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Feasibility Study of Fluid Driven Application in Ultraviolet Sterilisation

流體驅動紫外光殺菌可行性研究WEN-HUA ZHANG*

張　文　鏵Department of Engineering and System Science, National Tsing-Hua University,

Hsinchu City, Taiwan. Green Energy and Environment Research

Laboratories, Industrial Technology Research Institute, Hsinchu City, Taiwan.

Ph.D. Student

WEI-KENG LIN

林　唯　耕Department of Engineering and System Science, National Tsing-Hua University,

Hsinchu City, Taiwan. Professor

CHIEN-YU CHEN

陳　建　佑Department of Engineering and System Science, National Tsing-Hua University,

Hsinchu City, Taiwan. M.S. Student

SONG-BOR CHIANG

江　松　柏Green Energy and Environment Research

Laboratories, Industrial Technology Research Institute, Hsinchu City, Taiwan.

Researcher

SHIH-KUO WU

吳　世　國Green Energy and Environment Research

Laboratories, Industrial Technology Research Institute, Hsinchu City, Taiwan.

Researcher

ABSTRACT

This paper proposed a fluid-driven sterilisation equipment with a hydroelectric generator. The equipment consists of three components: (1) a fluid-driven power generator, (2) a sterilisation light source, and (3) a spiral flow channel. The potential energy of water is transformed into electric energy through the hydroelectric generator, and the generated electric energy is used to drive the ultraviolet (UV) light source. UV light can physically destroy pathogenic organisms such as viruses and bacteria in the water flowing through the device, so as to achieve water sterilisation. A UV light-emitting diodes (LED), as the light source of sterilisation, can miniaturize the volume of the sterilisation device and improve the utilisation efficiency of light energy. This research conducted the simulation on the characteristics of UV LED light source, thus evaluated the feasibility of its application in fluid-driven sterilisation. According to the test results, the potential energy of tap water can generate electricity greater than 30 W. The tap water flow was set at the entrance of the device, and the time of exposure to UV light was adjusted by the spiral channel. The sterilisation efficiency of different UV wavelengths was tested. In the experiment, the sterilisation efficacy of an Escherichia coli culture medium was tested. The results showed that UV C (200–280 nm) was the best light source for sterilisation. With an exposure time

* Corresponding author: Ph.D. Student / Department of Engineering and System Science, National Tsing-Hua University / 195, Sec. 4, Chung Hsing Rd., Chutung, Hsinchu, Taiwan / VanceZhang@itri.org.tw

臺灣水利　第 68 卷　第 2 期民國 109 年 6 月出版

Taiwan Water ConservancyVol. 68, No. 2, June 2020DOI: 10.6937/TWC.202006/PP_68(2).0002

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1. INTRODUCTION

Water is an indispensable element of human life. In modern society, especially, people are paying increasing attention to the hygiene of their diet and, in turn, to the cleanliness of water. A high proportion of all instances of disease are caused by unsafe drinking water and ineffective water purification systems. On World Water Day (the 22nd of March), the United Nations noted that more than one billion people worldwide lack access to clean drinking water. Statistics have shown that one in six people do not have access to safe and clean water (Nada, 2017).

Common methods of water purification include disinfection by chlorine, ozone, and ultraviolet (UV) rays. The wide application of chlorination for drinking water treatment has led to the appearance of chlorine-resistant bacteria, which pose a severe threat to public health (Ding, 2019). When ozone is used to treat water, bromides in water are converted into carcinogenic bromates that can impact human health (Karadurmuş, 2019).

Chemical sterilisation also produces some harmful by-products. UV sterilisation of water is relatively safe. When microorganisms are exposed to UV radiation, the nucleic acid inside them absorbs UV light energy and thereby damaged and destroyed, killing the microorganisms. Aihara utilised UV light-emitting diodes (LEDs) for sterilisation during food production and processing (Aihara, 2014). The results showed that the UV system is safe, effective, and does not harm the food.

UV light was first discovered in 1801. In 1877, Downes and Blunt discovered that sunlight can prevent microbial growth. It was later shown that the ability of sunlight to destroy microorganisms, depending on the wavelength of radiation; this provided further proof for the germicidal effects of UV light (Hamblin, 2017; Donghai, 2015). Luckiesh et al. then clarified how the germicidal effects of UV light are related to its wavelength (Luckiesh, 1999). UV light sterilisation has been widely used in recent years. It is preferred for sterilising large areas or large spaces as well as for air and water disinfection, both of which are examples of physical disinfection

of 20 s, the sterilisation rate for E. coli could reach 92% through the spiral channel. As the feasibility of fluid-driven sterilisation is evaluated, there is a potential that this technology can be further applied to water purification in remote and underdeveloped areas or in portable water purification devices.

Keywords: Sterilisation, Potential Energy, Ultraviolet Light, Wavelength.

摘　　　　　要

這項研究提出了一種帶有水力發電機的流體驅動殺菌設備，本設備包含三種元件整合，1. 流體驅動發電裝置；2. 滅菌光源；3. 螺旋流道。主要是利用擁有位能的水源經過水力發電裝置，將位能轉換成電能，產生的電能供應紫外光源驅動，紫外線可以對流經該裝置水中所含的病毒、細菌等致病體進行物理破壞，達到對水殺菌的目的。UV LED應用於殺菌光源，可以縮小殺菌裝置之體積、提升光能利用效率。本文模擬UV LED光源特性，評估其應用在流體驅動滅菌的可行性。經過測試，一般的水龍頭的所含的位能，可產生大於30W的電能。在裝置的入口端設定水龍頭流量，使用螺旋通道調整水暴露於紫外光的時間，並測試不同紫外線波長的殺菌效率。實際以大腸桿菌培養液測試殺菌效果。結果顯示，光源選用UV C波段(200-280 nm)的殺菌效果最好，經過螺旋式流道，延長曝光時間至20秒，大腸桿菌滅菌率可達92%。本評估了流體驅動滅菌的可行性，該技術預計可延伸應用在偏遠落後地區的水質淨化或旅行隨身攜帶淨水裝置。

關鍵詞： 殺菌，位能，紫外光，波長。

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(Alois, 2016; Meagan, 2018). UV wavelength of 200–400 nm shows a strong and fast sterilisation effect.

This study develops a novel fluid-driven sterilisation system using a UV LED light source powered by a high-efficiency hydroelectric power module; the system also includes a completely reflective closed chamber and optimised spiral pipe flow channel design to reduce UV energy loss. This system does not require an additional power supply for performing sterilisation. UV LEDs, as the light source, make the device easier to assemble and smaller in size, which can solve the problems related to clean water shortage. This technology is expected to be further applied in water purification in remote and underdeveloped areas or in portable water purification devices.

2. PRINCIPLE AND EXPERIMENTAL SETUP

The concept proposed in this study consists of three main parts: (1) fluid-driven power generator, (2) liquid flow channel and closed chamber, and (3) UV LED light source. Figure 1 shows the design and architecture of the proposed fluid-driven sterilisation system. The hydroelectric power generator converts the mechanical energy of water into electrical energy to power the UV LED light source that in turn sterilises the water as it flows through the flow channel. The closed chamber’s

inside walls are coated with a high-reflection low-absorption material to ensure the maximum possible UV energy is used for sterilising water. Furthermore, the spiral flow channel increases the exposure of water to UV light, thus increasing the likelihood of viruses or bacteria in the water getting killed.

Irradiation of 200–400 nm UV light destroys the DNA of most bacteria in water (Bohrerova, 2008). Furthermore, sterilisation using high-intensity high-energy UV light, taking only a few seconds to kill almost all bacteria, viruses, parasites, pathogens, algae, etc. without producing secondary pollution or toxic substances (Patrick, 2017; Rajib, 2014). UV sterilisation is also non-corrosive and non-polluting for the subject being sterilised, and it does not leave any residues.

Water purification is often graded using Escherichia coli as a standard, and we used the same as the experimental specimen for evaluating our UV sterilisation system. We also experimentally compared the sterilisation effects of different UV wavelengths, namely, UV A, UV B, and UV C.

A highly transparent spiral flow channel was designed in a fully reflective chamber to increase the exposure of water to UV light. If the sterilisation light source power is constant, the irradiation time (t) and sterilisation efficiency of the liquid inside the chamber can be theoretically estimated from the tube diameter, average flow rate, and length; these parameters may then be used to design the highly

Fig. 1. Architecture of fluid-driven sterilisation system.

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transparent spiral flow channel.The UV LED light is characteristically

concentrated in certain wavelengths, making it very suitable for sterilisation and water purification. According to ultraviolet germicidal irradiation (UVGI) technology standards, each microorganism has a specific lethal UV wavelength and lethal UV dose. The UV dose is the product of the irradiation intensity and irradiation time. The amount of exposure at each radiation time was calculated as E = P × t, where E is energy density (dose) in mJ/cm2; P, the power density (irradiance) in mW/cm2; and t, the time in s (Takada, 2017). The above equation suggests that high-intensity irradiation over a short duration or low-intensity irradiation over a long duration will produce the same effect. To provide sufficient irradiation intensity and sterilisation time, a fully reflective chamber was used to enable continuous reflection of UV light within the chamber and to minimise attenuation, thus achieving high irradiation intensities; furthermore, the chamber contains a transparent spiral flow channel made of quartz to increase the exposure duration of water to UV light.

3. EXPERIMENTAL RESULTS AND DISCUSSION

When water flows out of the generator and into the spiral quartz tube, its exposure to UV light is increased, thereby providing better germicidal effects. Furthermore, the inside wall of the closed chamber is coated with a reflective material that maximises the irradiation efficiency. The flow channel (Figure 2) was made from highly UV-

transparent quartz. The volume flow rate of tap water was set to Q = 0.00008 m3/s. (Set up experiments based on average faucet flow)

The inner tube diameter must match the faucet diameter, r = 0.015 m. The spiral diameter, R = 0.2 m. The number of spiral tubes: N loops. And total length of quartz tube: L = N (πR). Therefore, theoretical calculations were performed for the design of the flow channel, Irradiation time (s): t = (π/4)×(r)2×(NπR) (r: tube diameter; R: spiral diameter; N: number of spiral tubes; Q: volume flow rate)

Figure 3 shows the relationship between the number of spiral tubes and exposure time, given the aforementioned quartz tube parameters and a constant flow rate.

The UV light sterilisation system includes a 3D-printed blade that absorbs most of the impact of water. The inner ring of the magnet holder locates in the inner chamber of the generator, where water can flow through this chamber, and the outer ring magnet locates in the outer chamber of the generator. The inner chamber and outer chamber are not connected with each other but have the same cover shell. The two-magnet seat is mounted on the concentric rotating shaft of the generator; water in the outer chamber results in the counter-clockwise rotation of the blade and drives the inner ring magnet seat rotation.

In the fluid-driven power generation experiment for powering the UV light source, the international average volume flow rate of a tap is 0.00002–0.00008 Fig. 2. Design of spiral quartz tube.

Fig. 3. Relationship between number of spiral tubes and exposure time.

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m3/s, and the hydraulic head of a tap water supply is ~4.0 m. In this study, we developed a DC hydropower generator that is suitable for commercial faucets. This generator was installed in a turbine designed in this study to test the amount of power generated by various inlet water flow levels. This experiment showed that the output power of our faucet-ready miniature hydropower generator can be tested through its installation in the sterilisation device. The kinetic power W of water generally exceeds 30 W.

Next, sterilisation efficiency tests were performed on UV light sources with different wavelengths. For this purpose, E. coli concentration tests that are commonly used in water quality inspections were used to test the sterilisation efficiency of our system. The light-emitting states of UV A, UV B, and UV C LEDs were partially simulated using our light source. The luminous

efficiencies of LEDs with different wavelengths were calculated using a fixed 30-W power input. The radiation energy and wavelength distribution of the aforementioned UV LEDs were approximated as closely as possible using a UV mercury lamp to simulate the light-emitting states of the UV LEDs. Figure 5 shows the experimental results. This light source experiment is based on the CIE 220:2016 – Characterisation and Calibration Method of UV Radiometers standard (Gugg-Helminger, 2016). Figure 5 shows that different luminous efficiencies were obtained owing to the limitations of current technologies; the luminous efficiency was especially poor at UV C wavelengths, and the actual radiation energies were as follows:-UV A: 320–400 nm; radiation energy 994.6 mW-UV B: 280–320 nm; radiation energy 935.9 mW-UV C: 200–280 nm; radiation energy 50.1 mW

Fig. 4. Relationship between various flow rate and power generation.

Fig. 5. UV light source measurement results.

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Figure 6 shows the configuration of the sterilisation efficiency experiment. The E. coli culture was placed at the inlet, and the pump was adjusted to the flow rate of a generic faucet. The E. coli culture was then pumped into the sterilisation system to simulate an actual sterilisation operation. The flow channel was designed to vary the exposure time (5–20 s) as water flowed into the chamber. The E. coli concentration at the water outlet was then tested to calculate the sterilisation efficiency of this system. The plate method was used to measure the E. coli concentrations (Chen, 2003; Yu, 2018), and the results were derived using statistical methods. Decimally serial dilution was used: 1 ml of the mixture was added to 9 ml of the buffer solution. Then, this mixture was oscillated and mixed evenly, and then 1 ml of this mixture was added to another 9 ml buffer solution. The procedures of this experiment are shown in Figure 7. Each dilution therefore had a dilution factor of 10. The experimentally measured bacterial concentrations

were expressed as the number of E. coli per 1.0 ml of sample.

Figure 8 shows the concentration measurement results; these illustrate the sterilisation efficiency at different wavelength ranges and exposure times. It can be seen from Figure 8 that the E. coli concentration at the inlet of the device is 4.0E+7 (CFU/ml). The flow of culture medium into the device was kept stable. The bacterial concentration at the outlet after 5 s, 10 s, and 20 s of exposure was recorded. The results showed that with a longer exposure time, the concentration of E. coli at the outlet was lower. Figure 9 shows the sterilisation efficiency at each wavelength range. With the same parameters, the germicidal efficacy of UV A, UV B, and UV C were compared by replacing three groups of light sources with different wavelengths. The results showed that the germicidal efficacy of light sources with different wavelengths varied dramatically: a shorter wavelength improves the germicidal efficacy. These results denote that the

Fig. 6. E. coli sterilisation experiment.

Fig. 7. E. coli plate counting method.

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Fig. 8. Relationship between exposure time and E. coli concentration after sterilisation.

Fig. 9. Sterilisation efficiency (%) experiment.

UV C light source achieved sterilisation efficiency of 92% with exposure time of 20 s.

4. CONCLUSIONS

This study proposed a fluid-driven sterilisation system that consists of three integrated elements: (1) flow channel design, (2) fluid-driven power

generation system, and (3) sterilisation light source. In this system, the potential energy of the water source is converted into electrical energy using a miniature hydropower generator that then powers the UV light source to sterilise the water. An E. coli culture was used to evaluate the efficiency of our fluid-driven sterilisation system. The experimental results show that the potential energy of an ordinary

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faucet could generate adequate electricity to supply and drive a UV light source. In addition, UV C wavelengths (200–280 nm) show the best sterilisation efficiency, and the exposure time of water to UV light was extended to 20 s through the use of a spiral flow channel design. This system achieved a sterilisation rate of 92% for E. coli. In this study, the feasibility of a UV LED light source in fluid-driven sterilisation was evaluated thoroughly. Combined with the design of spiral flow channel, the device is small and has an excellent sterilisation effect. In the future, this technology can be used in water purification in remote and underdeveloped areas as well as in portable devices.

ACKNOWLEDGMENTS

This study was financially supported by the Bureau of Energy of the Ministry of Economic Affairs, Taiwan.

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Received: 109/02/03

Revised: 109/03/03

Accepted: 109/04/24