*Electro-Peroxone and Photoelectro-Peroxone Hybrid Approaches: An Emerging Paradigm… DOI: http://dx.doi.org/10.5772/intechopen.102921*

declined within 90 minutes at pH 7.7 with large electrode surface area ratio (6:6) by which degradation was considerably enhanced [45]. Similarly, Acid red 14 (AR 14) wastewater (400 mg L<sup>1</sup> ) 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 [46]. Another attempt has been made on decomposition of crystal violet (CV) with Kapp of 2.69 <sup>10</sup><sup>2</sup> and 2.87 102 min<sup>1</sup> , for 100 and 200 mg L<sup>1</sup> 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. Electroperoxone approaches were provoked decolorization at alkaline media [48]. A novel approach has been made to smash Acid Violet 19 (AV19) in a lab-scale filter-pressbased plant employing 3-D gas diffusion electrode as a cathode to attain better oxygen reduction reaction *via* EP. This led to 60% mineralization and 100% decolorization, at 3 psi pressure that was employed to gas diffusion electrode with acidic pH medium (3). It was demonstrated that AV19 disintegration was consequence of *in situ* generated peroxide coupled with ozonation as well as an anodic oxidation [47].

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 [56–58]. 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 biorecalcitrant paracetamol (PCT). EP approach has exhibited good efficiency in full disintegration of PCT with rate constant of 0.1662 min<sup>1</sup> [32]. Levetiracetam (LEV) removal was a bit challenging owing to polar structures, which was not susceptible to ozone degradation [61]. Extremely water-soluble antiepileptic drug LEV has been manifested pseudo-first-order degradation kinetics *via* EP approach by means of promoted synergy between O3 and H2O2 for actively electrochemical generation of HȮ and led to withdrawn of 53.4% LEV at 15 minutes from wastewater [41]. Numerous antibiotics notably ciprofloxacin, norfloxacin, ofloxacin, and trimethoprim have been degraded with EP and tracked pseudo-first-order kinetics. Outcomes revealed that EP technique effectively eradicates antibiotics and ozone inert biocides within short time and lessen energy consumption than that of ozonation process [44]. Similarly, tetracycline (TC) and microbes were smashed into organic acids and after mineralization totally excluded from wastewater by EP approach [44]. Highly stable polyacrylonitrile-based carbon fiber cathode was designed for mineralization of phenol, where oxidation promoted transformation of pyridinic-N of polyacrylamide into pyridonic-N through EP, which endorsed cathode for oxygen reduction reaction. Major gratification of this procedure was 30-fold recyclability of fabricated cathode as well as cathodic potentials declined energy expenditure from 91.5% (simple cathode) to 48.2% (current cathode) for H2O2 formation [62]. Electro-peroxone approach was conducted by fabricating iron-modified carbonized metal organic framework (MOF) based cathode for treatment of biostatic drugs such as fluoroquinolones (FQs); these were selectively 99% decomposed by O3 and the rest of its ozone-reluctant transformed intermediates and side products were removed by HȮ. Moreover, HȮ was also liable to overall TOC removal, and its formation was promoted by surface functionalities of MOF-based cathode through synergic effect of adsorption and

*Electro-Peroxone and Photoelectro-Peroxone Hybrid Approaches: An Emerging Paradigm… DOI: http://dx.doi.org/10.5772/intechopen.102921*

activation [42]. Aforementioned hybrid EP approaches have been successfully applied for the treatment of synthetic wastewater.

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 [65]. 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 [37]. 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 [31]. 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 [35]. Several antibiotics conspicuously ciprofloxacin, norfloxacin, ofloxacin, and trimethoprim have been eliminated from secondary wastewater effluents through EP [44]. 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 [26]. 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<sup>1</sup> s <sup>1</sup> 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<sup>1</sup> s <sup>1</sup> would be rapidly eradicated by EP and ozonation [66]. 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 [67]. Similarly, real pesticide wastewater has been treated *via* 3D/EP system with elimination of 97.5% TOC and 95.1% COD up to 500 and 300 minutes sequentially; consequently, long reaction time contributes to more cost although 3-D/EP is more cost effective to that of 2-D EP. Moreover, 30 minutes later BODs/COD ratio has been incremented from 0.049 to 0.571 [68].

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 *via* O3 and HȮ, which were accountable for carboxylic acid like intermediates. Consequently, more intermediate formation lowered pH of wastewater, and thereby HȮ was also declined. Somehow it has been overcome *via* increasing inlet ozone as well as adjusting current and unlike ozonation more than 10% efficacy has been achieved *via* EP [69]. Electrode-separated compartmentalbased EP approach was carried out to eliminate para-aminobenzoic acid (PABA) from wastewater solution. As a result, 63.6%–89.5% PABA has been abolished by contribution of cathodic and anodic side reactions, respectively, at 10 minutes as well as incremented pseudo-first-order reaction kinetics and HȮ formation [70].
