Abstract
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.
Highlights
Human activities can significantly affect the surface waters quality due to the growing pollutant loads of different origin introduced to waters (Pirsaheb et al 2014)
In the developed countries municipal wastewater undergo advanced nutrient removal processes carried out in modern wastewater treatment plants (WWTPs), which are able to ensure effluent discharge limits concerning biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids, nitrogen (N) and phosphorus (P) loads set by legal regulations in almost every country (Rogowska et al 2019)
The presented case study provides real information on how does the river ecosystem react when a sudden discharge of untreated municipal wastewater is introduced to its ecosystem from one of the biggest agglomerations in Central Europe
Summary
Human activities can significantly affect the surface waters quality due to the growing pollutant loads of different origin introduced to waters (Pirsaheb et al 2014). Among point sources, untreated municipal wastewater has been identified as the most hazardous to water ecosystems due to the large amounts of nutrients and organics content (Collins et al 2018). In the developed countries municipal wastewater undergo advanced nutrient removal processes carried out in modern wastewater treatment plants (WWTPs), which are able to ensure effluent discharge limits concerning biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids, nitrogen (N) and phosphorus (P) loads set by legal regulations in almost every country (Rogowska et al 2019). The background monitoring data were used to assess the potential impact of actual water quality before the discharge of untreated wastewater. The monitored parameters for the analysis of the pollution impact on the wastewater receiver water quality were narrowed to COD, TP, TN, N-NH4, and DO (Table 1). The water quality in the mixing zone (MZ) of wastewater and river waters was constantly monitored by Regional
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