Impact assessment of treated wastewater on water quality of the receiver using the Wilcoxon test

Wastewater treatment is a process which aims to reduce the concentration of pollutants in wastewater to the level allowed by current regulations. This is to protect the receivers which typically are rivers, streams, lakes. Examination of the quality of treated wastewater allows for quick elimination of possible negative effects, and the study of water receiver prevents from excessive contamination. The paper presents the results of selected physical and chemical parameters of treated wastewater from the largest on the region in north-eastern Poland city of Bialystok municipal wastewater treatment and Biała River, the receiver. The samples for research were taken 3–4 a month in 2015 from two points: before and after discharge. The impact of the wastewater treatment plant on the quality of the receiver waters was studied by using non-parametric Wilcoxon test. This test determined whether the analyzed indicators varied significantly depending on different sampling points of the river, above and below place of discharge of treated wastewater. These results prove that the treated wastewater does not affect the water quality in the Biała River