Peroxi-coagulation Process Research Articles

Hybrid and combined electro-oxidation and peroxi-coagulation processes in effective treatment of textile reverse osmosis concentrate

In this study, the treatment of reverse osmosis concentrate from a textile industry by hybrid and combined electrochemical processes was investigated. Firstly, the operating parameters of single electro-oxidation (EO) and peroxi-coagulation (PC) processes were optimized, and then the performances of hybrid EO-PC, PC-EO, and combined EO/PC processes were evaluated in pollutant removal under optimum conditions. Optimum conditions for processes were determined as pH: 5, 22.5 mA/cm2, inter-electrode distance: 3 cm, 120 min. Removal efficiency of chemical oxygen demand (COD) for the optimum conditions of EO, PC, EO-PC, PC-EO, and EO/PC were 78.5 %, 73.0 %, 73.8 %, 82.0 %, and 91.9 %, respectively. Specific energy consumption of EO, PC, EO-PC, PC-EO, and EO/PC processes were 61.9, 74.0, 64.0, 60.9, and 56.8 kWh/kg COD, respectively. The EO/PC process was the most effective and feasible one among applied single, hybrid, and combined processes. With the EO/PC, reverse osmosis concentrate met the receiving environment discharge criteria.

Treatment of metronidazole pharmaceutical wastewater using pulsed switching peroxi-coagulation combined with electro-Fenton process

The aim of this study was to investigate the metronidazole (MNZ) degradation and real MNZ pharmaceutical wastewater treatment in the pulsed switching peroxi-coagulation (PSPC) process. Different pulsed switching frequencies and running times of H2O2 and Fe2+ productions were tested in the PSPC process. Results demonstrated that MNZ removal of 96.9 ± 1.2 % was realized in the PSPC process with a 200 mg/L MNZ and 0.1 M Na2SO4 solution within 80 min under a pulsed switching frequency of 6s: 1s and a current density of 20 mA/cm2 (H2O2) and 20 mA/cm2 (Fe2+). High MNZ removal could be attributed to efficient •OH production with the highest •OH concentration reached 321 ± 15 μM in the PSPC process. The hydroxyl and carboxyl groups of MNZ were sequentially oxidated by •OH and mineralized based on seven identified intermediates during the MNZ degradation. However, only 56.9 ± 6.7 % of COD was removed in the real MNZ wastewater treatment by the PSPC process within 90 min. A PSPC combined with electro-Fenton (EF) process was developed to enhance the COD removal in the MNZ wastewater. With MNZ wastewater as electrolytes, 3.3 ± 0.3 g/L of H2O2 was produced in a conventional EF reactor. The final COD removal reached 86–90 % using the mixture of effluent from the PSPC, the anode, and cathode chambers of the EF reactor, resulting in less than 80 mg/L COD in the effluent. Results from this study should provide a useful way to enhance real MNZ pharmaceutical wastewater treatment.

A sequential aerated electrocoagulation and peroxicoagulation process for the treatment of municipal stabilized landfill leachate by iron and graphite electrodes

Electrochemical treatment has emerged as a viable technology for the treatment of leachate due to its efficient removal of ammonaical nitrogen and other recalcitrant organics. The main technical issues that prevent its practical deployment are restricted performance of a single electrochemical process and the lengthy tertiary treatment time required to achieve the disposal quality standards. This study demonstrates the performance of electrochemical treatments such as peroxicoagulation (PC) and aerated electrocoagulation (A-EC) separately and also sequentially for the treatment of stabilized leachate. In aerated electro coagulation iron is used as both anode and cathode, whereas in peroxicoagulation, iron is used as anode and graphite as cathode. The area of electrode used for treatments was fixed as 12.5 cm2. The initial concentration of NH4–N, TN, COD, and TOC of the leachate was found to be 480 mg/L, 997 mg/L, 40,200 mg/L, and 9850 mg/L respectively. Removal efficiency of aerated electrocoagulation for NH4–N, TN, COD and TOC were 25.6%, 23.67%, 25.6% and 28.7% respectively, current density of 30 mAcm−2, electrolysis time of 60 min and pH 7.3. Meanwhile for peroxicoagulation, the removal efficiency was found to be 37.2%, 43%, 37.3%, and 45.6% for NH4–N, TN, COD, and TOC respectively, at an current density of 30 mAcm−2, electrolysis time of 120 min and a pH of 3. The sequential aerated electrocoagulation – peroxicoagulation process achieves a maximum removal efficiency of 63%, 68%, 78%, and 75% for NH4–N, total nitrogen, COD, and TOC respectively for a reaction time of 180 min. Removal of NH4–N, total nitrogen, COD and TOC from stabilized landfill leachate with a BOD/COD ratio less than 0.1 was very much effective with the sequential aerated electrocoagulation – peroxicoagulaton treatment. The results also indicate that for the treatment of leachate, a significant synergistic index of 1.22 exists between aerated electrocoagulation and peroxicoagulation.

Recent advancements in peroxicoagulation process: An updated review

The present article describes the recent advancements (since 2018) in peroxicoagulation (PC) process, which was introduced by Professor Enric Brillas and his group in 1997. Instead of checking the efficiency of PC process to degrade a targeted pollutant in synthetic wastewater, researchers started testing its efficacy for the treatment of complex real wastewater. Applications like disinfection and removal of heavy metals as well as oxidative removal of arsenite from water were tested recently. To improve the efficiency of PC process, modifications were made for electrode materials (both anode and cathode) and electrolytic cells. Performance of PC process in combination with other treatment technologies is also discussed.

Hybrid peroxi-coagulation/ozonation process for highly efficient removal of organic contaminants

Aromatic compounds such as phenols presented widely in coal chemical industry wastewater (CCW) render the treatment facing great challenge due to their biorefractory characteristics and potential risks to the environment and human health. Ozone-based advanced oxidation processes show promising for these pollutants removal, but the mineralization via ozonation alone is unsatisfactory and not cost-effective. Herein, a hybrid peroxi-coagulation/ozonation process (denoted as PCO) was developed using sacrificial iron plate as an anode and carbon black modified carbon felt as cathode in the presence of ozonation. An enhanced phenol removal of ∼100% within 20 min and phenol mineralization of ∼80% within 60 min were achieved with a low energy consumption of 0.35 kWh/g TOC. In this novel process, synergistic effect between ozonation and peroxi-coagulation was observed, and beside O3 direct oxidation, peroxone played a dominant role for phenol removal. In the PCO process, the hydrolyzed Fe species enhanced the generation of reactive oxygen species (ROS), while •OH was dominantly responsible for pollutant degradation. This process also illustrated high resistance to high ionic strength and better performance for TOC removal in real wastewater when compared with ozonation and peroxi-coagulation process. Therefore, this process is more cost-effective, being very promising for CCW treatment.

Generation of hydroxyl radicals in the peroxi-coagulation process with an air-diffusion cathode: Fluorescence analysis and kinetic modeling

Conventional peroxi-coagulation process is based on the combined occurrence of electrocoagulation and oxidation in a single unit, since H2O2 and Fe2+ are electrogenerated on site from cathodic and anodic reactions, respectively. The present work aims to evaluate the effect of pH and applied current on the generation of hydroxyl radicals (•OH) from Fenton’s reaction during peroxi-coagulation treatment. The electrochemical cell consisted of a gas-diffusion cathode with graphite cloth, and an iron plate anode. By using a fluorescence probe (coumarin) and kinetic modeling, it has been possible to estimate the •OH concentration at different current values and to determine the effect of pH on their production. A system with six ordinary differential equations was established and solved to predict the concentrations of the main species of Fenton’s reaction. In addition, the interference of possible by-products and side coumarin hydroxylation reactions in the determination of •OH was considered. The simulation results reveal that current increase from 10 to 50 mA positively influences the •OH generation, further decreasing when operating at 70 mA. This is attributed to: (i) the negative effect of an excessive H2O2 generation, and (ii) the increase in pH during the electrolysis. This latter phenomenon is detrimental because of the partial precipitation of Fe2+ catalyst. A sensitivity analysis was performed to determine the most influential kinetic constants of the model on •OH and 7-hydroxycoumarin concentrations. This work demonstrates the importance of considering possible side reactions, which may occur when coumarin is used as a probe compound to quantify the •OH.

Upgrading the peroxi-coagulation treatment of complex water matrices using a magnetically assembled mZVI/DSA anode: Insights into the importance of ClO radical.

The electrochemical technologies for water treatment have flourished over the last decades. However, it is still challenging to treat the actual complex water effluents by a single electrochemical process, often requiring coupling of technologies. In this study, an upgraded peroxi-coagulation (PC) process with a magnetically assembled mZVI/DSA anode has been devised for the first time. COD, NH3-N and total phosphorous were simultaneously and effectively removed from livestock wastewater. The advantages, influence of key parameters and evolution of electrogenerated species were systematically investigated to fully understand this novel PC process. The fluorescent substances in livestock wastewater could also be almost removed under optimal conditions (300mA, 0.2g ZVI particles and pH 6.8). The interaction between OH and active chlorine yielded ClO with a high steady-state concentration of 6.85×10-13M, which did not cause COD removal but accelerated the oxidation of NH3-N. The Mulliken population suggested that OH and NH3-N had similar electron-donor behavior, whereas ClO acted as an electron-withdrawing species. Besides, although the energy barrier for the reaction between OH and NH3-N (17.0kcal/mol) was lower than that with ClO (18.8kcal/mol), considering the tunneling in the H abstraction reaction, the Skodje-Truhlar method adopted for calculations evidenced a 17-fold faster NH3-N oxidation rate with ClO. In summary, this work describes an advantageous single electrochemical process for the effective treatment of a complex water matrix.

Insight into the dual-cathode peroxi-coagulation process for cost-effective treatment of organic wastewater: Increase pH application range and reduce iron sludge

An improved dual-cathode peroxi-coagulation (PC) process using natural air diffusion electrode (NADE) and HNO3 modified carbon felt (MCF) was first proposed to improve the removal efficiency of organic pollutants in neutral and alkaline wastewater and reduce the formation of iron sludge. The improved PC process does not require any additional oxidants or catalysts, nor does it need to adjust the pH of the wastewater in advance but can directly treat actual wastewater, achieving a target pollutant (C12H14N4O2S, sulfamethazine) removal of 87%-100% within 60 min and TOC removal of 46–76% within 240 min with the corresponding energy consumption below 0.02 kWh gTOC-1. Compared with the conventional PC process, this improved process could produce hydroxyl radical (•OH) and superoxide radical (O2•-) more efficiently, which greatly increased the SMT removal rate constant by 3–4 times and oxidative removal proportion of organic pollutants from 42 ∼ 47% to 85 ∼ 90%. Thanks to the Fe(II) regeneration capacity of MCF to promote iron circulation, the yield of •OH was 4.1 times higher while the iron sludge production was less than a quarter when compared with that of conventional PC. The improved PC process illustrated better purification performance and lower energy consumption for actual wastewaters such as pharmaceutical wastewater, surface water and rural decentralized domestic sewage than the conventional PC process. Our work elucidated the mechanism of promoting Fe(II) regeneration through MCF cathode under alkaline conditions to enhance •OH production and O2•- oxidation, showing a good environmental application prospect.

Removal of refractory organics and heavy metals in landfill leachate concentrate by peroxi-coagulation process

Landfill leachate is a complex effluent and it is difficult to deal with. Electrochemical methods have been considered as a promising alternative technology for treatment of landfill leachate with refractory organic contaminants and heavy metals. Peroxi-coagulation (PC) process with iron anode and modified graphite felt cathode was developed for efficient landfill leachate concentrate treatment. Compared to electro-Fenton (EF) and electrocoagulation (EC) processes, the PC process was more cost-effective due to the combined action of •OH oxidation and iron hydroxides coagulation. A maximal TOC removal of 77.2% ± 1.4% was obtained after 360 min at initial pH = 5.0 and current density of 10 mA/cm2. After the PC process, concentrations of all seven heavy metals in the final effluents were below the allowable emission limits given by the present regulatory standards. The method preference for heavy metal removal was PC > EC > EF. Based on the three-dimensional fluorescence spectroscopy coupled with regional integration analysis during the PC treatment, the florescence peaks of both humic acids and fulvic acids disappeared after treatment for 360 min. Decreasing trends were observed in the fluorescent regional standard volumes for aromatic protein I (31.4%), aromatic protein II (63.7%), fulvic acid-like (69.5%), soluble microbial by-product-like (75%) and humic acid-like regions (76.3%). The results indicate that comparing to the EF and EC process, the PC process provide a promising and more cost-effective alternative for the treatment of landfill leachate concentrate.

Insight into the Improved Dual-Cathode Peroxi-Coagulation Process for Cost-Effective Treatment of Organic Wastewater: Simultaneously Increase the Ph Application Range and Significantly Reduce Formation of Iron Sludge

Insight into the Improved Dual-Cathode Peroxi-Coagulation Process for Cost-Effective Treatment of Organic Wastewater: Simultaneously Increase the Ph Application Range and Significantly Reduce Formation of Iron Sludge

The oxidative immobilization of phosphonate by simulated solar light mediated peroxi-coagulation process sustained by the iron-air fuel cell

Phosphonates are an important type of phosphorus-containing compounds and is of primary concern due to its eutrophication potential. Herein, we achieved simultaneously oxidative immobilization of phosphorus from ethylene diamine tetra (methylene phosphonic acid) (EDTMP) in the simulated solar light mediated peroxi-coagulation process sustained by the iron-air fuel cell (IAFC). The integration of simulated solar light irradiation with IAFC could enhance the oxidation capacity, yield of iron ions and power density output. The highest total phosphorus (TP) removal efficiency (approximately 100%) could be obtained at pH 4.0 owing to the synergistic action of coprecipitation and oxidation of EDTMP to orthophosphate (o-PO4), accompanying the optimum power density of 2459 mW m−2 at 2086 mA m−2. The OH mediated oxidation and photodegradation of Fe(III)-EDTMP complex via ligand-to-metal charge transfer reaction worked together to transform EDTMP into o-PO4. In the precipitate, the immobilized phosphorus existed mainly in the forms of organic phosphorus and o-PO4. The presence of oxalic and citric acid enhanced the yield of OH, but the formation of soluble Fe(III)-carboxylate complexes negatively affected the TP removal due to the decreased precipitation capacity. Contrastly, the observed decrease in TP removal caused by humic acid was ascribed to its scavenging effect toward OH. In general, this study proposed an energy efficient and environmental friendly approach for mitigating the potential risk of phosphonates to environmental safety.

Hybrid electro-Fenton and peroxi-coagulation process for high removal of 2,4-dichlorophenoxiacetic acid with low iron sludge generation

2,4-D is one of the most predominant herbicides around the world, though many advanced oxidation processes (AOPs) including peroxi-coagulation (PC) have been applied for its removal, the traditional PC still has restricted application due to disadvantages of huge sludge generation for a high pollutant removal and increased subsequent disposal costs. Herein, we developed a hybrid EF and PC process, using iron and dimensionally stable anode (DSA) electrodes as anodes, and a natural air diffusion electrode (NADE) without external aeration as the cathode. The optimal conditions for the hybrid process were optimized (initial pH 3, initial 2,4-D concentration 100 mgL−1, and total current of 100 mA with the ratio of DSA anode and iron anode of 7:3). Under these optimal conditions, 2,4-D could be almost completely removed within 30 min, and the TOC removal reached 71.9% within 2 h with a low electric energy consumption (EEC) of 19.59 kWh kg−1 TOC. The performance was comparable with traditional PC process but the iron sludge generation significantly reduced by ~73%. Therefore this hybrid process would have more potential to replace traditional PC process with cost-effective pollutants removal, low iron sludge generation and low EEC.

1,4-dioxane degradation using a pulsed switching peroxi-coagulation process

Abstract Widely used in chemical product manufacture, 1,4-dioxane is one of the emerging contaminants, and it poses great risk to human health and the ecosystem. The aim of this study was to degrade 1,4-dioxiane using a pulsed switching peroxi-coagulation (PSPC) process. The electrosynthesis of H2O2 on cathode and Fe2+ production on iron sacrifice anode were optimized to enhance the 1,4-dioxane degradation. Under current densities of 5 mA/cm2 (H2O2) and 1 mA/cm2 (Fe2+), 95.3 ± 2.2% of 200 mg/L 1,4-dioxane was removed at the end of 120 min operation with the optimal pulsed switching frequency of 1.43 Hz and pH of 5.0. The low residual H2O2 and Fe2+ concentrations were attributed to the high pulsed switching frequency in the PSPC process, resulting in effectively inhibiting the side reaction during the ·OH production and improving the 1,4-dioxane removal with low energy consumption. At 120 min, the minimum energy consumption in the PSPC process was less than 20% of that in the conventional electro-Fenton process (7.8 ± 0.1 vs. 47.0 ± 0.6 kWh/kg). The PSPC should be a promising alternative for enhancing 1,4-dioxane removal in the real wastewater treatment.

A continuous flow-through system with integration of electrosorption and peroxi-coagulation for efficient removal of organics

A flow-through reactor with integration of electrosorption (ES) and peroxi-coagulation (PC) processes was designed for organics removal. Impacts of key parameters (solution pH, flow rate, initial concentration of organics, applied voltage) on the removal efficiency of Orange II were explored. Under the optimized conditions, 93% removal efficiency and 1043 mg g−1 removal capacity of Orange II could be obtained with an energy consumption of 31.9 kWh m−3 order−1. Controlled experiments of ES for pollutants removal, and the detections of dissolved irons and the generated hydroxyl radicals (•OH) were conducted, demonstrating the coupling effect and contribution ratio of ES and PC for organics removal in this flow-through system. The spatiotemporal efficiency of the integrated flow-through system was more than 10 times of conventional ES system, providing more potential for practical application of wastewater treatment. The flow-through system was also verified to be advantageous for removal of other organic pollutants including 2,4-dichlorophenoxyacetic acid, phenol and methylene blue with high removal efficiencies. This study proved that the integrated flow-through process was an efficient, comparative and applicable method for wastewater treatment.

Treatment of Arsenite‐Contaminated Water by Electrochemical Advanced Oxidation Processes

AbstractArsenite removal from aqueous medium is quite challenging as most of the conventional methods fail to exhibit arsenite removal completely. The present article examines the possibility of electrochemical advanced oxidation processes to remove arsenite from water medium. Anodic oxidation and electro‐Fenton processes failed to remove generated arsenate in the system but found effective to oxidize arsenite completely from its initial concentrations of 1 mg/L and 10 mg/L. Arsenite oxidation is mainly due to in‐situ generated hydrogen peroxide and hydroxyl radicals for anodic oxidation and electro‐Fenton processes. However, peroxicoagulation process was found effective for the oxidation of arsenite as well as removal of arsenic in water. Complete removal of arsenic was observed within 30 min of electrolysis time for pH range in between 3 to 11. Overall, peroxicoagulation is an effective way to remove arsenic from aqueous solution.

Hydroxyl radical formation in the hybrid system of photocatalytic fuel cell and peroxi-coagulation process affected by iron plate and UV light.

The hybrid electrochemical system of photocatalytic fuel cell - peroxi-coagulation (PFC-PC) is a combined technology of advanced oxidation process (AOP) which involve the hydroxyl radical formation for simultaneous degradation of organic pollutant and electricity generation. The p-nitrosodimethylaniline (RNO) spin trapping technique was applied by analyzing the RNO bleaching performance to detect the OH at the PFC and PC reactors. The presence of UV light showed higher RNO bleaching rate at the PFC reactor (11.7%) with maximum power density (Pmax=3.14mWcm-2). Results revealed that the optimum of maximum power density was observed at iron plate size of 30cm2. UV light became a limiting factor in the PFC system as a power source in the PFC-PC system. Meanwhile, iron plate plays an important role to supply the soluble Fe2+ ions by oxidation process and become a suitable catalyst for in-situ production of H2O2 and OH through the PC process to degrade the organic molecules.

Wastewater treatment by microbial fuel cell coupled with peroxicoagulation process

A microbial fuel cell is a rapidly growing, eco-friendly and green technology. As per this technology, the microorganisms are employed to convert the chemical energy stored in the biodegradable portion of organic matter into direct electric current by simultaneously treating the wastewater. In this study, dual-chambered H-type mediator-less and membrane-less microbial fuel cell was operated and was optimized using synthetic wastewater as a substrate. The influence of various factors such as cathodic electron acceptors, electrode configuration, electrode spacing on chemical oxygen demand removal and current output were investigated. The maximum current of 1.72 mA was obtained using synthetic wastewater with potassium permanganate as effective catholyte, electrode spacing of 2 cm from the salt bridge and surface area of 98 cm2. This study also investigated the effect of substrate in the optimized MFC by applying different real wastewaters (municipal wastewater, dairy wastewater, cassava wastewater) and found a superior performance by dairy wastewater with maximum current output of 5.23 mA and chemical oxygen demand removal of 94%. Electron microscopic observations revealed the development of biofilm on the electrode surface, which was responsible for biocatalytic activity in the microbial fuel cell during the operation. The current generated using microbial fuel cell was supplied to peroxicoagulation process and was used for the removal of rhodamine B dye. Decolorization of 98% achieved by the novel microbial fuel cell-coupled peroxicoagulation system. The novel microbial fuel cell-coupled peroxicoagulation is an energy-efficient as well as cost-effective technique.

Peroxi-coagulation process: a comparison of the effect of oxygen level on color and TOC removals

Peroxi-coagulation process: a comparison of the effect of oxygen level on color and TOC removals

Elucidating the effects of different photoanode materials on electricity generation and dye degradation in a sustainable hybrid system of photocatalytic fuel cell and peroxi-coagulation process

The hybrid system of photocatalytic fuel cell – peroxi-coagulation (PFC-PC) is a sustainable and green technology to degrade organic pollutants and generate electricity simultaneously. In this study, three different types of photocatalysts: TiO2, ZnO and α-Fe2O3 were immobilized respectively on carbon cloth (CC), and applied as photoanodes in the photocatalytic fuel cell of this hybrid system. Photocatalytic fuel cell was employed to drive a peroxi-coagulation process by generating the external voltage accompanying with degrading organic pollutants under UV light irradiation. The degradation efficiency of Amaranth dye and power output in the hybrid system of PFC-PC were evaluated by applying different photoanode materials fabricated in this study. In addition, the effect of light on the photocurrent of three different photoanode materials was investigated. In the absence of light, the reduction of photocurrent percentage was found to be 69.7%, 17.3% and 93.2% in TiO2/CC, ZnO/CC and α-Fe2O3/CC photoanodes, respectively. A maximum power density (1.17 mWcm−2) and degradation of dye (93.8%) at PFC reactor were achieved by using ZnO/CC as photoanode. However, the different photoanode materials at PFC showed insignificant difference in dye degradation trend in the PC reactor. Meanwhile, the degradation trend of Amaranth at PFC reactor was influenced by the recombination rate, electron mobility and band gap energy of photocatalyst among different photoanode materials.

A pulsed switching peroxi-coagulation process to control hydroxyl radical production and to enhance 2,4-Dichlorophenoxyacetic acid degradation

The aim of this study was to develop a new pulsed switching peroxi-coagulation system to control hydroxyl radical (∙OH) production and to enhance 2,4-Dichlorophenoxyacetic acid (2,4-D) degradation. The system was constructed with a sacrifice iron anode, a Pt anode, and a gas diffusion cathode. Production of H2O2 and Fe2+ was controlled separately by time delayers with different pulsed switching frequencies. Under current densities of 5.0 mA/cm2 (H2O2) and 0.5 mA/cm2 (Fe2+), the ∙OH production was optimized with the pulsed switching frequency of 1.0 s (H2O2):0.3 s (Fe2+) and the ratio of H2O2 to Fe2+ molar concentrations of 6.6. Under the optimal condition, 2,4-D with an initial concentration of 500 mg/L was completely removed in the system within 240 min. The energy consumption for the 2,4-D removal in the system was much lower than that in the electro-Fenton process (68±6 vs. 136±10 kWh/kg TOC) The iron consumption in the system was ∼20 times as low as that in the peroxi-coagulation process (196±20 vs. 3940±400 mg/L) within 240 min. The system should be a promising peroxi-coagulation method for organic pollutants removal in wastewater.