For wastewater disinfection before mixing with a polymer for sludge decantation and dewatering, a municipality in Denmark has installed a Hanovia medium pressure UV disinfection system.

To ensure wastewater is effectively disinfected before being mixed with a polymer for subsequent sludge decantation (separation) and dewatering, the Stege Kommune municipality in Denmark has installed a Hanovia medium pressure UV disinfection system. The wastewater/polymer mixture decants the sludge into two phases as part of the dewatering process. The sludge, which is subsequently used for agricultural purposes, is disinfected by heat treatment prior to decantation, so the wastewater/polymer mixture needs to be completely free from bacteria, viruses and other microbial contaminants.

The treated wastewater is also used to clean the sludge decanter at the end of the process.

To ensure optimum performance, the Hanovia UV system is fitted with a hand-operated wiper.

This keeps the quartz sleeve surrounding the UV lamp free from fouling and means UV output is always at its maximum.

The system has a capacity of 10.8m3/hr.

UV is widely used to remove harmful pathogens from drinking water and wastewater.

It is a completely clean technology which does not rely on the use of chemicals and leaves no unwanted residues or by-products.

Recent research suggests medium pressure UV is more effective at permanently destroying micro-organisms than the alternative method - low pressure UV.

In the research, the two methods were compared and micro-organisms were shown to repair themselves after exposure to low pressure UV, but not medium pressure UV.

This research has serious implications for operators of water and wastewater treatment plant and is one of the reasons why more and more of them are switching to medium pressure UV technology.

Many WWTP 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 5C.

Medium pressure lamps are unaffected by these temperature ranges - they always start up easily, show no change in UV output and do not age any quicker than lamps used at 'normal' temperatures.

According to the Hanovia Danish distributor, the Stege Kommune is very satisfied with the performance of the Hanovia system, which was chosen for its quality and fast pay-back time.