V) removal increased with the growth of current concentration as well as Mn content in the anode. However, the Sb(V) removal rate was inhibited when Mn content exceeded 20%. Moreover, the flocs generated during the Fe and Fe-Mn EC (Fe flocs and Fe-Mn flocs) were analyzed both structurally and theoretically using XRD, SEM, BET, and adsorption experiment. The results indicated that the components of Fe-Mn flocs were mostly Mn-substituted FeOOH, which appeared as the structure of nanometer flakes and large internal surface areas. Meanwhile, the Fe-Mn flocs had the ability of much faster Sb(V) adsorption rate; its Sb(V) adsorption capacity was 2.5 times more than that of the Fe flocs. The thermodynamics constants of both Fe and Fe-Mn flocs proved that adsorption was associated with monolayer physical adsorption. To the best of our knowledge, this is the first report of the electrocoagulation with composite scrap iron-manganese as an anode to remove Sb, which provide a new idea and potential technical support for the removal of Sb(V).

Investigation on Mechanism of Tetracycline Removal from Wastewater by Sinusoidal Alternating Electro-Fenton Technique

Sinusoidal alternating electro-Fenton (SAEF) is a new type of advanced electrochemical oxidation technology for the treatment of refractory organic wastewater. In this research, the removal performance and degradation mechanism of tetracycline (TC) were investigated, and the optimal operation parameters were determined. Scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrometer (FTIR) were used to characterize the morphology, elemental composition, crystal structure, function groups of sludge produced by SAEF. UV-visible spectroscopy (UV) and liquid chromatograph-mass spectrometer (LC-MS/MS) were employed to determine the concentration of organic matter, middle products of decomposed organics in the SAEF process, respectively. The results showed that the removal rates of TC, chemical oxygen demand (COD), electric energy consumption (EEC) and the amount of produced sludge (Ws) are 94.87%, 82.42%, 1.383 kWh⋅m−3 and 0.1833 kg⋅m−3 by SAEF, respectively, under the optimal conditions (pH = 3.0, conductivity (κ) = 1075 μS⋅cm−1, current density (j) = 0.694 mA⋅cm−2, initial c (TC) = 100 mg·dm−3, c [30%H2O2] = 1.17 cm3⋅dm−3, frequency (f) = 50 Hz, t = 120 min). Compared with pure direct electro-Fenton (DEF) or sinusoidal alternating current coagulation (SACC), SAEF was a highly effective method with low-cost for the treatment of TC wastewater. It was found that the conjugated structure of TC was destroyed to generate intermediate products, and then most of them was gradually mineralized into inorganic materials in the SAEF process.

Sheep Dung Ash as a Low-Cost Adsorbent for the Reduction of COD of Highly Polluted Oilfield-Produced Water

Herein, we introduce a low-cost, available, renewable, and effective solid adsorbent used for oilfield-produced-water treatment using a straightforward treatment process. In the present study, sheep dung ash was prepared using the same way this waste is produced in rural areas when sheep dung is used as a source of energy for cooking and heating: by burning sheep dung with a direct flame. The prepared ash was characterized using FTIR, EDX, and SEM analysis techniques. The feasibility of the ash as a low-cost, available, renewable, and effective adsorbent for reducing the COD of oilfield-produced water with the initial COD of 21,600 mg/L was investigated. The effect of adsorbent dose, contact time (in hours and days), initial pH value, and initial COD value on the efficiency of sheep dung ash in COD adsorption was examined at room temperature. With shaking, the maximum capacity of sheep dung ash for COD reduction was found to be 71.8% at an adsorbent dosage of 30 g/L, an initial pH of 7, and a contact time of 1 h. Without shaking, a maximum capacity of 75% for COD reduction was obtained at an adsorbent dosage of 30 g/L, an initial pH of 7, and a contact time of 4 days. By applying the experimental results on Langmuir and Freundlich models of adsorption, it was found that the adsorption process of COD causing molecules follows both Langmuir and Freundlich models.

Improving Degradation Efficiency of Organic Pollutants through a Self-Powered Alternating Current Electrocoagulation System

Although electrocoagulation technology has been widely researched in wastewater treatment, high energy consumption and electrode passivation are still the main challenges for its widespread applications. Here, we propose a self-powered electrocoagulation system based on a triboelectric nanogenerator (TENG) with alternating current (AC) outputs to solve these two issues, and thus enhance the removal efficiency of organic pollutants. Compared with the direct current source, the AC power source can reduce the electrode passivation, produce more aluminum hydroxide compounds after consuming an equal amount of charges, and thus improve the degradation efficiency. Moreover, the removal efficiency can be further enhanced by decreasing the frequency AC, in which a 5.7-fold improvement was achieved at 0.2 Hz compared to DC at 1.8 Hz. Inspired by the low frequency of ocean wave water, we developed a self-powered AC-electrocoagulation system to directly drive the electrocoagulation reaction by harvesting water wave energy, which can effectively remove 94.8% of xylenol orange and 98.8% of water-oil emulsion, and thus completely address the problem of energy consumption. This study further promotes the application of self-powered electrochemical systems in treating environmental pollution.

Study on the treatment of Cu2+-organic compound wastewater by electro-Fenton coupled pulsed AC coagulation

Electro-Fenton (EF) coupled with Pulsed alternating current coagulation (PACC) is an effective technology for the treatment of Cu²⁺-organic wastewater. In this study, the removal efficiency (R_e), electrical energy consumption (EEC) and removal mechanism of Cu²⁺-organic were analyzed and the optimal operation parameters were determined. SEM, EDS, XRD and FTIR were used to characterize the morphology, elemental composition, crystal structure, function groups of sludge produced in the EF-PACC. UV, ESR and GC-MS were employed to determine concentration of organic matter, existence of OH, middle products of decomposed organic matter in EF-PACC, respectively. The results show that under the optimal conditions of initial pH = 2.5, current density (j) = 2 A/m², initial c(Cu²⁺) = 50 mg/L, c(chemical oxygen demand, COD) = 500 mg/L, c[H₂O₂] = 10 mL/L, frequency (f) = 1 Hz, t = 20 min, the R_e(Cu²⁺) can reach 99.59%. R_e(COD) is 90.21%, EEC 1.695 × 10^-1 kWh/m³, and the amount of produced sludge (W_s) is 0.9283 kg/m³. Compared with single EF and PACC processes, the order of treatment efficiency is EF-PACC > EF > PACC. EF-PACC technique was a highly effective method in the treatment of Cu²⁺-organic compound wastewater. The EF-PACC coupled process includes that electrolyzed Fe³⁺ produces electrocoagulation and OH produces degradation of organic compounds. The combined action of the two effects can effectively remove Cu²⁺-organic from wastewater.

The Tolerance of Anoxic-Oxic (A/O) Process for the Changing of Refractory Organics in Electroplating Wastewater: Performance, Optimization and Microbial Characteristics

In order to investigate the tolerance of an anoxic-oxic (A/O) process for the changing of refractory organics in electroplating wastewater, optimize the technological parameters, and reveal the microbial characteristics, a pilot-scale A/O process was carried out and the microbial community composition was analyzed by high-throughput sequencing. The results indicated that a better tolerance was achieved for sodium dodecyl benzene sulfonate, and the removal efficiencies of organic matter, ammonia nitrogen (NH4+-N), and total nitrogen (TN) were 82.87%, 66.47%, and 53.28% with the optimum hydraulic retention time (HRT), internal circulation and dissolved oxygen (DO) was 12 h, 200% and 2–3 mg/L, respectively. Additionally, high-throughput sequencing results demonstrated that Proteobacteria and Bacteroidetes were the dominant bacteria phylum, and the diversity of the microbial community in the stable-state period was richer than that in the start-up period.

Mesoporous Composite Networks of Linked MnFe2O4 and ZnFe2O4 Nanoparticles as Efficient Photocatalysts for the Reduction of Cr(VI)

Semiconductor photocatalysis has recently emerged as an effective and eco-friendly approach that could meet the stringent requirements for sustainable environmental remediation. To this end, the fabrication of novel photocatalysts with unique electrochemical properties and high catalytic efficiency is of utmost importance and requires adequate attention. In this work, dual component mesoporous frameworks of spinel ferrite ZnFe2O4 (ZFO) and MnFe2O4 (MFO) nanoparticles are reported as efficient photocatalysts for detoxification of hexavalent chromium (Cr(VI)) and organic pollutants. The as-prepared materials, which are synthesized via a polymer-templated aggregating self-assembly method, consist of a continuous network of linked nanoparticles (ca. 6–7 nm) and exhibit large surface area (up to 91 m2 g−1) arising from interstitial voids between the nanoparticles, according to electron microscopy and N2 physisorption measurements. By tuning the composition, MFO-ZFO composite catalyst containing 6 wt.% MFO attains excellent photocatalytic Cr(VI) reduction activity in the presence of phenol. In-depth studies with UV-visible absorption, electrochemical and photoelectrochemical measurements show that the performance enhancement of this catalyst predominantly arises from the suitable band edge positions of constituent nanoparticles that efficiently separates and transports the charge carriers through the interface of the ZFO/MFO junctions. Besides, the open pore structure and large surface area of these ensembled networks also boost the reaction kinetics. The remarkable activity and durability of the MFO-ZFO heterostructures implies the great possibility of implementing these new nanocomposite catalysts into a realistic Cr(VI) detoxification of contaminated wastewater.