Environmental Processes

The study is an attempt to assess the pollution impact on the aquatic ecosystem related with an emergency discharge of untreated municipal wastewater from the “Czajka” wastewater treatment plant (WWTP) in Warsaw. The present case study is based on the analysis of available monitoring data for chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen (N-NH₄), and total phosphorus (TP) in the effluent mixing zone (MZ), the stretch of the river and before the discharge point. Data analysis was supported by a basic statistical analysis based on Pearson’s correlation coefficient. The results proved the importance of efficient and reliable nutrient removal technologies used in modern WWTPs. A statistically significant correlation was achieved between the COD (r = 0.567) and TP (r = 0.714) discharged loads and their concentration in the MZ. However, no significant correlation has been identified with TN and N-NH₄. Furthermore, the dissolved oxygen (DO) deficits in the MZ were observed within 7 days of the discharge period resulting in an average DO concentration decrease from 8.4 to 7.1 mgO₂/L. The river stretch has not been affected by DO deficits while the average observed DO concentration 30 km behind the discharge point was 9.1 mgO₂/L. The analysis results present the pollutants assimilation capacity of a river ecosystem and its real reaction to sudden excessive nutrient loads discharge.