**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 [94].

$$\text{SEC}\_{\text{EP}} = \frac{\mathbf{U} \times \mathbf{I} \times \mathbf{t} + \mathbf{r} \times \mathbf{CO}\_3}{(\mathbf{TOC}\_0 - \mathbf{TOC}\_t) \times \mathbf{V}} \tag{29}$$

$$\text{SEC}\_{\text{PEP}} = \frac{\mathbf{P}\_{\text{UV}} \times \mathbf{t} + \mathbf{U} \times \mathbf{I} \times \mathbf{t} + \mathbf{r} \times \mathbf{CO}\_3}{(\mathbf{TOC}\_0 - \mathbf{TOC}\_t) \times \mathbf{V}} \tag{30}$$

$$\text{SER}\_{\text{PEP}} = \frac{\text{UIT} \times \text{U}\_{\text{photolysis}} \times \text{rCO}\_3}{(\text{COD}\_0 \text{-COD}\_t) \times \text{V}} \tag{31}$$

$$\text{SEC}\_{\text{EP}} = \frac{\text{U} \times \text{I} \times \text{t} + \text{r} \times \text{CO}\_3}{([\text{PCT}]\_0 - [\text{PCT}]\_t) \times \text{V}} \tag{32}$$

$$\text{Energy consumption} = \frac{\mathbf{U} \times \mathbf{I} \times \mathbf{t}}{\mathbf{V}} \tag{33}$$

$$\text{EC} = \frac{\text{U} \times \text{I} \times \text{t}}{\text{V} \times \Delta \text{(TOC}\_{\text{exp}})} \tag{34}$$

$$\text{EC} = \frac{\left(\text{V} \times \text{I} + \text{ozone generator energy}\right) \times \text{t} \times 1000}{\text{C}\_{\text{dye removal}} \times \text{cell volume}} \tag{35}$$

$$\text{SEC}\_{\text{EP}} = \frac{\mathbf{U} \times \mathbf{I} \times \mathbf{t} + \mathbf{C} \times \mathbf{Q} \times \mathbf{t} \times \mathbf{R}}{(\mathbf{C}\_0 - \mathbf{C}\_t)\mathbf{V}} \tag{36}$$

$$\text{EEC} = \frac{\mathbf{U} \times \mathbf{I} \times \mathbf{t} + \mathbf{Q}\_{\text{gas}} \times \mathbf{a} \times \mathbf{CO}\_3}{\mathbf{V}} \times \mathbf{10}^{-3} \tag{37}$$

$$\text{EEC} = \frac{\mathbf{1000} \times \mathbf{U} \times \mathbf{I} \times \mathbf{t} + \mathbf{Q}\_{\text{gas}} \times \mathbf{a} \times \mathbf{CO}\_3}{(\mathbf{TOC}\_0 - \mathbf{TOC}\_t)\,\mathrm{V}} \tag{38}$$

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�<sup>1</sup> ), [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) [108], Δ(TOCexp) represents change in the concentration of TOC [89], (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 [41], a represents energy attained for ozone formation, Qgas designates feed gas volume, and CO3 reveals feed gas comprising ozone concentration [26].

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) �<sup>1</sup> respectively [30]. Similarly, SECEP and SECPEP of 0.22 and 0.30 kWh (gTOCremoved) �<sup>1</sup> have been achieved by removing TOC from 1,4-dioxane containing wastewater sequentially [100]. Nitrophenol decomposition has been

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

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 [40] SERPEP of 1.5 kWh (gCODremoved) <sup>1</sup> has been consumed in landfill leachate treatment using Eq. (31) [36]. Entire PCT breakdown *via* EP has expended SECEP of 0.1164 kWh (gPCTremoved) <sup>1</sup> based on Eq. (32) [32]. 1.676 and 22.86 kWh m<sup>3</sup> energy have been expended during hybrid bio-EP and solely EP, respectively, calculated through Eq. (33) [39]. Electrolytic energy consumption (EC) of 0.27 kWh (gTOCremoved) <sup>1</sup> was obtained *via* Eq. (34) during levofloxacin mineralization employing 3-D perforated electrode by EP [89]. 37.7% and 41.1% COD have been excluded via EP and 3-D TiO2/GAC system within 90 minutes by exhausting electrical energy of 0.1 and 0.08 kWh (gCODremoved) 1 , respectively [68]. Additionally, 39.2% and 43.6% COD have been eliminated from real pesticide wastewater with energy expenditures of 0.088 and 0.079 kWh (gCODremoved) <sup>1</sup> *via* CF-EP and N-rGOs/CF-EP system sequentially [88]. Eq. (35) was taken into an account; afterward, 53 kWh kg<sup>1</sup> (kg denote weight of removed dye) energy has been estimated during Acid Orange 7 disintegration with 99% COD exclusion during EP in cylindrical reactor [54]. To diminish SEC, another attempt was made in which Acid Orange 7 was entirely pulverized (99% CODremoval) through EP with EC of 8 kWh kg<sup>1</sup> founded on Eq. (35) [45]. AV19 dye has been 60% mineralized with energy expenditure of 0.085 kWh (gTOCremoved) <sup>1</sup> by laboratory-scale EP plant equipped with 3-D electrode based on Eq. (34) [47]. Similarly, LEV drug was smashed through EP approach with SECEP of 0.326 kWh (gLEVremoved) <sup>1</sup> on the basis of Eq. (36) [41]. Electrical energy consumption (EEC) of 0.47 kWh m<sup>3</sup> has been calculated through Eq. (37) in decontamination of municipal wastewater and TC disintegration *via* EP approach [26]. In the same way, IBU elimination through EPF system used up 0.16 kWh m<sup>3</sup> energy [91]. Sequential EEC of 1136.8 and 828.4 kWh (kgTOC) <sup>1</sup> have been achieved for virgin EP and hybrid peroxi-coagulation/EP system founded on Eq. (38) [37]. Likewise, 99.9% COD exclusion has been achieved during treatment of BDE of rice grains through EP approach *via* EEC of 3.8 kWh m<sup>3</sup> [31].

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.

### **6. Conclusions**

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.
