The aim of the research was the evaluation of wastewater management in terms of stability and efficiency of wastewater treatment, using statistical quality control. For this purpose, the analysis of the operation and operation of the “Kujawy” Sewage Treatment Plant was made, which is one of the most important and largest sewage management facilities in the city of Cracow. This assessment was done using control charts x for 59 observations. The analysed research period covered the multi-year from 2012 to 2016. Five key pollutant indicators were used to evaluate the work of the tested object: BOD5, CODCr, total suspension, total nitrogen and total phosphorus. In the case of the majority of them, based on the analysis of control charts, full stability of their removal was found in the tested sewage management facility. The exception was total nitrogen, for which periods of disturbed stability of its disposal processes were noted. Analysis of the effectiveness of wastewater treatment showed each time that the required efficiency of reduction of the analysed pollution indicators in the “Kujawy” Sewage Treatment Plant was achieved.

The aim of the study was to determine the impact of selected factors on the reduction of organic pollutants, expressed in BOD₅ and COD_Cr, in wastewater treated in a laboratory scale model of moving bed biofilm reactor (MBBR). The factors included in the experiment: the degree of filling the fluidized bed with biomass carriers, hydraulic load, and aeration intensity. The tested model of the bioreactor consisted of five independent chambers with diameter D = 0.14 m and height H = 2.0 m, which were filled with biomass carriers at 0%, 20%, 40%, 60%, 70% of their active volume. During the test period, hydraulic loads at the level of Q_h1 = 0.073 m³·m^-2·h^-1 and Q_h2 = 0.036 m³·m^-2·h^-1 were applied, which ensured one-day and two-day sewage retention, respectively.The said reactors were subjected to constant aeration at P₁ = 3.0 dm³·min^-1 and P₂ = 5.0 dm³·min^-1. The highest efficiency of the reduction of the analysed indicators was demonstrated by reactors filled with carriers in the degree of 40–60%. Based on the statistical analyses (the analyses of the ANOVA variations and the Kruskal-Wallis test) carried out, it was found that the studied factors significantly modified the mutual interaction in the process of reducing BOD₅ in treated wastewater of the reactors tested. The significance of the impact of the discussed factors on the values of the studied indicators in treated wastewater depends on mutual interactions between the investigated factors.

The subject of the study was to evaluate the stability and reliability of the sewage treatment plant in Nowy Sącz. The scope of the analysed indicators included the main indicators of wastewater contamination: BOD5 (biochemical oxygen demand), CODCr (chemical oxygen demand), total suspended solids (TSS), total nitrogen (Ntot), and total phosphorus (Ptot). The operation stability of the sewage treatment plant in Nowy Sącz was determined on the basis of control cards x for 24 observations made in the period 2018–2019 (2 years). Moreover, the technological reliability of the tested sewage treatment plant (WN) was determined based on the values of the analysed pollution indicators in treated sewage and their permissible values. On the basis of the conducted analyses, full stability of the removal process of most of the analysed contaminants was found. In no case was there any crossing of the control lines, only a single grouping of samples above the help line in the case of total nitrogen, which could indicate a periodical disturbance in the stability of the removal process of this compound. On the basis of the obtained values of the reliability coefficient, which were below WN = 1.00, reliable operation of the analysed facility was found, with a high degree of reduction (ƞ) of the analysed pollutants. The method of determining the technological reliability and stability of the treatment plant with the use of control cards is an effective and easy tool for detecting any disturbances and instabilities in the processes taking place in the tested facility. It enables the operator to take quick action to remove them, thus ensuring a safe wastewater treatment process for the environment and human health.

The aim of the study was to model the operation of a wastewater treatment plant using the Monte Carlo method and selected probability distributions of random variables. Pollutant indices in treated wastewater were analysed, such as: biological oxygen demand ( BOD ₅), chemical oxygen demand ( COD _Cr), total suspended solids ( TSS), total nitrogen (N _tot), total phosphorus (P _tot). The preliminary analysis of pollution indicators series included the: calculation of descriptive statistics and assessment of biological degradability of wastewater. The consistency of the theoretical distributions with the empirical ones was assessed using Anderson–Darling statistics. The best-fitting statistical distributions were selected using the percent bias criterion. Based on the calculations performed, it was found that the analysed indicators of pollution in treated wastewater were characterised by an average variability of composition for BOD ₅, COD _Cr and TSS, and a high variability of composition for N _tot and P _tot. The best fitted distribution was log-normal for BOD ₅, TSS, N _tot and P _tot and general extreme values for COD _Cr. The simulation carried out using the Monte-Carlo method confirmed that there may be problems associated with the reduction of nutrients (N _tot and P _tot) the analysed wastewater treatment plant. Results of values obtained of the risk values of negative control of wastewater treatment plant operation for biogenic compounds, different from 1, indicate that the number of exceedances at the outflow may be higher than the acceptable one.