The aim of the work was to analyze the effi ciency and reliability of pollutants removal (total suspended solids – TSS, BOD5, COD) in a collective wastewater treatment plant with activated sludge and hydroponic lagoon during its long term operation. The tested object was designed to treat wastewater in flowing through the sewerage system and wastewater delivered by the septic truck. The projected capacity of the treatment plant was 1200 m3∙d-1. The technological system for wastewater treatment

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... onsisted of a mechanical part, a flowing biological reactor working according to the BARDENPHO process, a secondary settling tank and a hydroponic lagoon. The efficiency and reliability of pollutants removal in the analyzed treatment plant were assessed on the basis of the data concerning influent and effluent wastewater collected during the years 2011–2018. On the basis of the measurements results, there were determined characteristic values of the selected pollution indicators in wastewater and the average efficiency of pollutants removal. The technological reliability of the wastewater treatment plant was assessed for the basic pollution parameters (BOD5, COD, TSS) in accordance with the elements of the Weibull's reliability theory, with regard to normative values of the indicators specified in the Regulation of the Minister of Environment. The analysis was carried out using the Statistica 13.1 software. It was proved that in the wastewater treatment plant with an activated sludge and hydroponic lagoon the level of organic pollutants removal expressed by BOD5 was on average 99.5%, COD – 98.1% and TSS – 99.4%. The technological reliability of the system was 100% in terms of the removal of pollutants from the basic group, which means that during the long term operation (8 years) it provided failure-free operation and guaranteed the fulfillment of the requirements that can be found in the Polish law regulations concerning the analyzed pollutants.