There are four key components of water treatment. These are screening, flocculation, filtration, and final treatment, which involves disinfection. The final stage is achieved using ultraviolet (UV) light treatment or chemicals, like chlorine.
The effectiveness of each stage has a knock-on effect on the next. As filters do most of the heavy lifting by removing potentially harmful particles and sediment, having a reliable filtration process ensures water is properly prepared for final treatment.
With only one stage between filtration and water reaching consumers’ taps, it’s crucial to have the best filters for the job to preserve water quality.
How does industrial UV water treatment work?
UV water treatment disinfects water to protect against protozoa, bacteria, and some viruses. Short-wavelength UV light disrupts the DNA of these hazards so they can’t reproduce.
How can filters help the industrial UV water treatment process?
If water has high turbidity at the UV treatment stage, UV light isn’t effective. The particles causing murkiness in the water act as a shield so the UV light doesn’t penetrate far enough to kill protozoa, bacteria, and viruses. This is also known as shadowing and means improperly treated water can reach the public water supply.
If this happens, it can cause sickness, damage brand reputations, and mean water companies don’t meet water quality regulations. Having an efficient filtration solution to reduce water turbidity can help to stop this from happening by ensuring the effectiveness of UV water treatment to improve the overall quality of water processed.
The Drinking Water Inspectorate outlines the importance of this in its Guidance on the use of ultraviolet (UV) irradiation for the disinfection of public water supplies:
4.2. A number of water quality properties may adversely affect the performance of UV disinfection processes.
Of primary importance is the production of waters with consistently low turbidities. Accordingly, treatment works should be designed and operated at all times in a manner that minimises turbidity in the water entering processes used for disinfection, as well as the size, frequency, and duration of any turbidity peaks.
Regulation 26 requires that turbidities remain below 1 NTU, reflecting long standing World Health Organization (WHO) disinfection criteria. It should also be noted that, for effective disinfection, WHO currently advise that median turbidities should ideally be below 0.2 NTU (WHO, 2011).
The recently amended European Drinking Water Directive takes its cue from the WHO's recommendations. However, it's provides a list of additional parameters around turbidity. Specifically, the directive highlights the importance of low turbidity in ensuring the effective disinfection of water using technology such as UV
or chlorination. As such, it deems 1 NTU as too high and advises a rating of 0.3 NTU to guarantee trouble free disinfection at water treatment facilities.
Water suppliers are additionally reminded of the various recommendations arising out of the Group of Experts (Badenoch, 1995; Bouchier, 1998), which DWI continues to endorse as good operational practice, irrespective of the microbiological challenge or disinfection process used.
What do filters do?
Filters support UV water purification systems by:
- Removing waterborne microbial contaminants
- Reducing turbidity to limit shadowing
What to look for in water turbidity filter solutions
Some key features to look for in a water turbidity filter are:
- Longevity
Filters in water systems should last a long time. This means using filters with graded density to maximise dirt-holding capacity and increase efficiency. Depth filters are good at dealing with a high volume of particulate. They’re also good at dealing with different particle sizes, giving them more flexibility than a membrane filter.
- Flow rate
It’s important to have a flow rate that allows the filter to remove particulate effectively. If the flow rate is too high it could overload the filter, causing it to block prematurely and not filter the water properly. This will leave you with the expense of replacing filters before you should need to and will mean water that’s processed doesn’t meet quality standards.
If your water is particularly turbid, it’s worth considering a two-stage filtration process. It might be more efficient and cheaper to pass water through a 10-micron and 1-micron filter before it goes to UV treatment.
- Size
Ensure your filter has the correct micron rating to remove all particles necessary to meet water quality regulations. The size you need will depend on the makeup of the water in your region as well as factors like new boreholes which can increase turbidity.
Micron ratings are shown in micrometers, often using the µm symbol, but it’s important to remember that there are two types of micron ratings. A filter with an absolute rating will stop 99.9% of the particles that are the same size or bigger than the micron rating from passing through.
Filters with a nominal rating will have a percentage rating substantially below 99.9%, meaning they stop most particles that are the same size or bigger than the micron rating from passing through – this is usually around 75-85%.
Improve your industrial UV water treatment
If you’re looking to improve the efficiency of your UV water treatment, remember to look at the whole water treatment process for areas to make efficiencies. The biggest factor you can influence is the quality of the water that flows to the UV treatment stage.
