TRENDS IN DOMESTIC WASTE-WATER TREATMENT IN SWEDEN

The requirements on domestic waste water treatment in Sweden are very hard, For example, in 1995 the requirement on Nitrogen removal in the southern part of Sweden for plants close to the sea will be at least 50% reduction (effluent less than 15 mg/l) and in some cases 60 to 75% reduction (effluent less than 8-12 mg/l). Regarding Phosphorus removal the present requirement is 0.5 mg/l P-total and in some cases 0.3 mg/l. A consequence of the requirements is that the waste water treatment technology is very advanced in Sweden. All densely built-up areas in Sweden have therefore today domestic waste water treatment plants with a high degree of treatment. The aim of the treatment is to remove or reduce: coarse pollution suspended matters organic material, BOD and also the nutrients Phosphorus, P, and Nitrogen N The requirement on degree of treatment depends on the condition of the receiving water and the treaty of 1989 between the countries within the Baltic Sea catchment area regarding the restoration of the Baltic Sea (The Helsinki Convention). The paper will describe the requirements on treatment during different conditions and the corresponding treatment processes with special attention to Nitrogen and Phosphorus removal and the present trends on Nitrogen and Phosphorus removal. A separate section will deal with sludge handling and process control.