What are the pros and cons of UV water treatment when it comes to operation?

In this article we summarize the pros and cons of industrial UV water treatment with an emphasis on operation

In countries where water supply is based on groundwater, the water is rarely polluted with microorganisms (bacteria, virus, etc.) and there’s usually no need for additional security measures at a utility level. Nevertheless, some utilities opt for additional security measures against microbiological pollution in the form of UV systems.

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Pros and cons – risk of complacency

A common worry when establishing UV water treatment systems as an additional security measure is that the UV system will result in complacency and – in effect – replace a well-functioning utility. This effect can be countered by regulating drinking water quality before the water is UV treated.

Pros and cons – education and operation

A UV installation is relatively simple to operate based on flow, UV intensity, and UV transmission (UVT) measurements. Furthermore, a UV installation requires relatively little maintenance and enjoys operational stability as long as it is properly dimensioned and is sufficiently equipped with measuring and alarm systems. If scaling cannot be controlled with in-situ wipers and regular cleaning, operation can become tedious & laborious.

Looking at the cons, it is not possible to directly measure the UV dose, which means that operation will be based on indirect measurements of flow, UV intensity, and UV transmission.

UV installations are dependent on stable and good power supplies. Even short power outages and voltage variations of more than 10-30% can result in UV lamps shutting down and becoming nonoperational for time periods of up to 5 minutes. If there’s a risk of less than optimal power supply, it is recommendable to supplement with emergency power supply and UPS (uninterruptible power supply) to ensure the installation fulfills the UV dose requirements at all times.

Most UV lamps are only guaranteed down to a water temperature of 5 degrees Celsius. Lower temperatures may result in reduced lifespan, increased risk of certain types of scaling, increase hydraulic pressure loss, and so on.

The difference in operation between small and large installations lies mostly in the system control. Large installations will typically have more advanced control systems, which take into account variations in UV transmission and flow.

In smaller installations the control systems will be simpler; mainly ensuring that operational limits for flow (i.e. the flow doesn’t exceed a predetermined limit) and UV intensity (i.e. the measured intensity doesn’t fall below a predetermined limit). The simpler controls result in a increased risk of sub-optimal operation for smaller installations.

Since operating UV installations is relatively simple only limited training & education is needed. That being said, UV system suppliers should provide basic education of personnel upon installation and commissioning. The education should at a very minimum cover UV theory, allowable operational parameters, cleaning & maintenance (including exchange of lamps), appropriate response to alarms and various operating scenarios & safety issues, sensor control, and troubleshooting,

Pros and cons – operational expenditure

According to largest Danish suppliers of UV systems, the operational expenditure for UV disinfection of drinking water ranges from $0,004 to 0,02 SGD/m3 depending on installation size and water quality. With the cost of electricity and lamp replacement being roughly equal.

Pros and cons – energy consumption

UV installations are commonly dimensioned to accommodate the expected flow maximum and UV transmission minimum. Hence, in periods where the maximum doesn’t coincide with the minimum UV transmission, the UV installation will be over-dimensioned. This will be the case in most operational situations, which means that the UV dose is often higher than needed – resulting on higher energy consumption, higher operating costs, and potential formation of byproducts. As a point of reference, the energy consumption of UV-based disinfection ranges from 0,013 to 0,074 kWh per m3 of treated water. In comparison, the energy consumption involved in regular treatment of groundwater ranges from 0,4 to 0,5 kWh/m3.

Pros and cons – chemical consumption

In a UV installation, chemicals are used for cleaning of quartz sleeves and various sensors. Knowledge and care is needed to handle the chemicals. In manual systems the UV lamps are taken out for cleaning and – as such – chemicals do not enter the system.

Pros and cons – environmental considerations

Pros: UV installations do not discharge Volatile Organic Compounds (VOCs) and other toxic airborne pollutants. In addition, there are no odor-related problems, which includes the treated water.

Pros: UV installations only use chemicals for cleaning of lamps and sensors. Hence, chemicals are not directly exposed to the water. On the flip-side, chemical handling requires knowledge and care. Clear instructions should be made available on how to conduct safe cleaning procedures alongside personal protection equipment such as – but not excluded to – gloves and protective glasses.

Cons: The biggest environmental concern is related to disposal of used lamps (due to the mercury content). However, the risk of lamp breakage is very low, which translates to a corresponding low risk of waterborne mercury pollution.

Cons: Most UV lamps contain mercury vapors, which is why handling of lamps – especially broken ones – constitutes an occupational health risk. Hence, clear instructions and personal protection equipment should also be made available when handling lamps.

Cons: UV light is harmful in large doses. It is therefore important to implement efficient shielding of the lamps. As well as automatic lamp shutdown if the lamps are unintentionally exposed while in operation. Visual access points should be equipped with UV filters and operators should have access to UV resistant personal protection equipment.

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