The aim of this study was to determine the biodegradability of organic and biogenic contaminants in wastewater flowing into biological reactors in the treatment plant in Nowy Targ. The research period covered the years 2016 and 2017, when 87 samples of raw wastewater and 87 samples of wastewater after mechanical treatment were collected and subjected to physico-chemical analysis. In both types of wastewater, the size of the following indicators was analyzed: BOD5, COD, total kjeldahl nitrogen (TN) and total phosphorus (TP). The study verified the amount of pollutants in the raw wastewater in order to determine whether they are household wastewater. In the next stage of the analysis, the characteristic values of the analyzed indicators in wastewater after the mechanical treatment process were determined in order to indicate mutual dependences of organic and biogenic indicators. Based on the analysis, it was found that wastewater after mechanical treatment (in the case of its susceptibility to biological decomposition processes of organic pollutants) has an unfavorable COD/BOD5 ratio. With regard to the susceptibility of wastewater to nitrification, denitrification and dephosphatation processes, in the majority of cases, wastewater is susceptible to these processes. It is recommended to apply an additional source of organic carbon to wastewater prior to biological treatment in order to improve the biodegradation of the analyzed pollutants.