UV solution for giardiasis outbreak in Norway
When the city of Bergen's water supply was identified as the source of giardia infection in the population, the proposed solution was to install a UV system. As Ben Kalisvaart, microbiology specialist and European sales manager for Dutch contractor Berson, reports, the urgency of the project meant that it was realised within two months of being put into action.
Situated on the west coast, Bergen is Norway's second largest city with a population of about 250,000. The affected water supply serves about 60,000 people in the city centre and is drawn from Lake Svartediket. Until the outbreak, water treatment was by chlorination, but water was not filtered. Norway has a number of similar high quality surface water supplies which are used without filtration, although most serve smaller populations than the Bergen supply.
The outbreak may have been triggered by heavy rainfall; 120mm of rain was recorded in the two-week period before giardiasis case numbers began to rise and heavy rain then continued over several weeks. Levels of coliform bacteria in the raw water also peaked just after the initial rain event. A possible source of contamination was sewage from homes and restaurants overlooking the lake.
Giardia lamblia, the species of giardia infectious to humans, is a parasite found widely in sewage and surface water supplies. Infections are transmitted by tiny egg-like cells called cysts.
Chlorination is able to provide some degree of disinfection against giardia cysts (up to 1.5 to 2 logs removal), however, in countries such as Norway, very cold water temperatures in winter makes this difficult to achieve. Norway draws almost all of its drinking water from surface water sources and a survey of raw water sources in 1998 and 1999 found 9% of samples contained giardia cysts and 2.5% contained both giardia and cryptosporidium cysts.
UV is widely used around the world to remove harmful pathogens, including giardia and cryptosporidium cysts, from drinking water and wastewater. Recent advances in UV technology mean it can also be used to reduce pesticides and other non-organic contaminants from groundwater. It is a completely clean technology which does not rely on the use of chemicals and leaves no unwanted residues or byproducts.
A new water treatment plant with filtration and UV disinfection had already been commissioned for the affected water supply before the outbreak occurred. The proposed installation date was 2007, but, following the outbreak, it was decided that the filtration and UV systems should be installed as quickly as possible by adapting the existing facility.
Following a tender process, Netherlands-based Berson UV-techniek was chosen to supply the equipment through its local distributor HOH Birger Christensen. Berson's new InLine+ medium-pressure UV systems were chosen for their compact design and small footprint. This was an important consideration as it meant they could be accommodated in the existing water plant without major modifications to the existing building.
The order was placed in December 2004 and four large units, with a total capacity of approximately 3000m3/hr of water were fully installed and commissioned in February 2005, just two months from the initial order. The units are designed according to the German Technical and Scientific Association for Gas and Water (DVGW) standard at a UV dose rate of 400J/m2.
The UV systems are linked to a central process control unit by UVtronic+ controllers. These automatically control UV dose by monitoring water volume and water transmittance, ensuring optimum UV output at all times.
The UV dose for each of the two lines is displayed on the central control unit's instrument panel. The UVtronic+ controllers ensure the UV systems are always providing an effective level of disinfection at the lowest possible running cost.
The UV systems are also fitted with automatic wipers. These move up and down the quartz sleeves (which cover the UV lamps) once an hour, keeping them free from mineral deposits and ensuring optimum UV output at all times. The use of automatic wipers does away with the need for manual or chemical cleaning.
It is well known that bacteria and other microorganisms contain enzymes that can repair UV-damaged DNA. This is known as 'reactivation' and poses obvious problems for operators of UV disinfection plant.
Recent research into the process, however, has produced interesting new developments. When comparing photoreactivation of E.coli and cryptosporidium DNA after exposure to UV wavelengths emitted by low and medium pressure lamps, independent researchers have shown that the DNA underwent extensive repair following exposure to UV from low-pressure UV lamps, but virtually none following exposure to UV from medium-pressure lamps.
The researchers concluded that it was the broad UV output of medium-pressure lamps, between 185-400nm, that creates this desirable effect. By emitting UV over a wide range of the UV spectrum, medium-pressure lamps appear to damage other intracellular molecules, such as enzymes, in addition to DNA. It is this damage which seems to permanently inactivate the cells' DNA repair mechanisms.
Low pressure UV lamps produce only a single UV peak at 254nm which only affects DNA. Additional research shows medium pressure UV is also highly effective against giardia lamblia cysts in particular.
Many water treatment plants, especially in northern Europe, can experience both low and high wastewater temperatures at various times of the year. The efficiency of low-pressure lamps is known to fall off significantly at these extremes, and can even fall to zero when the incoming wastewater temperature is below 5oC.
Medium-pressure lamps are unaffected by these temperature ranges - they always start up easily, show no change in UV output during operation and do not age any quicker than lamps used at 'normal' temperatures.
These findings all have serious implications for operators of water and wastewater treatment plants and explain why some are switching to medium-pressure UV technology.
Since the UV systems were installed to treat Bergen's water supply, they have been running constantly with no shut-downs. The systems' performance has been regularly monitored, with water sampling and analyzing by the local health authorities. No evidence of giardia lamblia has been found since switching to UV. In addition, chlorine usage has been reduced to a residual amount to prevent re-infection of the water once it leaves the waterworks.
Contact: Berson UV-techniek