The objective of this study was to model the operation of a vertical-flow constructed wetland (VF-CW) for domestic wastewater, using Monte-Carlo simulations and selected probability distributions of various random variables. The analysis was based on collected wastewater quality data, including the values of the pollutant indicators BOD₅ (biochemical oxygen demand), COD_Cr (chemical oxygen demand), and TSS (total suspended solids), in the 2017–2020 period. Anderson–Darling (A–D) statistics were applied to assess the fit of the theoretical distributions to the empirical distributions of the random variables under study. The selection of the best-fitting statistical distributions was determined using the percentage deviation (PBIAS) criterion. Based on the analyses that were performed, the best-fitting statistical distributions for the pollution indicators of the raw wastewater were the generalised extreme value distribution for BOD₅, the Gaussian distribution for COD_Cr, and the log-normal distribution for TSS. For treated effluent, the log-normal distribution was the best fit for BOD₅ and COD_Cr; the semi-normal distribution, for TSS. The new data generated using the Monte-Carlo method allowed the reliability of the VF-CW operation to be assessed by determining the reliability indices, i.e., the average efficiency of the removal of pollutants (η), the technological efficiency index (R), the reliability index (CR), and the risk index of the negative control of the sewage treatment plant operation (Re). The obtained results indicate that only in the case of COD_Cr, the analysed treatment facility may fail to meet the requirements related to the reduction of organic pollutants to the required level, which is evidenced by the values of the indicators CR = 1.10, R = 0.49, and η = 0.82. In addition, the risk index of the negative operation of the facility (Re) assumes a value of 1, which indicates that during the period of its operation, the VF-CW system will not operate with the required efficiency in relation to this indicator. The novelty of this work is the implementation of the indicated mathematical simulation methods for analysing the reliability of the operation of the domestic wastewater treatment facility.

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 study was the analyze of the impact of hydraulic load on the changes in the concentration of pollution indicators in raw sewage in years 2009-2014 in the small wastewater treatment plant. Qualitative analysis for raw sewage was included three parameters: total suspension solid, BOD and COD. The characteristics relation between the concentration of pollution indicators in raw sewage (depend variable) from the hydraulic load(independent variable) was presented by the Pearson linear correlation. In the 6 year study period were collected 32 samples of raw wastewater. Based on the result of linear regression analysis, showed that along with the increasing amount of wastewater in the sewer decrease the concentration of pollutions in raw wastewater. For total suspension solid, increase by 1 m³ of quantity of raw sewage inflowing to wastewater treatment plant, causes a decrease in the concentration of this indicator by 0,53 g·m^-3. For the both organic indicators (BOD and COD), the was found that an increase of 1 m³ the amount of raw sewage inflowing to wastewater treatment plant, caused a decrease of 0,75 gO₂·m^-3 BOD value and 0,66 gO₂·m^-3 COD value in raw sewage.

The aim of study was the analyze of the reliability pollution removal in wastewater treatment plant in Mińsk Mazowiecki. The article presents the results of the reliability of BOD, COD and total suspended solids removal of wastewater treatment plant with actived sludge. Physical and chemical analyses of raw wastewater and treated effluent were carried out in the years 2016–2017 (2 years). The designed size of the treatment plant with actived sludge, expressed in PE is 82 200 residents. During this study period, 50 wastewater samples were collected and analyses. For each of pollution indicators descriptive statistic, percentage reduction and and treatment plant reliability factors (WN) were calculated. The average effectiveness of BOD5 (Biochemical Oxygen Demand), COD_Cr(Chemical Oxygen Demand) and TSS (Total Suspended Solid) removal in this period of study were respectively: 99.1%, 96.3% and 98.9%. A reliability analysis was performed using the Weibull probability model.

The objective of this study was to assess the functionality of the wastewater treatment plant in Nowy Sącz by means of tools to determine the efficiency and reliability of the operation of the analysed facility. The range of analysed indicators included the main indicators of wastewater pollution: BOD5, CODCr, total suspended solids, total nitrogen and total phosphorus. The performance of the analysed treatment plant was evaluated based on the results of the three years 2017–2019. The percentage reduction efficiency and the technological reliability coefficients of the treatment plant were determined using the values of pollutant concentrations in raw and treated wastewater. A reliable level of operation of the analysed facility was found (the resulting reliability coefficient values WN = 0.31–0.77) with high efficiency of wastewater treatment (reduction of analysed pollutants h = 83.03% to 99.62%). The limit values were not exceeded, which is a requirement of the applicable legislation. The method of determining technological reliability and the reduction of particular pollutants is an easy and important tool for assessing the operation and performance of wastewater treatment plants.

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.