Enhancement of photocatalytic activity of TiO2 by immobilization on activated carbon for degradation of pharmaceuticals

Accepted Manuscript Title: Enhancement of photocatalytic activity of TiO2 by immobilization on activated carbon for degradation of pharmaceuticals Author: Mohamed Gar Alalm Ahmed Tawfik Shinichi Ookawara PII: DOI: Reference:

S2213-3437(16)30102-6 http://dx.doi.org/doi:10.1016/j.jece.2016.03.023 JECE 1025

To appear in: Received date: Revised date: Accepted date:

23-12-2015 12-3-2016 12-3-2016

Please cite this article as: Mohamed Gar Alalm, Ahmed Tawfik, Shinichi Ookawara, Enhancement of photocatalytic activity of TiO2 by immobilization on activated carbon for degradation of pharmaceuticals, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece.2016.03.023 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.

1 2

Enhancement of photocatalytic activity of TiO2 by immobilization on activated carbon for degradation of pharmaceuticals

3

Mohamed Gar Alalma* [email protected], [email protected], b c [email protected], Ahmed Tawfik , Shinichi Ookawara

4 5 6 7 8 9 10 11 12 13

a

Department of Public Works Engineering, Faculty of Engineering, Mansoura University, Mansoura, 35516, Egypt b

Department of Environmental Engineering, School of Energy, Environmental, Chemical and Petrochemical,, Egypt-Japan University of Science and Technology (E-Just), New Borg El Arab City, 21934, Alexandria, Egypt c

Department of Chemical Engineering, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 1528552, Japan *

Corresponding author. Tel. fax. +2-03-4599520

14

1

15

Abstract

16

This work evaluates the photocatalytic activity of bare TiO2 and TiO2 immobilized

17

on activated carbon (TiO2/AC) for degradation of pharmaceuticals. Four selected

18

pharmaceuticals namely amoxicillin, ampicillin, diclofenac, and paracetamol were

19

oxidized using solar irradiation. The TiO2/AC composite was prepared by a

20

temperature impregnation method. Characterization of TiO2/AC by Brunauer–

21

Emmett–Teller (BET) analysis, Fourier transforms infrared spectroscopy (FTIR),

22

and scanning electron microscope (SEM) revealed successful immobilization of

23

TiO2 particles on activated carbon. Amoxicillin and ampicillin were completely

24

degraded by TiO2/AC, while 89% of amoxicillin and 83% of ampicillin were

25

removed by bare TiO2. Likely, TiO2/AC attained higher removal of diclofenac

26

(85%) and paracetamol (70%) as compared to bare TiO2. Amortization and

27

operating costs of full scale solar photocatalytic reactor were estimated. It was

28

found that TiO2/AC is more economic.

29

Keywords: Solar; photocatalytic; pharmaceuticals; TiO2; TiO2/AC

30

2

31

1. Introduction

32

The pharmaceutical industrial facilities produce various products which are used

33

for human and animal medications [1]. Unfortunately, wastewater generated from

34

pharmaceutical industries contains non-biodegradable organics such as drugs and

35

antibiotics which are ineffectively removed by conventional wastewater treatment

36

systems [2–4]. Therefore, treatment of pharmaceutical wastewater is urgently

37

needed for prior treatment before being released into water streams in order to

38

avoid

39

pharmaceuticals are not only found in pharmaceutical industrial wastewater but

40

also low concentrations of different pharmaceuticals were detected in municipal

41

wastewater, surface water and ground water [5,6]. Among all the pharmaceutical

42

compounds that may be harmful to the environment, scientists expressed serious

43

concerns about antibiotics and drugs because of their high consumption rate in

44

both veterinary and human medication [7,8]. In addition, the widespread presence

45

of antibiotics in low concentration leads to development of antibiotic resistant

46

bacteria [9].

47

Biological treatment is preferable due to its low cost. However, the presence of

48

toxic and bio-recalcitrant chemicals detracts the viability of biological treatment

49

process for treatment of pharmaceutical wastewater [10,11]. Advanced oxidation

50

processes (AOPs) have been realized as particularly efficient technologies for

51

treatment of toxic wastewater and non-biodegradable organics [12–14]. In AOPs

52

powerful reactive species like hydroxyl radicals (•OH) are generated by specific

53

chemical reactions in aqueous solutions [15]. Hydroxyl radicals are able to destroy

54

the most resistant organic molecules and break them down into relatively less

55

persistent organics and end products such as CO2 and H2O [16]. Among AOPs,

56

heterogeneous photocatalysis using artificial ultraviolet (UV) light source or solar

57

irradiation has been recognized to be effective for the degradation of several types

serious

environmental

problems.

Researchers

have

found

that

3

58

of

59

pharmaceuticals [17]. In heterogeneous UV/TiO2 processes, ultraviolet light (λ<

60

400nm) is utilized as an energy source and TiO2 acts as a semiconductor photo-

61

catalyst[18–20]. Nano-scale TiO2 is distinctive with big surface area, good particle

62

size distribution, high chemical stability, and the possibility of using sunlight as a

63

source of irradiation [12]. In photocatalysis process, the photons with energies

64

higher than the band-gap energy cause excitation of valence band (VB) electrons

65

which then enhance the reaction of TiO2 with organic molecules [21]. Illumination

66

of the catalyst active sites with sufficient energy produces positive holes (h+) in the

67

valence band and in electrons (e-) in the conduction band. The positive holes

68

oxidize either the organic pollutants or H2O to induce hydroxyl radicals [7,22].

69

Many researchers investigated immobilization of TiO2 nano particles on different

70

support materials to improve the photocatalytic activity and make the separation of

71

treated effluent more effective [23–25]. Coating surfaces with TiO2 has relatively

72

low improvement on photocatalytic reaction because of the low particles

73

dispersion and limited mass transfer between the pollutants molecules and the

74

catalyst [26,27]. Catalysts can be more effective and easily separated from the

75

effluent if they are supported on adsorbent surface such as powdered activated

76

carbon (PAC) [28–30]. Activated carbon (AC) has no photocatalytic activity but it

77

certainly enhances the photocatalytic reaction between TiO2 and the contaminants

78

due to the adsorption of pollutants on its surface [31,32]. Increased adsorption

79

contributes to higher concentration of contaminants around TiO2 active sites [33].

80

Activated carbon has a good developed pore structure, very large surface area, and

81

high adsorption capacity. Therefore, it is widely used as an adsorbent for organic

82

and inorganic pollutants [34]. The AC in the TiO2/AC catalyst would act as a

83

reaction station where organic molecules are adsorbed before transferring to the

84

decomposition center [32,35]. Many researchers used Langmuir–Hinshelwood

persistent

organics

such

as

phenolic

compounds,

pesticides,

and

4

85

model to describe the kinetics of photocatalytic degradation of different organics in

86

aqueous solutions [36]. The model basically relates the rate of degradation (r) and

87

concentration of substrate (C) in water at reaction time (t) [37].

88

The main objective of this investigation is to assess the efficiency of solar

89

photocatalytic oxidation process using TiO2 versus TiO2/AC for degradation of

90

pharmaceuticals. Two antibiotics namely amoxicillin and ampicillin and two

91

prevalent drugs (diclofenac and paracetamol) were used as model substrates.

92

TiO2/AC catalyst characterization was carried out and factors affecting on the

93

photo degradation process such as pH and catalyst loading were extensively

94

studied. Furthermore, the pseudo-first order kinetic reaction was tested according

95

to the Langmuir–Hinshelwood model.

96 97

2. Materials and methods

98

2.1 Chemicals

99

Amoxicillin, ampicillin, paracetamol, and diclofenac were purchased from Glaxo

100

Smith Kline. The TiO2 and powdered activated carbon (AC) with bulk density of

101

0.37 g/cm3 in Nano scale was obtained form from Acros and Adwic respectively.

102

2.2 Catalyst preparation

103

Immobilization of TiO2 on activated carbon (AC) was executed according to the

104

high temperature impregnation method described by El-Sheikh et al [38]. A slurry

105

of 20 g TiO2 was heated and stirred with 300 ml of distilled water at a temperature

106

of 70˚C. AC was added with a ratio of TiO2 being 1:2 respectively. The mixture

107

was continuously stirred for 120 minutes at a temperature of 70˚ C. The dark black

108

color of AC and white color of TiO2 were observed at the beginning at which the

109

mixture was gradually changed into a gray color. This observation implies that the

5

110

interaction between AC and TiO2 certainly occurred. The mixture was settled for

111

15 minutes and then the supernatant was decanted and the precipitate was dried in

112

the oven at a temperature of 200˚ C for 12 hrs.

113

2.3 Photocatalysis experiments

114

Photocatalysis experiments were carried out using a solar reactor equipped with

115

compound parabolic collectors (CPCs). The reactor was placed at the city of Borg

116

Alarab, Egypt (Latitude 30°52’, Longitude 29°35’). The reactor consists of six

117

borosilicate tubes (0.36 m2) with a diameter of 2.5 cm and a length of 75 cm

118

mounted on curved polished aluminum sheets with radius of curvature 9.2 cm. The

119

module was fed with pharmaceutical mixtures in a closed cycle. The feed stock of

120

pharmaceuticals solution was continuously circulated in a closed cycle in the

121

module. A schematic diagram of the experimental set-up is shown in Fig 1. The

122

reactor was initially fed with 4 L of a pharmaceutical solution (50 mg/l) for a

123

period of 210 minutes. The first 30 minutes was used to assess the adsorption

124

process without illumination and 180 minutes for photocatalytic process. TiO2 or

125

TiO2/AC were used as catalysts. Effects of pH values, TiO2 and TiO2/AC dosage

126

were investigated. The pH value of the mixture was changed from 3 to 10 using

127

H2SO4, and NaOH (50%). TiO2 and TiO2/AC dosages varied from 0.2 to 0.8 and

128

from 0.4 to 1.6 g/L respectively. The solar irradiation was measured by Met, one

129

Portable Weather Station (Model Number 466A). The normalized illumination

130

time (t30w) was used to compare between photo-catalytic experiments instead of

131

exposure time (t). The normalized illumination time was calculated by the

132

following equations [16,39]:

133

t30w,n  t30w,n1  tn UV / 30 Vi / Vt 

(4)

134

6

135

tn  tn – tn1

136

Where tn : contact time, UV : average solar ultraviolet radiation (W/m2) measured

137

during ∆tn, t30W : the normalized illumination time, which refers to a constant solar

138

UV power of 30W/m2 (typical solar UV power on a perfectly sunny day around

139

noon), Vt : the total reactor volume and Vi : the total irradiated volume.

140

2.4 Analytical methods

141

The concentrations of pharmaceuticals were quantified by Shimadzu HPLC using

142

C-18 phenomenex reverse phase column, degasser (20A5), pump (LC-20AT), and

143

prominences Diode Array Detector (SPD-M20A). The samples were filtered by

144

micro syringe filters (0.2 µm). The mobile phase was (60:40) 0.025M KH2PO4

145

buffer solution in ultrapure water and acetonitrile. The flow rate was 0.50 mL/min

146

and the temperature was 60˚C. For characterization of TiO2 deposition on activated

147

carbon, FTIR spectra were recorded on a VERTEX 70 spectrometer over the wave

148

number range 3800-400 cm-1 using KBr pellets for sample preparation. Scanning

149

electron microscope (SEM) images were taken with a JEOL 611. Pore size and

150

surface area of the catalyst were determined by Brunauer–Emmett–Teller (BET)

151

analysis using Belsorp-max automated apparatus using liquid N2 adsorption at a

152

temperature of 77 K.

153

2.5 Kinetic study

154

The model of Langmuir–Hinshelwood was used to relate the rate of degradation (r)

155

and concentration of substrate (C) in water at reaction time t. The model can be

156

expressed by the following equation [40];

157

r 

dC Kr Kad C  dt 1  Kad C

(2)

(3)

7

158

Where kr : the rate constant and Kad : the adsorption equilibrium constant. In the

159

process of photocatalysis when the adsorption is relatively weak like and/or the

160

reactant concentration is low, Equation (3) can be simplified to the pseudo- first

161

order kinetics with an apparent first-order rate constant kapp [36]:

162

C  ln  0   Kr Kad t  Kappt C

163

Where C0: is the initial concentration of pharmaceuticals.

(4)

164 165

3. Results and discussion

166

3.1 Characterization of TiO2/AC

167

The results of Brunauer–Emmett–Teller (BET) analysis for AC and TiO2/AC are

168

summarized in Table. 1. The specific surface area of AC was decreased from

169

1325.23 to 849.2 m2/g by impregnation of TiO2 into its surface, which certainly

170

attributed to the deposition of TiO2 on the pores and external surface of AC. The

171

decreasing of the surface area of the TiO2/AC can be interpreted in terms of the

172

calcinations at high temperature (200˚ C) which induced the formation of anatase

173

TiO2 on the surface and the pores of activated carbon [38]. In addition, total pore

174

volume of AC was slightly decreased from 0.8645 to 0.7804 cm3/g after the

175

deposition of TiO2. However, mean pore diameter of AC increased from 2.57 to

176

3.74 nm after the deposition process. Both processes mainly occurred due to the

177

partial pore collapse and shrinkage after impregnation at high temperature that may

178

lead to discrepancies in pore structure from micropores to mesopores [41].

179

Furthermore, the larger pore size is mainly caused by the formation of inter-

180

agglomeration particles [42].

8

181

The (SEM) images of naked activated carbon and the composite of TiO2/AC are

182

shown in Figs. 2a and b. The images show that the naked activated carbon

183

particulates have irregular shapes (Fig. 2a). Moreover, the surface of the activated

184

carbon particulates is rough with heterogeneous pores, which certainly indicates a

185

high prospect for TiO2 to be entrapped and adsorbed onto the surface and the pores

186

of activated carbon. For the TiO2/AC, The SEM image (Fig.2b) shows that TiO2

187

particulates are uniformly immobilized on the surface of activated carbon. It can be

188

seen that the supported TiO2 which appears in image by gray color covered most

189

of the surface of activated carbon, and also it is reported that some of TiO2 could

190

deposit in the mesopores and macrospores of activated carbon [29]. Since the

191

photocatalysis process strongly depends on light intensity, deposition of TiO2 on

192

the external surface of AC will undoubtedly provide more chance to be exhibited

193

to light and subsequently will improve the photocatalytic degradation process.

194

Moreover a high content TiO2 on the external surface of activated carbon is

195

favored to enhance and accelerate the photocatalytic activity of the catalyst [35].

196

The spectra of Fourier transform infrared spectroscopy (FTIR) spectra of AC, and

197

TiO2/AC are illustrated in Fig. 3. The spectrums revealed that the impregnation of

198

TiO2 with the activated carbon produced a broad peak from 400 to 800 cm-1 which

199

could be attributed to the formation of bulk Titania framework on the surface and

200

the pores of activated carbon [19]. This result indicated a good interaction between

201

the activated carbon surface and titanium dioxide. In addition, the peak at 1650 cm-

202

1

203

appeared in the spectrum of TiO2/AC. This shift was probably caused by the Ti-O-

204

C band owing to the electron affinity of carbon when using hydrothermal methods

205

in preparation of TiO2/AC [28]. The peak at 2382 cm-1 which refers to O–H

206

stretching [43] became smaller after TiO2 immobilization. Moreover, the band at

assigned to –OH vibration was shifted to 1585 cm-1. A new peak at 1165 cm-1

9

207

3400 cm-1 that assigned to –OH stretching [44] was disappeared in TiO2/AC

208

spectra.

209

3.2. Photocatalytic degradation by bare TiO2

210

Fig.4 depicts the efficiency of TiO2 photocatalytic degradation of pharmaceuticals

211

(amoxicillin, ampicillin, diclofenac, and paracetamol). The obtained results

212

indicated that the removal efficiencies of amoxicillin, ampicillin, diclofenac, and

213

paracetamol after 30 minutes without illumination were 5%, 4% 5% and 6% which

214

are considered very limited comparing to the removal in illumination period. The

215

removal of pharmaceuticals during the first 30 minutes was mainly due to

216

adsorption of pharmaceuticals on the catalyst active sites. The photocatalytic

217

degradation after the illumination is allowed was influenced by irradiation time as

218

shown in Fig 4. The major portion of pharmaceuticals was removed by TiO2

219

photocatalysis during the first 90 minutes of irradiation (86 % for amoxicillin, 72%

220

for ampicillin, 58% for diclofenac, and 40% for paracetamol). The higher

221

degradation rates at the first 90 minutes are attributed to the abundance of hydroxyl

222

radicals. In the second 90 minutes of irradiation the degradation rates were

223

diminished which resulted in final removal efficiency of 89 % for amoxicillin,

224

83% for ampicillin, 68% for diclofenac, and 57% for paracetamol. This can be due

225

to the exhausting of the active sites of the catalyst and hence the produced

226

hydroxyl radicals were completely consumed at the late stages of the reaction. The

227

difference in photocatalytic degradation efficiency from pharmaceutical to another

228

is attributed to the adsorbability of pharmaceutical molecules towards the active

229

sites of TiO2 where the hydroxyl radicals are available.

230

3.3. Photocatalytic degradation by TiO2/AC

231

The degradation of pharmaceuticals by TiO2/AC is shown in Fig. 5. The

232

elimination of pharmaceuticals in the dark process by TiO2/AC was higher than

10

233

bare TiO2 resulting in removal efficiencies of 17% for amoxicillin, 9 % for

234

ampicillin, 10% for diclofenac, and 11% for paracetamol. This indicates that the

235

adsorption capacity of TiO2 /AC is substantially higher than naked TiO2 as

236

expected[45]. During the first 90 minutes of irradiation high degradation rates of

237

pharmaceuticals were observed. This founding is due to the free surface of

238

activated carbon at early stage which led to higher adsorbability of the catalyst. In

239

addition, at early stage of the process there is abundance of hydroxyl radicals near

240

the surface of the catalyst. Nevertheless, the produced hydroxyl radicals are

241

completely consumed at the late stages of the reaction which diminished the

242

photocatalytic degradation rates as shown in Fig. 5. Complete degradation of

243

amoxicillin was attained after 120 minutes of irradiation. This was better than

244

naked TiO2 as 89% of amoxicillin was removed after 150 minutes of irradiation.

245

This indicates that TiO2/AC does not only attain higher degradation efficiency of

246

amoxicillin but also accelerate the photocatalytic process. Similar trends were

247

observed for the removal of ampicillin, diclofenac, and paracetamol. Apparently,

248

the immobilization process enhanced the reaction between the produced hydroxyl

249

radicals and the amoxicillin molecules on the surface of TiO2/AC because the

250

attraction of pharmaceutical molecules to the catalyst active sites has been

251

increased. Moreover, the variation in degradation efficiency of pharmaceuticals

252

can be attributed to the different affinity to the binding sites on the catalyst. The

253

enhancement of photocatalytic degradation of pharmaceuticals by using TiO2/AC

254

is in accordance with the finding of other researchers who examined the

255

immobilization of TiO2 on activated carbon for removal of different organic

256

compounds [30,32,46,47].

257

Comparing these results with our previous work for degradation of the same

258

pharmaceuticals by solar photo-Fenton process [1], it is found that photo-Fenton

259

process is more effective. Complete degradation of all pharmaceuticals was

11

260

attained after irradiation time ranged between 60 and 120 minutes. In addition,

261

there is no big difference in the estimated costs as shown in part 3.5. However,

262

there are some problems associated with photo-Fenton process. First, photo-Fenton

263

process is favored at lower pH (optimum pH≈3) which may cause some problems

264

such as corrosion of mechanical facilities and it needs neutralization stage. Second,

265

traces of iron remained in the treated effluent [48]. Third, considerable amount of

266

sludge is produced during Fenton process. On the other hand, there is no

267

considered sludge produced during photocatalysis process and the remained

268

amount of TiO2 is not harmful to the environment. For all these reasons,

269

photocatalysis may be preferred in spite of the lower efficiency.

270

3.3. Parameters affecting photocatalytic degradation

271

3.3.1. Effect of initial pH on degradation efficiency

272

The pH of the solution affects the surface charge of activated carbon, TiO2, and the

273

dissolved organic molecules. Subsequently adsorption, and photocatalysis process

274

are affected [26,49,50]. Fig. 6 shows the effect of initial pH on the degradation

275

efficiency of pharmaceuticals. Complete removal of amoxicillin and ampicillin

276

was achieved at pH 10. However, the removal efficiency was dropped at pH values

277

ranging from 3 to 5 as shown in Fig 6a and b. Similar was observed for diclofenac,

278

and paracetamol which the removal efficiencies were decreased from 82% and

279

70% at pH value of 10 to 60% and 58% at pH 3 respectively. The effect of pH on

280

degradation of pharmaceuticals can be explained in terms of the ionization state of

281

the TiO2 and the substrate. The surface charge of the activated carbon and the

282

loaded catalyst depends on the zero point of charge (pHpzc) and the pH of the

283

solution. The surface charge of the adsorbent is negative and its surface functional

284

group is protonated by the H+ ions from the dissolved matter in the solution at pH

285

˃ pHpzc,. On the contrary, at pH ˂ pHpzc, the surface charge of the adsorbent is

12

286

positive and the functional groups is deprotonated by the excess of OH- ions [51].

287

In literature [7] the zero point of charge of TiO2 is 6.4. Accordingly, increasing

288

the pH of the solution changed the surface charge of TiO2 from positive to

289

negative. The pHpzc of the activated carbon is reported to be between 3 and 7

290

regarding to the preparing method and the used material [43,45,52]. On the other

291

hand, amoxicillin has a negative charge when the pH is lower than 5 [53]. In the

292

acidic conditions, amoxicillin, free active sites of carbon and TiO2 particulates are

293

positively charged which led to repulsive forces between amoxicillin and the

294

catalyst which inhibited the degradation.

295

At alkaline conditions the catalyst and pharmaceuticals are negatively charged.

296

This also produces repulsive forces which detract the adsorption on the active sites

297

of the catalyst. The observed enhancement in degradation efficiency of amoxicillin

298

on higher pH could be attributed to the increasing of hydroxyl radicals production

299

in alkaline conditions because of the availability of hydroxyl ions production on

300

TiO2 surface which can be oxidized to form more hydroxyl radicals [7]. This

301

finding is in accordance with other researchers who investigated the effect of pH

302

on photocatalytic oxidation of pharmaceuticals [53–55].

303

3.3.2. Effect of catalyst loading

304

The effect of dosage of TiO2/AC on the removal efficiency of pharmaceuticals is

305

shown in Fig. 7a. The results obtained revealed that photocatalytic degradation

306

performance was substantially improved with increasing the amount of TiO2/AC

307

and reached a plateau at a dosage of 1.2 g/L. This finding is mainly due to the

308

increasing of active sites of activated carbon and TiO2 by providing a higher

309

amount of catalyst. Consequently, the production of electron-hole pairs on the

310

surface of TiO2 and the high reactive hydroxyl radicals was improved [56].

311

Increasing the dosage of TiO2/AC up to 1.6 g/L attained a slight improvement in

13

312

degradation process in spite of the increasing of the active sites. This finding can

313

be attributed to the decreasing of light penetration due to higher turbidity. Fig 7.b

314

depicts the effect of TiO2 loading on the removal of pharmaceuticals. Increasing

315

the amount of TiO2 substantially improved the degradation efficiency of

316

pharmaceuticals due to the enhancement of production of hydroxyl radicals.

317

However, the loading of TiO2 more than 0.6 g/L led to more turbidity of the

318

solution because TiO2 particulates are very fine. Subsequently, a smaller amount of

319

the TiO2 in the suspension was activated only near the reactor wall, where the

320

sunlight can penetrate [57]. Moreover, increasing the TiO2 loading may deactivate

321

the previously activated particulates by collision with ground-state catalysts.

322

Moreover, agglomeration and sedimentation of TiO2 may also occur under large

323

amount of loadings which leads to lower surface area [58].

324

3.4. Degradation kinetic studies

325

Fig.8 shows the linear relationship between ln (C0/C) and irradiation time. Kapp and

326

R2 were calculated for TiO2/AC and TiO2 which are illustrated in Table 2. The

327

photocatalytic degradation by TiO2/AC shows high reaction rates compared to the

328

TiO2 which confirms the enhancement of photocatalytic performance by

329

immobilization of TiO2 on activated carbon. Moreover the high correlation

330

coefficient values revealed that the photocatalytic degradation of the used

331

pharmaceuticals strictly followed Langmuir–Hinshelwood model.

332

3.5 Economic evaluation

333

The design and construction of industrial wastewater treatment plant are certainly

334

influenced by the efficiency of contaminants removal, and the costs of different

335

alternatives [59]. Estimation of construction and operation costs depends on the

336

optimization of operational conditions i.e., irradiation time and dosage of

337

chemicals [60].

14

338

In this investigation, capital and running costs of photocatalytic oxidation process

339

by TiO2 and TiO2/AC were assessed. The results obtained from the experimental

340

work were used to estimate the costs of treatment plant with a capacity of 30 m3/d

341

and contaminated of 100 mg/L of one pharmaceutical. The capacity (C ) of the

342

proposed wastewater treatment plant is estimated using equation (5) [61].

343

C Vt

tt tw D

5

344

Where Vt: volumetric treated wastewater in one year, tt: operation time for the

345

treatment plant facilities in one batch, tw: working time per day for wastewater

346

treatment plant, and D: the number of working days in a year. The ratio between

347

treatment time and working time was assumed 35% which corresponded to the

348

optimum irradiation time concluded from the experiments and the average solar

349

UV flux in Egypt. The ratio of irradiated volume to the total treatment plant

350

volume was assumed 75%, and the illumination area of the plant (Ap) is 4.5 m2

351

according to the volumetric rate of the wastewater.

352

Amortization costs of the investment (AMC) and operating costs (OC) per cubic

353

meter of liquid waste were considered for costs estimation. The amortization costs

354

were calculated taking into consideration the constructing materials and the

355

required equipment. The investment cost per year (I) is calculated according to the

356

illumination area of the treatment plant (Ap), and the treatment plant life time (L)

357

using equation (6) [61]:

358

I

ApCp L

6 

359

Where Cp: the cost per one m2 of the illuminated surface in the plant. A value of

360

800 €/m2 is considered according to the costs of durable reflection surface,

15

361

borosilicate tubes, tanks, and other mechanical equipment. The amortization costs

362

per m3 is calculated by equation (7) [62]:

363

AMC 

I Vt

 7

364

The operating costs include maintenance, the reactants and the energy consumed.

365

The staff costs are not calculated in this estimation for the simplicity of the

366

calculations. In addition, the solar photocatalytic reactor is independent on

367

manpower [62]. The maintenance costs are assumed to be 2% of the yearly

368

investment according to previous studies [63,64].

369

including catalysts and pH adjustment reagents are calculated as the concentration

370

(Ci) (kg/m3) multiplied by the unit price (Pi) (€/kg). Prices of chemicals were taken

371

as the average values from different suppliers inside and outside of Egypt. The

372

prices of commercial TiO2 and powdered activated carbon for industrial use were

373

taken 2.3 €/kg and 0.45 €/kg respectively. The energy cost (EC) (€/m3) is

374

calculated concerning the required power for pumping the liquid waste in the

375

treatment plant by equation (8).

376

EC 

EPti w D Vt

The costs of chemicals

8

377

Where E: the power for pumping the wastewater from the tank to the reactor, Pi:

378

the unit price of energy. It is assumed that the costs of energy is 0.12 €/kw.h

379

according to the rates in Egypt. The calculated treatment costs including

380

amortization costs (AMC) by using TiO2 and TiO2/AC are illustrated in Table 3.

381

According to the fixed volume of liquid waste and plant life cycle, the

382

amortization cost was 1.52 €/m3 for all the cases. Table 3 reveals that the variation

383

of operating costs mainly depend on the type and dosage of the catalyst. Moreover,

16

384

for all types of pharmaceuticals using TiO2/AC was more economic than using

385

TiO2 in terms of removal efficiency. For instance, the maximum removal

386

efficiency of amoxicillin by TiO2/AC was 100% and costs 3.19 €/m3. On the other

387

hand, the maximum removal efficiency of amoxicillin by TiO2 was 91% and costs

388

3.29 €/m3. This trend is similar to the trend of ampicillin, diclofenac, and

389

paracetamol as illustrated in table 3.

390 391

4. Conclusions

392

Solar photocatalytic degradation of four types of pharmaceuticals namely

393

amoxicillin, ampicillin, diclofenac, and paracetamol using TiO2 nano-particles

394

versus TiO2 immobilized on powdered activated carbon (TiO2/AC) was

395

investigated. The images of TiO2/AC taken by SEM revealed successful

396

impregnation of TiO2 on PAC. This was also confirmed by the FTIR spectra and

397

BET analysis for activated carbon and the prepared TiO2/AC. Complete removal

398

of amoxicillin and ampicillin was achieved by TiO2/AC after 120 and 180 minutes

399

of irradiation respectively. This was not the case for bare TiO2, where 89 and 83%

400

of amoxicillin and ampicillin were removed. Similar trends were observed for the

401

removal of diclofenac and paracetamol. The removal efficiency of diclofenac and

402

paracetamol were increased from 68 to 85% and from 57 to 70% respectively

403

using TiO2/AC. Photocatalytic degradation efficiency of pharmaceuticals was

404

strongly dependent on the pH values and dosage of the catalysts. The estimated

405

total costs to attain optimum removal of pharmaceuticals by TiO2/AC were 3.19

406

€/m3 while the total costs to attain optimum removal by bare TiO2 were 3.29 €/m3.

407

Based on these results it is recommended to use TiO2 immobilized on activated

408

carbon (AC) for removal of pharmaceuticals from industrial wastewater.

409

17

410

Acknowledgments

411

The authors wish to acknowledge Ms. Iman Abdelaal for the valuable revision of

412

this paper.

413

education which granted him a full PhD scholarship.

The first author is grateful for the Egyptian ministry of higher

414

18

414 415

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642 643

Fig. 1 Schematic diagram of the solar compound parabolic collectors reactor.

644 645 646 647 648 649 650

28

651 652

(a)

653

654 655

(b)

656

29

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Fig. 2 Scanning electronic micrographs (SEM) of (a) PAC, (b) TiO2/AC.

658 659 660 661 662 663

664 665

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666 667 668

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670 671 672

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673 674 675 676

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677 678 679

Fig. 5 Degradation of pharmaceuticals by TiO2/AC, Initial concentration of all pharmaceuticals = 50 mg/L, TiO2/AC dosage = 1.2 g/L.

680 681 682

32

683 684 685 686

Fig. 6 Effect of initial pH on degradation of pharmaceuticals by photocatalysis, Initial concentration of all pharmaceuticals = 50 mg/L, TiO2/AC dosage = 1.2 g/L, (a) Amoxicillin, (b) Ampicillin, (c) Diclofenac, (d) Paracetamol

687

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688 689 690 691

692 693 694 695

Fig. 7 Effect of catalyst dosage on Degradation of pharmaceuticals by photocatalysis, Initial concentration of all pharmaceuticals = 50 mg/L, Initial pH = 10, t30,w = 180 min, (a) by TiO2/AC, (b) by TiO2.

696

34

697

698 699 700 701 702

Fig. 8 Kinetic analysis for photocatalytic degradation of pharmaceuticals, Initial concentration of all pharmaceuticals = 50 mg/L, Initial pH = 10, (a) by TiO2/AC, (b) by TiO2.

703

35

704

Tables

705

Table. 1 Brunauer–Emmett–Teller (BET) analysis of AC and TiO2/AC Parameter

AC

TiO2/AC

Specific surface area SBET (m2/g)

1325.2

849.2

Total pore volume (cm3/g)

0.8645

0.7804

Mean pore diameter (nm)

2.57

3.74

706 707

36

708 709

Table 2. kinetic analysis by Langmuir–Hinshelwood model. Catalyst

TiO2/AC

TiO2

Pharmaceutical

Kapp

R2

Amoxicillin

0.037

0.997

Ampicillin

0.022

0.984

Diclofenac

0.010

0.973

Paracetamol

0.006

0.903

Amoxicillin

0.013

0.830

Ampicillin

0.011

0.955

Diclofenac

0.005

0.898

Paracetamol

0.004

0.943

710 711 712 713 714 715 716 717 718 719 720 721 722

37

723

Table 3. Costs estimation for TiO2/AC and TiO2 solar photocatalysis TiO2 dose (mg/L)

AC dose

TiO2/AC

133

TiO2/AC

Catalyst

Operating Total costs costs (€/m3)

(€/m3)

267

0.81

2.33

267

533

1.24

2.76

TiO2/AC

400

800

1.67

3.19

TiO2

200

0

0.85

2.37

TiO2

400

0

1.31

2.83

TiO2

600

0

1.77

3.29

Removal Pharmaceutical efficiency (%) Amoxicillin 62 Ampicillin 57 Diclofenac 51 Paracetamol 43 Amoxicillin 87 Ampicillin 84 Diclofenac 73 Paracetamol 63 Amoxicillin 100 Ampicillin 100 Diclofenac 85 Paracetamol 70 Amoxicillin 52 Ampicillin 55 Diclofenac 43 Paracetamol 40 Amoxicillin 88 Ampicillin 84 Diclofenac 64 Paracetamol 57 Amoxicillin 91 Ampicillin 89 Diclofenac 75 Paracetamol 63

724 725 726 727

38