Comparison of solar TiO2 photocatalysis and solar photo-Fenton for treatment of pesticides industry wastewater: Operational conditions, kinetics, and costs

Journal of Water Process Engineering 8 (2015) 55–63

Contents lists available at ScienceDirect

Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe

Comparison of solar TiO2 photocatalysis and solar photo-Fenton for treatment of pesticides industry wastewater: Operational conditions, kinetics, and costs Mohamed Gar Alalm a,∗ , Ahmed Tawfik a , Shinichi Ookawara b a 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 b Department of Chemical Engineering, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan

a r t i c l e

i n f o

Article history: Received 24 May 2015 Received in revised form 13 September 2015 Accepted 14 September 2015 Keywords: Photo-Fenton Kinetics Pesticides Photocatalysis Wastewater

a b s t r a c t Solar photo-Fenton and solar TiO2 photocatalysis processes were investigated for degradation of pesticides from real industrial wastewater. Chlorpyrifos, lambda-cyhalothrin, and diazinon were the major contaminants found in the wastewater. The effect of initial pH, chemical dosing, and irradiation time on the removal efficiency of pesticides and chemical oxygen demand (COD) were assessed. The maximum removal of COD by photo-Fenton process was 90.7%, while by TiO2 photocatalysis was 79.6%. Moreover, the photo-Fenton process was more efficient for degradation of pesticides fractions. Employing of H2 O2 in photocatalysis process (UV/H2 O2 /TiO2 ) improved the removal of COD (84%) and the degradation of pesticides. The kinetic study showed that the degradation of pesticides fractions follows pseudo-firstorder pattern. Amortization and operating costs of full scale solar oxidation plant were estimated. The estimated costs for photocatalysis and photo-Fenton processes were 8.69 and 5.2 D /m3 , respectively. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Pesticides and herbicides are the main constituents of wastewater generated from agrochemical industry [1]. The concern about the influence of pesticides over public health has heightened because of their low biodegradability and high toxicity [2]. As a consequence, the conventional biological treatment processes are not adequate for removal of pesticides. Coagulation–sedimentation method, and adsorption process are not efficient for removal of all types of pesticides, and also big amount of sludge is resulted [3]. Advanced oxidation processes (AOPs) have been realized as particularly efficient technologies for pesticides degradation [4–6]. In AOPs powerful reactive species like hydroxyl radicals (OH• ) are generated by specific chemical reactions in aqueous solutions [7], which are able to destroy even the most recalcitrant organic molecules and convert them into relatively benign and less persistent end products such as CO2 , H2 O and inorganic ions [8]. Among AOPs processes, heterogeneous photocatalysis and photo-Fenton processes have been recognized to be effective for

∗ Corresponding author. Fax: +20 03 4599520. E-mail address: [email protected] (M. Gar Alalm). http://dx.doi.org/10.1016/j.jwpe.2015.09.007 2214-7144/© 2015 Elsevier Ltd. All rights reserved.

the degradation of several types of pesticides existing in agrochemical wastewater industry [9–11]. Arques group found that solar photocatalysis using TiO2 achieved detoxification of methyloxydemeton present in wastewater and decreased the total organic carbon (TOC) value to the minimum level [12]. Fortunately, solar photo-Fenton reaction process was also reported to provide a full degradation of different pesticides and effectively convert them to easily biodegradable organic products [13]. In the heterogeneous UV/TiO2 technique, the ultraviolet light ( < 400 nm) is utilized as an energy source and TiO2 playing as a semiconductor photo-catalyst. TiO2 is distinctive with high surface area, good particle size distribution, high chemical stability, and the possibility of using sunlight as a source of irradiation [14,15]. In photocatalysis oxidation process, the photons with energies bigger than the band-gap energy cause the excitation of valence band (VB) electrons which then enhance the reactions with organic pollutants [16]. In addition, illumination of the catalyst active surface with sufficient energy, contribute to the creation of a positive hole (h+ ) in the valence band and an electron (e−) in the conduction band [17]. The positive hole oxidizes either the organic pollutant or H2 O2 to induce hydroxyl radicals. The electron in the conduction band reduces the oxygen adsorbed on the semiconductor surface. [18].

56

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63

Fig. 1. (a) Chemical structure of pesticides fractions in the industrial wastewater. (b) Schematic diagram of compound parabolic solar collector used for the experiments.

Table 1 Pesticides wastewater characteristics.

2.2. Chemicals

Parameter

Amount

pH Chemical oxygen demand (COD) (mg/l) Total dissolved solids (TDS) (mg/l) Chlorpyrifos (mg/l) Lambda-Cyhalothrin (mg/l) Diazinon (mg/l)

7.6 ± 0.3 7000 ± 450 5200 ± 350 200 ± 11 45 ± 4 11 ± 2

In photo-Fenton process, the basis of the chemistry is the Fenton reaction (Fe2+ +H2 O2 ) which produces HO• and results in oxidation of Fe2+ to Fe3+ [11,19]. Fe2+ ions are oxidized by H2 O2 to Fe3+ and one equivalent HO• is produced [1,20]. In aqueous solutions the resulted Fe3+ act as the light absorbing species that produces additional hydroxyl radical [21]. Photo-Fenton reaction typically enhances the reaction rates and causing a faster mineralization of recalcitrant organics than the dark reaction and can take the advantage of exploiting UV and visible irradiation from natural solar light [22–25]. This work aims to evaluate the viability of solar heterogeneous photocatalysis (UV/TiO2 ) and photo-Fenton (UV/Fe+2 /H2 O2 ) for treatment of agrochemical industry wastewater. For this purpose, lab scale of compound parabolic collectors (CPC) reactor was designed and fabricated. Moreover, operational conditions optimizing and costs estimation study were performed.

2. Materials and methods 2.1. Pesticides wastewater The wastewater was collected from an agrochemical and pesticides company situated in Nubaria, Egypt. Chlorpyrifos, lambda-cyhalothrin, and diazinon were the major contaminants existing in the wastewater. The characterization of wastewater is shown in Table 1. Chemical structures of pesticides are shown in Fig. 1(a).

Titanium dioxide (TiO2 ) used in photocatalysis process was purchased from Acros. Ferrous sulphate hydrate (FeSO4 ·7H2 O), hydrogen peroxide (H2 O2 ), sulfuric acid, acetic acid glacial, and acetonitrile were obtained from Sigma–Aldrich. 2.3. Experimental set-up Solar oxidation experiments were carried out using parabolic solar collector reactor as shown Fig. 1(b). The reactor was situated in Borg Alarab City, Egypt (Latitude 30◦ 52 , Longitude 29◦ 35 ). The energy source of the reaction was the natural irradiation from sunlight during the period from April to May, 2014. The photo-reactor module consists of six borosilicate tubes with a diameter of 2.54 cm and length 75 cm mounted on a curved polished aluminum reflector sheet with radius of curvature 9.2 cm. The reactor was fed with 4 L of the pesticide wastewater which flows in a closed cycle. Three series of experiments were carried out for photocatalysis experiments. Series 1 focused on the effect of pH values on the removal of different fractions of pesticides. The pH was adjusted by H2 SO4 or NaOH and ranged between 2.3 and 11.6. Series 2 was conducted to assess the effect of TiO2 dosage on the treatment process at pH and irradiation time of 4.0, and 120 min respectively. The dosage of TiO2 ranged between 0.5 and 2.5 g/l. In series 3, the effect of addition different dosages of H2 O2 on photocatalysis process was investigated. Dosage of H2 O2 ranged from 0.5 to 2 g/l. For photo-Fenton experiments, the pH was kept constant at value of ≈4.0 by H2 SO4 . H2 O2 and FeSO4 ·7H2 O were added with different doses ranged from 0.5 to 2.0 g/l and 1 to 5 g/l respectively.

Table 2 Kinetic analysis of pesticides degradation. Pesticide

Lambda-Cyhalothrin Chlorpyrifos Diazinon

UV/TiO2

UV/TiO2 /H2 O2 2

2

UV/H2 O2 /Fe+2

Kobs

R

Kobs

R

Kobs

R2

0.0080 0.0073 0.0042

0.942 0.964 0.985

0.0084 0.0083 0.0045

0.916 0.960 0.965

0.0116 0.0118 0.0057

0.955 0.963 0.941

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63

57

Fig. 2. Effect of irradiation time on photocatalysis degradation, (pH 4.0, TiO2 dose = 2 g/l).

Fig. 3. Effect of TiO2 dose on Photocatalysis degradation, (pH 4.0, irradiation time = 120 min).

Fig. 4. Effect of pH on photocatalysis degradation, (Irradiation time = 120 min, TiO2 dose = 2 g/l).

The solar irradiation was measured by Met one weather station (Model Number 466A) installed outdoor at the instillation unit. The normalized illumination time (t30w ) was used to compare between

experiments instead of exposure time (t). The normalized illumination time was calculated by Eqs. (1) and (2) [26,27].

t30w,n = t30w,n−1 + tn

 UV   V  i

30

Vi

(1)

58

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63

Fig. 5. Effect of H2 O2 on photocatalysis degradation, (Irradiation time = 120 min, TiO2 dose = 2 g/l).

Fig. 6. Effect of irradiation time on photo-Fenton process, (pH 4.0, H2 O2 dose = 1 g/l, FeSO4 ·7H2 O dose = 3 g/l).

tn = tn − tn−1

(2)

where tn : the experimental reaction time; UV: the average solar ultraviolet irradiation energy (W/m2 ) during a period of tn , t30W : the normalized illumination time which refers to a constant solar UV power of 30 W/m2 (typical solar UV power on a perfectly sunny day around noon), Vt : the total reactor volume and Vi : the total irradiated volume. 2.4. Analytical methods

degasser (20A5), pump (LC-20AT), and prominences Diode Array Detector (SPD-M20A). The influent and treated effluent was filtered by micro syringe filters (0.2 ␮m). Chlorpyrifos was quantified by a mobile phase of acetonitrile, water, and glacial acetic acid with ratio of 82:17.5:0.5 (v%) at wavelength of 300 nm and flow rate of 1.5 ml/min. Diazinon and lambda cyhalothrin were measured by mobile phase of acetonitrile, and water with ratio of 75:25 and 80:20 (v%), wavelength of 254 and 230 nm, respectively and constant flow rate of 1.5 ml/min. Analysis of COD was performed according to APHA (2005).

The concentration of pesticide fractions was measured by Shimadzu HPLC using C-18 phenomenex reverse phase column, Table 3 Economic and cost evaluation of solar TiO2 photocatalysis and solar photo-Fenton for treatment of wastewater containing pesticides. The amortization costs (AC) is 3.55-C/m3. Treatment process

COD removal (R%)

TiO2 dose (g/L)

H2 O2 dose (g/L)

FeSO4 ·7H2 O dose (g/L)

- /m3 Operating costs (OC)C

Total costs-C/m3

UV/TiO2 UV/TiO2 UV/TiO2 UV/TiO2 UV/TiO2 /H2 O2 UV/TiO2 /H2 O2 UV/H2 O2 UV/H2 O2 /Fe+2 UV/H2 O2 /Fe+2 UV/H2 O2 /Fe+2 UV/H2 O2 /Fe+2

29.5 54.3 71.2 79.6 68.4 83.1 51.8 77.8 83.4 90.7 82.3

0.2 0.5 1 1.5 0.5 1.5 0 0 0 0 0

0 0 0 0 1 1 1 1 1 1 0.5

0 0 0 0 0 0 0 1 2 4 4

0.93 1.74 3.09 4.44 2.44 5.14 1.09 1.23 1.37 1.65 1.30

4.48 5.29 6.64 7.98 5.96 8.69 4.64 4.78 4.92 5.20 4.85

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63

59

Fig. 7. Effect of (a) H2 O2 (b) FeSO4 ·7H2O on photo-Fenton process, (Irradiation time = 120 min, pH 4.0).

3. Results and discussion 3.1. Photocatalysis experiments 3.1.1. Effect of irradiation time The degradation efficiency of pesticide fractions (lambdacyhalothrin, chlorpyrifos, and diazinon) and COD versus t30,w are shown in Fig. 2. The rate of pesticides degradation was higher during the first 90 min of effective irradiation time. In the second 90 min, the degradation rate of pesticides gradually decreased. This was probably due to the consumption of hydroxyl radicals and the low remaining concentration of pesticides. After 120 min of irradiation the degradation of pesticides was limited. Hence, the optimum irradiation time is considered to be 120 min. The removal efficiency of lambda-cyhalothrin, chlorpyrifos, diazinon, and COD with 63.7%, 60.75%, 38.2%, and 79.6%, respectively. The proportional modesty of diazinon degradation efficiency is attributed to the low concentration in wastewater compared to Lambda-Cyhalothrin, and Chlorpyrifos, whereas it is reported that photocatalysis oxidation of Diazinon in synthetic wastewater has better performance [9,28]. 3.1.2. Effect of TiO2 The effect of TiO2 loading on the removal efficiency of pesticide fractions is shown in Fig. 3. The results revealed that the photocatalysis oxidation activity is improved with increasing the dosage of TiO2 i.e., Increasing the dosage from 0.5 to 2.0 g/l improved the removal efficiency of lambda cyhalothrin, chlorpyrifos, diazinon,

and COD from 20.2% to 60.3%; from 26.4% to 60.75%; from 23.6% to 38.2% and from 54.3% to 79.6%, respectively. This improvement can be attributed to the increasing of active sites by providing TiO2 , which plays the semiconductor role in the photocatalysis process. Consequently, the formation of electron-hole pairs and reactive hydroxyl radicals on the surface of semiconductor increased, which improved the oxidation of pesticides into other intermediates. However, increasing the dosage of TiO2 up to 2.5 g/l causes agglomeration of particulates, which decreases the active sites on the semi-conductor surface and subsequently little additional removal of pesticides occurred. Furthermore, the increasing of catalyst loading increases the turbidity of the treated wastewater, and detracts the amount of sunlight reaching to the active surfaces.

3.1.3. Effect of pH Fig. 4 shows the removal efficiency of lambda-cyhalothrin, chlorpyrifos, diazinon and COD by photocatalysis at different pH values. The results obtained indicated that the photocatalysis process is more effective under acidic conditions. The maximum degradation efficiencies of lambda Cyhalothrin, and Chlorpyrifos were 60.2 and 60.75%, respectively at pH value of 3.8, while they were 49.8% and 37.4% respectively at pH of 7.6. The optimum pH for degradation of Diazinon was 4.7 and the removal efficiency was 40.9%. Only 26.4% of Diazinon was eliminated at pH of 7.6. The effect of pH on degradation of organic matter assisted by the semiconductor oxides is influenced by the acid–base equilibrium governing the

60

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63

centration of the pesticides. H2 O2 function in the photocatalysis oxidation is to accept a photo generated electron from the conduction band of the semiconductor to form additional hydroxyl radicals [17]. The effect of H2 O2 dosage on the removal efficiency of pesticides and COD is depicted in Fig. 5. The removal efficiencies of pesticides were improved by increasing the H2 O2 . Maximum degradation of pesticides was achieved when H2 O2 dosage was not exceeding 1.5 g/l. The maximum removal efficiencies were 68.9%, 73.3%, 49.1%, and 84% for lambda-cyhalothrin, chlorpyrifos, diazinon, and COD respectively. Using catalytic oxidation (H2 O2 /TiO2 /UV) instead of (TiO2 /UV) increased the removal efficiency of lambda-cyhalothrin, chlorpyrifos, diazinon, and COD by values of 8%, 13%, 11%, and 5%, respectively. The enhancement of photocatalysis by the addition of H2 O2 is mainly attributed to the formation of new hydroxyl radicals whether by decomposition in the presence of UV energy from sunlight as described in Eq. (5), or by accepting generated electrons from the conduction band of the semiconductor as explained in the Eq. (6). H2 O2 + hv→2OH ·

(5)

H2 O2 + e− →OH · + OH−

(6)

Further increasing of H2 O2 dosing decreased the degradation of pesticides, and this could be ascribed to the fact that excess H2 O2 reacts with • OH and form • HO2 [17]. 3.2. Photo-Fenton experiments

Fig. 8. Kinetics of pesticides degradation, (a) Lambda-Cyhalothrin, (b) Chlorpyrifos, (c) Diazinon.

surface chemistry of metal oxides in water as shown in Eqs. (3) and (4): AtpH < PZC TiOH + H+ →TiOH+ 2 −

−

AtpH > PZC TiOH + OH →TiO + H2 O

(3) (4)

where Pzc is the point of zero charge of the semiconductor. It is defined as the pH at which the surface of an oxide is uncharged [28]. The point of zero charge of the TiO2 is reported to be about 6.25 [9,18]. The effect of pH on the photo-oxidation activity could be explained in terms of electrostatic interaction between active semiconductor sites and substrate molecules [17]. The interaction could be expected to influence the encounter probability of the resulted hydroxyl radicals with pesticides molecules. It is stated that the overall reaction would be improved or restrained depending on whether attractive or repulsive forces prevail, respectively [29]. The TiO2 has a positive charge when the pH is lower than the Pzc , while the pesticides have negative charge when the pH is greater than the pKa (acid dissociation constant at logarithmic scale). The optimal pH is expected to be in the intermediate value between the Pzc of the catalyst and the pKa of pesticides. For instance, the pKa of diazinon is reported to equal 2.6, the Pzc of TiO2 is equal 6.25 and the optimal pH found to be around 4.7 from the experiments. 3.1.4. Effect of adding H2 O2 in photocatalysis process The addition of H2 O2 is reported to be an effective procedure for enhancement of photocatalytic degradation [15]. In order to keep the efficiency of the added H2 O2 , it is necessary to investigate the optimum concentration of H2 O2 according to the type and con-

3.2.1. Effect of Irradiation time The removal efficiency of pesticides and COD was evaluated at different irradiation time t30,w , and the results are shown in Fig. 6. At early stages of the photo-Fenton reaction, molecules of pesticide are degraded by hydroxyl radicals, leading to formation of organic intermediates with a drop in COD concentration and reduction in pesticides concentration. After certain period with generation of more hydroxyl radicals from Fe+3 the value of COD decreased with the oxidation of organic substances. After 90 min of irradiation the degradation rates of pesticides decreased due to the consumption of hydroxyl radicals and low concentrations of pesticides compared to the beginning of the reaction. At irradiation time of 120 min, the removal efficiency of Lambda-Cyhalothrin, Chlorpyrifos, Diazinon, and COD was 80.65%, 78.05%, 50.9%, and 90.7%, respectively. Further increase in the illumination time (150 and 180 min) provided a slight improvement of the removal efficiency of pesticides and COD. This can be due to most of H2 O2 and Fe+2 are consumed, which detract the rate of organic matter degradation. Photo-Fenton reaction was more efficient in degradation of pesticides than photocatalysis processes (UV/TiO2 ) and (UV/H2 O2 /TiO2 ). This observation could be explained in terms of the sources of hydroxyl radicals in each process. In photocatalysis, the hydroxyl radicals are formed only when positive holes react with water. On the other hand, in photo-Fenton reaction the hydroxyl radicals are formed from several sources i.e. photolysis of Fe(OH)+2 , reaction of Fe+2 with H2 O2 , and photolysis of H2 O2 . In addition, photo decomposition of Fe+3 with caraboxylates in presences of visible light composes new Fe+2 which reproduce more radicals in presence of H2 O2 [30,31]. 3.2.2. Effect of H2 O2 Fig. 7(a) shows the removal efficiency of pesticides and COD at different dosages of H2 O2 . The degradation of pesticides was improved by increasing the dosage of H2 O2 up to 1 g/l. This improvement is probably due to the increasing of hydroxyl radicals produced from the photolysis of H2 O2 . Moreover, it is also suggested that increasing H2 O2 dosage enhances the reactions

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63

between Fe+2 and H2 O2 . H2 O2 dosage of 1 g/l provided removal efficiency of lambda-cyhalothrin (80.7%), chlorpyrifos (78.1%), diazinon (50.9%), and COD (90.7%). No significant improvement in the removal of pesticides was occurred at H2 O2 dosage exceeding 1 g/l. This could be attributed to the self-scavenging of hydroxyl radicals by excess of H2 O2 . The residual values of COD was increased by increasing the H2 O2 dosage (1.5 and 2 g/l). The explanation of this increment is that the residuals of H2 O2 after photo-Fenton reaction are contributed to COD value. 3.2.3. Effect of Fe+2 Iron dosage is a crucial parameter for design of large scale wastewater treatment plants. The concern is not only for the cost of iron salt, but also for its influence on the needed irradiation time which affects the reactor size. Moreover, the residuals of iron in treated effluent and settled sludge is very harmful to the environment, and needs further treatment to be separated [21]. Therefore, the dosage of iron should be optimized according to the initial concentration of pesticides and the desired degree of pesticides elimination [32]. Fig. 7(b) shows the removal efficiency of pesticides and COD at different dosages of FeSO4 ·7H2 O. The results indicated that increasing the dose of FeSO4 ·7H2 O from 1 to 3 g/l provided an improvement in degradation of pesticides. However, at a higher dosage of 4 and 5 g/l for FeSO4 ·7H2 O, the removal efficiency of pesticides and COD was almost constant. The relatively high dosage of FeSO4 ·7H2 O is attributed to the consuming of some Fe+2 ions in coagulation of fine suspended particulates existing in the wastewater. At a dosage of 3 g/l, the removal efficiency of lambda-cyhalothrin, chlorpyrifos, diazinon, and COD was 77.6%, 73.3%, 46.4%, and 89.3%, respectively. The photo-degradation of pesticides was poor when the process was free from Fe+2 as shown in Fig. 7(b). This could be explained by the increasing of hydroxyl radicals produced from photo-Fenton reaction. 3.3. Degradation kinetics of pesticides The photocatalysis and photo-Fenton processes for degradation of pesticides can be expressed by a pseudo-first-order pattern [9,12,16,20,33]. The differential Eqs. (6) and (7) demonstrate the relationship of remaining concentration and time. −

dC = kobs C dt

(7)

Integrating this differential equation leads to: ln

C0 = kobs t C

(8)

where kobs : the constant reaction rate, C0 : the initial concentration of target pollutant in aqueous solution, and C: the residual concentration of pollutant at time t. The model was applied for each type of pesticides using the optimal dosages concluded from previous sections. The values of ln (C0 /C) versus normalized illumination time in photocatalysis and photo-Fenton processes are shown in Fig. 8. Least square regression was used to calculate the kobs , and R2 for each pesticide. Results of regression are shown in Table 2. The high value of R2 indicated that the pseudo-first-order equation is successfully applied to the photo-oxidation processes. The constant reaction rate for diazinon degradation was proportionately small in comparison with lambda-cyhalothrin, and chlorpyrifos because the concentration of the wastewater was low compared to other contaminants which limited its chance to be adsorbed on the active sites of the semiconductor surface. The values of kobs of photo-Fenton process were greater than the corresponding values of TiO2 photocatalysis and UV/TiO2 /H2 O2 processes, which confirmed that the degradation

61

efficiency of the three types of pesticides is better in photo-Fenton process. 3.4. Economic and cost evaluation The experimental results obtained in this work for treatment of agrochemical wastewater were used to design a full scale treatment plant. The agrochemical company which produce the studied effluent was taken as a case study. The facility daily generates 6 m3 of pesticides contaminated wastewater. The capacity (C) of the proposed wastewater treatment plant is estimated using Eq. (9) [34]. C = Vt

tt tw D

(9)

where Vt : volumetric treated wastewater per year, tt : operation time for wastewater treatment plant, tw : working time per day for wastewater treatment plant, and D: the number of working days in a year. The ratio of treatment time to working time is assumed 35% which corresponded to the optimum irradiation time, and the average solar UV flux in the company site. The ratio of irradiated volume to the total treatment plant volume is assumed 75%, and the illumination area of the designed plant (Ap ) is 2.1 m3 . Amortization costs of the investment (AC) and operating costs (OC) per cubic meter of treated wastewater were considered for economic evaluation of the treatment processes. The amortization costs were calculated taking into account the basic constructing facilities and the required equipment. The investment cost per year (I) is calculated according to the illumination area of the treatment plant (Ap ), and the wastewater treatment plant life cycle (L) using Eq. (10) [34]: I=

A p Cp L

(10)

where Cp : the cost per one m2 of the plant illuminated surface. A value of 800 D /m2 is considered according to the costs of durable reflection surface, Pyrex tubes, construction of tanks and other mechanical facilities. The amortization costs per m3 of wastewater is calculated by Eq. (11) [35]: AC =

1 Vt

(11)

The operating costs include maintenance, the chemicals and the energy consumed. Since solar photo-oxidation treatment plant is independent on intensive manpower, the staff costs are not considered in this evaluation for the simplicity of calculations [35]. The maintenance costs are assumed to equal 2% of the yearly investment according to previous studies [36,37]. The costs of chemicals including oxidants and pH adjustment reagents are calculated as the concentration (Ci ) (kg/m3 ) multiplied by the unit price (Pi ) (D /kg). Prices of chemicals were taken as the average values from different suppliers inside and outside Egypt. The energy cost (EC) (D /m3 ) was calculated according to the power required for pumping wastewater in the treatment plant by Eq. (12). EC =

EPi tw D Vt

(12)

where E: the needed power for pumping the wastewater, Pi : the unit price of energy. It is assumed that the costs of energy is 0.12 D /kw.h. The calculated treatment costs including amortization costs (AC) for solar TiO2 photocatalysis and solar photo-Fenton are presented in Table 3. According to the unified volume of wastewater and plant life cycle for all processes, the amortization costs were 3.55 D /m3 . Table 3 shows that the variation of operating costs was mainly depend on to type and the dosage of chemicals. The maximum removal of COD in TiO2 photocatalysis process is 7.98 D /m3 . The

62

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63

use of H2 O2 in combination with TiO2 significantly improved the removal of COD and pesticides fractions. However, the total costs remained high as shown in due to the high costs of TiO2 . The results showed that, the cost of photo-Fenton process was 4.92 D /m3 for COD removal of ≈83%, which was more economical than (UV/TiO2 ) photocatalysis and (UV/TiO2 /H2 O2 ) processes. In addition, the maximum COD removal by photo-Fenton process was 90.7% and the costs were 5.20 D /m3 , which considered the best solution concerning the process performance. 4. Conclusions Photocatalysis and photo-Fenton processes for degradation of chlorpyrifos, lambda-cyhalothrin, and diazinon existing in real industrial wastewater were investigated. The most concluded remarks are: (i) In UV/TiO2 process, the pesticides degradation were 63.7%, 60.75%, and 38.2% for lambda-cyhalothrin, chlorpyrifos, and diazinon respectively using 2 g/L of TiO2 at optimum pH of 3.8. (ii) Using H2 O2 in photocatalysis process enhanced degradation of pesticides by 8%, 13%, and 11% for lambda-cyhalothrin, chlorpyrifos, and diazinon, respectively. (iii) Photo-Fenton process was better than UV/TiO2 process in degradation of pesticides in terms of removal efficiency, and reaction rates. Photo-Fenton achieved removal efficiencies of 80.65% for lambda-cyhalothrin, 78.05% for chlorpyrifos, 50.9% for diazinon, and 90.7% for COD. (iv) The degradation of pesticides by photocatalysis and photo-Fenton processes were expressed by a pseudo-first-order pattern and indicated high correlation. (v) Photo-Fenton process was more economic as compared to TiO2 photocatalysis and (UV/TiO2 /H2 O2 ) processes. The total costs for optimum photo-Fenton process were 5.20 D /m3 at optimum operating conditions. Acknowledgment The first author is grateful for the Egyptian ministry of higher education which provided him a full scholarship and for Japan International Cooperation Agency (JICA) for providing all the facilities to participate in this work. References [1] V.J.P. Vilar, F.C. Moreira, A.C.C. Ferreira, M.A. Sousa, C. Gonc¸alves, M.F. Alpendurada, et al., Biodegradability enhancement of a pesticide-containing bio-treated wastewater using a solar photo-Fenton treatment step followed by a biological oxidation process, Water Res. 46 (2012) 4599–4613, http://dx. doi.org/10.1016/j.watres.2012.06.038. [2] M. Gar Alalm, A. Tawfik, S. Ookawara, Combined Solar advanced oxidation and PAC adsorption for removal of pesticides from industrial wastewater, J. Mater. Environ. Sci. 6 (2015) 800–809. [3] M. Nasr, A. Tawfik, S. Ookawara, M. Suzuki, Environmental and economic aspects of hydrogen and methane production from starch wastewater industry, J. Water Environ. Technol. 11 (2013) 463–475. [4] T. Olmez-Hanci, I. Arslan-Alaton, Comparison of sulfate and hydroxyl radical based advanced oxidation of phenol, Chem. Eng. J. 224 (2013) 10–16, http:// dx.doi.org/10.1016/j.cej.2012.11.007. [5] Y.-H. Huang, Y.-J. Huang, H.-C. Tsai, H.-T. Chen, Degradation of phenol using low concentration of ferric ions by the photo-Fenton process, J. Taiwan Institute Chem. Eng. 41 (2010) 699–704, http://dx.doi.org/10.1016/j.jtice. 2010.01.012. [6] M. Mehrjouei, S. Müller, D. Möller, Design and characterization of a multi-phase annular falling-film reactor for water treatment using advanced oxidation processes, J. Environ. Manage. 120 (2013) 68–74, http://dx.doi.org/ 10.1016/j.jenvman.2013.02.021. [7] M. Gar Alalm, A. Tawfik, S. Ookawara, Investigation of optimum conditions and costs estimation for degradation of phenol by solar photo-Fenton process, Appl. Water Sci. (2014), http://dx.doi.org/10.1007/s13201-014-0252-0. [8] M. Gar Alalm, A. Tawfik, S. Ookawara, Solar photocatalytic degradation of phenol by TiO2 /AC prepared by temperature impregnation method, Desalinat. Water Treat. (2014) 1–10, http://dx.doi.org/10.1080/19443994.2014.969319. [9] J. Fenoll, P. Flores, P. Hellín, C.M. Martínez, S. Navarro, Photodegradation of eight miscellaneous pesticides in drinking water after treatment with semiconductor materials under sunlight at pilot plant scale, Chem. Eng. J. 204–206 (2012) 54–64, http://dx.doi.org/10.1016/j.cej.2012.07.077.

[10] A. Zapata, I. Oller, C. Sirtori, A. Rodríguez, J.A. Sánchez-Pérez, A. López, et al., Decontamination of industrial wastewater containing pesticides by combining large-scale homogeneous solar photocatalysis and biological treatment, Chem. Eng. J. 160 (2010) 447–456, http://dx.doi.org/10.1016/j.cej. 2010.03.042. [11] V. Sarria, An innovative coupled solar-biological system at field pilot scale for the treatment of biorecalcitrant pollutants, J. Photochem. Photobiol. A Chem. 8 (2003) 9–99, http://dx.doi.org/10.1016/S1010-6030(03) 105-9. [12] A. Arques, A. Garcia-Ripoll, R. Sanches, L. Santos-Juanes, A.M. Amat, M.F. Lopez, et al., Detoxification of aqueous solutions containing the commercial pesticide metasystox by TiO2 -mediated solar photocatalysis, J. Solar Energy Eng. Transact. ASME 7 (2007) 4–79, http://dx.doi.org/10.1115/1.2391205. [13] M. Gar Alalm, A. Tawfik, S. Ookawara, Degradation of four pharmaceuticals by solar photo-Fenton process: kinetics and costs estimation, J. Environ. Chem. Eng. 4 (2015) 6–51, http://dx.doi.org/10.1016/j.jece.2014.12.009. [14] J. Saien, Z. Ojaghloo, A.R. Soleymani, M.H. Rasoulifard, Homogeneous and heterogeneous AOPs for rapid degradation of Triton X-100 in aqueous media via UV light, nano titania hydrogen peroxide and potassium persulfate, Chem. Eng. J. 167 (2011) 172–182, http://dx.doi.org/10.1016/j.cej.2010.12.017. [15] J.C. Garcia, J.L. Oliveira, A.E.C. Silva, C.C. Oliveira, J. Nozaki, N.E. de Souza, Comparative study of the degradation of real textile effluents by photocatalytic reactions involving UV/TiO2/H2O2 and UV/Fe2+/H2O2 systems, J. Hazard. Mater. 147 (2007) 105–110, http://dx.doi.org/10.1016/j. jhazmat.2006.12.053. [16] M.V. Phanikrishna Sharma, V. Durga Kumari, M. Subrahmanyam, TiO2 supported over SBA-15: an efficient photocatalyst for the pesticide degradation using solar light, Chemosphere 73 (2008) 1562–1569, http://dx. doi.org/10.1016/j.chemosphere.2008.07.081. [17] E.S. Elmolla, M. Chaudhuri, Photocatalytic degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution using UV/TiO2 and UV/H2O2/TiO2 photocatalysis, Desalination 252 (2010) 46–52, http://dx.doi. org/10.1016/j.desal.2009.11.003. [18] S. Ahmed, M.G. Rasul, R. Brown, M.A. Hashib, Influence of parameters on the heterogeneous photocatalytic degradation of pesticides and phenolic contaminants in wastewater: a short review, J. Environ. Manage. 92 (2011) 311–330, http://dx.doi.org/10.1016/j.jenvman.2010.08.028. [19] R. Li, C. Yang, H. Chen, G. Zeng, G. Yu, J. Guo, Removal of triazophos pesticide from wastewater with Fenton reagent, J. Hazard. Mater. 167 (2009) 1028–1032, http://dx.doi.org/10.1016/j.jhazmat.2009.01.090. [20] S. Navarro, J. Fenoll, N. Vela, E. Ruiz, G. Navarro, Removal of ten pesticides from leaching water at pilot plant scale by photo-Fenton treatment, Chem. Eng. J. 167 (2011) 42–49, http://dx.doi.org/10.1016/j.cej.2010.11.105. [21] M. Gar Alalm, A. Tawfik, Fenton and solar photo-fenton oxidation of industrial wastewater containing pesticides, 17th International Water Technology Conference, 2013. [22] K.C. Namkung, A.E. Burgess, D.H. Bremner, H. Staines, Advanced Fenton processing of aqueous phenol solutions: a continuous system study including sonication effects, Ultrason. Sonochem. 15 (2008) 171–176, http://dx.doi.org/ 10.1016/j.ultsonch.2007.02.009. [23] R.F.F. Pontes, J.E.F. Moraes, A. Machulek, J.M. Pinto, A mechanistic kinetic model for phenol degradation by the Fenton process, J. Hazard. Mater. 176 (2010) 402–413, http://dx.doi.org/10.1016/j.jhazmat.2009.11.044. [24] W. Gernjak, T. Krutzler, A. Glaser, S. Malato, J. Caceres, R. Bauer, et al., Photo-Fenton treatment of water containing natural phenolic pollutants, Chemosphere 50 (2003) 71–78 http://www.ncbi.nlm.nih.gov/pubmed/ 12656231. [25] B. Iurascu, I. Siminiceanu, D. Vione, M.A. Vicente, A. Gil, Phenol degradation in water through a heterogeneous photo-Fenton process catalyzed by Fe-treated laponite, Water Res. 43 (2009) 1313–1322, http://dx.doi.org/10.1016/j. watres.2008.12.032. [26] I. Oller, W. Gernjak, M.I. Maldonado, L.A. Pérez-Estrada, J.A. Sánchez-Pérez, S. Malato, Solar photocatalytic degradation of some hazardous water-soluble pesticides at pilot-plant scale, J. Hazard. Mater. 138 (2006) 507–517, http:// dx.doi.org/10.1016/j.jhazmat.2006.05.075. [27] I. Michael, E. Hapeshi, C. Michael, A.R. Varela, S. Kyriakou, C.M. Manaia, et al., Solar photo-Fenton process on the abatement of antibiotics at a pilot scale: degradation kinetics, ecotoxicity and phytotoxicity assessment and removal of antibiotic resistant enterococci, Water Res. 46 (2012) 5621–5634, http:// dx.doi.org/10.1016/j.watres.2012.07.049. [28] N. Daneshvar, S. Aber, Photocatalytic degradation of the insecticide diazinon in the presence of prepared nanocrystalline ZnO powders under irradiation of UV-C light, Separat. Purif. Technol. 9 (2007) 1–98, http://dx.doi.org/10.1016/j. seppur.2007.07.016. [29] J. Blanco, S. Malato, P. Fernández, A. Vidal, Compound parabolic concentrator technology development to commercial solar detoxification applications, Solar Energy 67 (1999) 317–330. [30] N. Derbalah, Photocatalytic removal of fenitrothion in pure and natural waters by photo-Fenton reaction, Chemosphere 57 (2004) 635–644, http://dx. doi.org/10.1016/j.chemosphere.2004.08.025. [31] F. Javier Benitez, J.L. Acero, F.J. Real, Degradation of carbofuran by using ozone, UV radiation and advanced oxidation processes, J. Hazard. Mater. 89 (2002) 51–65. [32] I. Carra, J.L. Casas López, L. Santos-Juanes, S. Malato, J.A. Sánchez Pérez, Iron dosage as a strategy to operate the photo-Fenton process at initial neutral pH, Chem. Eng. J. 224 (2013) 67–74, http://dx.doi.org/10.1016/j.cej.2012.09.065.

M. Gar Alalm et al. / Journal of Water Process Engineering 8 (2015) 55–63 [33] W.K. Lafi, Z. Al-Qodah, Combined advanced oxidation and biological treatment processes for the removal of pesticides from aqueous solutions, J. Hazard. Mater. 137 (2006) 489–497, http://dx.doi.org/10.1016/j.jhazmat.2006.02.027. [34] I. Carra, E. Ortega-Gómez, L. Santos-Juanes, J.L. Casas López, J.A. Sánchez Pérez, Cost analysis of different hydrogen peroxide supply strategies in the solar photo-Fenton process, Chem. Eng. J. 7 (2013) 5–81, http://dx.doi.org/10.1016/ j.cej.2012.09.067. [35] L. Santos-Juanes Jordá, M.M. Ballesteros Martín, E. Ortega Gómez, A. Cabrera Reina, I.M. Román Sánchez, J.L. Casas López, et al., Economic evaluation of the photo-Fenton process, mineralization level and reaction time: the keys for increasing plant efficiency, J. Hazard. Mater. 186 (2011) 1924–1929, http://dx. doi.org/10.1016/j.jhazmat.2010.12.100.

63

[36] M. Molinos-Senante, F. Hernández-Sancho, R. Sala-Garrido, Economic feasibility study for wastewater treatment: a cost-benefit analysis, Sci. Total Environ. 408 (2010) 4396–4402, http://dx.doi.org/10.1016/j.scitotenv.2010. 07.014. ˜ S. Malato, A. Rodríguez, X. Domènech, Integration of environmental [37] I. Munoz, and economic performance of processes. Case study on advanced oxidation processes for wastewater treatment, J. Adv. Oxidat. Technol. 11 (2008) 270–275.