Integrated advanced oxidation process, ozonation-electrodegradation treatments, for nonylphenol removal in batch and continuous reactor

Accepted Manuscript Title: Integrated advanced oxidation process, ozonation-electrodegradation treatments, for nonylphenol removal in batch and continuous reactor Authors: Carlos E. Barrera-D´ıaz, Bernardo A. Frontana-Uribe, Mayra Rodr´ıguez-Pe˜na, J. Carlos Gomez-Palma, Bryan Bilyeu PII: DOI: Reference:

S0920-5861(17)30600-4 http://dx.doi.org/10.1016/j.cattod.2017.09.003 CATTOD 11008

To appear in:

Catalysis Today

Received date: Revised date: Accepted date:

21-3-2017 19-8-2017 2-9-2017

Please cite this article as: {http://dx.doi.org/ This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Integrated Advanced Oxidation Process, Ozonation-Electrodegradation Treatments, for Nonylphenol Removal in Batch and Continuous Reactor Carlos E. Barrera-Díaz*1, Bernardo A. Frontana-Uribe*1, Mayra Rodríguez-Peña1, J. Carlos Gomez-Palma1, and Bryan Bilyeu2 1

Centro Conjunto de Investigación en Química Sustentable, UAEM-UNAM, Carretera

Toluca-Atlacomulco, Km 14.5, Campus San Cayetano, C.P. 50200, Toluca Estado de México, México. 2

Department of Chemistry, Xavier University of Louisiana, New Orleans LA 70125.

Corresponding authors Email: CEB-D: [email protected] BAF-U: [email protected] Graphical abstract:

1

Highlights

Nonylphenol is an Endocrine Disruptive Chemical, it represents a threat for the environment. Treatment with ozone showed a 30% chemical oxygen demand degradation. Electrochemical methods lead to a 70 % degradation in the same process time. Ozone- electrochemical process working in a continuous mode delivers a high COD and TOC removal. This technology is highly effective, with low operational cost and no sludge generation.

Abstract Nonylphenol has been reported as an Endocrine Disruptive Chemical and aquatic organisms have shown acutely and chronically toxicity when they are exposed to this organic pollutant. Many technologies have been applied searching to degrade or remove this contaminant from wastewater; however, few proposals addresses for the technology scale up and possible real application. In this study, the results of integrating electrochemical and ozone process are presented. It is possible to propose that in acidic media electrochemical degradation is faster than ozone treatment, for example at 60 min of treatment, ozone showed a COD value of ca 30% degradation, whereas electrochemically 70 % degradation was obtained. When the electrochemical process working in a continuous mode is applied (without prior O3 treatment), COD and TOC removal takes two times the period of time required when an initial ozone dose was applied. A cost comparison between the three processes reveals that the use of the sequenced treatment reduces the cost. Furthermore, when the cost of the sequenced process is compared against other process (UV/O3) the cost reduction is significant making the proposed system an attractive alternative for the treatment of persistent pollutants. . Therefore, this technology proves to be highly effective, with low operational cost, simple operation and low environmental impact. Furthermore, no sludge is generated.

Keywords: Nonylphenol, degradation, ozone, electrochemical oxidation.

1. Introduction Nonylphenol (NP) is an important industrial raw material for detergents, emulsifiers and wetters and is also found in paints and pesticides [1]. However, NP and its ethoxylated 2

derivatives are known endocrine disrupters, so are listed as priority hazardous substances and most of their uses are heavily regulated [2]. These chemicals are produced in excess of one million pounds per year in the U.S. and thus are classified as high production volume chemicals. Nonylphenol ethoxylates (NPEOs) represent about 80-85% of all Alkylphenol polyethoxylates (APEOs), with an annual consumption estimated at 123,000-168,000 metric tonnes in the U.S. [3]. The APEOs are a mixture of nonylphenol ethoxylates (NPEOs) and octylphenol ethoxylates (OPEOs) with ethoxylate chain lengths ranging from 6 to 20. The toxicity of APEOs tends to increase as the ethoxylate chain length decreases because the short chain ethoxylates, carboxylates and alkylphenolic compounds possess a strong capability to mimic natural hormones by interacting with estrogen receptors [4]. A wide range of aquatic and terrestrial organisms have shown acute and chronic toxicity to NP [5]. Many organisms exhibit endocrine disruptive effects when exposed to NP. Furthermore, this exposure can result in significant upregulation of aromatase, damage to estrogen receptors, a rise of hepatic and plasma vitellogenin concentration and even skewed sex ratio toward female. Thus, the aquatic presence of NP can result in a threat to hormonal balance and reproductive development of organisms [6]; it has been reported that 4Nonylphenol induces apoptosis, autophagy and necrosis in Sertoli cells [7]. Due to the harmful effects of the degradation products of nonylphenol ethoxylates in the environment, the use and production of such compounds have been banned in EU and strictly monitored in many other countries such as Canada and Japan. The main alternatives for NPEOs include linear and branched alcohol ethoxylates, and glucose-based carbohydrates such as alkylpolyglucoside [8]. Although it has been shown that the concentration of nonylphenol in the environment is decreasing, it is still found at concentrations of 4.1 μg L-1 in river water

3

and 1 mg kg-1 in sediments [9]. NP can be bioaccumulated in tissues and organs in the body due to its lipophilic properties [10]. Direct human exposure to NPEOs is usually through the use of cosmetic products such as deodorants, shampoos and makeup. They are also present in municipal, industrial and even agricultural water discharges [11]. In the Czech Republic this pollutant is monitored in 79 places, which shows that the main source is the urban-municipal wastewaters with a content average between 0.113 – 0.2 μg L-1 [12]. Conventional wastewater treatment systems were not designed for this emerging compounds, so they can survive the treatment without degradation and get into the environment [8]. One case studied different treated sludge from Paris, where it was shown that the anaerobic digestion widely used all over the world to stabilize sludge and reduce the quantity of dry matter, has a high removal of alkylphenols (>50%) but only 40% of NP[13]. This is an important and worrying situation because NP shows a risk to human health, as estrogenicity with a wide variety of cell lines and receptors in human MCF7 cells, other studies have shown that the NP could adversely affect brain development and may cause neurodegeneration [1]. Since NP derivatives contain a branched alkyl chain the microbial attack on the molecule is not effective and the traditional biological methods for water treatment provide low removal yields [14]. For example, studies on the degradation by biological treatment of NP in water samples of the Erren river (southern Taiwan) showed a ca. 23% decrease of this compound, however the half-life (t1/2) for NP aerobic degradation varied from 13.6 to 99 days [15]. Therefore, potent technologies are required to achieve higher pollutant reduction; in this sense the use of the advanced oxidation processes (AOP) could be a reliable option. 4

The use of AOPs have advantages for water or wastewater treatment such as: i) a simple and flexible operation permitting easy implementation in existing plants, ii) have a partial or total elimination of organic pollutants, iii) usually develop at atmospheric pressure and standard temperature [16], iv) can be operated with solar irradiation in some process such as TiO2 photocatalysis and photo-Fenton processes to eliminate the operational cost for energy. However, the AOPs also have disadvantages, for example: i) the total mineralization of pollutants in industrial effluents can be expensive due the consumption of large amounts of expensive reactants and ii) in some process like Fenton’s Reagent large amounts of chemicals for acidifying effluents before decontamination and/or for neutralizing treated solutions, also could present parasitic reactions [16]. A previous study reports the use of a suspended catalyst reactor containing titanium dioxide nanoparticles which can degrade NP up to 90% [17]. However, a major drawback of this process is that it requires further separation between suspended catalyst and treated water. Another approach for NP degradation is to use a combined sonolytic-UV process in which the best performance was obtained by applying 3.44 × 10−6 einstein L−1s−1 UV intensities; the greater synergistic effect was obtained at acidic solution conditions [18]. Still, this process requires very specific energy values to reach the synergistic effect. Ozone has also been applied in a continuous-operating activated sludge process, which results in a zero yield of excess sludge using an ozone dose of 100 mg O3 g-1 SS However, since NP has a strong affinity for activated sludge and low biodegradability, NP effluent concentration remains essentially constant [19]. Another study in which the initial concentration of NP was 200 g L-1 indicates that the removal from water using ozone depends

5

on the ozone concentration, i.e., high ozone concentration contributes to a fast degradation, the removal rate is improved at basic pH values (10.34) and high temperatures (30°C) [20]. On the other hand, at high overpotentials in aqueous media, electrochemical oxidation using boron doped diamond electrodes (BDD), led to physisorbed •OH radicals on the electrode surface, which is a strong oxidant (•OH, E°•OH/H2O = 2.80 V vs. SHE) [21]. This methodology is known as electro-incineration [22] and has been successfully applied to destruction of persistent contaminants [23]. Combined processes have been shown to be more economically attractive than simple AOP processes alone [24,25]. For example, in comparing NPEO removal by a combined H2O2/UV-C process versus

Photo-Fenton alone, both were effective, reaching TOC

reductions of 76% and 67%, respectively [26]. Following the same idea, electrochemical advanced oxidation has been coupled with other oxidation processes like photodegradation [27] and biological degradation. Particularly for NP, a recent study indicates that the process of photo-assisted electrochemical oxidation with 250 W and a current density of 10 mA cm2

reduces the NP concentration in aqueous solution by around 70% [28].

This work evaluates a combined ozone-electrooxidation process as an effective treatment with low operational cost, simple operation and low environmental impact. Furthermore, no sludge is generated. 2. Methods and Materials 2.1 Electrooxidation reactor in batch mode A batch cylindrical electrochemical reactor was set up for the electrochemical process. The open reactor contains a BDD anode (Boron Doped Diamond film supported on 6

a niobium substrate) and one stainless steel plate as cathode; each electrode has a surface area of 25 cm2 (5 cm by 5 cm). The capacity of the reactor vessel was 0.25 L, 0.18 L of test solutions containing 50 ppm of NP in 0.05M H2SO4 was used at all experiments [20]. Gentile heating was necessary to dissolve the NP, but the solution was cooled to room temperature (18 ± 0.5 °C) before starting the electrolysis. A direct-current source electrically feed the reactor using current values in the range of 1–3 A, which correspond to a current density of 10, 20 and 30 mA cm-2. The temperature of NP solution increased through the process with initial temperature of 19°C and final temperature of 30°C. Figure 1 shows the set-up of the experiment. Triplicate experiments were carried out at pH values of 3, 5 and 7 and samples were taken at regular intervals during 2 hrs electrolysis to determine COD values. 2.2 Electrooxidation reactor in continuous mode The continuous electrochemical process was carried out in a flow DiaClean® cell model 101 equipped with a BDD electrode as anode (BDD film 2-3 µm supported on silicon substrate) and one stainless steel plate as cathode, each electrode has a surface area of 70 cm2. The separation between electrodes was made with separators provided by the cell supplier that provide a total length of 0.2 cm. This reactor is coupled to a system which operates continuously and in a recirculation mode, pumping the solution with a peristaltic pump (Masterflex B Model 77111-60) and passing through a polypropylene pipe connected by electrofusion (Tuboplus®). The speed of the peristaltic pump was adjusted to obtain an electrolyte flow rate of 12.6 dm3 min-1. The temperature was controlled with a finned heat exchanger tube installed at the reactor outlet; this element let to maintain a constant temperature of the solution during the degradation process, having a temperature of 20-23°C. The feed tank was made of HDPE with a capacity of up 1-10 dm3 where an agitation system (propel agitation motor) was installed which allows us to keep homogeneity of the test 7

solution. The reactor was electrically fed using a direct-current source (GW Laboratory Model, GPS3030D); current values in the range of 1–3 A, which correspond to a current density of 10, 20 and 30 mA cm-2, were used in this study. The sample water for treatment was prepared with distilled water adding 50 ppm of NP and 0.1 M H2SO4 (3 dm3 were used), adjusting the pH values to 3, 5 and 7 with NaOH. Samples were taken at regular intervals during 4 hrs to determine COD and TOC values. Figure 2 shows the experimental arrangements. The experiments were made in triplicate and the values shown are the average of the recorded data.

2.3 Ozonation reactor The ozonation experiments were conducted in a 1.2 L glass batch reactor at room temperature. Ozone was supplied by a Pacific Ozone Technology generator. The gas was fed into the reactor through a porous plate situated at the bottom of the reactor. The sample water (1 L) containing 50 ppm of NP in 0.05M H2SO4 was used in all experiments. Preparation of the test solutions was identical to the one followed in the two previous experiments. The mean concentration of ozone in the gas phase was measured using the indigo technique and keep at 5 ± 0.5 mg L-1[29] . Ozonation experiments were carried out at pH values of 3, 5 and 7 and samples were taken at regular intervals during 2 hrs in order to determine COD. 2.4 Sequenced ozone-electrochemical process For the sequenced ozone-electrochemical process, the sample (3 dm3) was divided into three batches; each one was treated for 30 minutes with ozone (section 2.3) before the 8

electrochemical treatment at pH 7. Next, the 3 batches were mixed in the feed tank of the electrolysis system (Fig 2). The second treatment was carried out in the continuous electrolysis system (section 2.2) for 90 minutes. A current density of 30 mA cm-2 was used. Samples were taken at regular intervals along the two steps of the process to determine COD and TOC values. The experiment was done in triplicate and the values shown are the average of the recorded data. 2.5 Physicochemical Analysis Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) were determined using the American Public Health Association standard procedures [30], using a Hach DR 5000 and a TOC-L Shimadzu Total Organic Carbon analyzer, respectively. The COD and TOC removal efficiency (%) at the different treatments were calculated as shown in Eq. 1.

𝐸=

𝐶0 − 𝐶𝑡 𝐶0

𝑥 100

(1)

Where E is the COD or TOC removal efficiency (%), C0 is the initial value of the COD or TOC (mg L-1) in the solution of Nonylphenol and Ct is the value of COD or TOC (mg L-1) at time t after the different treatments. For COD analysis 2 mL of sample were added to the Hatch tubes (21259 vial digestion, 20-1500 mg L-1 range), whereas for TOC, 10 mL sample were analyzed. The analysis was carried out before (crude sample) and during treatment at different time intervals.

2.6 Cyclic voltammetry experiments The cyclic voltammetry of the NP solution at different times of coupled treatment were performed using a standard three-electrode cell. The waveforms and potential were applied 9

by Autolab PGSTAT302N software GPES Manager version 4.9. A graphite electrode was used as the working electrode with the surface renewed through light polishing after each potential scan. The scan rate was 100 mV s-1 with an Ag/AgCl reference electrode and platinum counter electrode. The cyclic voltammetry was obtained by starting the potential scan in the positive direction.

2.7 UV-Vis spectrum NP degradation and the formation of other intermediates were spectrophotometrically monitored between 200 and 600 nm, using a PerkinElmer spectroscope and a 1 cm quartz cell. The spectrums were taken from the sample of NP solution without the treatment and during treatment at different time intervals.

3. Results and discussion 3.1 Electrochemical behavior of nonylphenol Cyclic voltammetry experiments of NP in 0.1 M H2SO4 at pH 3 on graphite showed a signal very close to the anodic and cathodic barriers which doesn’t produce a clear peak, but does modify the barrier shape. This indicates that the compound is oxidized at the electrode at potential values close to 2.0 V. At this value the organic compound must be oxidized directly at the electrode and on the BDD electrode by ●OH radicals produced at the surface giving a mixed oxidation process.

3.2 Electrochemical treatment in batch mode Different currents densities (ρ) were applied to investigate the electrochemical degradation of NP in a batch cell. The UV-Vis spectra were recorded during 120 min showing 10

the formation of organic intermediates depends on the current density applied. Thus, when 10 mA cm-2 was used the absorbance after 10 minutes of electrolysis was higher than the initial value, whereas when 30 mA cm-2 was applied after ten minutes the absorbance recorded was almost half of the initial value (Fig 4). At low current density (ρ) values quinonic intermediates, with high molar absorptivity coefficient should be formed, while at high current density (ρ), the degradation may form low chain carboxylic acids which have almost no absorbance. This behavior has been observed during the anodic degradation of phenol on BDD where the TOC removal is dependent of the current density applied [30]. At 30 mA cm-2 the initially formed intermediates are rapidly degraded during the electrolysis and after 120 min no signal was present indicating that the quinonic intermediates were already consumed (Fig 4 insert).

This behavior was confirmed by the COD analysis. Figure 5 shows that the COD removal increases as a function of electrolysis time and the removal rate increased when the applied current density is raised. The COD removal after 100 min of electrolysis was 57 % for 10 mA cm-2, 74% for 20 mA cm-2 and 87% for 30 mA cm-2. The results indicate that current density (ρ) is a key parameter in the removal of NP and degradation products. After 100 minutes of electrolysis all of the density current values stabilize. Higher current density values may generate a strong change of pH or excessive consumption of electricity. Fig. 6 shows the effect of the pH on the electrochemical degradation of NP. The pH of the solution has a significant effect on the amount of the COD removal. The COD decrease is 87%, 53% and 47% for pH 3, 5 and 7, respectively. As has been proposed by the electroanalytical experiments, degradation has two pathways: the direct electrolysis and the ●OH radical 11

oxidation. It has been reported that the latter is favored at low pH values thus, at pH of 3 the ●OH radical degradation must be faster that the direct electrolysis at removing the organic compounds [31,32].

The reaction kinetics of the electrochemical treatment of NP was adjusted to a first order model, obtaining a value for the rate constant k of 0.0188 min-1 (1.09 h-1). Therefore, one hour is required to achieve good (67%) COD removal. This observation correlates with the UV-Vis spectra obtained during the treatment, where after one hour the peaks observed disappear. After this time the COD removal doesn’t change significantly, remaining essentially the same through 120 min. This asymptotic trend in the curve of COD can be attributed to the presence of low molecular weight carboxylic acids which are among the final degradation products of NP. They are electrochemically stable species due to their high oxidation potential, making it difficult to degrade them with low current densities, limiting the total mineralization of NP [30].

3.3 Electrooxidation of NP in continuous mode The electrochemical treatment of NP was studied in the continuous reactor using the optimal conditions (pH 3 and 30 mA cm-2), obtaining an 83% removal of COD and 87% TOC in 4 hrs as shown in Figure 7.

3.4 Ozone treatment 12

During the ozonation treatment of the nonylpnenol solution, UV-Vis spectra were taken (Fig 8), and the typical absorption peak of nonylphenol located at 275-278 nm (t=0) moved completely after 10 min to 300 nm. This behavior contrasts with the one observed in the electrochemical BDD reactor where other species are being generated by the interaction with ozone and absorb at a higher wavelength. This species is oxidized by the ●OH radicals produced by ozone in basic media until its degradation. Nevertheless, 120 min is not enough time to totally consume this derivative.

COD values during ozonation were monitored as a function of treatment time at different pH values. As shown in Figure 9, COD reductions were 67%, 81% and 96% for pH 3, 5 and 7, respectively after 120 min of treatment. The pH value in the solution plays an important role in the degradation of pollutants using ozonation. At low pH, the direct electrophilic attack by molecular ozone is the predominant reaction mechanism occurring. At high pH, ozone decomposes in water forming •OH radicals which are stronger oxidizing agents than molecular ozone and favor degradation. These radicals induce the so-called indirect ozonation. Indirect ozone oxidation is non-selective and overall faster than direct ozonation [33]. Both reaction mechanisms lead to either mineralization or transformation of organics by formation of products with higher oxygen content. Therefore, it is possible to propose that in acidic media electrochemical degradation is faster than ozone treatment. For example, at 60 min of treatment, ozone showed a COD reduction of about 30% (Figure 8), whereas electrochemical reduction was 70% (Figure 6). This is confirmed by the reaction kinetics determination for ozone treatment, which adjusts to a first order model, obtaining a

13

value for the rate constant k of 0.0257 min-1 (1.54 h-1), therefore almost two hours are required to obtain 70% of degradation.

3.5 Electrochemical and Sequenced Ozone-electrochemical continuous treatment

The COD and TOC removal using the electrochemical process in continuous mode without O3 treatment takes twice as much time as that for the combined process, shown in Fig. 10.

The results and discussion presented in sections 3.1 to 3.5 indicate that NP degrades at different rates and conditions among the selected processes. However, the use of a sequenced ozonation-electrochemical process has significant advantages over the single treatment such as: higher NP degradation, increased reaction time and the possibility to perform the process in a continuous mode.

3.6 Associated Cost Table 1 shows the operational cost of the three different processes presented in this study under the best conditions: electrochemical process (pH 3 and 30 mA cm-2), ozonation process (pH 7 and 5 ± 0.5 mg L-1 of ozone ) and sequenced ozone-electrochemical. The power was calculated using Eq. 2. The energy in kilowatt-hour were obtained from Eq. 3., and the cost of operation is calculated with Eq. 4., 𝑃=

𝐼∗𝑉

(2)

1000

14

Where P is the power where P is the power in kW (kilowatt), I is the current intensity in A (amper), and V is the electric potential in V (volt). 𝐸 =𝑃∗𝑡

(3)

Where E is the energy in kWh (kilowatt-hour) and t is the time of the process in h (hour). 𝐶𝑜𝑠𝑡 = 𝐸 ∗ $𝑘𝑊ℎ

(4)

Where Cost is the operation cost of the reactors, E is the energy in kWh and $kWh is the cost . The average cost per kWh in Mexico to industries at August 2017 is $2.024 (CFE Federal Electricity Commission)

According to the Table 1 the sequenced ozone-electochemical treatment result no only faster that the electrochemical process, but also less energy consumption, resulting in a lower operational cost that electrochemical process and ozonation process presented in this study.

The sequenced ozone-electrochemical process is compared with another process, namely UV/O3 process [29], as indicated in Table 2. Note that the sequenced ozone-electrochemical process shows the best removal rate, less energy consumption which results in a lower operational cost, making it an attractive alternative for the treatment of persistent pollutants.

4. Conclusions NP in aqueous solution can be treated using ozone and electrochemical oxidation. However, the pH conditions required to achieve optimal conditions are different, the 15

electrochemical process requires acidic conditions whereas the ozone works better at neutral conditions. Using a diacell reactor the treatment can be performed continuously allowing higher volumes and concentrations. When ozonation is performed the continuous electrochemical treatment is faster and requires less energy. A cost comparison between the three processes reveals that the use of the sequenced treatment reduces the cost. Furthermore, when the cost of the sequenced process is compared against other process (UV/O3) the cost reduction is significant making the proposed system an attractive alternative for the treatment of persistent pollutants.

5. Acknowledgements The economical support through project CONACYT 252496 is recognized. The authors also thank the technical support of Citlalit Martinez Soto.

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Fig 1. Scheme of the batch mode electrolysis system. 1) DDB anode, 2) stainless steel plate cathode, 3) direct-current source

Fig 2. Scheme of the continuous and recirculation mode electrolysis system. 1) feed tank, 2) peristaltic pump, 3) direct-current source, 4) reactor, 5) sampling faucet, 6) heat exchanger tube, 7) propel agitation motor. 22

Fig 3. Cyclic voltammetry of nonylphenol in H2SO4 0.1 M at pH 3 on graphite electrode.

Fig 4. UV-Vis curves of the electrolysis solution after 10 min of degradation at different current densities. Insert: UV-Vis of the nonylphenol at initial (50 ppm) (─) and final treatment time (120 minutes) (─ ─) at ρ=30 mAcm-2 23

Fig 5. Effect of current density value (◊) 10 (■) 20 and (○) 30 mA cm-2 at pH=3 on the COD removal

Fig. 6. Effect of pH value on COD (◊ ) 3 (■) 5 and (○) 7 using 30 mA cm-2.

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Fig 7. A) COD removal during the electrochemical treatment of NP in continuous reactor (pH=3 and 30 mA cm-2); B) TOC removal during the electrochemical treatment of NP in continuous reactor (pH=3 and 30 mA cm-2).

25

Fig 8. UV-Vis curves of the ozonation treatment of nonylphenol 50 ppm solution after 10 min of degradation at different current densities pH=7.

Fig. 9. Effect of pH (◊) 3, (■) 5 and (Δ) 7 on the % COD removal of nonylphenol solution (50 ppm) vs ozonation time (min).

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Fig. 10 A) COD (◊) removal during the electrochemical treatment of NP in continuous reactor (pH=3 and 30 mA cm-2) and (■) coupled ozone-electrochemical process (pH =7 and 30 mA cm-2); B) TOC (◊)removal during the electrochemical treatment of NP in continuous reactor (pH=3 and 30 mA cm) and (■) coupled ozone-electrochemical process (pH =7 and 30 mA cm-2).

2

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Treatment Sequenced ozone-electrochemical process Electrochemical process

Ozonation process Ozonation

Electrochemical

P (kW)

0.0168

0.3

0.3

0.0168

E (kWh)

0.0672

0.6

0.05

0.0112

Cost $

0.1360128

1.2144

0.1012

0.02226

TOTAL COST ($/L)

0.1360128

1.2144

0.1234

Table 1. Operation cost of reactors in the three diferent process for degradation of NP: Electrochemical process (I = 2.1A, V =8Vand t= 4 hours), ozonation process (P= 0.3W and t= 2 hours) and sequenced ozone-electrochemical process (ozone: P= 0.3W and t= 0.5 hours; electrochemical: I= 2.1A, V=8V and t= 1.5hours).

Treatment

% Removal

t (hours)

Consumption of energy (kWh)

Cost ($/L)

Sequenced ozoneelectrochemical process

91

2

0.061

0.124

UV/O3 process [29]

86

2

1.806

3.656

Table 2. Comparison of operation cost of sequenced ozone-electochemical with UV/O3 process a

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