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Piotr Bugajski, Elwira Nowobilska-Majewska
University of Agriculture in Krakow, Poland
corresponding author’s e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract
In the study, the Weibull method was used to determine the technological reliability of a collective wastewater treatment plant in Nowy Targ in Poland in regard of its ability to meet effluent discharge standards for selected pollution parameters. In addition, relative exceedance frequencies were calculated for this facility. The experiments were conducted in 2016 and 2017. During this period, 87 samples of influent and effluent wastewater were collected and analyzed. The parameters investigated in the study included BOD5, COD, Total suspension and chromium Cr, for which the maximum permissible limits specified in the water quality permit are expressed as concentrations, and TN and TP, for which limit values are defined as minimum reduction rates (%). The technological reliability values for the parameters measured in concentration units were 72.5% for BOD5, 88% for COD, 65% for Total suspension, and 72.5% for Cr. The relative exceedance frequency was 23% of all measurement series for BOD5, 8% for COD, 25.3% for Total suspension, 16.1% for Cr, 2.5% for TN, and 2.0% for TP. It was found that the number of exceedances per year for all the investigated parameters was larger than the "tolerance limit" of five days laid down in the legal provisions in force in Poland relating to the quality of wastewater discharged to a reservoir. The results show that measures should be taken to identify the causes of the observed deficiencies in the reduction of the analyzed pollution parameters in the technological line of the treatment plant and that corrective action should be pursued.

Keywords 
wastewater, wastewater treatment plant, technological reliability, frequency of occurrence

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