The objective of this study was to assess the functionality of the wastewater treatment plant in Nowy Sącz by means of tools to determine the efficiency and reliability of the operation of the analysed facility. The range of analysed indicators included the main indicators of wastewater pollution: BOD₅, CODCr, total suspended solids, total nitrogen and total phosphorus. The performance of the analysed treatment plant was evaluated based on the results of the three years 2017–2019. The percentage reduction efficiency and the technological reliability coefficients of the treatment plant were determined using the values of pollutant concentrations in raw and treated wastewater. A reliable level of operation of the analysed facility was found (the resulting reliability coefficient values WN = 0.31–0.77) with high efficiency of wastewater treatment (reduction of analysed pollutants h = 83.03% to 99.62%). The limit values were not exceeded, which is a requirement of the applicable legislation. The method of determining technological reliability and the reduction of particular pollutants is an easy and important tool for assessing the operation and performance of wastewater treatment plants.
