Advice and guidelines for UV light in water treatment

Download the full report above under files and media.

UV is a technique widely used for killing bacteria in water.
Tubular UV works well when the water is clean of sludge and the UV rays can effectively reach the intended effect.

Treated wastewater normally contains some residual sludge flakes during operational disturbances and would therefore not really be suitable for treatment with UV light, therefore slightly different conditions are required to cope with this as sludge protection such as filters or sand filters.

The Aquatron UV filter is not sensitive to dirty water like tubular UV is, but is less able to handle high flows.

PRE-TREATMENT FOR DRINKING WATER

For optimal effect of UV treatment for drinking water, proper pretreatment is required. The recommended limit values below are a guide to the choice and possible need for pre-treatment of the water.

• Iron (Fe) < 0,3 ppm (0,3 mg/l)
• Hardness < 120 ppm (120 mg/l = 6,7°dH)
• UVT10 > 75%
• Total suspended solids (TSS) < 5 ppm (5 mg/l)
• For smaller flows, use a cartridge filter with 5 my cartridge.
• For larger flows, use a bag filter with 5 my filter bag.

HERE ARE SOME POINTS THAT SHOULD BE MET TO ACHIEVE THE OPTIMAL EFFECT OF UV TREATMENT:

• Proper pre-treatment of incoming water, with possible complete filter (for treatment of iron, manganese humus)
• Right flow rate in relation to UV plant capacity
• If the pump flow is too high in relation to the UV system, the flow should be throttled down
• Cleaning the quartz glass 2-3 times a year (in some cases more often)
• Changing the UV lamp in time.

FUNCTION

Microbiological growth, which occurs in water, can be effectively controlled with ultraviolet light. UV light with a wavelength of 254 nanometers (nm) kills bacteria, viruses, algae and fungi by breaking down the DNA of microorganisms. Disinfection with UV light can be used for virtually all types of water.

The pros and cons of classic UV chambers do not apply to Aquatron UV, which has other pros and cons.
UV light is a well-known and widely advocated disinfection method with predominant
advantages. Nevertheless, it is important to always keep in mind that UV is not always problem-free and that
there are also a number of disadvantages.

Advantages:
1. UV disinfection (with sufficient dose) provides effective inactivation of bacteria, parasites and most viruses
2. UV does not normally cause serious changes in water quality or formation of disinfection by-products
3. UV disinfection has relatively low investment and operating costs compared to other processes (possibly with the exception of chlorination)
4. A UV plant is relatively uncomplicated to operate and in principle only requires measurement of two parameters (intensity and flow)
5. A UV plant is relatively compact and can often be easily built into an existing plant
6. The operation of the plant does not require any input chemicals, in some cases with the exception of small amounts of washing solution

Disadvantages:
1. UV does not produce any residual effect in the drinking water network, which in some cases means that UV should be combined with chlorine or chloramine
2. Since it is not possible to measure UV dose directly, one must rely on indirect measurements such as intensity, flow and possibly UV absorbance 3. UV absorbance
3. If you have water that causes problems with deposits on quartz glass and sensor windows, operation can be relatively labor-intensive
4. UV lamps contain mercury and can thus pose a health and safety risk if a lamp is broken and a risk of contamination of the water if the quartz glass is also damaged
5. At high UV doses and a water with a high content of humus or other organic material, there is a risk that the UV light breaks down substances so that easily degradable and/or in some cases odorous substances are created
6. The UV system and its electronics can be relatively sensitive to short power dips and power spikes, which can cause operating problems or damage to the electronics

Quartz glass tubes
The UV lamps are embedded in quartz glass tubes to avoid direct contact with the water. If the water has a tendency to create deposits, the quartz glass may need to be cleaned at regular intervals. As quartz glass tubes are exposed to intense UV light, they age slowly and may need to be replaced over time. The lifetime is often difficult to assess, but if the quartz is of good quality, the “transparency” should not be significantly affected for 10 years.

Rules in Sweden
In Sweden there are not many detailed regulations. What you have to stick to is the Drinking Water Regulations § 3, which states, among other things, “The preparation shall be provided with a sufficient number of safety barriers against microbiological contamination. If disinfection is included, it must be checked that the disinfection is effective…” and § 4 which states, among other things, “Waterworks must have – equipment that warns when errors occur during pH adjustment and disinfection”.
This is explained in more detail in the guidance to the regulation. It states that UV light counts as a barrier and that a minimum requirement for inactivation of microorganisms for a process to count as a barrier is 99% reduction (2 log). This means that a certified unit with a biodosimetric dose of 400 J/m2 more than meets the requirement for a microbiological barrier. Even a biodosimetric dose of 250 J/m2 should be considered to meet the requirement.

Read this entire report under the tab below “files and media” conducted on behalf of Swedish Water, a survey of Swedish UV installations.

Different microorganisms are differently sensitive to UV light. Among the more sensitive are E-coli and the two chlorine-resistant protozoa (parasites) giardia and cryptosporidium, while norovirus, for example, is somewhat less sensitive to UV light.

Several spore-forming bacteria are more resistant to UV, and the most resistant is adenovirus, which requires very high doses of UV light for good inactivation. However, adenoviruses are considered to be of very little importance in the context of drinking water.

As a measure of the inactivation of a particular microorganism, the term ‘log reduction’ or ‘log inactivation’ is often used:

Log reduction = log (N0/N)

Where N0 is the level of the micro-organism in question before disinfection and N is the level after.

This means that a log reduction of 1 means that 90% of

UV dose required for 4 log reduction of some microorganisms. NOTE: the scale

is expressed in mJ/cm2 (i.e. the value is multiplied by 10 to get J/m2

Advice and guidelines for UV light in water treatment

For advice! Call us 010-490 10 50 or email info@avloppscenter.se

Shop directly as an individual or through your contractor.

No files available.