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Clean water by efficient treatment

13.03.2003


The United Nations World Water Development Report: Water for People, Water for Life considers the water in Finland cleanest in the world. The secret is not only in the quality of raw water, but also in the water treatment methods.



The report, published last week, ranked 122 countries based on the quality of their water and their ability and willingness to improve it. Finland also scored the highest number of points on the overall Water Poverty Index which graded 147 countries according to their water use.

Finland has large resources of high quality raw water. About 60 per cent of drinking water is derived from groundwater, of which some 10 per cent is artificially recharged groundwater, and it usually undergoes little or no treatment. The rest of the drinking water is obtained from surface waters, i.e. from rivers and lakes.


Water quality is classified as good or excellent in about 80 per cent of the country’s lakes and in 40 per cent of the rivers. Surface waters must be treated due to their high concentration of natural organic carbon which can, for example, lead to bad taste and odour.

“In surface water treatment plants, which are usually large, water is subjected to efficient treatment including at least chemical coagulation, sedimentation or flotation and sand-filtration. In many plants this conventional treatment train is followed by ozonation and activated carbon filtration. Finally, the surface water is always disinfected with low doses of chlorine or chloramines,” explains Riku Vahala, Water Quality Expert at the Finnish Water and Waste Water Works Association. The quality of drinking water is continuously monitored by local authorities who report the results to the regional health authorities.

“The Finnish speciality in surface water treatment is dissolved air flotation (DAF), which is widely used instead of sedimentation,” notes Vahala. In the DAF process particles are floated with the aid of adherent tiny air bubbles. From the surface of the basin the floc is periodically removed to a sludge channel and, depending on the size of particles, they are either attached into microbubbles or into other particles. Hence, the range of the particle size to be removed is large.

Practically all wastewaters receive effective treatment in Finland and there has been a significant reduction in the environmental load caused by the municipal wastewaters. Since the early 1970s, the total load of organic matter (BOD) from public wastewater plants into rivers, lakes and sea areas has fallen by 87 per cent, and the load of total phosphorus by 88 per cent.

One of the factors behind efficient water management in Finland is the sensitivity of the country’s water bodies. The groundwater aquifers are generally shallow and small and therefore vulnerable to pollution. The lakes are also shallow and sensitive to pollution. “Unlike in many countries in southern Europe, we don’t have a river which would take the pollutants out of our neighbourhood,” points out Vahala. “We have had to cope with our own discharges in the nearby lake which slowly end up in the sensitive Baltic Sea. These factors together have led to active pollution prevention programs which date back to the 1960s when the massive construction of wastewater treatment plants begun. Nowadays, Finland is one of the leading countries in environmental protection, but this has been mainly due to natural vulnerability, which does not forgive much.”

Mira Banerjee-Rantala | alfa
Further information:
http://www.tekes.fi

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