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Impact Assessment of the Wastewater Treatment Plants’ Discharges on Maritsa River

Data analysis of wastewater samples at the outlets of wastewater treatment plants (WWTPs) of Pazardzhik, Plovdiv and Svilengrad, which discharge into the Maritsa River is presented. Total monthly loads for 2017 at the outlets are calculated using the monthly averages for the concentrations of chemical oxygen demand, biochemical oxygen demand, total phosphorus and total nitrogen (TN) and the monthly averages for the flow rates. The contributions of the WWTPs to the total river loads emphasize that the impact of WWTPs of Pazardzhik and Plovdiv is significantly greater than WWTP of Svilengrad. Additionally, river water samples were collected before and after the discharge points of the WWTPs in August 2018 and analyzed for water quality parameters listed in Directive 75/440/EEC. Comparison between the river concentrations before the outlet of WWPT - Pazardzhik and after the last sampling point (the outlet of WWTP - Svilengrad) indicates an increase for all the studied parameters, except for Al and Cu. Based on the results obtained for TN, the category of the surface water is significantly deteriorated after discharge of the WWTP - Plovdiv. Wastewater effect on the river surface water is also estimated by using a battery of ecotoxicological tests. The results are presented and compared by the classical approach using categorization based on water quality indicators.