A German water treatment plant has recently switched its disinfection treatment from chlorine dioxide to a more sustainable ultraviolet (UV) solution. Using Xylem’s certified Wedeco Quadron UV disinfection system, the plant’s new process minimizes energy consumption and reliably removes bacteria, viruses and parasites, without creating any disinfection by-products.

The water treatment plant in Witten, Germany, managed by Verbund-Wasserwerk Witten GmbH, supplies drinking water to approximately 100,000 people. The vast majority of the water comes from the Ruhr River. The risk of contaminants from surface water, especially of microbiological nature, requires an intensive, multi-step treatment process.

In 2012, the company decided to move from traditional chlorine dioxide disinfection to the sustainable option of UV disinfection. Since this process does not involve the use of chemicals, it does not create any disinfection by-products.

“The inactivation of bacteria, viruses and parasites, including those that are chlorine resistant, with UV light is a tried and tested disinfection method,” says Klaus Döhmen, head of production and treatment at Verbund-Wasserwerk Witten GmbH. “The UV light changes the DNA of the targeted pathogens, thereby preventing further cell division. More than 99.99 percent of all pathogens can thus be rendered harmless in a matter of seconds.”

A compact, reliable solution

Because of restricted space, the treatment plant had to rule out low-pressure UV reactors and was instead looking for a compact solution. The system also needed to be compatible with the plant’s existing automation and control system and be able to handle a high throughput of 1,000 m3/h per UV reactor.

“The flexibility offered by Xylem was a key factor when choosing to install the Wedeco solution,” says Döhmen. “We were looking for a reliable, sustainable and cost-effective alternative to chemicals.”

Xylem was commissioned to deliver two Wedeco Quadron 1200 medium-pressure UV systems. The systems were installed in spring 2013 and, following a two-month trial period, they were placed in fully automatic operation.

Due to the space limitations, the UV systems were installed above the existing water main piping. As Xylem’s patented Wedeco OptiCone flow diverter guarantees the perfect flow to the UV lamps regardless of the supply pattern, it was capable of handling this irregularity.

Reducing energy use and maintenance costs

“Two other factors in choosing this technology were Wedeco’s OptiDose control feature and the wide ranging intelligent dose control of 30-100 percent power input, which ensures adequate disinfection while minimizing energy consumption in all operating conditions,” Döhmen says. “This feature was of particular importance to us due to the seasonal variations in the water quality of the river.”

An automatic cleaning function with a chemical-free mechanical wiper system also supports optimum operating conditions and reduces maintenance costs. UV lamps and sensors are accessible from one side and can be replaced quickly and easily without having to empty the reactor. In addition, a service hatch enables internal system maintenance to be carried out without the need to remove the system from the pipe work.

“Xylem clearly demonstrated its ability to tailor solutions to our needs by drawing on their strong engineering capabilities and broad expertise in the area of UV treatment,” says Döhmen.