Photo: Stig Stasig

New lighting engineering well suited to urban purposes 

In a Danish demonstration project, bacteria in urban wet weather discharges are being killed off with the aid of powerful light — a compact solution that takes up little space on expensive urban sites.

New technology that involves cleaning combined wastewater and rainwater with the aid of powerful light can also be used in other cities where there is a lack of space for storing water. Here it is a case of finding compact solutions that do not take up so much space on expensive sites. A Danish pilot project promises to offer a handy solution.

At Svanemølle Bay north of Copenhagen, the quality of the water is being tested at a new plant prior to its official opening in August. The trial is the first of its kind, where a mixture of urban wastewater and rainwater is being purified. This is being done by illuminating the water with powerful fluorescent lamps to kill off the bacteria.

The objective is to find new ways of cleaning wastewater when it rains so heavily that the sewers overflow. The plant can purify 500 litres of water a second. That’s more water every second than a typical family uses in a day.

Photo: Stig Stasig


Big cities will face problems in future

Together with a new reservoir designed to collect water north of the capital, the purification plant will help improve water quality in Svanemølle Bay, making it possible to improve the quality of the bathing water to a level where it will once again be possible to swim in the bay.

"We’re the first ones to test the quality of the runoff water that bypasses the sewers when there’s a heavy downpour. As a result, we’ve quickly come to see the problems facing many towns and cities in the years ahead," says Niels Kofod Andersen, head engineer at Copenhagen Energy (KE).

Sewers under pressure

Both in Denmark and abroad, sewers will be under increasing pressure once future climate change sets in. In Denmark residents of Zealand can expect a greater number of short, sharp, heavy showers, whereas the inhabitants of Jutland will be in for long, intense downpours. But there has also been a greater focus on health, feels Niels Kofod Andersen:

"It’s my view that there is a greater focus on hygiene and bathing facilities today. That’s partly due to globalization, which is instrumental in circulating new bacteria we’re not resistant to, and partly to the need to use the water for more recreational purposes."

By: Christina Tækker
Published on 27.06.2005


Cheap method for purifying water  
To carry out the project, COWI is taking part in a project group together with the municipal authorities of Aarhus, Odense and Copenhagen and the relevant water body authorities. If the plant works as intended, the water company expects to be able to save somewhere between DKK 40m and 100m in terms of building new water storage tanks and reservoirs, which is the alternative way of solving the problems.

The water is purified in three stages: First the water flows through a drum filter, which screens off waste like toilet paper and sanitary towels. Later on, the water passes through a finer-meshed net, finally drifting past long, thin UV lights, which destroy the cell membranes in the harmful microorganisms, like Salmonella, E. coli, viruses and parasites.