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The paper presents the results of the analysis concerning the verification of the actual hydraulic load and the load of organic pollutants compared to the conditions designed for 4 household wastewater treatment plants. The researches were carried out in the annual period from May 2015 to April 2016. Based on the conducted analysis, it was found that objects act as underloaded hydraulically and the actual inflow of sewage to the analysed objects during the research period ranged from 7.3% to 32.7% in relation to the inflow assumed in the project. Furthermore, in the case of loading the treatment plant with the load of pollutants expressed as PE, it was fund that the actual PE values were lower than assumed in the project. Therefore, it is important that the sizes of the series of household sewage treatment plants were selected depending on the individual conditions of household, i.e. the number of inhabitants or the amount of consumed water.

The aim of the study was to analyze the mean daily wastewater load from the corporate wastewater treatment plant in Nowy Targ. The study analyzed the wastewater load expressed by BOD5, COD, total nitrogen (Ntot), total phosphorus (Ptot) and chromium ions (Cr). The study was conducted from 2006 to 2016, in which 591 samples of raw wastewater were collected and analyzed in a control well before the treatment plant with a mean of 4 times a month. The scope of research in the analytical part covered the variability of wastewater loads in individual years and determined the characteristic values of mean daily load in particular months. Mean daily wastewater load for BOD5 – 7 053 kg·d−1 for COD – 23 437 kg·d−1 for total nitrogen – 1 464 kg·d−1 for total phosphorus – 197 kg·d−1 and for chromium ions – 129 kg·d−1. For each of the analyzed index, it was found that in the each months mean daily wastewater load in raw wastewater is variable. In the analyzed period the mean daily discharged wastewater oscillated within 13 924 m3·d−1, which accounted for about 66% of the projected load.

The study presents the effects of precipitation on the amount and quality of raw sewage entering a sewage treatment plant in Wodzisław Śląski. It covers a six-year period between January 2010 and December 2015. The research period was divided into seven classes of precipitation intensity. The classes were characterized for their basic descriptive statistics of the raw sewage entering the investigated sewage treatment plant (STP). Data obtained from the collected material and derived from an analysis indicated a considerable influence of precipitation on the amount of sewage entering the investigated facility. Mean amount of sewage entering the STP was by 10.5% (884.9 m3·d-1) greater in B class and by 69.6% (6,153.9 m3·d-1) greater in G class than during dry weather. Individual classes of precipitation intensity were compared for their mean values of raw sewage contamination. Precipitation intensity was found to significantly affect concentrations of the investigated parameters of raw sewage contamination. Basic parameters of sewage contamination (BOD5, CODCr, total suspended solids) were determined and their basic descriptive statistics, such as median, mean, minimum and maximum value, standard deviation and coefficient of variation were calculated.

The paper analyzes the effect of precipitation water that inflowing to sanitary sewage system as accidental water on the changes in the total amount of treated sewage. The effects of accidental water supply on the total amount of sewage inflowing to treatment plant were analyzed based on mean daily amounts from the investigated periods and mean daily amounts from incidental supplies. The study was conducted in the years 2010–2015. Six characteristic research periods were identified (one per each calendar year), when the amount of sewage in the sanitary sewage system was greater than during dry weather. The analysis of changes in the amount of sewage supplied to the sewerage system in the six investigated periods revealed that the accidental water constituted from 26.8% to 48.4% of total sewage inflowing to the wastewater treatment plant (WWTP). In exceptional situations, during intense rains, the share of precipitation water in the sewerage system would increase up to 75%. Then, the rainwater inflowing the sewerage system caused hydraulic overloading of the WWTP by exceeding its maximum design supply.

The aim of the study was to analyze an influence of an inflow penetrating into two selected small sewerage systems during a rainy weather on pollutant concentration and load in raw sewage. Studies were conducted in 2010–2015 on two small sewerage systems in Małopolska province. The studies confirmed that the inflow penetrating into the sewerage systems resulted in a decrease of pollutant concentrations in sewage. However, they also showed that this dilution was not constant for all types of pollutants. The most important outcome of the study was demonstrating that despite its diluting effect on pollutants, the intense inflow into a sewerage system resulted in an increase of a sewage pollutant load. This increase was not regular, but it was rising dramatically when the inflow share in sewage exceeded 50%. The study indicated that the inflow penetrating into the sewerage system should not be disregarded, as it actually presented a significant threat to the wastewater treatment process and in consequence to the quality of recipient waters.

The study provides a comparative analysis of the quality of sewage discharged from selected sewerage systems. The analyzed data were collected from 10 agglomeration sewerage systems discharging sewage into collective wastewater treatment plants (WTP). The investigated pollution indicators included BOD5, CODCr, total suspended solids and biogenic indicators such as total nitrogen and total phosphorus. These results were compared with the outcomes reported in commonly available research papers on sewage disposal. Considering the concentration of individual pollution indicators, more detailed categories of sewage pollution were adopted in this work. The sewage was divided into five basic groups: I – highly concentrated, II – concentrated, III – moderately concentrated, IV – diluted, and V – highly diluted. The sewage categories accounted for the following pollution indicators: BOD5, CODCr, total suspended solids, total phosphorus and total nitrogen. Mean BOD5, CODCr and total suspended solids in raw sewage were higher than average values reported in the referenced literature. Contrary to that, concentration of total phosphorus in raw sewage was significantly lower than reported by other authors. The outcomes of this study suggest that the predictions concerning pollution degree of raw sewage made at WTP design stage should not be based exclusively on general values provided in literature reports.