Diverse EP approaches are exemplified for diverse wastewater treatment under standard reaction conditions.
Electrochemical advanced oxidation practices (EAOPs), remarkably, electro-peroxone (EP), photoelectro-peroxone (PEP), and complementary hybrid EP approaches, are emerging technologies on accountability of complete disintegration and elimination of wide spectrum of model pollutants predominantly biodegradable, recalcitrant, and persistent organic pollutants by engendering powerful oxidants in wastewater. A concise mechanism of EP and PEP approaches along with their contribution to free radical formation are scrutinized. Furthermore, this chapter provides a brief review of EP, PEP, and complementary hybrid EP-based EAOPs that have pragmatically treated laboratory-scale low- and high-concentrated distillery biodigester effluent, refractory pharmaceutical, textile, herbicides, micropollutant, organic pollutant, acidic solution, landfill leachates, municipal secondary effluents, hospital, and industries-based wastewater. Afterward, discussion has further extended to quantitatively evaluate energy expenditures in terms of either specific or electrical energy consumptions for EP and PEP practices through their corresponding equations.
- complementary hybrid EP approaches
- energy consumption
In current scenario, diverse industrial setups have been expanded very rapidly. Consequently, numerous industrial effluents particularly textile, oil, and gas, pharmaceutical, paint, fertilizer, petrochemical, metal, and mining industries have made major contribution to wastewater. These industrial effluents contain toxic dyes, nitrates, 2,4-dichlorophenoxyacetic acid herbicide (2,4-D herbicide), toxic heavy metals, pharmaceutical waste, organic waste, total ammonia nitrogen (TAN), micropollutants, and so on . Wastewater comprising these noxious chemicals is lethal to humans as well as aquatic life. In this frame of reference, several techniques have been exploited for wastewater treatment in the literature explicitly, biological techniques, chemical procedures, and physical methods. Since biological techniques were constrained due to toxic contaminants, long processing time, as well as insufficient degradation of pollutants, that is, perfluorinated compounds is devoid of biological disintegration owing to 533 kJ mol−1 energy content required to fracture C▬F bond [2, 3], and physical adsorption is a nondestructive method, which could not oxidize pollutants entirely, solely accountable for shifting pollutants from one phase to another as well as pricey method for a powerful adsorbent, which cannot regenerate , and chemical methods, which increase cost as well as generate toxic sludge .
Over the last few decades, diverse advanced oxidation processes, namely peroxone, ozonation, and electro-oxidation, have been carried out for wastewater treatment through hydroxyl-free radical (HȮ) production [6, 7]. Peroxone technique is a blend of hydrogen peroxides (H2O2) and ozone (O3), and on this account several free radicals are produced, which oxidize waste organic compound present in water, but requirement of hydrogen peroxide enhances its cost as well as its storage and transport problem . Furthermore, peroxone has shortcomings of low oxygen ozone conversion rate and been suppressed under neutral and acidic environments . Likewise, ozonation is highly resourceful practice for treatment of large bio-recalcitrant-based wastewater; such type of waste usually required high quantity of energy to decay and has the ability to resist microbes; being an oxidizing agent, a large number of intermediates are generated by ozone, which initiated chain reaction and hence degraded waste. On the contrary, ozone reacts with naturally occurring bromide ions in water to form carcinogenic bromates as side products  and has less oxidation potential of 2.07 as well as inadequacy of degrading ozone refractory compounds . Although electro-oxidation process has been provoked in treatment of refractory compounds  and micropollutants-based wastewater, nevertheless it has a drawback of more energy consumption (3–5 V) during electrolysis . Additionally, electrochemical-based electrocoagulation techniques are where current is passed across wastewater solution containing electrodes, and metallic ions released from dissolution of anode result in coagulation
To overcome these dilemmas of traditional advanced oxidation techniques, researchers have been devising various electrochemical advanced oxidation practices notably, electro-Fenton, photoelectro-Fenton, electro-peroxone, and photoelectro-peroxone for wastewater treatment. Nonetheless, homogeneous electro-Fenton and photoelectro-Fenton techniques catalyzed degradation of persistent organic pollutants only under acidic media, and its alternative heterogeneous techniques could conduct full mineralization of same pollutants under neutral pH . In this circumstance, hybrid electro-peroxone (EP) and photoelectro-peroxone (PEP) have been accredited for wastewater treatment under alkaline, neutral, acidic pH, posed good disintegration, and mineralization rates [16, 17, 18]. As a matter of fact, EAOPs are hybrid approaches, which have been constructed by integrating two or more practices for enhanced ȮH formation to accelerate abatement of pollutants in wastewater . As a matter of fact, ȮH species is the second strongest oxidant with 2.8 V oxidation potential usually prompting nonselective attacks on C▬H bond to oxidize and mineralize pollutants very swiftly as demonstrated through Eq. (6) . Additionally, ȮH could randomly demolish refractory pollutants when existing satisfactorily in water and exploited admirable degradation rate of 108 to 1010 M−1 s−1 .
Similarly, electro-peroxone is basically hybrid of two elementary approaches, which includes ozonation and electrolysis. In this context, all these techniques were taken into an account to mitigate their drawbacks and develop a novel method named electro-peroxone by putting all together . Solely, oxygen was injected into ozone generator, which interleaved its inlet sparged effluent within cathode at electrolytic cell, where oxygen reduction
Even though EP is an expedient approach, its rate of degradation of pollutants usually diminishes with acidity of solution; these acids further make complex with ions, thereby preventing their oxidation. Furthermore, much quantity of O3 is consumed during EP process . Therefore, existing techniques were modified by incorporating UV light as energy source into electro-peroxone to devise hybrid PEP approach. Photo-electro-peroxone is fundamentally hybrid of three elementary approaches, which include ozonation, electrolysis, and photolysis; these methodologies were coupled to endorse full abatement of pollutants by ȮH formation, which could be proceeded either through Eq. (7) or through (8)
This chapter study aimed to theoretically probe environmentally friendly, cost-effective, comparatively less energy consuming, no secondary toxic side product instigating, and highly versatile novel techniques for wastewater treatment. In this context, recently EAOPs-based hybrid EP and PEP approaches have been discussed for wastewater treatment. Photo-electroperoxone and EP have vividly treated distillery biodigester effluent , refractory pharmaceutical , hospital , ballast water , herbicides , micropollutants , organic pollutant , acidic , landfill leachates , industrial , and municipal secondary effluents -based wastewater. Degradation rate of pollutants could be written in terms of rate law to demonstrate chemical kinetic of pollutants during wastewater treatment by electro-peroxone approach. When uniform current is provided to reactor, HȮ formation rate also turns out to be constant and in Eq. (14) becomes equal to kapp based on Eq. (15) pseudo-first-order rate constant. Here, is rate of disintegration of pollutants in solution; while [P], [HȮ], k, and kapp denote concentration of pollutants and hydroxyl-free radicals in wastewater, absolute rate constant, and apparent rate constant, respectively [38, 39].
2. Setup devised for electro-peroxone (EP) and photoelectro-peroxone (PEP)
Experimental setup has been devised for degradation of pollutants in wastewater through EP and PEP approaches, which is illustrated in Figure 1. Wastewater treatment was processed in air-proof semi-batch reactor . One-liter wastewater was incorporated inside the reactor, and pairs of electrodes, that is, cathode and anode 1 cm apart, were interleaved in the middle of the reactor. Quartz jacket-enclosed UV lamp was perpendicularly immersed in reactor for UV photolysis during PEP process. Bubble diffuser and magnet stirrer bar were placed to diffuse mixture of ozone and O2 gases in aqueous solution and to mix content inside the reactor. Electrolytic operations such as EP and PEP were performed under galvanostatic conditions
3. Electro-peroxone approaches for diverse wastewater treatment
In the literature, a wide spectrum of wastewater applications such as textile, pharmaceutical, biodigester effluents, refractory compounds, and real wastewater treatments have been successfully conducted by researchers as demonstrated by Table 1.
|Category of wastewater||Anode||Cathode||Standard reaction conditions||References|
|Secondary effluent from coal industry||Dimension-ally stable anode (DSA)||Natural air diffusion electrode||pH: 4, current: 200 mA, electrolyte: 0.3 M Na2SO4, treatment time: 3 h, inlet ozone dose: 6 mg min−1, flow rate: 100 mL min−1|||
|BDE of rice grains||Al||Polytetrafluoroethylene (PTFE)||pH: 6, current: 0.032 mA m−2, electrolyte: 0.15 M Na2SO4, treatment time: 50 min, inlet ozone dose: 135 mg L−1, flow rate: 70 L min−1|||
|Hospital wastewater||Pt sheet||Activated carbon fiber||pH: 9, current: 400 mA, electrolyte: 0.05 M Na2SO4, inlet ozone dose: 5 g h−1, flow rate: 1 L min−1|||
|Ballast water||Perforated DSA||PTFE and carbon black-modified graphite felt (GF)||pH: 7, current: 50 mA, aeration rate: 50 mL min−1, temperature: 25°C, |||
|Refractory OMPs||Mixed oxides of ruthenium and iridium (RuO2/IrO2) coated Ti plate||Stainless steel plate||Current: 60 mA, treatment time: 15 min, inlet ozone dose: 7 mg L−1, concentration of model pollutant: 150 μg L−1, flow rate: 0.15 L min−1|||
|LEV||Pt mesh||Carbon fiber composite||pH: 6.8, current: 140 mA, electrolyte: 0.05 mol L−1 Na2SO4, treatment time: 15 min, inlet ozone dose: 47 mg L−1, temperature: 25°C, flow rate: 0.08 mg L−1|||
|TC and disinfections||Perforated dimension stable anode||Carbon black and PTFE-modified GF||pH: 7, current: 50 mA, electrolyte: 0.05 M Na2SO4, aeration rate: 50 mL min−1, E coli: 1000 CFU mL−1, concentration of model pollutant: 700 μg L−1, flow rate: 35 mL min−1|||
|Multiple FQs||Pt plate||Fe-modified carbonized MOF||pH: 4.2, current: 210 mA, treatment time: 10 min, inlet ozone dose: 40.2 mg L−1, temperature: 25°C, concentration of model pollutant: 20 mg L−1, flow rate: 50 mL min−1|||
|Carbamazepine||Carbon rod||CeOx/GF||pH:5, current: 0.05 mA, electrolyte: 0.05 Na2SO4 mol L−1, treatment time: 60 min, ozone output: 50 mg h−1, temperature: 25°C, concentration of model pollutant: 10 mg L−1, flow rate: 0.5 L min−1|||
|Antibiotics and biocides||Pt||Carbon-PTFE||Phosphate buffer: 50 mM, current: 35 mA, electrolyte: Na2SO4 50 mM, inlet ozone dose: 4.5 mg L−1, temperature: 15°C, concentration of model pollutant: 10 μg L−1, flow rate: 0.35 L min−1 for each|||
|Acid orange 7||Graphite (4 cm2)||Graphite (4 cm2)||pH:7.7, current: 0.5 A, anode to cathode ratio: 6: 6, electrolyte: 0.1 M Na2SO4, treatment time: 10 min, temperature: 25°C, concentration of model pollutant: 500 mg L−1, ozone flow rate: 8.5 L min−1|||
|AR14||Pt sheet||Carbon-PTFE (XC-72 carbon powder)||pH:10, current: 0.7 A, electrolyte: 0.1 M Na2SO4, treatment time: 30 min, temperature: 25°C, concentration of model pollutant: 400 mg L−1, flow rate: 0.25 L min−1|||
|AV19||Ti|IrSnSb-oxide plate||3D GDE||pH: 3, current density: 20 mA cm−2, electrolyte: 0.05 M Na2SO4, inlet ozone dose: 14.5 mg L−1, temperature: 25°C, concentration of model pollutant: 40 mg TOC L−1, electrolyte flow rate: 2 L min−1, pressure exerted at GDE: 3 psi|||
|CV||Pt rod||Stainless steel wool||pH: 9, current: 0.1 A, electrolyte: 100 mg L−1 NaCl, inlet ozone dose: 2 mg L−1, temperature: 22°C, concentration of model pollutant: 50 mg L−1, peroxide: 15 mmol L−1|||
Textile industries are producing huge volume of wastewater nearly 30–50 cm3 water volume ton−1dyes. Subsequently, dyestuff effluents (10–20 mg L−1) have been discharged into sewages and rivers [49, 50]. Treatment of textile wastewater is inappropriate through biological treatment meanwhile it culprits toxic secondary by products at the end, alternatively several oxidants have been reported which were being restricted on accountability of structural intricacy of dyestuffs. Consequently, textile wastewater treatment is prompted by EAOPs. [51, 52, 53]. Anionic dye Acid Orange 7(C6H11N2NaO4S) containing wastewater (500 mg L−1) has been fully decontaminated with 90% and 99% exclusion of TOC and chemical oxygen demand (COD), respectively, within 90 minutes through EP approach carried out in cylindrical reactor . Likewise, Acid Orange 7 was pulverized in a cylindrical baffled reactor to boost exchange among reactants and well-organized electrode arrangement by EP approach. Acid Orange 7 (500 mg L−1) mineralization cleared out 92% TOC and 99% COD were declined within 90 minutes at pH 7.7 with large electrode surface area ratio (6:6) by which degradation was considerably enhanced . Similarly, Acid red 14 (AR 14) wastewater (400 mg L−1) has been disintegrated in Ep-based Box-Behnken experimental setup. Full disintegration of AR 14 was accomplished, and 69% COD exclusion was achieved within 60 minutes at 10 pH . Another attempt has been made on decomposition of crystal violet (CV) with Kapp of 2.69 × 10−2 and 2.87 × 102 min−1, for 100 and 200 mg L−1 CV in wastewater, respectively. About 98% CV was eliminated at pH range of 7–9 within 5 minutes through combination of electrolysis/peroxone/H2O2, and corresponding treated wastewater was manifested no toxicity for microbes. Electro-peroxone approaches were provoked decolorization at alkaline media . A novel approach has been made to smash Acid Violet 19 (AV19) in a lab-scale filter-press-based plant employing 3-D gas diffusion electrode as a cathode to attain better oxygen reduction reaction
Recurring detection of personal care and pharmaceutical compounds in water has increased health heedfulness and environmental considerations [55, 56]. Wastewater treatment plant could not completely eliminate antibiotics through traditional activated sludge and sedimentation techniques; as a result, these have been monitored in secondary wastewater effluents in certain quantity [56, 57, 58]. In contrast to traditional ozonation practices, ozone recalcitrant micropollutants notably chloramphenicol, ibuprofen, and clofibric acid have been effectively pulverized and accelerated degradation kinetics through triggering HȮ production by means of EP approach [59, 60]. Numerous advanced oxidation techniques have been launched to smash bio-recalcitrant paracetamol (PCT). EP approach has exhibited good efficiency in full disintegration of PCT with rate constant of 0.1662 min−1 . Levetiracetam (LEV) removal was a bit challenging owing to polar structures, which was not susceptible to ozone degradation . Extremely water-soluble antiepileptic drug LEV has been manifested pseudo-first-order degradation kinetics
Real wastewater in contrast to synthetic wastewater is more complex, having abundant organic micropollutants with varieties of molecular structures accompanying physicochemical properties [63, 64]. Biochemical oxygen demands (BODs)/COD ratio has been commenced for probation of biodegradability prospects and wastewater encompassing 0.4 or its onward ratio has manifested good biodegradability as well as decline in bio-toxicity . Electro-peroxone approach was carried out for processing of reverse osmosis concentrate obtained from industrial coal wastewater. As a result, 92% decolorization, 89% UV254, and 71.2% TOC have been eradicated within 6 hours . After treatment, 91.3% color reduction and 99.9% COD elimination were detected in distillery biodigester effluents (BDE) through EP approach, and low cost of 1 m3 BDE/2$ and less sludge formation are major gratification of this approach . Chloramphenicol and clofibric acid such as ozone obstinate micropollutants in surface water have been oxidized by EP system and subsequently resulting in hypochlorous and hypobromous acids, which are the main culprit of engendering chlorinated and brominated derived byproducts were efficiently quenched by electrochemically produced H2O2 in surface water . Several antibiotics conspicuously ciprofloxacin, norfloxacin, ofloxacin, and trimethoprim have been eliminated from secondary wastewater effluents through EP . Electro-peroxone practice was also employed to process municipal secondary effluents with negligible disinfection side products as well as 65% COD and 44% BOD were declined . Diverse 89 pharmaceutical compounds were examined in terms of organic micropollutants (OMPs) exclusively existing in a real wastewater to evaluate their ozone reactivities and physiochemical properties by means of quantitative structure activity relationship (QSAR) for the sake of kinetic assessment. Pharmaceutical compounds having partial charge moieties, and branched, electrophiles, and lowest unoccupied molecular orbital energies were categorized as ozone-resistant compounds with ozone rate constant (kO3) < 102 M−1 s−1 and were degraded by sole EP. Conversely, ozone reactive pharmaceuticals accompanying with nucleophilic species, highly occupied molecular orbital energies, and conformation contingent charge descriptors were deemed to be ozone reactive with rate constant greater than 102 M−1 s−1 would be rapidly eradicated by EP and ozonation . Additionally, ultrasound coupled EP system and virgin EP has been applied for textile industry effluent at 5.8 pH. 93% and 99% decolorization have been accomplished through virgin EP and the integrated ultrasound EP process within 60 minutes after treatment . Similarly, real pesticide wastewater has been treated
In context of acidic wastewater treatment, few attempts have been made to mend EP process. Tannic acid has been oxidatively smashed by EP approach in two phases firstly tannic acid pulverized
3.1 Miscellaneous electrode texture-based electro-peroxone approaches for wastewater treatment
Carbon nanotubes (CNTs) have exhibited brilliant adsorption to pollutants, and this tendency along with adsorption kinetic was further enhanced in terms of electro-sorption by employing them as electrodes . Furthermore, CNTs have been demonstrated good electrochemical oxidation of pollutants, good chemical stability, electrical conductivity, and noteworthy mechanical strength during electrolysis  and photolysis . Advanced oxidation approach has been integrated with adsorption to construct hybrid system for actively pulverization of pollutant in wastewater [74, 75]. Pharmaceutical compounds, particularly diclofenac sodium (DS), were completely fragmented by carbon nanotubes-polytetrafluoroethylene (CNTs-PTFE) electrode over five consecutives cycles exploiting pseudo-second-order kinetics. Where negatively charge diclofenac sodium was exhibited electro-sorption to CNTs-PTFE anode afterward, adsorption phenomena switched this anode into cathode and corresponding adsorbed pollutants were subsequently disintegrated by EP approach within 10 minutes and 99% TOC were eliminated after 1 hour . Likewise, copper ferrite-modified carbon nanotubes (CuFe2O4/CNTs) were used as catalysts having brilliant recyclability to decomposed fluconazole (FLC) wastewater through EP. Catalyst has adsorbed FLC on its sphere and enhanced FLC mass transfer to electrode surface and thereby eliminated 89% FLC and integrated adsorption-EP technique has contributed 10% efficiency to virgin EP approach .
Similarly, carbon nitride-multiwall carbon nanotubes-based nanocomposite (n-C3N3/MWCNT) catalyst has actively smashed sodium oxalate in wastewater by endorsing adsorption of pollutant and accelerating electron transfer, which trigger O3 and O2 electro reduction ; consequently, H2O2 and Ȯ3− were generated, which has further enhanced HȮ formation . On account of large surface area, activated carbons are good in elimination of micropollutants (MPs); on the contrary, MPs saturated activated carbons having high affinity for adsorbates pose a major challenge in regeneration of electrode, which was overwhelmed by oxidation of MPs through ozonation process  but some sorts of MPs were inert toward ozonation reaction . In this frame, EP coupled with ozonation to exclude diverse MPs, namely trimethoprim, ciprofloxacin, perfluorooctanoic acid, carbamazepine, diclofenac, and benzotriazole from wastewater and efficiently pulverized MPs from ozone. Afterward, ozone-resistant MPs were disintegrated
Electro-peroxone approaches have been well organized at alkaline and neutral pH; on the contrary, its progress was constrained at acidic pH, which bounds rate constant of H2O2 as of 9.6 × 106 to 0.01 M−1 s−1 for 11 to 3 pH, respectively. Hence, reaction between ozone and deprotonated peroxide has no more yielded reactive oxygen species . Manganese carbon nitride-carbon nanotubes (C3N4-Mn/CNT) composite catalyst overcomes drawbacks of disintegrating pollutants in strongly acidic solution
Traditional EP approaches were mostly carried out by commencing 2-D electrode system, which have been demonstrated low mass transfer; therefore, to boost electrode performances for additional optimization of conducted treatment were suggested for forthcoming generation [78, 83]. Reticulated enamel carbon, graphite felt, polytetrafluoroethylene, and carbon felt-based cathodic materials were manifested O2 reduction for H2O2 formation . Unlike conventional 2D-electrode in EP approach, 3D-electrode system could considerably promote the electrochemical efficiency of reactor owing to large surface area, which boosted H2O2 formation . TiO2-loaded granular-activated carbon (TiO2-GAC) as a 3D electrode in EP system was applied for decomposition of diuron, which is a phenyl urea herbicide wastewater, hybrid 3-D/EP system was demonstrated two times more pseudo-first-order disintegration rate (effectiveness) than those of sole EP system. Diurons were adsorbed by TiO2-GAC and later polarized to synthesize microelectrodes, which yields ȮH. Moreover, TiO2-GAC has considerably enhanced H2O2 formation in a corresponding solution . Being a 3-D activated carbon system, carbon felt (CF) has been shown elegant electrolytic proficiency, good mechanical stability, and cost effective . N-doped-reduced graphene oxides (N-rGOs) supported carbon as well-designed cathode was demonstrated to improve oxygen reduction feedback for H2O2 generation, better conductivity, boosted electrocatalysis, and electron transfer rate [87, 88]. Diuron was completely smashed at 9 pH within 15 minutes through EP approach using versatile N-rGO/CF-based cathode electrode. Furthermore, N-rGO/CF exploited good efficiency in H2O2 formation and lessen energy expenditures for 10 cycles continuously to that of sole CF cathode. This system has led to processed real pesticide wastewater having COD of 3680 mg L−1 after processing till 360 minutes, and COD was declined to 47.7 mg L−1. Moreover, BOD/COD ratio of 0.4 and 0.04 has been obtained for processed and unprocessed real pesticide wastewater, respectively . Another attempt was made in which a filter-press flow cell integrated with three-dimensional air diffusion electrode-based lab scale plant was devised to disintegrate levofloxacin and 63% mineralization accomplished at 3 pH . Likewise, GF was modified with cerium oxides (CeOx) to well-designed cathode, and H2O2 exhibited chemisorption with CeOx; consequently, it will prompt reaction with O3 as compared with bulk H2O2. Consequently, CeOx/GF-EP system has been manifested 69.4% TOC exclusion in disintegration of carbamazepine within 60 minutes at pH range of 5–9 with upright fivefold recyclability. In contrast to traditional EP, this strategy is perquisite for degradation of refractory organic pollutants under acidic media by proficiently activating ozone, upgraded surface hydrophilicity, and lessen energy expenditure for electro-generation of H2O2 .
A novel hybrid approach comprising three electrodes in EP system for oxalate-containing wastewater has been developed. After elaboration of reaction mechanism, it was suggested that all reactions in combination subsidizes HȮ formation in EP. In contrast to two electrode systems, three electrodes system could be comparatively privilege in providing precise control and purifying salt-rich wastewater .
3.2 Complementary hybrid electro-peroxone approaches for wastewater treatment
To proficiently mineralize and eliminate a wide range of biodegradable contaminants along with refractory pollutants from wastewater by low electrical energy requirement in cost effective and easy ways, some conventional approaches conspicuously biological treatment, ultrasound, electrocoagulation, and low-pressure filtration were coupled with electro-peroxone to devise novel complementary hybrid electro-peroxone system [67, 90, 91]. In this circumstance, synergy overcome constrained individual approaches that have low efficiency independently and accelerated attenuation of wastewater in terms of complementary hybrid electro-peroxone system.
Bio-electroperoxone (Bio-EP) approach has been devised for a two-way treatment of pharmaceutical wastewater, where microbes biodegrade some compounds at electrically bound biofilm reactor (EBBR), and the rest of all compounds that did not undergo biological oxidation was pulverized
Hydroxyl-free radicals could be synthesized by fracturing bubbles cavitation in aqueous medium through ultrasound (US) based on Eq. (16) . Moreover, US also splits up ozone and peroxide based on Eqs. (17) and (18) [93, 94]. Integrated US/EP approach was applied to fragmentize acid orange 7 at pH 7, which has manifested 88% mineralization, 99% decolorization, and 85% COD elimination with pseudo-first-order kinetics .
Shale gas fracturing flowback water (SGFFW) was processed with electroperoxone-integrated electrocoagulation (EC/EP) or ECP approach and led to 82.5% COD exclusion up to 90 minutes, with 29.9% average current effectiveness. In ECP technique, coagulant hydroxyl-aluminum at anode eliminates colloids and suspended items  as well as catalyzed HȮ formation by reaction with O3 to breakdown pollutants
Low-pressure filtration was coupled with EP approach to design hybrid electro-peroxone filtration (EPF) system, which was continuously eliminated 64.87% ibuprofen (IBU) at less filtration pressure (0.8 kPa) within 8 seconds in its very low concentration of 1 mg L−1. IBU elimination efficacy was comparatively three times than that of individual efficiencies achieved from electrochemical filtration and ozone filtration. In contrast to sole EP, EPF was promoted mass transfer of HȮ and O3 owing to membrane permeation drift .
Downflow bubble column electrochemical reactor (DBCER) has led to incremented mass transfer and contact area owing to energetically liquid inflow, and small bubble formation takes place to cause commotion as well as did not let out electrochemically synthesized
4. Photoelectro-peroxone practices for wastewater treatment and their comparison with EP
Simple ozonation, photolysis, and electrolysis mechanisms were integrated to fashion novel hybrid PEP approach for wastewater treatment to overcome shortcoming of low mineralization rate during EP at acidic pH and dwindle corresponding electrical energy consumption. Henceforth, PEP and EP approaches have been contributed to synergistic effect, which has been quantitatively determined through enhancement factor calculated by Eqs. (22) and (23) .
Where kEP, kPEP, kO, kUV, and kE denote rate constants during pollutant disintegration for EP, PEP, ozonation, photolysis, and electrolysis, respectively. Enhancement factors along with degradation rate constants have been comparatively incremented during PEP approaches than those of EP for same wastewater treatment (e.g., Table 2).
|Category of wastewater||Conducted approach||Anode||Cathode||Apparent degradation rate constant Kapp||Enhancement factor||Ref.|
|Nitrobenzene||PEP||12 cm2 platinum sheet||40 cm2 carbon-PTFE||93.0||5.8|||
|Nitrophenol||PEP||50 cm2 carbon belt||50 cm2 BDD||0.145||13.2|||
|Reactive Yellow F3R||PEP||Ti/TiO3||Graphite||1.176||1.38|||
|CBZ||EP||Carbon rod||CeOx/GF||2 × 10−2||3.12|||
|Organic contaminant||Bio-EP||Nematic liquid crystal display electrode||Pt coated titanium||0.0177|||
|Methylene blue||Bio-EP||Activated carbon granules||XC-72 carbon black||0.237|||
Organic pollutants containing plentiful wastewater have been magnificently treated by PEP. In this framework, derivatives of benzene particularly nitrobenzene, chlorobenzene, and benzaldehyde containing wastewater were processed through electro-peroxone and photoelectro-peroxone approaches. Although both approaches have been drawn out 98% TOC, PEP exhibited good degradation kinetics, and consumed less energy than that of EP and other advanced oxidation processes, which have been exploited slow degradation kinetics and used up high energy . Similarly, 1,4-dioxane, a major contributor to refractory organic pollutant, is exclusively found in industrial wastewater and landfill leachates and was disintegrated with 33 times proficient pseudo-first-order rate constant
Similarly, PEP approaches have been eliminated herbicides at both alkaline and neutral pH. In this context, 2,4-D herbicide was entirely degraded within 25 minutes and its degradation kinetics has exploited first-order reaction rate by PEP approach having rate constant of about 2.5-folds higher than the rate constant of EP. Furthermore, 58.9% TOC has been wiped out during 2,4 D mineralization at pH of 7 from wastewater solution. On contrary to stainless steel and graphite felt, cathodic-activated carbon has promoted reaction rate by engendering H2O2 . Likewise, another attempt has been made to boost 2,4-D herbicide disintegration through UV-assisted PEP. Complete fragmentation of 2,4-D herbicide in solution (58 mg L−1) was obtained at 5.6 pH in 112 minutes along with its 91% elimination; moreover, 76% TOC has been withdrawn during 2,4-D herbicide mineralization after 2 hours. Low pH and 85% COD along with trapping assessment revealed that both species ȮH and Ȯ2− have contributed to wastewater treatment ; hence, approximately at slightly acidic pH reaction could be proceeded between H+ ions and Ȯ3− to produce reaction active species (HȮ−)
Furthermore, PEP-based some attempts have been made in textile wastewater treatment. In this circumstance, MY dye containing wastewater has been processed by incorporating zero-valent iron (ZVI) as a nano-catalyst in the solution, which was further followed by PEP process and accelerated wastewater treatment. This hybrid PEP/ZVI approach has successfully decolorized wastewater solution (50 mg L−1) at acidic pH 3 within 25 minutes, as acidic media promotes H2O2 electrolytically based on Eq. (25) . Moreover, reactive yellow F3R (RY F3R) wastewater was pulverized by PEP manifesting first-order kinetics and 97.66% decolorization and 84.64% TOC has been excluded with 14 and 1.4 times more degradation rate constant as compared with photolysis and EP sequentially.
Moreover, real textile wastewater also has been treated by PEP effectively by withdrawing TOC  and decolorization rate could be promoted by incorporating transition metals that in turn produce Fenton reagent. Fe+2 triggers ozone activation and hydroxyl-free radical formation as discussed in Eqs. (26) and (27) [28, 106].
In addition, COD parameter was applied to analyze pollutant concentration in landfill leachate and lower the pollutant concentration, and lesser oxidant would be acquired; hence, lower COD exclusion would be attained. Percentage of COD exclusion could be calculated by Eq. (28) where C0 and Cf denote quantity of COD that has been consumed by leachate before and after its treatment . In this frame, 83% COD exclusion has been achieved at 5.6 pH through PEP .
5. Energy expenditures for electro-peroxone, complementary hybrid EP, and photoelectro-peroxone approaches
Some amount of energy has required to perform electrochemical oxidation of wastewater. In this framework, specific energy is mandatory to disintegrate pollutants in innumerable wastewater treatment. Therefore, Eqs. (29) and (30) have been proposed to estimate energy supplied during EP, PEP, and complementary hybrid EP approaches .
Where SECEP and SECPEP are the specific energy consumptions for EP and PEP sequentially measured in kWh (gTOCremoved)−1, and SERPEP is the specific energy consumption or electrical energy requirement measured in kWh (gCODremoved)−1. U is an average cell voltage (V), I denotes current (A), t represents reaction time (h), r symbolizes energy requirements for ozone formation (kWh (kgO3)−1), CO3 designates ozone quantity consumed during EP and PEP approaches, TOC0 and TOCt indicate total organic carbon in the solution at 0 time and any time t (mg L−1), [PCT]0 and [PCT]t symbolize concentrations of unprocessed and processed paracetamol (PCT), respectively, V shows solution volume (L), PUV denotes power of UV lamp (W) , Δ(TOCexp) represents change in the concentration of TOC , (C0 − Ct) is the concentration of LEV in untreated and treated wastewater sequentially, R denotes energy expenditure for ozone formation, C symbolizes concentration of inlet ozone, Q indicates flow rate of gaseous ozone , a represents energy attained for ozone formation, Qgas designates feed gas volume, and CO3 reveals feed gas comprising ozone concentration .
Total organic carbon was effectively discarded from wastewater during mineralization of benzene derivatives through SECEP and SECPEP, of 1.07 and 0.66 kWh (gTOCremoved)−1 respectively . Similarly, SECEP and SECPEP of 0.22 and 0.30 kWh (gTOCremoved)−1 have been achieved by removing TOC from 1,4-dioxane containing wastewater sequentially . Nitrophenol decomposition has been expended SECEP and SECPEP, of 7.5 and 4.1 kWh (gTOCremoved)−1, respectively, for entire elimination of TOC. In addition to PEP, BDD electrode dramatically enhanced reaction kinetic; therefore, deducted energy requirement  SERPEP of 1.5 kWh (gCODremoved)−1 has been consumed in landfill leachate treatment using Eq. (31) . Entire PCT breakdown
Overall, PEP dwindled almost 45% specific energy consumption than that of EP approaches for a same category of wastewater under unchanged reaction conditions; nevertheless, some exceptions may be commenced conspicuously in degradation of 1,4-dioxone. Complementary hybrid EP approaches have foremost expedience of comparatively reducing energy expenditures to that of a virgin EP as well as enhanced abatement of pollutants in wastewater treatment. In this milieu, bio-electroperoxone system offered much indulgence by in taking very low energy. In contrast to conventional 2-D electrodes, latest 3-D electrodes-based EP approaches have been manifested less energy consumption.
High-operating cost-advanced oxidation processes on accountability of derisory performance to wastewater treatment have been exploited sundry shortcomings, which urge necessity for EAOPs-based alternative techniques. In this framework, to exaggerate traditional 2-D EP system has been transformed into 3-D EP by modification in electrode texture as a result, more peroxide formation was catalyzed by large electrode surface area as well as considerably SEC were also dwindled. Notwithstanding PEP approaches were established to overcome dilemma of existing EP techniques under harsh conditions, where UV accelerated further prevailing hydroxyl-free radicals and synergistic effect of individual mechanisms involved in PEP have been substantially boosted enhancement factor along with degradation kinetics of pollutants in wastewater thereby diminishing energy expenditures in the form of SECPEP. Additionally, to improve some conventional methods more conspicuously filtration, electrocoagulation and biological treatments were coupled with EP to devise novel complementary hybrid EP-based EAOPs, which have demonstrated pragmatic mineralization effectiveness and declined required electrical energy consumption.
Over the last decade, EAOPs in wake of nonselective oxidation and prohibition of secondary products have been acquainted for wastewater treatment. Henceforth, EAOPs more conspicuously novel complementary hybrid EP and PEP approaches could be more economical option for wide spectrum of synthetic and real wastewater treatment along with reducing energy expenditures, which could be fruitful from laboratory to large scale.
Conflict of interest
The authors declare no conflict of interest.
Prabakar D et al. Pretreatment technologies for industrial effluents: Critical review on bioenergy production and environmental concerns. Journal of Environmental Management. 2018; 218:165-180. DOI: 10.1016/j.jenvm an.2018.03.136
Li Z et al. Highly efficient degradation of perfluorooctanoic acid: An integrated photo-electrocatalytic ozonation and mechanism study. Chemical Engineering Journal. 2020; 391:123533. DOI: 10.1016/j.cej.2019.123533
Kundu D, Hazra C, Chaudhari A. Biodegradation of 2, 6-dinitrotoluene and plant growth promoting traits by Rhodococcus pyridinivoransNT2: Identification and toxicological analysis of metabolites and proteomic insights. Biocatalysis and Agricultural Biotechnology. 2016; 8:55-65. DOI: 10.1016/j.bcab.2016.08.004
Wu Y et al. Effects of composition faults in ternary metal chalcogenides (ZnxIn2S3+x, x= 1–5) layered crystals for visible-light-driven catalytic hydrogen generation and carbon dioxide reduction. Applied Catalysis B: Environmental. 2019; 256:117810. DOI: 10.1016/j.apcatb.2019.117810
Gunatilake S. Methods of removing heavy metals from industrial wastewater. Methods. 2015; 1(1):14. ISSN: 2912-1309
Deng Y, Zhao R. Advanced oxidation processes (AOPs) in wastewater treatment. Current Pollution Reports. 2015; 1(3):167-176. DOI: 10.1007/s40726-015-0015-z
Umamaheswari J et al. A feasibility study on optimization of combined advanced oxidation processes for municipal solid waste leachate treatment. Process Safety and Environmental Protection. 2020; 143:212-221. DOI: 10.1016/j.psep.2020.06.040
Chow C-H, Leung KS-Y. Removing acesulfame with the peroxone process: Transformation products, pathways and toxicity. Chemosphere. 2019; 221:647-655. DOI: 10.1016/j.chemosphere.2019.01.082
Ding Y et al. Oxygen vacancy of CeO2 improved efficiency of H2O2/O3 for the degradation of acetic acid in acidic solutions. Separation and Purification Technology. 2018; 207:92-98. DOI: 10.1016/j.seppur.2018.06.027
Yang J et al. Enhancement of bromate formation by pH depression during ozonation of bromide-containing water in the presence of hydroxylamine. Water Research. 2017; 109:135-143. DOI: 10.1016/j.watres.2016.11.037
Yao W et al. Comparison of methylisoborneol and geosmin abatement in surface water by conventional ozonation and an electro-peroxone process. Water Research. 2017; 108:373-382. DOI: 10.1016/j.watres.2016.11.014
Särkkä H, Bhatnagar A, Sillanpää M. Recent developments of electro-oxidation in water treatment—a review. Journal of Electroanalytical Chemistry. 2015; 754:46-56. DOI: 10.1016/j.jelechem.2015.06.016
Wang C et al. Insights of ibuprofen electro-oxidation on metal-oxide-coated Ti anodes: Kinetics, energy consumption and reaction mechanisms. Chemosphere. 2016; 163:584-591. DOI: 10.1016/j.chemosphere. 2016.08.057
Syam Babu D et al. Industrial wastewater treatment by electrocoagulation process. Separation Science and Technology. 2020; 55(17):3195-3227. DOI: 10.1080/01496395.2019.1671866
Ye Z et al. Mechanism and stability of an Fe-based 2D MOF during the photoelectro-Fenton treatment of organic micropollutants under UVA and visible light irradiation. Water Research. 2020; 184:115986. DOI: 10.1016/j.watres.2020.115986
Wang Y et al. The electro-peroxone process for the abatement of emerging contaminants: Mechanisms, recent advances, and prospects. Chemosphere. 2018; 208:640-654. DOI: 10.1016/j.chemosphere.2018.05.095
Ghalebizade M, Ayati B. Acid Orange 7 treatment and fate by electro-peroxone process using novel electrode arrangement. Chemosphere. 2019; 235:1007-1014. DOI: 10.1016/j.chemosphere.2019.06.211
Kermani M, Mehralipour J, Kakavandi B. Photo-assisted electroperoxone of 2,4-dichlorophenoxy acetic acid herbicide: Kinetic, synergistic and optimization by response surface methodology. Journal of Water Process Engineering. 2019; 32:100971. DOI: 10.1016/j.jwpe. 2019.100971
Oturan MA, Brillas E. Electrochemical advanced oxidation processes (EAOPs) for environmental applications. Portugaliae Electrochimica Acta. 2007; 25(1):1. DOI: 10.4152/pea.200701001
Asgari G et al. Sonophotocatalytic treatment of AB113 dye and real textile wastewater using ZnO/persulfate: Modeling by response surface methodology and artificial neural network. Environmental Research. 2020; 184:109367. DOI: 10.1016/j.envres.2020.109367
Buxton GV et al. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (·OH/·O−) in aqueous solution. Journal of Physical and Chemical Reference Data. 1988; 17(2):513-886. DOI: 10.1063/1.555805
Li X et al. Electro-peroxone treatment of the antidepressant venlafaxine: Operational parameters and mechanism. Journal of Hazardous Materials. 2015; 300:298-306. DOI: 10.1016/j.jhazmat.2015.07.004
Lin Z et al. Perchlorate formation during the electro-peroxone treatment of chloride-containing water: Effects of operational parameters and control strategies. Water Research. 2016; 88:691-702. DOI: 10.1016/j.watres. 2015.11.005
Bakheet B et al. Electro-peroxone treatment of Orange II dye wastewater. Water Research. 2013; 47(16):6234-6243. DOI: 10.1016/j.watres.2013.07.042
Xia G et al. The competition between cathodic oxygen and ozone reduction and its role in dictating the reaction mechanisms of an electro-peroxone process. Water Research. 2017; 118:26-38. DOI: 10.1016/j.watres.2017.04.005
Zhang Y et al. Simultaneous removal of tetracycline and disinfection by a flow-through electro-peroxone process for reclamation from municipal secondary effluent. Journal of Hazardous Materials. 2019; 368:771-777. DOI: 10.1016/j.jhazmat.2019.02.005
Wang H et al. Mechanisms of enhanced total organic carbon elimination from oxalic acid solutions by electro-peroxone process. Water Research. 2015; 80:20-29. DOI: 10.1016/j.watres.2015.05.024
Jaafarzadeh N, Barzegar G, Ghanbari F. Photo assisted electro-peroxone to degrade 2,4-D herbicide: The effects of supporting electrolytes and determining mechanism. Process Safety and Environmental Protection. 2017; 111:520-528. DOI: 10.1016/j.psep.2017.08.012
Agustina TE, Ang HM, Vareek VK. A review of synergistic effect of photocatalysis and ozonation on wastewater treatment. Journal of Photochemistry and Photobiology C: Photochemistry Reviews. 2005; 6(4):264-273. DOI: 10.1016/j.jphotochemrev.2005.12.003
Frangos P et al. A novel photoelectro-peroxone process for the degradation and mineralization of substituted benzenes in water. Chemical Engineering Journal. 2016; 286:239-248. DOI: 10.1016/j.cej.2015.10.096
Dubey S et al. Electro-peroxone treatment of rice grain based distillery biodigester effluent: COD and color removal. Water Resources and Industry. 2021; 25:100142. DOI: 10.1016/j.wri.2021.100142
Öztürk H, Barışçı S, Turkay O. Paracetamol degradation and kinetics by advanced oxidation processes (AOPs): Electro-peroxone, ozonation, goethite catalyzed electro-fenton and electro-oxidation. Environmental Engineering Research. 2021; 26(2):1-13. DOI: 10.4491/eer.2018.332
Zheng H-S et al. Electro-peroxone pretreatment for enhanced simulated hospital wastewater treatment and antibiotic resistance genes reduction. Environment International. 2018; 115:70-78. DOI: 10.1016/j.envint.2018.02.043
Zhang Y et al. Disinfection of simulated ballast water by a flow-through electro-peroxone process. Chemical Engineering Journal. 2018; 348:485-493. DOI: 10.1016/j.cej.2018.04.123
Yao W et al. The beneficial effect of cathodic hydrogen peroxide generation on mitigating chlorinated by-product formation during water treatment by an electro-peroxone process. Water Research. 2019; 157:209-217. DOI: 10.1016/j.watres.2019.03.049
Kermani M et al. Optimization of UV-electroproxone procedure for treatment of landfill leachate: The study of energy consumption. Journal of Environmental Health Science and Engineering. 2021; 19(1):81-93. DOI: 10.1007/s40201-020-00583-9
Jiao Y et al. Treatment of reverse osmosis concentrate from industrial coal wastewater using an electro-peroxone process with a natural air diffusion electrode. Separation and Purification Technology. 2021; 279:119667. DOI: 10.1016/j.seppur.2021.119667
Guivarch E et al. Degradation of azo dyes in water by electro-Fenton process. Environmental Chemistry Letters. 2003; 1(1):38-44. DOI: 10.1007/s10311-002-0017-0
Srinivasan R, Nambi IM. Liquid crystal display electrode-assisted bio-electroperoxone treatment train for the abatement of organic contaminants in a pharmaceutical wastewater. Environmental Science and Pollution Research. 2020; 27(24):29737-29748. DOI: 10.1007/s11356-019-06898-x
Bensalah N, Bedoui A. Enhancing the performance of electro-peroxone by incorporation of UV irradiation and BDD anodes. Environmental Technology. 2017; 38(23):2979-2987. DOI: 10.1080/09593330.2017.1284271
Wu D et al. Elimination of aqueous levetiracetam by a cyclic flow-through electro-peroxone process. Separation and Purification Technology. 2021; 260:118202. DOI: 10.1016/j.seppur.2020.118202
Yao J et al. Interfacial catalytic and mass transfer mechanisms of an electro-peroxone process for selective removal of multiple fluoroquinolones. Applied Catalysis B: Environmental. 2021; 298:120608. DOI: 10.1016/j.apcatb.2021.120608
Wang X et al. Electro-catalytic activity of CeOx modified graphite felt for carbamazepine degradation via E-peroxone process. Frontiers of Environmental Science & Engineering. 2021; 15(6):122. DOI: 10.1007/s11783-021-1410-x
Wang H et al. Oxidation of emerging biocides and antibiotics in wastewater by ozonation and the electro-peroxone process. Chemosphere. 2019; 235:575-585. DOI: 10.1016/j.chemosphere.2019.06.205
Ghalebizade M, Ayati B. Investigating electrode arrangement and anode role on dye removal efficiency of electro-peroxone as an environmental friendly technology. Separation and Purification Technology. 2020; 251:117350. DOI: 10.1016/j.seppur.2020.117350
Shokri A, Karimi S. Treatment of aqueous solution containing acid red 14 using an electro peroxone process and a box-Behnken experimental design. Archives of Hygiene Sciences. 2020; 9(1):48-57. DOI: 10.29252/ArchHygSci.9.1.48
Cornejo OM et al. Degradation of Acid Violet 19 textile dye by electro-peroxone in a laboratory flow plant. Chemosphere. 2021; 271:129804. DOI: 10.1016/j.chemosphere.2021.129804
Abdi M et al. Degradation of crystal violet (CV) from aqueous solutions using ozone, peroxone, electroperoxone, and electrolysis processes: A comparison study. Applied Water Science. 2020; 10(7):1-10. DOI: 10.1007/s13201-020-01252-w
Paździor K, Bilińska L, Ledakowicz S. A review of the existing and emerging technologies in the combination of AOPs and biological processes in industrial textile wastewater treatment. Chemical Engineering Journal. 2019; 376:120597. DOI: 10.1016/j.cej.2018.12.057
Cetinkaya SG et al. Comparison of classic Fenton with ultrasound Fenton processes on industrial textile wastewater. Sustainable Environment Research. 2018; 28(4):165-170. DOI: 10.1016/j.serj.2018.02.001
El-Desoky HS et al. Oxidation of Levafix CA reactive azo-dyes in industrial wastewater of textile dyeing by electro-generated Fenton's reagent. Journal of Hazardous Materials. 2010; 175(1-3):858-865. DOI: 10.1016/j.jhazmat.2009.10.089
Gebrati L et al. Inhibiting effect of textile wastewater on the activity of sludge from the biological treatment process of the activated sludge plant. Saudi Journal of biological sciences. 2019; 26(7):1753-1757. DOI: 10.1016/j.sjbs.2018.06.003
Garcia-Segura S et al. Comparative degradation of the diazo dye Direct Yellow 4 by electro-Fenton, photoelectro-Fenton and photo-assisted electro-Fenton. Journal of Electroanalytical Chemistry. 2012; 681:36-43. DOI: 10.1016/j.jelechem.2012.06.002
Ghalebizade M, Ayati B, Ganjidoust H. Capability study of electro-peroxone process in a cylindrical reactor in degrading Acid Orange 7. Linnaeus Eco-Tech. 2018:87-87. ISBN: 978-91-88898-28-9
Yang Y et al. Occurrences and removal of pharmaceuticals and personal care products (PPCPs) in drinking water and water/sewage treatment plants: A review. Science of the Total Environment. 2017; 596:303-320. DOI: 10.1016/j.scitotenv.2017.04.102
Michael I et al. Urban wastewater treatment plants as hotspots for the release of antibiotics in the environment: A review. Water Research. 2013; 47(3):957-995. DOI: 10.1016/j.watres.2012.11.027
Östman M, Fick J, Tysklind M. Detailed mass flows and removal efficiencies for biocides and antibiotics in Swedish sewage treatment plants. Science of the Total Environment. 2018; 640:327-336. DOI: 10.1016/ j.scitotenv.2018.05.304
Liu W-R et al. Biocides in wastewater treatment plants: Mass balance analysis and pollution load estimation. Journal of Hazardous Materials. 2017; 329:310-320. DOI: 10.1016/j.jhazmat.2017.01.057
Wang H et al. Comparison of pharmaceutical abatement in various water matrices by conventional ozonation, peroxone (O3/H2O2), and an electro-peroxone process. Water Research. 2018; 130:127-138. DOI: 10.1016/ j.watres.2017.11.054
Yao W et al. Pilot-scale evaluation of micropollutant abatements by conventional ozonation, UV/O3, and an electro-peroxone process. Water Research. 2018; 138:106-117. DOI: 10.1016/j.watres.2018.03.044
Kovalova L et al. Elimination of micropollutants during post-treatment of hospital wastewater with powdered activated carbon, ozone, and UV. Environmental Science & Technology. 2013; 47(14):7899-7908. DOI: 10.1021/es400708w
Xia G et al. Evaluation of the stability of polyacrylonitrile-based carbon fiber electrode for hydrogen peroxide production and phenol mineralization during electro-peroxone process. Chemical Engineering Journal. 2020; 396:125291. DOI: 10.1016/j.cej.2020.125291
Lee Y et al. Prediction of micropollutant elimination during ozonation of a hospital wastewater effluent. Water Research. 2014; 64:134-148. DOI: 10.1016/j.watres.2014.06.027
Lee Y et al. Prediction of micropollutant elimination during ozonation of municipal wastewater effluents: Use of kinetic and water specific information. Environmental Science & Technology. 2013; 47(11):5872-5881. DOI: 10.1021/es400781r
Preethi V et al. Ozonation of tannery effluent for removal of cod and color. Journal of Hazardous Materials. 2009; 166(1):150-154. DOI: 10.1016/ j.jhazmat.2008.11.035
Mustafa M et al. Identification of resistant pharmaceuticals in ozonation using QSAR modeling and their fate in electro-peroxone process. Frontiers of Environmental Science & Engineering. 2021; 15(5):1-14. DOI: 10.1007/s 11783-021-1394-6
Ghanbari F et al. Enhanced electro-peroxone using ultrasound irradiation for the degradation of organic compounds: A comparative study. Journal of Environmental Chemical Engineering. 2020; 8(5):104167. DOI: 10.1016/j.jece.2020.104167
Asgari G et al. Diuron degradation using three-dimensional electro-peroxone (3D/E-peroxone) process in the presence of TiO2/GAC: Application for real wastewater and optimization using RSM-CCD and ANN-GA approaches. Chemosphere. 2021; 266:129179. DOI: 10.1016/j. chemosphere 2020.129179
Dinc O. Tannic acid oxidation by electroperoxone. Journal of the Faculty of Engineering and Architecture of Gazi University. 2020; 35(1):51-60. DOI: 10.17341/gazimmfd.425326
Wu D et al. Removal of aqueous para-aminobenzoic acid using a compartmental electro-peroxone process. Water. 2021; 13(21):2961. DOI: 10.3390/w13212961
Wang S et al. Electrochemically enhanced adsorption of PFOA and PFOS on multiwalled carbon nanotubes in continuous flow mode. Chinese Science Bulletin. 2014; 59(23):2890-2897. DOI: 10.1007/s11434-014-0322-6
Vecitis CD, Gao G, Liu H. Electrochemical carbon nanotube filter for adsorption, desorption, and oxidation of aqueous dyes and anions. The Journal of Physical Chemistry C. 2011; 115(9):3621-3629. DOI: 10.1021/jp111844j
Sampaio MJ et al. Carbon nanotube–TiO2 thin films for photocatalytic applications. Catalysis Today. 2011; 161(1):91-96. DOI: 10.1016/j.cattod. 2010.11.081
Shan D et al. Preparation of ultrafine magnetic biochar and activated carbon for pharmaceutical adsorption and subsequent degradation by ball milling. Journal of Hazardous Materials. 2016; 305:156-163. DOI: 10.1016/j.jhazmat.2015.11.047
Quesada-Peñate I et al. Degradation of paracetamol by catalytic wet air oxidation and sequential adsorption–catalytic wet air oxidation on activated carbons. Journal of Hazardous Materials. 2012; 221:131-138. DOI: 10.1016/j.jhazmat.2012.04.021
Huang Q et al. Enhanced adsorption of diclofenac sodium on the carbon nanotubes-polytetrafluorethylene electrode and subsequent degradation by electro-peroxone treatment. Journal of Colloid and Interface Science. 2017; 488:142-148. DOI: 10.1016/j.jcis.2016.11.001
Wu D et al. Adsorption and catalytic electro-peroxone degradation of fluconazole by magnetic copper ferrite/carbon nanotubes. Chemical Engineering Journal. 2019; 370:409-419. DOI: 10.1016/j.cej.2019.03.192
Guo Z et al. High activity of g-C3N4/multiwall carbon nanotube in catalytic ozonation promotes electro-peroxone process. Chemosphere. 2018; 201:206-213. DOI: 10.1016/j.chemosphere.2018.02.176
Guo Z et al. Towards a better understanding of the synergistic effect in the electro-peroxone process using a three electrode system. Chemical Engineering Journal. 2018; 337:733-740. DOI: 10.1016/j.cej.2017.11.178
Östman M et al. Effect of full-scale ozonation and pilot-scale granular activated carbon on the removal of biocides, antimycotics and antibiotics in a sewage treatment plant. Science of the Total Environment. 2019; 649:1117-1123. DOI: 10.1016/j.scitotenv.2018.08.382
Mustafa M et al. Regeneration of saturated activated carbon by electro-peroxone and ozonation: Fate of micropollutants and their transformation products. Science of the Total Environment. 2021; 776:145723. DOI: 10.1016/j.scitotenv.2021.145723
Guo Z et al. C3N4–Mn/CNT composite as a heterogeneous catalyst in the electro-peroxone process for promoting the reaction between O3 and H2O2 in acid solution. Catalysis Science & Technology. 2018; 8(23):6241-6251. DOI: 10.1039/C8CY01517A
Kishimoto N et al. Effect of separation of ozonation and electrolysis on effective use of ozone in ozone-electrolysis process. Ozone: Science & Engineering. 2011; 33(6):463-469. DOI: 10.1080/01919512.2011.615282
Turkay O, Ersoy ZG, Barışçı S. The application of an electro-peroxone process in water and wastewater treatment. Journal of the Electrochemical Society. 2017; 164(6):E94. DOI: 10.1149/2.0321706jes
Banuelos JA et al. Study of an air diffusion activated carbon packed electrode for an electro-Fenton wastewater treatment. Electrochimica Acta. 2014; 140:412-418. DOI: 10.1016/j.electacta.2014.05.078
Mi X et al. Enhanced catalytic degradation by using RGO-Ce/WO3 nanosheets modified CF as electro-Fenton cathode: Influence factors, reaction mechanism and pathways. Journal of Hazardous Materials. 2019; 367:365-374. DOI: 10.1016/j.jhazmat.2018.12.074
Le TXH et al. High removal efficiency of dye pollutants by electron-Fenton process using a graphene based cathode. Carbon. 2015; 94:1003-1011. DOI: 10.1016/j.carbon.2015.07.086
Asgari G et al. Carbon felt modified with N-doped rGO for an efficient electro-peroxone process in diuron degradation and biodegradability improvement of wastewater from a pesticide manufacture: Optimization of process parameters, electrical energy consumption and degradation pathway. Separation and Purification Technology. 2021; 274:118962. DOI: 10.1016/ j.seppur.2021.118962
Cornejo OM, Nava JL. Mineralization of the antibiotic levofloxacin by the electro-peroxone process using a filter-press flow cell with a 3D air-diffusion electrode. Separation and Purification Technology. 2021; 254:117661. DOI: 10.1016/j.seppur.2020.117661
Chen S et al. Enhanced recalcitrant pollutant degradation using hydroxyl radicals generated using ozone and bioelectricity-driven cathodic hydrogen peroxide production: Bio-E-peroxone process. Science of the Total Environment. 2021; 776:144819. DOI: 10.1016/j.scitotenv.2020.144819
Yang Q et al. Ibuprofen removal from drinking water by electro-peroxone in carbon cloth filter. Chemical Engineering Journal. 2021; 415:127618. DOI: 10.1016/j.cej.2020.127618
Mahamuni NN, Adewuyi YG. Advanced oxidation processes (AOPs) involving ultrasound for waste water treatment: A review with emphasis on cost estimation. Ultrasonics Sonochemistry. 2010; 17(6):990-1003. DOI: 10.1016/j.ultsonch.2009.09.005
Kıdak R, Doğan Ş. Medium-high frequency ultrasound and ozone based advanced oxidation for amoxicillin removal in water. Ultrasonics Sonochemistry. 2018; 40:131-139. DOI: 10.1016/j.ultsonch.2017.01.033
Zhang H et al. Degradation of CI Acid Orange 7 by ultrasound enhanced ozonation in a rectangular air-lift reactor. Chemical Engineering Journal. 2008; 138(1-3):231-238. DOI: 10.1016/j.cej.2007.06.031
AlJaberi FY, Ahmed SA, Makki HF. Electrocoagulation treatment of high saline oily wastewater: Evaluation and optimization. Heliyon. 2020; 6(6):e03988. DOI: 10.1016/j.heliyon.2020.e03988
Wang Y-K et al. The synergistic effect of electrocoagulation coupled with E-peroxone process for shale gas fracturing flowback water treatment. Chemosphere. 2021; 262:127968. DOI: 10.1016/j.chemosphere.2020.127968
Comninellis CCG. Electrochemistry for the Environment. New York, London: Springer; 2010
Santana-Martínez G et al. Downflow bubble column electrochemical reactor (DBCER): In-situ production of H2O2 and O3 to conduct electroperoxone process. Journal of Environmental Chemical Engineering. 2021; 9(4):105148. DOI: 10.1016/j.jece.2021.105148
Thiam A et al. Electrochemical advanced oxidation of carbofuran in aqueous sulfate and/or chloride media using a flow cell with a RuO2-based anode and an air-diffusion cathode at pre-pilot scale. Chemical Engineering Journal. 2018; 335:133-144. DOI: 10.1016/j.cej.2017.10.137
Shen W et al. Kinetics and operational parameters for 1, 4-dioxane degradation by the photoelectro-peroxone process. Chemical Engineering Journal. 2017; 310:249-258. DOI: 10.1016/j.cej.2016.10.111
Ahmadi M, Ghanbari F. Degradation of organic pollutants by photoelectro-peroxone/ZVI process: Synergistic, kinetic and feasibility studies. Journal of Environmental Management. 2018; 228:32-39. DOI: 10.1016/ j.jenvman.2018.08.102
Joy AC et al. Photoelectro-peroxone process for the degradation of reactive azo dye in aqueous solution. Separation Science and Technology. 2020; 55(14):2550-2559. DOI: 10.1080/01496395.2019.1634732
Trojanowicz M et al. Advanced oxidation/reduction processes treatment for aqueous perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS)–a review of recent advances. Chemical Engineering Journal. 2018; 336:170-199. DOI: 10.1016/j.cej.2017.10.153
Wang S et al. Photocatalytic degradation of perfluorooctanoic acid and perfluorooctane sulfonate in water: A critical review. Chemical Engineering Journal. 2017; 328:927-942. DOI: 10.1016/j.cej.2017.07.076
Nawrocki J, Kasprzyk-Hordern B. The efficiency and mechanisms of catalytic ozonation. Applied Catalysis B: Environmental. 2010; 99(1-2):27-42. DOI: 10.1016/j.apcatb.2010.06.033
Zeng Z et al. Ozonation of acidic phenol wastewater with O3/Fe(II) in a rotating packed bed reactor: Optimization by response surface methodology. Chemical Engineering and Processing: Process Intensification. 2012; 60:1-8. DOI: 10.1016/j.cep.2012.06.006
Hassan M, Zhao Y, Xie B. Employing TiO2 photocatalysis to deal with landfill leachate: Current status and development. Chemical Engineering Journal. 2016; 285:264-275. DOI: 10.1016/j.cej.2015.09.093
Katsoyiannis IA, Canonica S, von Gunten U. Efficiency and energy requirements for the transformation of organic micropollutants by ozone, O3/H2O2 and UV/H2O2. Water Research. 2011; 45(13):3811-3822. DOI: 10.1016/j.watres.2011.04.038