The study aimed to assess the operation of the mechanical and biological wastewater treatment plant in Michów (Poland) in terms of the effectiveness of removing contaminants from mixed wastewater (dairy and domestic) and technological reliability. The wastewater treatment plant is owned by the Dairy Cooperative "Michowianka." It is intended to treat mixed sewage, consisting of technological and sanitary sewage as well as part of rainwater from the plant, domestic wastewater supplied by a sewerage system from Michów, and wastewater delivered from septic tanks. In 2017 and in the first quarter of 2018, the permeate from the whey thickening process was also sent to the treatment plant. The period 2017-2021 was covered by the analysis. The analysis included the indicators from the fundamental group (TSS, BOD5, COD), biogenic indices (total phosphorus, total nitrogen, and ammonium nitrogen). The applied technology ensured the removal of total suspended solids, BOD5, and COD at the level of over 96%. Total phosphorus was removed with an average efficiency of 91%. Slightly lower effects were found in the elimination of total nitrogen -78.5% on average, while the ammonium nitrogen removal rate was 88% on average. Due to the high efficiency of the facility, the values of the standard contamination indicators at the outflow, as a rule, met the requirements specified in the water permit. The technological reliability of the wastewater treatment plant in Michów, determined by the Weibull method, was at a high level, usually exceeding 90%. The reliability analysis shows that the facility in Michów has a high capacity to treat wastewater to the extent required for the wastewater receiver, and that the treated wastewater discharge does not cause negative changes in the environment. It indicates a high probability of obtaining the wastewater quality at the outflow from the treatment plant meeting the water permit requirements.

Chemical phosphorus removal in wastewater treatment plants can be carried out by precipitation with iron or aluminum salts or by filtering wastewater through a bed of active sorptive material. This work aimed to investigate whether using a meander flow filter filled with the sorption material Rockfos® would improve phosphorus removal efficiency in a selected wastewater treatment plant. Tests were performed under laboratory conditions using a model of a meander flow filter and a similar filter under field conditions at full technical scale. This filter was the final element of a hybrid constructed wetland located in the village of Białka in the municipality of Dębowa Kłoda in southeastern Poland. A laboratory model of a phosphorus removal filter with vertical incomplete baffles forcing a meandering water flow was constructed to determine the hydraulic conditions of the flow. After one year of operation, the filter with horizontal wastewater flow operating at its full technical scale (without meanders) was modified by inserting appropriate baffles that were analogous to those in the laboratory model. The analysis of the hydraulic conditions in the laboratory model showed that, under the assumed conditions, wastewater flows through the filter layer in a laminar motion, so such filters can be modeled using the Kozeny–Carman formula. It was shown that, after approximately a year of operation in a filter operating at full technical scale, before modification, dead spaces formed, thus causing the channel and primarily surface flow of wastewater. The phosphorus removal efficiency during this test period averaged 9.4%. After introducing baffles and forcing meander flow in the filter chamber, the efficiency increased to 40.6%. The results indicate that meander flow filters can improve phosphorus removal efficiency in small wastewater treatment plants.

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