DISINFECTION, UV (ultraviolet)
Posted on by AWTAsia
20
Oct
In this article we summarize the pros and cons of UV water treatment of drinking water.
When it comes to treatment of drinking water, UV systems are considered an additional security to prevent microbiological contamination. Without the additional security from an UV system, a substantial amount of contaminated water may reach the end users before the contamination is picked up by regular controls.
Please check out our other articles in this series:
Pros and cons – disinfection ability of UV treatment
UV treatment is largely independent of other water quality parameters. That being said, the content of iron and manganese should be lower than the drinking water requirements of 0.1 mg/l and 0.05 mg/l respectively. Additionally, to avoid scaling, the hardness should be below 15 °dH. If the hardness is higher wipers should be installed to clean the lamps.
The mode of operation differs significantly when comparing UV disinfection with chemical disinfection using chlorine or ozone. UV disinfection inactives microorganisms so they are unable to multiply. One disadvantage of UV treatment is that the disinfection only works within the UV aggregate and – as such – doesn’t protect against subsequent contamination in the distribution network.
In chemical disinfection, the cell membranes of microorganisms are oxidized and destroyed, which kills the organisms. Chemical disinfection is effective as long as the water contains the chemical agent. Hence, chemical disinfection is a better choice if there’s a risk of contamination in the distribution network or at the end user herself.
UV treatment with dosages of 400 J/m2 effectively inactivates bacteria, parasites, and most viruses. Including Giadia and Cryptosporidium. The exception is Adeno-virus, which is highly UV resistant and therefore requires a higher dosage.
Another advantage of UV-based disinfection is that the process is very fast – with typical exposure times lasting only a few seconds.
A disadvantage of UV treatment is that is doesn’t instill a residual effect in the water and – as a result – there’s no disinfection in the distribution network. If this is needed, one must add a chemical disinfection agent (e.g. chlorine) after the UV treatment step.
Finally, some microorganisms can repair & revert the damages caused by UV treatment. That being said, these effects are limited when UV dosages of at least 400 J/m2 are used.
Pros and cons – water quality
The advantage of UV treatment is that is doesn’t affect the water quality in any significant way. This is the case for both pH, corrosiveness, turbidity, and TOC.
The taste of the water is not affected and with UV dosages of 400 J/m2, there will be no significant occurrence of disinfection bi-products, which is often the case with chlorine treatment.
A disadvantage is that UV treatment can cause algae growth in the part of the tubes surrounding the lamps. This is the case if the lamps are not sufficiently shielded from the part of the light spectrum that is constituted by natural light. This is especially a problem with medium-pressure lamps, which emit a spectrum of light with higher content of natural light.
AWTAsia
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