Identification of significant pressures and assessment of wastewater discharge on Krivaja River water quality

Abstract

One of the key stages of the process of preparing management plans for the river basin is the analysis of pressures and impacts, as well as the risk assessment of failing to achieve the environmental objectives. DPSIR framework (Driving Forces-Pressure-State-Impact-Response) was developed by the European Agency for the environmental protection, and makes the conceptual basis for the pressures and impacts analysis, taking into account the complexity of the interactions in the environment and represents the tool for their analysis. Impact assessment of the water body requires some quantitative information to describe the condition of the water body and/or the pressures that act on it. The aim of the study was to determine the effect of wastewater discharge on Krivaja watercourse. Impact assessment is carried out based on data of polluters? wastewater and monitoring information for water in Krivaja. For each site at which sampling was performed, the specific risk quotients for surface water were calculated, as the ratio of the each pollutant concentration in surface water at the sampling point and environmental quality standards for pollutants, as well as their sum that represents the risk index. In order to have the integrated perceive of processes in the Krivaja River, taking into account cumulative effects from point sources, the concept of total maximum daily load was applied, using which the pollution amount, that can be discharged daily in a water body without degrading his prescribed/required quality, was calculated. Comparison of emitted loads from pollution point sources with maximum allowable ones was performed. Wastewaters of different polluters located on Krivaja are, due to insufficient treatment, very loaded with organic matter and nutrients. Krivaja receives daily 1332 m3 of wastewater, 999 kg COD, 722 kg BOD, 144 kg of nitrogen, 4.3 kg of phosphorus and 627 kg of suspended solids. Of the total wastewater volume, the majority (69%) originates from municipal wastewater, 81% of the total amount of organic matter comes from the industry, while nutrients mostly originate from municipal wastewater. Loading of Krivaja with wastewater is major, uneven and unbalanced. Water quality of Krivaja is unsatisfactory. According to national legislation there is the exceedance of maximum permissible values for Class II for watercourse (good status) for most parameters, in all sampling locations and in both sampling periods. Parameters that exceeded the value for the Class II are dissolved oxygen, organic matter content, suspended solids, nutrients. Water flow in the river is not sufficient to receive the total amount of the pollutant load from point sources. Risk assessment, based on the monitoring results, indicates that the river Krivaja is possibly at risk of failing to meet the required water quality because the most of the values exceeded the limit values. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR37004]