**2.2 Objective pesticides and other reagents**

Five pesticides (Table 1) were selected for an objective pesticide. These pesticides were used in the Onga River Basin and their aiming standard values in tap water quality were established (Ando, 2004). Their structural formulas were shown in Fig. 1. Dinitrophenol (DNP) was used as a chemical substance for the capability evaluation of alumina carrier (Okumura et al., 2003). These chemical substances were obtained from Hayashi Pure Chemical Industries, Wako Pure Chemical Industries and Tokyo Kasei Kogyo Co.. Each standard solution was prepared by the dilution with acetone. An alumina carrier was obtained from Sumitomo Chemical Co.. The properties of the alumina and silica gel carriers, comparative carriers, were shown in Table 2. Two types of alumina, NK124 and NKHO24

(Fig. 2), and silica gel carrier-TiO2 photocatalysts were produced by the Sol-Gel Method (Okumura et al., 2004; Tanizaki et al., 1997). All solvents were the grade reagents for pesticide residue analysis, which were obtained from Kanto Chemical Co. and Wako Pure Chemical Industries. Other reagents were special grade reagents, which were obtained from Wako Pure Chemical Industries. Anhydrous Na2SO4 and NaCl were heated at 800 oC for 3 h after acetone-washing. The water was purified using a Millipore Milli-Q Ultra-pure Water System.


Table 1. The shipped amounts and the aiming water qualities of the objective pesticides in the Onga River Basin

Gas chromatograph/mass spectrometer (GC/MS) was a Hewlett Packard HP-5890 series and a JEOL auto mass system. Total nitrogen (T-N) analysis was performed using a Tokyo Kasei Ind. Co. TCI-NOX 1000, GASTORR GT-102, VISIBLE DETECTOR S-3250 and AUTO SAMPLER SS-3600, while other determinations Hitachi Co. U-2000A a spectrophotometer

Five pesticides (Table 1) were selected for an objective pesticide. These pesticides were used in the Onga River Basin and their aiming standard values in tap water quality were established (Ando, 2004). Their structural formulas were shown in Fig. 1. Dinitrophenol (DNP) was used as a chemical substance for the capability evaluation of alumina carrier (Okumura et al., 2003). These chemical substances were obtained from Hayashi Pure Chemical Industries, Wako Pure Chemical Industries and Tokyo Kasei Kogyo Co.. Each standard solution was prepared by the dilution with acetone. An alumina carrier was obtained from Sumitomo Chemical Co.. The properties of the alumina and silica gel carriers, comparative carriers, were shown in Table 2. Two types of alumina, NK124 and

(Fig. 2), and silica gel carrier-TiO2 photocatalysts were produced by the Sol-Gel Method (Okumura et al., 2004; Tanizaki et al., 1997). All solvents were the grade reagents for pesticide residue analysis, which were obtained from Kanto Chemical Co. and Wako Pure Chemical Industries. Other reagents were special grade reagents, which were obtained from Wako Pure Chemical Industries. Anhydrous Na2SO4 and NaCl were heated at 800 oC for 3 h after acetone-washing. The water was purified using a Millipore Milli-Q Ultra-pure Water

(kg)

Aiming standard value (mg l-1)

a The values in 2003

Pesticide Use Shipped amount a

Chlorthalonil Disinfectant 185 0.05

Pencycuron Disinfectant 686 0.04

Cafenstrole Herbicide 1,946 0.008

Thiobencarb Herbicide 155 0.02

Trifluralin Herbicide 5,238 0.06

Table 1. The shipped amounts and the aiming water qualities of the objective pesticides in

**2. Material and methods** 

**2.2 Objective pesticides and other reagents** 

**2.1 Instruments** 

was used.

NKHO24

System.

the Onga River Basin

Trifluralin

Fig. 1. Structural formulas of the objective pesticides

Photodecomposition Behaviors of Pesticides in the Source

Fig. 3. Apparatus for the photodecomposition of the pesticides

Fig. 4. Structure of photoreactor

for Water Supply Using an Alumina Carrier-Titanium Dioxide Photocatalyst 55


Table 2. Properties of alumina and silica gel carriers

NK124 NKHO24

Fig. 2. Prepared alumina carrier-TiO2 photocatalysts

#### **2.3 Apparatus for the photodecomposition of the pesticides**

The apparatus for the photodecomposition experiments of the pesticides and DNP was shown in Fig. 3. The photoreactor (Fig, 4) was made of stainless steel and equipped with a 6 W low pressure mercury lamp (a Matsushita Electric Ind. Co. GL6/Q) and a stabilizer (Nihon Fluorescence Electric Co.). Eighty five milliliters of each photocatalyst was packed in a thickness of about 5 mm. The UV illumination intensity on the surface of catalyst was 10 mW cm-2. Sample water was circulated with a roller pump (Furue Science Co.).

Particle size (mm) 2-4 2-4 1.7-4

Al2O3 contents (%) 99.9 99.7 -

Micropore volume (cm3 g-1) 0.77 0.58 -

Relative surface area (m2 g-1) 130 160 -

Compacting strength (kg) 2 6 -

Supporting ratio (%) 20 17 25

NK124 NKHO24

The apparatus for the photodecomposition experiments of the pesticides and DNP was shown in Fig. 3. The photoreactor (Fig, 4) was made of stainless steel and equipped with a 6 W low pressure mercury lamp (a Matsushita Electric Ind. Co. GL6/Q) and a stabilizer (Nihon Fluorescence Electric Co.). Eighty five milliliters of each photocatalyst was packed in a thickness of about 5 mm. The UV illumination intensity on the surface of catalyst was 10

mW cm-2. Sample water was circulated with a roller pump (Furue Science Co.).

NK124 NKHO24 Silica gel

Item Carrier

Table 2. Properties of alumina and silica gel carriers

Fig. 2. Prepared alumina carrier-TiO2 photocatalysts

**2.3 Apparatus for the photodecomposition of the pesticides** 

Fig. 3. Apparatus for the photodecomposition of the pesticides

Fig. 4. Structure of photoreactor

Photodecomposition Behaviors of Pesticides in the Source

**3. Results and discussion** 

**photocatalysts** 

TiO2 photocatalyst.


Fig. 5. Photodecomposition rates of DNP

**3.2 Photodecomposition behaviors of pesticides** 




0


ln(C

/

C

o)




for Water Supply Using an Alumina Carrier-Titanium Dioxide Photocatalyst 57

Figure 5 shows the photodecomposition rates of DNP using the alumina and silica gel carrier-TiO2 photocatalysts. DNP was decreased exponentially with reaction time (t) and the rate of DNP disappearance was nearly represented by a first-order process. The values of pseudo-first-order rate constant (k: C=C0e-kt) of NK124, NKHO24 and silica gel carrier-TiO2 photocatalysts determined from the plot of data points (C/C0 vs. t) were 0.027, 0.016 and 0.030 min-1, respectively. The rate constant of NK124 carrier-TiO2 photocatalyst was near that of silica gel-TiO2 photocatalyst.The micropore volume of NK124 is lager than that of NKHO24 but its relative surface area is smaller than that of NKHO24. The supporting ratio of NK124 was higher than that of NKHO24. It was supposed that the deference of DNP photodecomposition rate was caused by the deference of supporting ratio. Then, the photodecomposition experiments of the pesticides were performed using a NK124 carrier-

0 50 100 150

k=0.016 min-1

k=0.027 min-1

Figure 6-10 show the photodecomposition ratios of the pesticides. These pesticides were decomposed faster than DNP and the removal efficiencies after 3 min UV irradiation were 94% (Cafenstrole), 92% (Chlorthalonil), 75% (Thiobencarb), 67% (Pencycuron), 58% (Trifluralin) and 8% (DNP). After 30 min UV irradiation, the removal efficiencies of Cafenstrole and Chlorthalonil, and Thiobencarb, Pencycuron and Trifluralin, were 98 and 94%, respectively. The UV illumination intensity in the experiments was so strong that the

k=0.030 min-1

same removal efficiencies as with the photocatalyst were obtained without the

**3.1 Comparison of the photodecomposition capability of alumina carrier-TiO2**

#### **2.4 Analyses of pesticides, DNP and other items**

The quantification of the pesticides and DNP in UV irradiated solution was performed in the next procedure. About 2 g of NaCl was added in 40 ml of UV irradiated solution and each pesticide or DNP was extracted with 4 ml of dichloromethane. The dichloromethane layer was separated from aqueous layer, dehydrated with anhydrous Na2SO4 and analyzed by the GC/MS method (Nakano et al., 2004; Yamaguchi et al., 1997). The GC/MS conditions were shown in Table 3. Each calibration curve showed good linearity in the quantification range. Their recoveries by the method were over 85%.

pH, suspended solid matter (SS), BOD, KMnO4 consumption, total nitrogen (T-N), total phosphorus (T-P) and electric conductivity (EC) were measured by the method of Japanese Industrial Standard K0102 (Japan Industrial Standards Committee, 1995).


Table 3. GC/MS conditions

#### **2.5 The photodecomposition capability experiments of alumina carrier-TiO2 photocatalysts and photodecomposition experiments of pesticides**

Each alumina or silica gel carrier-TiO2 photocatalyst was packed in the photoreactor. The water samples for DNP and pesticides experiments were prepared by adding 3 ml of each 1,000 mg l-1 DNP or pesticide acetone solution in 3 l of purified water (for the photodecomposition capability experiment of photocatalyst) or the river water (Table 4) (for the photodecomposition experiment of pesticide). The water sample was vigorously shaken for 30 min using a separatory funnel and placed in 5 l glass bottle. The water sample was firstly circulated for 30 min at l min-1 of flow rate by stirring and the system was allowed to reach equilibrium. Then the mercury lamp was switched on. The UV irradiated solution was periodically withdrawn during irradiation and DNP or each pesticide was quantified by the GC/MS method. The photodecomposition experiments of pesticides without a photocatalyst were also performed.


Table 4. Quality of the river water used for this experiment
