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The total amount of phosphorus (P) removed last year, 1,576 tonnes (metric tons), makes up about 64 per cent of the estimated total intake at municipal sewage treatment plants and separate treatment facilities in sparsely populated areas.
Municipal sewage treatment plants removed 72 per cent of added phosphorus last year. The average purification efficiency rate for phosphorus in municipal plants was highest in the counties along the coast from Østfold to Vest-Agder (the North Sea counties), with 91 per cent. The lowest purification efficiency rate was posted by counties from Rogaland northwards, with 37 per cent. The difference is the result of different treatment principles.
Phosphorus has been chosen as the parameter in estimating the production of pollution. This is because phosphorus plays a major role in the over-fertilization of rivers, lakes and ocean areas. In addition, treatment plants release varying amounts of nitrogen, organic substances and various heavy metals.
563 tonnes of phosphorus released by treatment plants
Around 80 per cent of the population of Norway live in areas with municipal sewage systems. In 1996, municipal sewage treatment plants released an estimated total of 563 tonnes of phosphorus. The average purification efficiency of municipal treatment plants was 72 per cent and the rate for the entire country has been around 70 per cent for the past three years. After declining slightly from 1993 to 1995, purification efficiency rose three per cent in 1996. The change could also be attributed to variations in the quality of the data and reporting.
Weekly Bulletin issue no. 50, 1997