How does the UV Tube work?
The UV-Tube design concept incorporates a germicidal bulb suspended over water in a horizontal tube or covered trough. The water enters at one end through an inlet in the top of the tube, and then flows along the bottom (beneath the germicidal bulb) until it reaches an outlet at the opposite end where it exits. The height of the outlet sets the depth of the water in the tube and regulates the hydraulic retention time. Because the UV-Tube does not require water pressure to operate, it may be connected directly to a faucet or filled with a bucket.
What kind of testing has been done on UV disinfection systems?
UV disinfection is a safe and well-understood process that has been used for more that 100 years. Similar to a number of commercial water treatment plants in Europe and the United States, UV Tubes use ultraviolet (UV-C) light emitted from a germicidal bulb to inactivate waterborne bacteria, viruses and protozoa. The only difference with commercial systems is that UV Tubes are easy to use and can be constructed from locally available and low-cost materials.
The UV Tube has been developed by the University of California at Berkeley based on rigorous testing carried out both in laboratories and field conditions throughout the past five years. Extensive laboratory analysis has been performed on the UV Tube. These tests include tracer studies to determine the hydraulic retention time, MS2 tests to identify the dose of UV-light delivered, and membrane filtration experiments to measure disinfection performance. A materials degradation test has also been conducted to clarify if any disinfection byproducts are created by the UV Tube.
Do outside agencies like the World Health Organization recommend UV disinfection?
Water treatment by ultraviolet disinfection with lamps at the household and community scales is recommended by the World Health Organization and approved by the National Sanitation Foundation International.
A UV Tube model designed for the Mexico, called AquatUVo, was independently tested and approved by the government managed Mexican Institute for Water Technology.
Does the ultraviolet light react with oxygen to form ozone, which can be hazardous to people?
Ozone can be produced from oxygen exposed to UV light in the region of 140nm to 190nm. Ozone absorbs UV light in the region of 220nm to 280nm, effectively transforming the ozone molecules back into oxygen.
The low-pressure mercury bulbs used by the UV Tubes emit a low intensity line at 184.9nm that has the capability of producing ozone. However since most of the energy emitted by the bulbs is produced at 253.7nm, the little ozone that is produced almost instantly transforms back into oxygen. Because of this, no ozone builds up inside a UV Tube and no ozone ever escapes the UV Tube.
With what types of water supply systems can the UV-Tube be paired?
The UV-Tube employs a flexible design concept that can be adapted to fit a variety of water supply situations, including piped water, rainwater catchment systems, wells, or springs.
What does the UV-Tube need to operate?
The UV Tube is powered by electricity and therefore must be connected to a reliable electricity source, i.e. grid or solar panel. To disinfect water the UV Tube targets DNA at the wavelength of 254 nm and consequently requires source water to have a low absorbance level at 254nm.
Can the flow rate be adjusted for use with a sand filter?
The UV-Tube is designed to work effectively at a flow rate of up to 5 liters per minute. Anything less than that is fine.
If water has high turbidity, then it is possible that it has high absorbance and therefore the UV Tube will not work as effectively. In areas where the water has high absorbance, a sand filter will reduce the absorbance and increase the effectiveness of the UV Tube.
Sand filters, when maintained properly, are effective in improving the taste and appearance of the water, as well as removing some pathogens. However, sand filters cannot remove viruses. A UV Tube installed after a sand filter would ensure that all pathogens are eliminated.
How much does a UV Tube system cost?
The cost of the UV-Tube depends on the locally available materials and the specific design adapted to a region. The cost can range from $60-$150 (USD).
What are the maintenance costs of a UV-Tube?
UV Tubes are designed to require minimal maintenance. If properly installed, a UV Tube should not need any components replaced for over one year (the lifespan of a UV bulb). A new UV bulb costs about $9 in the US and $15-$25 (USD) in other countries. The higher cost in other countries is due to low demand and high import taxes.
How effective is the UV Tube?
The UV-Tube emits UVC light which inactivates microorganisms by damaging their genetic material (DNA) and rendering them unable to replicate. The UV-Tube is effective in inactivating most pathogens, including bacteria, virus, fungi, spore forming organisms, and cyst forming protozoa. These organisms can cause diarrhea and intestinal worms as well as life threatening diseased such as, cholera, typhoid, giardia, hepatitis A, and polio.
What is the UV Tube not effective against?
The UV-Tube disinfects water by preventing pathogens from reproducing. It does not filter the water or remove metals, salinity, nitrates, and other non-biological contaminants.