Summary:

The paper presents the assessment of the operation of a sewage treatment plant in Haczów before and after its modernization. The analysis of results was conducted based on data data for the period from January 2011 to March 2015. The paper describes the process line of the studied object and the qualitative assessment of treated sewage based on three basic sewage contamination indicators: BOD5, CODCr and total suspended solids. Moreover, the amount of sewage flowing into the treatment plant over the period of four consecutive years was analyzed. The operation of the sewage treatment plant was assessed for two periods, i.e. before and after its modernization. The conducted analysis showed a significant improvement in the quality of treated sewage after the modernization of the treatment plant. After the modernization, the mean value of the BOD5 indicator in the treated sewage was 8,4 mgO2.dm-3 and was more than seven times lower than in the period prior to modernization. Similar situation was observed for CODCr as its mean value for treated sewage after the modernization was 61,7 mgO2.dm-3 while before the modernization it was 227,9 mgO2.dm-3. A significantly lower value of the mean total suspended solids concentration was also observed in treated sewage after (18,7 mg.dm-3) than before the modernization (62,9 mg.dm-3). The analyses of the collected data evidence much positive effect of the conducted modernization of the studied treatment plant, which resulted in a significant improvement of the quality of sewage discharged into the receiver.