Hanovia Ltd - a Halma Company

In-Pipe UV Disinfection of Wastewater - The Advantages

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Source: Hanovia Ltd - a Halma Company

More and more operators of wastewater treatment facilities are now opting for in-pipe, medium pressure UV disinfection systems. They are choosing this technology in favour of older open-channel, low pressure UV systems.

The reasons for this change are due in part to the drawbacks of open-channel technology, as well as the advantages of in-pipe systems.

The disadvantages of open-channel, low pressure UV technology include the danger of personnel being exposed to UV light; the growth of algae in the open channels; and the difficulty of cleaning the UV lamps, which have to be either cleaned manually - a  laborious procedure as there are so many of them - or physically lifted and moved to an acid bath.

In addition, amalgam* low pressure UV lamps - the most common type – are usually powered by electronic ballasts. Because low pressure wastewater systems use a high number of lamps, the corresponding high number of electronic ballasts are extremely costly to maintain and replace. To get round this some low pressure UV suppliers try and run two lamps from a single ballast. If the ballast fails, however, power to both lamps is lost. In addition, if one of the lamps fails, the circuit is broken, so the other lamp is also extinguished. In both cases, the efficiency of the UV system is compromised.

In-pipe medium pressure UV systems, on the other hand, do not present these problems. As fewer UV lamps are required, the number of electronic ballasts is fewer and there is always one for each lamp. In addition, in-pipe systems present no hazard to staff because the UV lamps are enclosed in a stainless steel chamber; this also eliminates the problem of algal growth. Each lamp is fitted with a mechanical wiper on its protective quartz sleeve which keeps it clean. Periodic additional cleaning, if required, is simple and can be done ‘in-line’ without removing the lamps. In addition, lamp change-over is easy and can be done in minutes.

An added benefit of medium pressure lamps is that they cause permanent, irreversible damage to microorganisms in wastewater. It is known that some microorganisms can repair themselves after being exposed to UV from low pressure lamps (1). This does not happen with medium pressure UV and is another reason why  plant operators are switching to in-pipe, medium pressure UV technology.

* All UV lamps contain small amounts of mercury. Some low pressure UV lamps also contain a small amount of another metal (e.g., indium or gallium) which forms an ‘amalgam’, or mixture, with the mercury. This allows the lamps to operate at a higher current, with a correspondingly higher UV output.

1. Zimmer, J. L., Slawson, R. M. & Huck, P.M. (2002). Potential repair of Escherichia coli DNA following exposure to UV radiation from both medium- and low-pressure UV sources used in drinking water treatment. Applied & Environmental Microbiology, Vol. 68, No. 7, 3293-3299.

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