Domestic waste water contains phosphorus, nitrogen, organic material, bacteria and viruses. Together with discharges from industry, agriculture and aquaculture it has an impact on environmental conditions in rivers and lakes, fjords and coastal waters.
Waste water causes local and regional pollution
In Norway water closets came into general use around 1900, and sewer systems were built to carry the waste water into rivers, lakes or fjords. In many cases, waste water treatment plants were not built until conditions in the the river, lake or fjord became very poor or a popular demand arose. Large-scale development of treatment plants in Norway started around 1970. Today, practically all waste water is treated before being discharged into a recipient.
Discharges of domestic waste water add to the general nutrient load in fjords and coastal waters. Nutrients and organic material in waste water, together with similar substances discharged by agriculture, industry and aquaculture, contribute to eutrophication problems in fjords and coastal waters. Discharges of waste water may cause local or regional pollution. Domestic waste water also contains bacteria, viruses and hazardous chemicals.
Visual impact and environmental problems
The local impacts of discharges of waste water include unsightly littering of the sea or lake floor, the water masses or beaches, and hygiene problems. In addition, waste water can be deposited on plants and animals and reduce light penetration through the water. Infective agents such as eggs and cysts of intestinal parasites, bacteria and viruses may disperse through much of a recipient. Sunlight, sedimentation and grazing by larger organisms help to reduce the concentrations of such infective agents.
Settlement patterns and standard of living
In the last 50 years, there have been major changes in settlement patterns and patterns of leisure activity in Norway. More and more people have moved from rural districts to urban areas, and major improvements have been needed in the way waste water from towns and urban areas is managed and treated.
In rural areas, tourism has become an important industry. As a result, large numbers of cabins and holiday homes have been built, and people are also demanding much higher standards of comfort. These developments have made it necessary to construct more waste water treatment plants and extensive sewer systems to reduce the pressure on recipients.
Improved treatment capacity - reduced discharges
Local authorities own most of the waste water treatment plants. The number of treatment plants in a particular area is largely determined by settlement patterns and the water treatment standard required, and the numbers vary widely from county to county.
There is not necessarily any connection between the number of treatment plants and the proportion of waste water treated. The average treatment capacity per plant is often small in counties that have a large number of plants, and high in counties that have few plants. For example, the treatment capacity of Norway's largest waste water treatment plant, VEAS in Akershus, is about twice that of all plants in Nordland county.
Various forms of treatment are used
There are strict standards for waste water treatment in the counties that release waste water into coastal waters between the Swedish border and Lindesnes, or to recipients that drain into these waters. A large proportion of the treatment plants in this area therefore use chemical or biological methods. In other parts of the country, the pollution control authorities may set less stringent standards, and the municipalities often choose to use simpler and cheaper processes, such as mechanical treatment. In the counties from Østfold to Vest-Agder, which constitute the North Sea counties or region, 95 per cent of the total hydraulic capacity is now at chemical and biological treatment plants, whereas the corresponding figure for the rest of Norway, from Rogaland to Finnmark, is 28 per cent.
All treatment processes remove suspended matter from the waste water, but in varying amounts. The material removed is called sewage sludge.
In the 1950s and 1960s, most of the treatment plants built in Norway provided mechanical and/or biological treatment of the waste water. However, from the beginning of the 1970s it became more common to build plants that also include a chemical purification process to remove phosphorus. The figure also shows a sharp increase in hydraulic capacity for mechanical treatment in 1998-1990. It was during this period that the authorities started to register plants with strainers and sludge separators as mechanical treatment plants. Thus, the apparently large increase in capacity is only partly a real increase.
Chemical treatment plants account for 36 per cent of Norway's hydraulic capacity, chemical and biological plants for 28 per cent, mechanical plants for 23 per cent, biological plants for 2 per cent and other types of plants or plants where the treatment method is unknown for 2 per cent. About 9 per cent of all waste water is discharged untreated.
Monitoring, focus on recipients and improved treatment standards
Norway's waste water treatment policy is recipient-oriented. This means that the standards for waste water treatment plants are set on the basis of conditions in the water bodies used as recipients and the quantities of waste water discharged, and are intended to provide a balance between the costs of measures to reduce discharges of pollutants, the user interests involved and the conservation value of different areas. There are monitoring programmes for several recipients at national, regional and municipal level.