The UV Waterworks water-disinfection unit, with a plastic cover and cutaway reflector revealing its interior.
In the developing world, waterborne diseases such as cholera, typhoid fever, gastroenteritis, dysentery, and infectious hepatitis worldwide kill more than 400 children every hour and result in the loss of billions of hours of worker productivity each year. Municipal tap water is uncommon in many developing-country households, and two out of three people in the world must fetch water from outside their homes. In India, water-purity issues are particularly important during the monsoon season when heavy rainfall washes raw sewage and other contaminated material from the fields into the wells and surface water. Disinfecting water by boiling it over cookstoves increases the burden on those collecting the fuelwood, mostly women and children, and also stresses the biomass resource. Gathering wood occupies time that might be spent productively in other activities.
To address this significant public health and energy problem, an effort is underway at the Center's Indoor Environment Program to introduce a water-purification system using ultraviolet light to rural villages in India, Mexico, and South Africa. The goal of this project is to design and field-test a water-purification device for developing countries that is durable, easy to use, and inexpensive and can be constructed and maintained locally. It has resulted in the development of a prototype device called UV Waterworks.
We began our research early in the summer of 1993 and increased our efforts considerably in August 1993, when an outbreak of cholera was reported in India, Thailand, and Bangladesh. A year later, the cholera epidemic continued to be a problem in India-approximately 2,200 people died from cholera in the state of Bihar, between the months of May and August 1994. Other waterborne diseases also pose a serious health threat to Indian communities. In the state of Orissa alone, approximately 300 infants die every day as a result of waterborne gastrointestinal diseases.
We estimate that UV Waterworks can disinfect drinking water for 2¢ per ton of water, including the cost of electricity and consumables and the annualized capital cost of the unit. Its first cost is about $300, and, using only 40 watts of electricity, it provides four gallons of disinfected drinking water per minute. The disinfection process is highly energy-efficient and uses approximately 20,000 times less primary energy than the standard alternative-boiling water over a cookstove.
By our calculation, one unit serving a typical developing-nation community of 1,000 people for 15 years will avert 15 deaths of children below age 5 and avoid the stunted growth of 150 children. Under aggravated conditions, (e.g., epidemics) life savings and health benefits will be much larger. Because women are primarily responsible for collecting fuelwood, fetching water, and bearing and caring for children, the UV disinfection system could greatly improve women's quality of life by reducing their workloads as well as the number of children they lose to waterborne diseases.
The technology uses ultraviolet (UV) light to kill waterborne pathogens (bacteria, viruses, and molds) in the local water supply. UV light is classified by three wavelength ranges.* UV-C light is "germicidal"; that is, it destroys bacteria, viruses, and other pathogens by inactivating their DNA and thus their ability to reproduce. Light with a wavelength of 254 nm gives the highest germicidal efficacy in the UV range. Because this is the wavelength at which a low-pressure mercury vapor lamp emits roughly 90% of its light, the standard fluorescent lamp technology can be used in the system.
The glass tubes of the fluorescent lamps that light our offices and kitchens are coated with a phosphor that absorbs UV light and gives off visible light. The lamp used in the UV disinfection system is similar to a standard fluorescent lamp, but the lamp tube is not coated with a phosphor and is made of a special glass that is transparent to UV light. This "germicidal" variety of lamp is already manufactured by many large companies that make standard fluorescent lamps. Consequently, lamps, ballasts, and starters for the UV disinfection system can be bought off the shelf, with the full benefits of mature volume production (at low cost and free of technical bugs).
The $300 one-time capital cost of UV Waterworks includes materials, fittings, and labor. The life of the metal unit is expected to be approximately 15 years; the UV lamp requires replacement in alternate years. Assuming the system operates for 12 hours per day and the price of electricity is 8¢/kWh, the annual electricity cost of operating a UV system is expected to be approximately $14.
Based on these assumptions regarding cost and system life span and a 12% discount rate the total annualized cost of the UV system is approximately $70 per year. This includes the annualized cost of the 35-watt UV lamp, the ballast, the metal chamber, and the cost of electricity. It is assumed that the villagers provide their own hand pump for groundwater or storage tanks and sand filter; the raw materials for these components are readily available and inexpensive. If the system operates for 12 hours per day, 4,000 tonnes (4 million liters) of water can be disinfected every year. Using a per- capita drinking water requirement of 10 liters per day, a single system can provide enough water for approximately 1000 villagers. Accordingly, using a UV system to ensure potable water for a rural community of this size year-round costs about 5¢ per villager per year.
LBNL's Technology Transfer Office has received licensing inquiries from dozens of interested businesses. To encourage wide dissemination, we are now seeking funding support for extended field trials to identify and incorporate any user-requested design improvements and document the device's performance in the field.
*[UV-C from 100 nanometers (nm) to 280 nm; UV-B from 280 nm to 315 nm; and UV-A from 315 nm to 400 nm.]
Indoor Environment Program
(510) 486-4651; (510) 486-6658 fax
This work was supported by USAID, DOE, a Pew-Scholar Award to Ashok Gadgil, and private charities and corporate donations.
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