Scholarly article on topic 'Facilitated ultrasonic irradiation in the degradation of diazinon insecticide'

Facilitated ultrasonic irradiation in the degradation of diazinon insecticide Academic research paper on "Chemical engineering"

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Abstract of research paper on Chemical engineering, author of scientific article — Chi-Kang Wang, Yi-Heng Shih

Abstract In this study, the degradation of diazinon insecticide was investigated using ultrasound facilitated by Fenton's and Fenton-like reagents under various experimental conditions. The effects of oxidant (persulphate ions, S2 O 8 2 − and hydrogen peroxide (H2O2)), transition metal (including Co2+, Ag+ and Fe2+), Fenton's reagent concentration and temperature on diazinon degradation were examined. A solution with an initial diazinon concentration of 50 mg L−1 was used in this study. Ultrasonic irradiation in combination with Fenton's and Fenton-like reagents not only effectively degraded diazinon but also rapidly reduced its toxicity. The optimal experimental conditions were determined as follows: 20 mg L−1 Fe2+, 150 mg L−1 H2O2, 25 °C and pH 3. After reacting for 60 min, the diazinon removal efficiency reached 98%, with a mineralization efficiency of 30%. Degradation occurred primarily via oxidation and resulted in the substitution of sulphur with oxygen in the diazinon PS bond.

Academic research paper on topic "Facilitated ultrasonic irradiation in the degradation of diazinon insecticide"

Accepted Manuscript

Facilitated ultrasonic irradiation in the degradation of diazinon insecticide Chi-Kang Wang, Yi-Heng Shih

PII: S2468-2039(16)30009-7

DOI: 10.1016/j.serj.2016.04.003

Reference: SERJ 9

To appear in: Sustainable Environment Research

Received Date: 7 July 2015 Revised Date: 24 September 2015 Accepted Date: 2 December 2015

Please cite this article as: Wang C-K, Shih Y-H, Facilitated ultrasonic irradiation in the degradation of diazinon insecticide, Sustainable Environment Research (2016), doi: 10.1016/j.serj.2016.04.003.

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1 Manuscript Received: July 7, 2015

2 Revision Received: September 24, 2015

3 and Accepted: December 2, 2015

4 Facilitated ultrasonic irradiation in the degradation of diazinon insecticide

5 Chi-Kang Wang* and Yi-Heng Shih

6 Department of Environmental Engineering and Health

7 Yuanpei University of Medical Technology

8 Hsinchu 306, Taiwan

9 Key Words: Diazinon, mineralization, toxicity, transition metals, ultrasound

10 Corresponding author

11 Email: ckwang@mail.ypu.edu.tw

13 ABSTRACT

14 In this study, the degradation of diazinon insecticide was investigated using

15 ultrasound facilitated by Fenton's and Fenton-like reagents under various experimental

16 conditions. The effects of oxidant (persulphate ions, S2O8 - and hydrogen peroxide (H2O2)),

17 transition metal (including Co2+, Ag+ and Fe2+), Fenton's reagent concentration and

18 temperature on diazinon degradation were examined. A solution with an initial diazinon

19 concentration of 50 mg L-1 was used in this study. Ultrasonic irradiation in combination with

20 Fenton's and Fenton-like reagents not only effectively degraded diazinon but also rapidly

21 reduced its toxicity. The optimal experimental conditions were determined as follows: 20 mg

-1 2+ -1

22 L-1 Fe, 150 mg L-1 H2O2, 25 °C and pH 3. After reacting for 60

min, the diazinon removal

23 efficiency reached 98%, with a mineralization efficiency of 30%. Degradation occurred

24 primarily via oxidation and resulted in the substitution of sulphur with oxygen in the diazinon

25 P=S bond.

26 1. Introduction

27 The widespread presence of pesticides in the environment is a noteworthy problem,

28 particularly given the broad use of pesticides in agriculture and hygiene throughout the world.

29 Organophosphorus pesticides are among the most frequently encountered pesticides around

30 the world [1]. They inhibit acetylcholinesterase in insects, producing toxic conditions, and are

31 toxic to humans [2]. Therefore, studies should be conducted to identify and implement

32 methods for removing organophosphorus pesticides. One commonly used insecticide in the

33 organophosphate chemical family, diazinon (O,O-diethyl O-(2-isopropyl-6-methylpyrimidin-

34 4-yl)thiophosphate, C12H21N2O3PS), was commercially introduced in 1952 [3]. Diazinon is

35 used worldwide in agricultural production to protect plants by controlling a variety of sucking

36 and leaf-eating insects and has been classified by the World Health Organization as a

37 moderately hazardous Class II chemical [3]. Diazinon is stable at pH 7 and is not easily

volatilised from soil or water. Thus, it can persist in the environment for up to six months [4]. Furthermore, the degradation by-products of diazinon pose health risks for humans and the environment.

Several technologies, such as ionised gamma irradiation, ozonation, UV, photo-TiO2, X-ray and ultrasound, have been used to degrade diazinon [5-8]. In most cases, treatment of 120 min was required to achieve complete diazinon degradation. Ultrasonic methods have been widely used in such studies and have mainly been applied to synthetic solutions spiked with one or several contaminants [9]. However, ultrasound alone was unable to fully degrade the organic compounds [3]. Consequently, methods for enhancing the degradation efficiency and reducing the necessary time required for oxidation were investigated.

Processes combining ultrasound and other chemicals or oxidation processes are referred to as sonochemical processes and represent unique and advanced oxidation methods for degrading refractory compounds [10]. For example, the sono-Fenton process combines ultrasound and Fenton's reagent (Eq. 1) and is a proven innovative method for degrading different types of pollutants, such as carbofuran [11], ethylenediamine [12], and tetracycline

[13], over short reaction durations. Additionally, the sono-Fenton process has been used to

reduce the toxicity of wastewater. However, because adding H2O2 and Fe increases the toxicity of treated wastewater and the formation of ferric hydroxide sludge, many researchers have tried replacing H2O2 and Fe2+ with different chemicals, such as S2O82", Ag+ and Co2+ [14-16]. Consequently, these chemicals have been referred to as Fenton-like reagents.

Fe2+ + H2O2 + ))) ^ Fe3+ + ^OH +OH" (1)

This study attempted to degrade diazinon and reduce its toxicity using ultrasonic irradiation facilitated by Fenton's and Fenton-like reagents. Three transition metals (Fe2+,

+ 2+ 263 Ag and Co ) and two oxidants (H2O2 and S2O8 -) were used in different combinations for

64 diazinon degradation. The effects of transition metals, oxidants, Fenton's reagent dosages and

65 temperature on the degradation of diazinon were investigated. Additionally, the toxicity

66 based on cell viability was measured before and after treatments, and possible degradation

67 by-products and oxidation pathways were proposed.

68 2. Materials and methods

69 2.1. Standards and reagents

70 Diazinon (analytical standard) was purchased from Sigma-Aldrich (St. Louis, MO,

71 USA). The purest grade commercially available chemical reagents including H2SO4, NaOH,

72 FeSO4-7H2O, AgNOs, Co(NO3)2-6H2O, (№^208, and an aqueous solution of H2O2 (30%,

73 w/w in water) were used in this study.

74 2.2. Experimental apparatus and designs

75 A 20 kHz sonicator (Microson VCX 750, USA) equipped with a titanium probe tip

76 was carried out in this study. The detailed information of ultrasonic treatment unit was

77 summarized in our earlier study [11], and the output ultrasonic power was maintained at 100

78 W in this study. The working volume of ultrasonic reactor was 1 L. A circulating temperature

79 controller was used to maintain the desired reaction temperature (15-55 °C). Other reaction

80 parameters included H2O2 concentrations of 0-150 mg L- (0-4.41 mM) and Fe

81 concentrations of 0-20 mg L-1 (0-0.306 mM). In addition to H2O2 and Fe2+, S2O82- (100 mg L-

82 1, 0.521 mM), Co2+ (10 mg L-1, 0.170 mM) and Ag+ (10 mg L-1, 0.093 mM) were used to

83 investigate the effects of reaction parameter on the degradation of diazinon. During the

84 reaction, the reactor was aerated at 0.2 L min-1 to provide sufficient dissolved oxygen. The

85 reactor was equipped with pH and ORP (oxidation-reduction potential) meters (Suntex PC-

86 3200, Taiwan) to monitor the profiles of pH and ORP values.

87 2.3. Sample extraction and analysis

To isolate the diazinon and its oxidation by-products from aqueous solution, dichloromethane and n-hexane were carried out in a liquid-liquid extraction procedure. Diazinon and oxidation by-products were identified during the oxidation process using a gas chromatography/mass spectrometry detector (GC/MS, Shimadzu GC/MS-GC2010 Plus, Shimadzu, Kyoto, Japan) with a HP-5MS column (length 30 m, thickness 0.25 p,m, diameter 0.25 mm) and the concentration of diazinon was detected using a GC/flame ionisation detector (Varian GC 3400, Mulgarve, Victoria, Australia) equipped with a DB-1 fused silica capillary column. The pre-treatment of diazinon solution before analysis and analytic setups were followed the study proposed by Wang and Shih [17]. 2.4. TOC and toxicity analysis

Diazinon mineralization was investigated by determining the total organic carbon (TOC) concentration using a TOC analyser (TOC-500, Shimadzu, Japan). Each sample collected during the reaction was analysed in triplicate. The toxicities of the diazinon samples were determined by assessing the cell viability based on cell counting. In all experiments, cells were treated with diazinon water samples for 24 h before and after treatment. The steps for cell counting, including the incubation of rat liver cells and measurement method of cells, have been detailed in our earlier publication [12].

3. Results and discussion 3.1. Degradation of diazinon by various processes

Table 1 shows the preliminary studies involving diazinon degradation and

mineralization using the ultrasound, ultrasound/Fe , ultrasound/H2O2, Fenton and sono-

2+ 1 1

Fenton processes, with the Fe and H2O2 concentrations of 10 mg L- and 100 mg L- in the

Fenton and sono-Fenton processes, respectively, and a reaction duration of 60 min. As shown

in Table 1, the degradation efficiencies of diazinon subjected to ultrasound, ultrasound/Fe and ultrasound/H2O2 were 22, 25 and 26%, respectively, which indicated that only

unsatisfactory increases in diazinon degradation when Fe and H2O2 were used independently with ultrasound. Thus, ^OH-oxidation did not significantly contribute to diazinon degradation, and most of the achieved degradation occurred through the ultrasonic thermal cleavage. During the Fenton process, 62% of the diazinon was degraded and 6% of the TOC was removed. Because sufficient ^OH radicals were formed during the Fenton process, the refractory organic compounds could be readily degraded [18]. However, the ratio of TOC removal to diazinon removal by the Fenton process was only 0.1, which is lower than that observed for other ultrasonic processes. This result indicates that most of the degraded diazinon is transformed into other by-products and could not be mineralized as CO2. Combining ultrasound with the Fenton process resulted in the highest diazinon degradation (96%), which was higher than that obtained using ultrasound or the Fenton process alone.

This could be proven that a synergetic effect occurred when combining ultrasound and the

Fenton process [12,19]. Equation 2 shows the Fenton reaction and it is found that the Fe is

oxidized to Fe , then the Fe reacts with H2O2 to produce a complex intermediate (Fe-

OOH2+) as shown in Eq. 3. The ultrasound spontaneously decomposes the Fe-OOH to Fe

• 2+ •

and OOH (Eq. 4) and the isolated Fe can react subsequently with H2O2, produce OH again

(Eq. 2), and thus establishing a cyclic mechanism. Even the degradation of diazinon achieved using the sono-Fenton process was significantly greater than that achieved by each of the other processes shown in Table 1, however, the ratio of TOC removal/diazinon removal was still low when using the sono-Fenton process, which indicated that better experimental designs were necessary.

Fe2+ + H2O2 ^ Fe3+ + ^OH + OH- (2)

Fe3+ + H2O2 ^ Fe-OOH2+ + H+ (3)

Fe-OOH2+ + ))) ^ Fe2+ + ^OOH (fast) (4)

3.2. Effect of pxidants

Recently, the use of sulphate radical-based advanced oxidation processes (AOPs) 2-

produced by S2O8 - has been proven to be a promising method for oxidising organic pollutants [16]. Sulphate radicals fSO4-) have a high standard redox potential (E0 = 2.6 V), which makes them very strong oxidants, and are capable of more selective oxidation than

•OH radicals at acidic pH. Consequently, ^SO4" can degrade and mineralize contaminants

2- • -more efficiently. When S2O8 - and transition metals react, SO4- can be formed (Eq. 5) and

degrade organic compounds. In addition, ^SO4" can undergo hydrolysis or react with OH- to

form •OH (Eqs. 6 and 7). This process is an improvement upon the disadvantage(s) of

traditional AOPs, which must be carried out at low pH [16]. Ultrasonic irradiation converts

2- • - 2-S2O8 " to two SO4- molecules (Eq. 8). Thus, S2O8 " can be considered a suitable oxidant when

used with ultrasound and transition metals to develop a sono-Fenton-like process [20].

S2O82" + Men+ ^-SO4" + SO42" + Me(n+1)+ (5)

•SO4" + H2O ^ SO42" + -OH + -H (6)

•SO4" + OH" ^ SO42" + -OH (7)

S2O82" + ))) ^ 2-SO/ (8)

2- 2-Therefore, this study used H2O2, S2O82- and a combination of H2O2/S2O82- with

sonolysis to further increase mineralization efficiency. As shown in Fig. 1, 96, 95 and 94% of

diazinon was degraded when H2O2, H2O2/S2O8 - and S2O8 - were added, respectively. The initial ORP value was approximately 276 mV and sharply increased to between 500 and 550

mV once the oxidants were dosed. After 60 min of reaction, the final ORP values were 570,

2- 2546 and 530 mV when H2O2, H2O2/S2O8 and S2O8, respectively, were added. The

163 ultrasound/Fe /H2O2 process resulted in the highest ORP value and diazinon degradation

164 efficiency; however, these measurements were only slightly greater than those of the other

165 two processes. In addition, the amounts of TOC removed by these three processes were 13,

166 12 and 10%, respectively, which indicated that the degraded diazinon could not be

167 mineralized to CO2. Based on the above discussion, H2O2 performed as the best oxidant for

168 degrading diazinon when it was used in conjunction with the sonochemical process.

169 3.3. Effect of transition metals

170 In Eq. 9, it is found that adding external H2O2 can increase the formation of ^OH and

171 may increase the oxidation rate, and such effects have been observed in the presence of

172 metallic ions especially Cu2+, Fe3+ and Ag+. Ling et al. [21] and He et al. [22] have both

173 proposed that the added Co or Ag would react with H2O2 and produce -OH radicals. In

• 2+

174 addition, the OH radicals produced by the ultrasound/Co /H2O2 system would react with

175 organic pollutants and result in their degradation and mineralization. Hence, in this study,

176 seven different combinations (Fe2+, Ag+, Co2+, Fe2+/Ag+, Fe2+/Co2+, Ag+/Co2+ and

2+ + 2+ -1 -1

177 Fe /Ag /Co (transition metals were all 10 mg L-1)) were examined, each with 100 mg L-

178 H2O2. Among these seven combinations, the ultrasound/Fe /H2O2 was the most effective one.

180 H2O2 + metaln+ + H+ ^ -OH + H2O + metal(n+1)+ (9)

182 When Ag+ was used only, degradation and mineralization of diazinon achieved using

183 the ultrasound/Ag+/H2O2 process were 41 and 8%, respectively, which were slightly better

184 than those obtained using ultrasound alone or the combined ultrasound/H2O2 process (as

185 shown in Table 2). However, in this study, the effects of Ag+ addition were much less

186 significant than those of Fe addition. This result could be explained by Eqs. 10-11, which

187 points out that the Ag+ reacts with ^OH radicals under acidic conditions to form Ag2+ or Ag3+.

Thus, the number of •OH radicals would become insufficient for degrading the organic matter [23].

-OH + Ag+ + H+ ^ H2O + Ag2+ (10)

2-OH + Ag+ + 2H+ ^ 2H2O + Ag3+ { (11)

2+ • Similarly, the addition of Co resulted in a competition effect by reacting with OH

radicals and producing ^OH radicals by sono-Fenton or sono-Fenton-like processes and could

not be used to degrade diazinon [17]. Also, degradation and mineralization of diazinon were

slightly higher when two or three transition metals were used in the solution than when either

Ag or Co was present, as shown in Table 2. Degradation and mineralization in the

presence of 2 to 3 transition metals, however, were slightly lower than the Fe was used

2+ • alone, indicating that the addition of Fe2+ could help the system provide more •OH radicals

for degrading organic compounds.

3.4. Effect of Fenton's reagent concentration

Table 3 shows the values for diazinon degradation and TOC removal and the ratios of

TOC removal/diazinon degradation at different Fe concentrations, H2O2 concentrations and

temperatures. Diazinon degradation by the ultrasound/H2O2 process (no Fe2+ addition) was only 26% with 5% TOC removal, which could be explained by the insufficient formation of

-OH radicals for diazinon degradation. However, diazinon degradation significantly increased

2+ 2+ when Fe was added to the solution. When the Fe concentration became greater than 10

mg L-1 with 150 mg L-1 H2O2, diazinon degradation was higher than 86%. It is understood

that increasing amounts of Fe enable the formation of -OH radicals [18,24]. However,

exceeding a specific iron-salt dose decreased the treatment efficiency, which would be

expected if -OH molecules were being reduced by excessive amounts of Fe [25-27]. Hence,

diazinon degradation and TOC removal were both lower in the presence of 30 mg L- Fe

compared with 20 mg L-1 Fe2+. The ratios of TOC removal/diazinon degradation shown in

Table 2 were between 0.15 and 0.30, and the ratio obtained when no Fe addition was

2+ -1 slightly greater than those observed when Fe was at 10 and 15 mg L- . This finding

indicates that the major degradation pathway of diazinon by the ultrasound/H2O2 process

2+ 2+ (without Fe ) was ultrasonic thermal cleavage. As Fe was added, the formation of 'OH

increased and allowed for more diazinon degradation. However, if this 'OH increase does not

result in the total destruction of the diazinon, then TOC removal remains as a consequence of

thermal cleavage inside of cavitation bubbles [10], and the ratio of TOC removal/diazinon

degradation decreases.

Increasing the H2O2 concentration in the sono-Fenton process is useful for increasing

the degradation efficiency of organic compounds [28]. In each case, Table 3 shows that the

degradation of diazinon was higher than 85% at 10 mg L- Fe at four different H2O2 concentrations and that the diazinon degradation efficiency increased with increasing H2O2 concentrations. More effective diazinon degradation was observed at 150 mg L-1 H2O2. However, the differences in diazinon degradation and mineralization that were obtained when the H2O2 concentration was between 100 mg L-1 and 150 mg L-1 were insignificant. More addition of H2O2 led to the more formation of 'OH and resulted in the oxidation of the organic compounds [29]. However, additional doses of H2O2 in the solution phase could capture the 'OH radicals and quench the reactions between 'OH and organic compounds [30]. Consequently, the degradation efficiency of diazinon decreased when 200 mg L-1 of H2O2 was added to the solution. Although H2O2 is generally used as an oxidant and disinfectant in water and wastewater treatment processes, the detergent characteristics of H2O2 inactivate the microorganisms during biological processes [9]. Hence, based on the comparable results obtained for 100 and 150 mg L-1 H2O2, as shown in Table 3, if a higher treatment efficiency

238 is the priority for diazinon degradation by the sono-Fenton process, then combining 150 mg

1 1 2+

239 L- H2O2 with 20 mg L- Fe provides better experimental conditions. Otherwise, if

240 operational costs and the detergent characteristics of H2O2 are important factors, the addition

1 1 2+

241 of decreased amounts (such as 100 mg L- H2O2 with 10 mg L- Fe ) is preferred.

242 3.5. Effect of temperature

243 Generally, higher reaction temperatures produce more cavitation bubbles for

244 degrading organic pollutants [9]. However, extremely high temperatures could lead to Fe

245 unstable and self-decomposition of H2O2, which would reduce the reaction rates or

246 degradation efficiencies of organic compounds [31]. The increase in temperature also results

247 in the faster cushioning of cavitation bubbles compared with low temperatures. Thus,

248 increasing the temperature could decrease the degradation efficiencies of organic pollutants

249 [32]. As shown in Table 3, the degradation of diazinon at the five temperatures varied from

250 96 to 98%, which indicated that the effect of temperature on diazinon degradation was

251 insignificant. However, the results of diazinon mineralization differed from the

252 accompanying degradation results, in which the TOC removal slightly increased from 26%

253 (15 °C) to 30% (25°C) then generally decreased to 16% (55°C). These results indicated that

254 the faster cushioning of cavitation bubbles at higher reaction temperatures inhibited the

255 complete diazinon mineralization and resulted in decreasing TOC removal. In addition, the

256 results obtained for TOC removal/diazinon degradation were comparable to those obtained

257 for TOC removal, for which the optimal ratio of TOC removal/diazinon degradation occurred

258 at 25 °C.

259 3.6. Possible degradation by-products and pathway for diazinon

260 In this study, the possible degradation by-products of diazinon were identified using

261 the GC/MS, and the diazinon degradation pathways were proposed based on suggestions

262 from the literatures [3,6,8,33,34]. The experimental results indicated that four by-products,

diethyl phosphonate, 2-isopropyl-6-methyl-4-pyrimidinol (IMP), diazoxon and hydroxydiazin, were observed during degradation of diazinon (Fig. 2a). The proposed degradation pathway for diazinon is shown in Fig. 2b. It was understood that the formation of diazoxon, which resulted from the substitution of sulphur with oxygen (on the P=S bond through oxidation) [33], occurred first. Then, IMP was produced from the hydrolysis of diazoxon, which involved cleavage of the P-O bond on the pyrimidine group [3,6]. As the diazinon was degraded, an important pathway basing on the attack of *OH on the -O- functional group dividing the diazinon into two by-products, which resulted in the formation of diethyl phosphonate and IMP [8]. The third pathway identified was hydroxylation, where the *OH group became attached to the isopropyl functional group in diazinon and produced hydroxydiazinon. Based on further hydrolysis, it was possible to divide hydroxydiazinon into diethyl phosphonate and IMP. 3.7. Toxicity profiles

Even the sono-Fenton process can effectively degrade diazinon, TOC removal only reached approximately 30%, which indicated that 70% of the carbon content remaining in the solution phase. This un-mineralized carbon content could increase or decrease toxicity. Hence, in addition to the degradation efficiencies, further investigations were carried out regarding the determination of toxicity changes based on cell viability measurements. Figure

3 shows the cell-viability results that were obtained from untreated diazinon (item I), treated

wastewater after 60 min reaction with ultrasound (item II), ultrasound/Fe (item III), ultrasound/H2O2 (item IV), Fenton (item V) and sono-Fenton process (item VI), as well as in the blank (Reverse Osmosis water, in which cell viability was defined as 100%, item VII). Before degradation, the cell viability of the untreated diazinon was 49%. As the diazinon was

treated, the cell viability increased to 54-84%, which indicated that the toxicity of diazinon

was slightly reduced by ultrasonic treatment alone, ultrasound/Fe and ultrasound/H2O2

processes, moderately reduced in the treatments using the Fenton process, and significantly reduced in the treatments using the sono-Fenton process. Figure 4 depicts the satisfactory relationships between diazinon degradation and cell viability and shows a liner relationship between TOC removal and cell viability. An increase in cell viability obviously resulted from diazinon degradation and the removal of TOC. In addition, the R value of diazinon degradation and cell viability was greater than that of TOC removal, which indicated that diazinon degradation could be the primary reaction involved in reducing toxicity. Additionally, by reducing diazinon toxicity via the sono-Fenton process, this wastewater could be further treated using biological methods.

4. Conclusions

This study examined the effectiveness of different sonochemical processes, namely, a

combination of ultrasound with three transition metals and two oxidants, for diazinon

degradation. The addition of Ag+ and Co2+ negatively affected diazinon degradation and

mineralization. The contributions of H2O2, S2O8 - and H2O2/S2O8 - to the degradation of diazinon in the sonolysis systems were comparable. However, H2O2 appeared to be the better oxidant. The maximum diazinon degradation efficiency, which was achieved by combining ultrasound with the Fenton process, was 98% with the mineralization of 30%. In addition, the toxicity of treated diazinon significantly decreased based on a remarkable increase in cell viability. The effect of increasing temperature was insignificant. Four intermediates were observed during diazinon degradation, and hydrolysis and *OH radical oxidation were the major reaction mechanisms that resulted in the breakdown of the diazinon structure. There was a strong relationship between diazinon degradation and toxicity reduction, which indicated that the diazinon degradation was a key step in toxicity reduction.

Acknowledgements

The financial support of the Ministry of Science and Technology, Republic of China

(grant 101 -2221 -E-264-005 and 103-2221-E-264-001-MY2), is gratefully appreciated.

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398 Table 1 Diazinon degradation and TOC removal results and the ratios of TOC

399 removal/diazinon degradation obtained using different treatment processes.

Methods Diazinon degradation (%) TOC removal (%) TOC removal/Diazinon degradation

Ultrasound 22 4 0.18

Ultrasound/Fe2+ a 25 5 0.19

Ultrasound/H2O2 b 26 5 0.20

Fenton a,b 62 6 0.10

Sono-Fenton a,b 96 13 0.14

400 aFe2+ concentration was 10 mg L-1; bH2O2 concentration was 100 mg L-1

Table 2 Results for diazinon degradation and TOC removal and ratios of TOC

removal/diazinon degradation when different transition metals were added.

Factorsa TOC Diazinon degradation (%) . removal I TOC removal/Diazinon degradation (%)

t-< 2+ Fe 96 130 0.14

Ag+ 41 8 0.13

Co2+ 34 6 0.17

Fe2+/Ag+ 58 6 0.11

Fe2+/Co2+ 79 9 0.12

Ag+/Co2+ 38 4 0.09

Fe2+/Ag+/Co2+ 70 8 0.12

405 aH2O2 concentration was 100 mg L-1 406 metal was 10 mg L-1. at pH 3 and 25 °C; the concentration of each transition

409 Table 3 Results obtained when the sono-Fenton process was used, including the diazinon

410 degradation and TOC removal percentages and the ratios of TOC removal/diazinon

411 degradation using varying concentrations of H2O2 and Fe2+ at different reaction

412 _temperatures._

Factors Diazinon degradation TOC (%) removal (%) TOC removal/Diazinon degradation

Fe2+ concentration (mg L-1)a

0 26 5 0.20

10 96 15 0.15

15 97 18 0.18

20 98 30 0.30

H2O2 concentration (mg L-1)b

0 25 5 0.19

50 92 13 0.14

100 96 13 0.14

150 96 15 0.15

Temperature (°C)c

15 96 26 0.27

25 98 30 0.30

35 98 25 0.25

45 97 19 0.20

55 97 15.6 0.16

aH2O2 concentration was 150 mg L-1 at 25 °C; bFe2+ concentration was 10 mg L-1at 25 °C; cFe2+ and H2O2 concentrations were 20 and 150 mg L-1, respectively.

H2O2 S2O82- H2O2/S2O82-

417 2 2

418 Fig. 1. Degradation and mineralization of diazinon obtained using a sono-Fenton-like process

419 with H2O2 and S2O82- (both 100 mg L-1) and 10 mg L-1 of Fe2+.

423 (a)

hydrolysis

Diethyl phosphonate

2-isopropyl-6-methyl pyrimidein-4-ol

Hydroxydiazinon

Fig. 2. (a) GC/MS spectra of diazinon and its degradation by-products; (b) proposed degradation pathway for diazinon under sono-Fenton treatment.

«•H ©

(I) (II) (III) (IV) (V) (VI)

Fig. 3. Cell viability profiles for (I) untreated diazinon, wastewater after 60 min of treatment by (II) ultrasound, (III) ultrasound/Fe2+, (IV) ultrasound/H2O2, (V) the Fenton process, and (VI) the sono-Fenton process and (VII) the blank (RO water).

« > ©

■a =

20 40 60 80

Cell viability (% of RO water)

Fig. 4. The relationship between the profiles of cell viability and diazinon degradation or TOC removal.