1:45 PM - 3:15 PM
[HCG25-P05] Development of a Home-use Water Disinfection System using Ultraviolet Light for Areas without Water Purification Facilities
Keywords:Ultraviolet LED, home-use water disinfection system, sustainability
There are about 2 billion people in the world who do not have access to drinking water daily due to economic reasons or inadequate infrastructural facilities. These people are forced to use unsanitary water from rivers and ponds as drinking water. As a result, infectious diseases caused by unsanitary drinking water are serious, especially in developing countries, and are one of the reasons why many infants die from infectious diseases.
In these poor areas, people are unable to secure safe, sterilized drinking water for economic reasons. Some attempts have been made to assist by digging local wells and building water purification systems. Still, these efforts are often problematic due to a lack of funds and unsustainable management. Therefore, systems to disinfect local water at low cost are attracting attention. Water is disinfected by boiling, ozone treatment, chlorine dioxide treatment, tablets, and chemicals, but these methods are often not economically sustainable because they take too long to disinfect, require large and complex equipment, and are expensive to treat secondary contaminants. They are often economically unsustainable.
We focus on the ultraviolet (UV) water disinfection method, which is easy to handle, can be used for a long period of time, and has no cross-contamination. However, there are several problems with conventional UV water disinfection devices. First, they are designed to be installed in facilities with water purification equipment. They are not directly applicable to muddy water pumped from rivers and ponds, and they are expensive (about 100,000 yen). This study aimed to develop an inexpensive UV water disinfection device that can be distributed to households in low-income households in Africa (at the cost of about 100 yen/month) by overcoming these problems through the use of UV LEDs and various innovations.
River water, which is used for daily life in impoverished areas, has a certain degree of turbidity, so it is necessary to have equipment that can sterilize such water with UV light. According to the Ministry of Health, Labour and Welfare, the requirements for the application of UV treatment are as follows: 1. a transmittance of 75 % (less than 0.125 abs./10 mm) in the UV (around 253.7 nm); 2. a UV irradiation dose of 10 mJ/cm2 or more at any time for at least 95% of the water volume passing through the UV irradiation tank (around 253.7 nm). Since the UV transmittance depends on the irradiation intensity and the turbidity of the water, we attempted to design a device that would satisfy both of these requirements at all times. The system features are: 1) filtering out particles from the river water to reduce turbidity, and 2) designing a water purification tank that keeps the depth of the filtered river water (assuming a turbidity of 10) at 5 mm or less at all times. To protect the UV-LED elements from water, inexpensive polyethylene film (10 yen) with high UV transmittance was used instead of expensive quartz glass (5,000 yen), which has been used in the past to reduce the cost of the device. Furthermore, an experiment was conducted to verify the effectiveness of UV light in sterilizing using a commercially available UV-LED device (wavelength 100-280 nm, 3 light sources, about 60 yen). 2 ml (100 g/L) of a solution in which yeast were dissolved was irradiated with UV-LEDs for 15 seconds at a position 5 mm from the water surface, set up. After 24 hours, the irradiated solution showed no colony formation compared to the non-irradiated solution. Since yeast require about twice as much energy for sterilization as infectious disease-causing bacteria (typhoid, cholera, etc.), the results indicated that the sterilization effect was sufficient to provide drinking water.
In these poor areas, people are unable to secure safe, sterilized drinking water for economic reasons. Some attempts have been made to assist by digging local wells and building water purification systems. Still, these efforts are often problematic due to a lack of funds and unsustainable management. Therefore, systems to disinfect local water at low cost are attracting attention. Water is disinfected by boiling, ozone treatment, chlorine dioxide treatment, tablets, and chemicals, but these methods are often not economically sustainable because they take too long to disinfect, require large and complex equipment, and are expensive to treat secondary contaminants. They are often economically unsustainable.
We focus on the ultraviolet (UV) water disinfection method, which is easy to handle, can be used for a long period of time, and has no cross-contamination. However, there are several problems with conventional UV water disinfection devices. First, they are designed to be installed in facilities with water purification equipment. They are not directly applicable to muddy water pumped from rivers and ponds, and they are expensive (about 100,000 yen). This study aimed to develop an inexpensive UV water disinfection device that can be distributed to households in low-income households in Africa (at the cost of about 100 yen/month) by overcoming these problems through the use of UV LEDs and various innovations.
River water, which is used for daily life in impoverished areas, has a certain degree of turbidity, so it is necessary to have equipment that can sterilize such water with UV light. According to the Ministry of Health, Labour and Welfare, the requirements for the application of UV treatment are as follows: 1. a transmittance of 75 % (less than 0.125 abs./10 mm) in the UV (around 253.7 nm); 2. a UV irradiation dose of 10 mJ/cm2 or more at any time for at least 95% of the water volume passing through the UV irradiation tank (around 253.7 nm). Since the UV transmittance depends on the irradiation intensity and the turbidity of the water, we attempted to design a device that would satisfy both of these requirements at all times. The system features are: 1) filtering out particles from the river water to reduce turbidity, and 2) designing a water purification tank that keeps the depth of the filtered river water (assuming a turbidity of 10) at 5 mm or less at all times. To protect the UV-LED elements from water, inexpensive polyethylene film (10 yen) with high UV transmittance was used instead of expensive quartz glass (5,000 yen), which has been used in the past to reduce the cost of the device. Furthermore, an experiment was conducted to verify the effectiveness of UV light in sterilizing using a commercially available UV-LED device (wavelength 100-280 nm, 3 light sources, about 60 yen). 2 ml (100 g/L) of a solution in which yeast were dissolved was irradiated with UV-LEDs for 15 seconds at a position 5 mm from the water surface, set up. After 24 hours, the irradiated solution showed no colony formation compared to the non-irradiated solution. Since yeast require about twice as much energy for sterilization as infectious disease-causing bacteria (typhoid, cholera, etc.), the results indicated that the sterilization effect was sufficient to provide drinking water.