The aim of the work was to develop a new empirical model for calculating the peak annual flows of a given frequency of occurrence (Q_T) in the ungauged catchments of the upper Vistula basin in Poland. The approach to the regionalization of the catchment and the selection of the optimal form of the empirical model are indicated as a novelty of the proposed research. The research was carried out on the basis of observation series of peak annual flows (Q_max) for 41 catchments. The analysis was performed in the following steps: statistical verification of data; estimation of Q_max flows using kernel density estimation; determination of physiographic and meteorological characteristics affecting the Q_max flow volume; determination of the value of dimensionless quantiles for Q_T flow calculation in the upper Vistula basin; verification of the determined correlation for the calculation of Q_T flows in the upper Vistula basin. Based on the research we conducted, we found that the following factors have the greatest impact on the formation of flood flows in the upper Vistula basin: the size of catchment area; the height difference in the catchment area; the density of the river network; the soil imperviousness index; and the volume of normal annual precipitation. The verification procedure that we performed made it possible to conclude that the developed empirical model functions correctly.

COD is an arbitrary indicator of the content of organic and inorganic compounds in wastewater. The aim of this research was to determine the effect of COD of industrial wastewater on the nitrification process. This research covered wastewater from acrylonitrile and styrene–butadiene rubbers, emulsifiers, polyvinyl acetate, styrene, solvents (butyl acetate, ethyl acetate) and owipian^® (self-extinguishing polystyrene intended for expansion) production. The volume of the analyzed wastewater reflected the active sludge load in the real biological treatment system. This research was carried out by the method of short-term tests. The nitrification process was inhibited to the greatest extent by wastewater from the production of acrylonitrile (approx. 51%) and styrene–butadiene (approx. 60%) rubbers. In these wastewaters, nitrification inhibition occurred due to the high COD load and the presence of inhibitors. Four-fold dilution of the samples resulted in a two-fold reduction in the inhibition of nitrification. On the other hand, in the wastewater from the production of emulsifiers and polyvinyl acetate, a two-fold reduction in COD (to the values of 226.4 mgO₂·dm⁻³ and 329.8 mgO₂·dm⁻³, respectively) resulted in a significant decrease in nitrification inhibition. Wastewater from the production of styrene, solvents (butyl acetate, ethyl acetate) and owipian^® inhibited nitrification under the influence of strong inhibitors. Lowering the COD value of these wastewaters did not significantly reduce the inhibition of nitrification.

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 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, COD_Cr, 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, COD_Cr, total suspended solids, total phosphorus and total nitrogen. Mean BOD₅, COD_Cr 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.

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.