Aim of the study:
The main aim of the research was to prove the thesis, that formal and legal restrictions on the use of phosphorus compounds, particularly polyphosphates, in detergents significantly introduced in recent years reduced the concentration and load of this nutrient in a raw sewage inflowing to the selected treatment plant. Additionally, it was tested whether the phosphorus decreasing in a raw sewage reduced the concentrations and loads of total phosphorus in treated sewage, and thus reduced negative sewage anthropopression of the water body.

Material and methods:
In this paper, during the 15-years study (2003–2015), the concentrations and loads of total phosphorus in domestic sewage flowing into the selected treatment plant, as well as in treated sewage discharged into the receiving water body were observed.

Results and conclusions:
Based on the research, it was stated that multidirectional activities implemented, both in Poland and Europe, to phosphates limitation in detergents have significantly reduced the concentration and load of this nutrient in domestic sewage inflowing to the treatment plant. Over the past 15 years, the total phosphorus concentration in household wastewater has decreased from 14.4 to 5.7 mg·dm-3, i.e. by 60.4%. The observed tendency corresponds to the decrease of the unit load value, related to 1 inhabitant. This parameter decreased by 68% from 2.25 mg·person-1·d-1 in 2003 to 0.72 mg·person-1·d-1 in 2017. The total phosphorus concentration in treated sewage discharged from the tested sewage treatment plant decreased from 5.1 to 2.0 mg·dm-3, i.e. by 60.8%, in the years 2003–2017.