Chemosphere xxx (2014) xxx–xxx

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Application of immobilized TiO2 photocatalysis to improve the inactivation of Heterosigma akashiwo in ballast water by intense pulsed light Daolun Feng a,⇑, Shihong Xu b, Gang Liu c a b c

College of Ocean Science and Engineering, Shanghai Maritime University, Shanghai 201306, PR China School of Environmental Science and Engineering, Donghua University, Shanghai 201620, PR China Maritime College, Shandong Jiaotong University, Shandong Province 264200, PR China

h i g h l i g h t s  TiO2 photocatalysis is firstly incorporated into pulse intense light inactivation.  Here pulse intense light/TiO2 photocatalysis obtains 40.15% elevation in inactivation.  Here pulse intense light/TiO2 photocatalysis saves 35.71% energy consumption.  Pulse intense light/TiO2 shows the potential for applying in ballast water treatment.

a r t i c l e

i n f o

Article history: Received 6 April 2014 Received in revised form 25 November 2014 Accepted 25 November 2014 Available online xxxx Handling Editor: Shane Snyder Keywords: Ballast water Intense pulsed light/TiO2 Heterosigma akashiwo Energy consumption

a b s t r a c t Ballast water exotic discharge has been identified as a leading vector for marine species invasion. Here immobilized TiO2 photocatalysis is introduced to improve the performance of intense pulsed light. For intense pulsed light/TiO2 photocatalysis, a typical inactivation of 99.89 ± 0.46% can be achieved under treatment condition of 1.78 L min1 flow rate, 300 V pulse peak voltage, 15 Hz pulse frequency and 5 ms pulse width. Moreover, within tested 220–260 V peak voltage, 18.37–40.51% elevation in inactivation is observed in comparison with intense pulsed light treatment alone. The rough energy consumption of the tested intense pulsed light/TiO2 treatment system is about 1.51–2.51 times higher than that of the typical commercial UV ballast water treatment system. The stability of the photocatalytic reactivity and intactness of loaded TiO2 film is proved within 20-d’s test, while local erosion on stainless steel support is observed after 30-d’s test. The results indicate that intense pulsed light/TiO2 photocatalysis is likely to be a competitive ballast water treatment technique, while further measures is needed to reduce the energy consumption and ensure the performance of TiO2 film in a long run. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Ballast water is an idea media and is essential for keeping the balance and stability of the unladen ships (Lacasa et al., 2013). While the discharge of ballast water around the world lead to the risk of biological invasion. Nowadays, invasive species are found in 84% of the world’s 232 marine eco-regions, and ballast water exotic discharge has been identified as a leading vector for marine species invasion (Delacroix et al., 2013). To minimize the negative impacts on health, environment and economy, the International Maritime Organization (IMO) adopts ⇑ Corresponding author at: Shanghai Maritime University, 1550 Haigang Avenue, Pudong New District, Shanghai 201306, PR China. Tel.: +86 (021) 38284332; fax: +86 (021) 38284342. E-mail address: [email protected] (D. Feng).

the International Convention for the Control and Management of Ships’ Ballast Water and Sediments in 2004 (IMO, 2004). D-2 discharge standard attached in this convention regulate the maximum concentration of viable organisms in ballast water that can be released. The convention will enter into force 12 months after 30 countries representing 35% of the world merchant shipping tonnage have ratified it. Therefore, different treatment methods have been proposed to prevent the biological invasion via ships’ ballast water. It is estimated that a total of 68 different ballast water treatment systems were available in September 2012 (Delacroix et al., 2013). Of these, 75% of the treatment system is based on UV inactivation or using chlorine as active substances. While UV inactivation is actually not a reliable inactivation method for all kinds of microorganisms in ballast water, and regrowth of microorganisms in ballast water

http://dx.doi.org/10.1016/j.chemosphere.2014.11.060 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Feng, D., et al. Application of immobilized TiO2 photocatalysis to improve the inactivation of Heterosigma akashiwo in ballast water by intense pulsed light. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.11.060

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D. Feng et al. / Chemosphere xxx (2014) xxx–xxx

is observed after UV irradiation (Martínez et al., 2013; Zhang et al., 2014). Chlorine and other chemical disinfectant are considered to be effective, while these substances may cause corrosion of ballast tanks due to strong oxidizing ability, and generate undesirable byproducts (Delacroix et al., 2013). Moreover, overview from IMO also supports to find novel treatment methods that can meet the needs of safe, practical, economical, effective and environmental friendliness simultaneously and strictly (Gregg et al., 2009). Therefore, the development of more effective and environmental friendly treatment techniques is still necessary and urgent. In our previous work, relative to UV treatment, due to the advantage of more environmental friendliness, faster and more effective inactivation, and no tailing effects (Oms-Oliu et al., 2010; Schaefer et al., 2007; PSU, 2014), intense pulsed light (IPL) is introduced to inactivate two kinds of typical microalgae in sea water. The results indicate that IPL is effective in inactivating microalgae, while the energy consumption seems to be a big challenge for this technique to be applied in treating ballast water. Since the first report of UV induced redox chemistry on TiO2 in early 1970s (Fujishima and Honda, 1972), considerable attention is paid on improving the sterilization efficiency of UV based on photocatalysis (Nakata and Fujishima, 2012). Within different kinds of photocatalysts, TiO2 is the most widely studied and used because of its excellent photocatalytic reactivity, chemical stability, long durability, nontoxicity, low cost and other unique characteristics. (Hashimoto et al., 2005; Nakata and Fujishima, 2012). For ballast water treatment, the enhancement of UV inactivation performance with TiO2 photocatalysis is also in progress (Wu et al., 2011; Zhang et al., 2014). In comparison with UV treatment alone, UV/TiO2 photocatalysis shows excellent inactivation effects, and can inhibit the regrowth of treated organisms in ballast water (Martínez et al., 2012; Martínez et al., 2013). For IPL sterilization technique, almost a half of the emitted energy is within UV range (Ferrario et al., 2013). Hence, here the widely used TiO2 photocatalyst is firstly introduced into IPL sterilization technique to enhance its inactivation efficiency substantially, and to decrease its energy consumption. Although fine powdered TiO2, especially in nano-scale, shows excellent photocatalytic reactivity due to more reactive surface area (Henderson, 2011), the separation of TiO2 powder is a time consuming and costly process (Shan et al., 2010). As a result, immobilizing photocatalyst on an inert support is widely researched (Shan et al., 2010) and presently seems to be a feasible way for large scale application. Hence, here TiO2 is immobilized onto the inner 316L stainless steel surface, and coupled with IPL to treat synthetic ballast water. Typical red tide microalgae: Heterosigma akashiwo is chosen to test the treatment efficacy. 2. Materials and methods 2.1. H. akashiwo and culture medium H. akashiwo is purchased from Ocean University of China, and f/ 2 medium is applied to culture H. akashiwo.

2.2. Loading of TiO2 film on 316L stainless steel 2.2.1. Cleaning of support 316L stainless steel (0.5 mm thick) slice is subsequently grounded on both sides with silicon carbide paper, degreased in acetone for 30 min, pickled in 0.9 M HNO3 solution for 30 min and sonicated in de-ionised water for 30 min to remove surface impurities and contaminations.

2.2.2. Preparation of TiO2 sol–gel Precursor solution for TiO2 loading is prepared by the following procedure (Fu et al., 2012). Tetra-n-butyl titanate (20.42 mL) and diethanol amine (5.76 mL) is sequentially dissolved into 70.74 mL continuously-agitated ethanol, and then further agitated for 1 h. Subsequently, the mixture of water (1.08 mL) and ethanol (2.0 mL) is dripped gradually into as-prepared continuously-agitated solution, further agitated for 2 h, and then stand in the dark for another 24 h. Consequently, a transparent, homogeneous and stable TiO2 sol–gel is prepared. 2.2.3. Preparation of TiO2 film Firstly, cleaned 316L stainless steel slice is immersed in TiO2 sol–gel for 3 min, pulled out with rate of 20 mm min1, and then dried under ambient temperature for 1 h. Secondly, the dried and coated stainless steel slice is heated in muffle furnace with 5 °C min1 temperature elevation rate until the given temperature is reached. Thirdly, the heating lasts for 60 min under desired temperature; then the slice is cooled naturally to ambient temperature. Consequently, a layer of TiO2 film is loaded on 316L stainless steel slice. The procedure is repeated to achieve desired layers of TiO2 film. 2.3. Characterization of loaded TiO2 film The crystal structure of TiO2 loaded film is evaluated using a D/max–2550PC X-ray diffractometer (Rigaku Inc., Japan); The microscopic surface morphology and thickness of TiO2 loaded film is observed with FEI Magellan 400 XHR-SEM (FEI Company, USA); The film is pretreated for measuring its thickness with Leica EM TIC 3X Triple Ion Beam Cutter (Leica Microsystems GmbH, Germany). A rough comparison of surface morphology before and after 20-d’s experiment is evaluated by Leica S8AP0 stereoscopic microscope (Leica Microsystems GmbH, Germany). 2.4. Photocatalytic decomposition of methyl orange The microalgae inactivation experiment is complicated and time-consuming. Thus at the beginning, degradation of methyl orange is used to test the photocatalytic activity of loaded TiO2. The testing process is the following: TiO2 loaded stainless steel slice is emerged into methyl orange solution in a quartz container. An external UV light source is used to provide UV radiation to test the photocatalytic decomposition ability. The area of TiO2 loaded stainless steel slice is kept constant through all the tests. The concentration of methyl orange is determined at regular intervals to calculate the decomposition percentage (details see Section 2.6). 2.5. IPL/TiO2 inactivation experiments Inactivation of H. akashiwo is performed in a self-designed IPL inactivation set-up (Fig. 1). The experimental process is the following: firstly, Culture medium with H. akashiwo at its logarithmic growth stage is diluted with artificial sea water (prepared by dissolving 1 g sea salt into 30 mL deionized water), and stored in raw water tank as raw ballast water. Then, raw ballast water is pumped by dosing pump (GM0120PQ1MNN, Milton Roy Industrial (Shanghai) Co., LTD, China) and flow into the treatment chamber, where the viable H. akashiwo is inactivated by IPL/TiO2 photocatalysis. The treated water is finally collected by the treated water tank. Raw and treated ballast water is sampled in triplicate at 2-min intervals to numerate the concentration of viable H. akashiwo. Also the treated water temperature is recorded by an OMEGAÒ thermometer (HH500RA, Omegadyne, Sunbury Ohio).

Please cite this article in press as: Feng, D., et al. Application of immobilized TiO2 photocatalysis to improve the inactivation of Heterosigma akashiwo in ballast water by intense pulsed light. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.11.060

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Sampling point 1 Inner surface TiO2 film

Dosing pump Sight port Optical glass Raw water tank

Inlet Temperature probe

Outlet Xenon lamp

Sampling point 2

Drain

Treated water tank Pulse light power source Fig. 1. Schematic of intense pulsed light/TiO2 inactivation set-up.

2.6. Calculation of methyl orange decomposition percentage

C ¼ 13:373  OD461  0:0409 where C is the methyl orange concentration, mg L1; OD461 is the absorbance of methyl orange at wavelength of 461 nm. 2.7. Determination of viable H. akashiwo concentration Flow Cytometry (Cyflow Cube 6, Partec GmbH, Münster, Germany) is used to determine the low viable H. akashiwo concentration in ballast water accurately. A GuavaÒ ViaCountÒ reagent (Guava Technologies Inc., Millipore, USA) is used to stain H. akashiwo to distinguish the viable cells, non-viable cells, their nucleus-containing debris and other impurities. Firstly, 10 mL water is sampled into 40 mL centrifugal tube and is well agitated. Subsequently, 400 lL homogeneous sample and 400 lL ViacountÒ reagent are added into a sample tube, and after well agitation, the sample is stained in the dark for 30 min. Then the stained sample is diluted by 200 lL sea water, and numerated by flow cytometry.

Decomposition percentage (%)

70

The absorbance of methyl orange at 464 nm wavelength is determined with Varian Cary 400 UV/Vis Spectrometer. The following standard curve is plotted and used to calculate the methyl orange concentration.

1 layer 2 layer 3 layer 4 layer 5 layer

60 50 40 30 20 10 0 20

40

60

80

100

120

140

160

Time (min) Fig. 2. Impacts of loaded TiO2 layer on photocatalytic decomposition effects. Methyl orange concentration 10 mg L1, treated solution volume 25 mL.

3. Results and discussion

layer of TiO2 film. As the results, the photocatalytic decomposition rate increases with the number of loaded layer of TiO2 film. Nevertheless, when the loaded layer of TiO2 film further increases, the outer TiO2 molecules will block the inner one and form TiO2 particles, accelerate the recombination of the generated electrons and holes, thus lower the efficiency of light quantization (Henderson, 2011). Moreover, the active surface area of TiO2 particles decreases gradually since only the outer surface can have contact with the methyl orange solution. As the results, the photocatalytic decomposition rate drop gradually after reach the peak value. Surface morphology and sectional depth of TiO2 film loaded on the surface of 316L stainless steel with different layers is also characterized by SEM, and the results are shown in Fig. 3. After loaded, the film depth increases with the number of loaded layer, and reaches about 408 nm after 3-time’s loading. Moreover, a compact and uniform TiO2 film can be achieved after 3-time’s loading. Thus, hereinafter, three layers of TiO2 film will be loaded on 316L stainless steel slice.

3.1. Impacts of loaded layer on TiO2 photocatalytic activity

3.2. Impacts of incinerated temperature on TiO2 photocatalytic activity

Different layers of TiO2 film are loaded on the surface of 316L stainless steel, and their photocatalytic effects are shown in Fig. 2. The photocatalytic decomposition rate increases with the number of loaded layer of TiO2 film, and reaches the highest value (67.1% after 150 min decomposition time) with three loaded layers. After that, the photocatalytic decomposition rate decreases with the number of loaded layer of TiO2 film. Initially, the number of TiO2 molecules that can be involved in the photocatalytic reaction increases with the number of loaded

The photocatalytic effects of TiO2 film under different incinerated temperature are tested, and the results are shown in Fig. 4. The photocatalytic decomposition rate of loaded film increases with incinerated temperature, and reaches the highest value (67.1% with 150 min decomposition time) with 500 °C incinerated temperature. After that, the photocatalytic decomposition rate decreases with incinerated temperature. TiO2 film incinerated under different temperature is tested with XRD, and the results are shown in Fig. 5. For 450 °C incinerated

2.8. Calculation of energy consumption The energy consumption (Ws, J m3 treated water) for IPL inactivation is calculated by the following equation:

Ws ¼

P  60  1000 Q

where P is the input power (W); Q is the volumetric flow rate (L min1).

Please cite this article in press as: Feng, D., et al. Application of immobilized TiO2 photocatalysis to improve the inactivation of Heterosigma akashiwo in ballast water by intense pulsed light. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.11.060

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D. Feng et al. / Chemosphere xxx (2014) xxx–xxx

A-1layer

B-1 layer

Pt TiO2-274.3nm

B-3 layers

A-3 layers

Pt TiO2-408.7nm

A-5 layers

B-5 layers

Pt

TiO2-866.0nm

Fig. 3. SEM image of TiO2 film loaded on 316L stainless steel slice with different layers. A: morphology of loaded TiO2 film; B: cross section images of loaded TiO2 film.

temperature, crystal TiO2 presents with only anatase phase. For 500 °C incinerated temperature, rutile TiO2 emerges. Subsequently, the proportion of rutile TiO2 increases with incinerated temperature. Normally, anatase TiO2 presents higher photocatalytic reactivity than that of rutile TiO2 (Wang et al., 2013), while a certain ratio mixing of anatase and rutile TiO2 may enhance the photocatalytic reactivity obviously (Li et al., 2009; Su et al., 2011). Hereinafter, TiO2 will be loaded three times with 500 °C incinerated temperature. 3.3. Inactivation of H. akashiwo by IPL/TiO2 photocatalysis Inactivation of H. akashiwo is performed with IPL/TiO2 photocatalysis, and a control experiment is also conducted with IPL treatment alone, all these result are shown in Fig. 6. IPL/TiO2 treatment shows an excellent inactivation effects on H. akashiwo.

For 220 V peak voltages, 25.11 ± 2.64% inactivation can be achieved, in comparison with that of only 6.74 ± 0.24% inactivation in IPL treatment. Similarly, for 260°V peak voltages, the inactivation percentage for IPL/TiO2 and IPL treatment is 98.26 ± 0.19 and 70.47 ± 0.16 respectively. Within 220–260 V peak voltage, 18.37– 40.51% elevation in inactivation is observed. The results indicate that TiO2 photocatalysis improve the inactivation efficiency of IPL treatment dramatically. The amount of viable H. akashiwo without and with treatment is numerated by flow cytometry, and a typical result is presented in Fig. 6. After high percentage inactivation, the amount of dead cell and its nucleus-containing debris is about 23.09% more than that before treatment, which indicates at least the same percentage of cell debris produced after treatment. For IPL/TiO2 treatment, Electron-hole pair is generated inside the TiO2 by activation from IPL

Please cite this article in press as: Feng, D., et al. Application of immobilized TiO2 photocatalysis to improve the inactivation of Heterosigma akashiwo in ballast water by intense pulsed light. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.11.060

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D. Feng et al. / Chemosphere xxx (2014) xxx–xxx

105 o

450 C o 500 C o 550 C o 600 C

60

Inactivation percentage (%)

Decomposition percentage (%)

75

45

30

15

90 75 60 45 30 15 0 216

0 20

40

60

80

100

120

140

160

228

240

252

264

276

288

300

Pulse peak voltage (V)

Time (min) Fig. 4. Impacts of incinerating temperature on photocatalytic decomposition effects. Methyl orange concentration 10 mg L1, solution volume 25 mL.

Anatase

Rutile

o

Intensity

600 C o

550 C o

500 C

o

450 C 16

20

24

28

32

Fig. 6. Impacts of peak voltage on inactivation of Heterosigma akashiwo. h – intense pulsed light, N – intense pulsed light/TiO2 photocatalysis. Initial viable Heterosigma akashiwo concentration is 41 141 cell mL1, flow rate 1.78 L min1, temperature 20 °C, pulse frequency 15 Hz and pulse width 5 ms.

36

40

2 theta(degree) Fig. 5. XRD diffractogram of loaded TiO2 incinerated under different temperature.

with wavelength

Application of immobilized TiO2 photocatalysis to improve the inactivation of Heterosigma akashiwo in ballast water by intense pulsed light.

Ballast water exotic discharge has been identified as a leading vector for marine species invasion. Here immobilized TiO2 photocatalysis is introduced...
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