During heavy precipitation, chemical and biological pollutants from urban and agricultural areas enter the waters from storm overflows as a result of infiltration and inflow, as well as via uncontrolled outflows from water treatment plants. Infiltration and inflow of rainwater into sewers is an especially popular and major worldwide problem. Climate forecasts indicate changes in climatic conditions towards an increase in the intensity and frequency of torrential rainfalls. It may therefore be assumed that the negative impact of rainwater on water quality will increase. This article attempts to address the question of the impact of pollution from wastewater introduced into water during rainy weather to the receiver. The assessment of the impact of rainfalls on a receiver was carried out on the basis of a simulation of pollution loads from sewage introduced into a river by storm overflows based on data from monitoring the amount of rainfall and simulating the operation of storm overflows using Environmental Protection Agency Storm Water Management Model (EPA SWMM). The obtained results were compared with the pollutant loads discharged at the same time from the sewage treatment plant (STP). In addition, the article assesses possible improvement solutions to reduce the negative impact of storm overflows on water.

Achieving high efficiency of biological waste treatment in mechanical–biological treatment (MBT) plants requires reliable methods for measuring the degree of biodegradation of organic substances. For this purpose, several physical, chemical, and biological indices are used. This paper presents respirometric activity (AT4), biogas potential (GB21), total and dissolved organic carbon (TOC and DOC, respectively), and loss on ignition (LOI) values, as well as the correlations between the indices selected for stabilized waste produced in 18 MBT plants in Poland, which use various technologies for biological processing of the organic fraction of municipal solid waste. The study confirms that there is a linear relationship between AT4 and GB21 for stabilized waste produced in MBT plants, regardless of the waste treatment technology used. It has also been found that there is a linear relationship between AT4 and the concentration of dissolved carbon in water extract from stabilized waste. This indicates that DOC can be used for monitoring the organic matter stabilization process in mechanical–biological waste treatment plants. Its advantage is a shorter time needed for measurements in comparison to AT4 and GB21 tests.

To ensure high fermentation efficiency, it is necessary to assess the biodegradability of a substrate. These parameters are most often determined on the basis of the amount of loss on ignition and total organic carbon. We are more and more often using chemical indices. However, these indices do not provide information on how much an organic substance is susceptible to biodegradation. The actual assessment of the content of easily biodegradable matter in substrates that are used for fermentation should be performed on the basis of aerobic (AT4) and anaerobic tests (BMP), which require specialised equipment and are time consuming. The AT4 index is being more and more frequently adopted for the analysis of substrates that are used in the fermentation process, because AT4 takes a much shorter time than BMP and provides information on the biodegradability of substrates. The aim of the article is to answer the question of whether the AT4 parameter can be used to assess the suitability of the substrate from the agricultural sector for the fermentation process. The results show that the AT4 index could be used instead of the BMP parameter.

The efficiency of waste degradation can be expressed by the rate of waste decomposition in individual phases. This article presents the durations of degradation phases of pretreated and untreated waste stabilized in anaerobic laboratory reactors. In this investigation, the quantities of organic and nitrogen contaminants emitted from the waste during the study are presented. The study confirmed the beneficial effects of aerobic pretreatment of waste before landfilling on reducing the duration of hydrolysis and acid phases, and speeding up the start of the stable methane phase. In the pretreated waste reactor, the stable methane phase began about 19 weeks earlier than in the untreated waste. The total amounts of contaminants removed from the aerobic pretreatment waste were lower than from untreated waste, with values of COD, TOC, BOD₅, and VFA corresponding to 21, 18, 6, and 23 %, respectively, and values of TKN and NH₄ of 7 and 50 %, respectively.

In sewage treatment plants for removing nitrogen compounds are used biological processes of nitrification and denitrification. The parameters determining the efficiency of biological processes of nitrogen removal are organic carbon ratio (BOD₅) to total Kjeldahl nitrogen (TKN), temperature and pH. The impact of these parameters on the operation of the sewage treatment plant with an RLM of 45,000 based on operational data from the period 2011-2013 has been assessed. The efficiency of removing nitrogen compounds from sewage in the analysed treatment plant depended on the temperature of sewage and the quotient BOD₅/TKN. Even at the optimal ranges of BOD₅/TKN ratio temperature at 10°C nitrogen concentration in the treated wastewater was about 3 times higher than the limit value, and the removal efficiency of nitrogen varied between about 30 to 60%.

One of the major tasks of municipal waste management in European Union countries is the systematic reduction of waste that is removed and transported to landfills. This refers particularly to biodegradable waste. One of the methods employed to decrease waste amount is Mechanical-Biological Treatment (MBT) of the waste, before it is stored. The article presents characteristics of MSW and biologically pre-treated municipal solid waste, organic carbon loads emitted in biogas and leachate during waste deposition in a landfill. Its decomposition rate constants were determined on the basis of modified Zacharof and Butler’s stochastic model. The values of decomposition rate constants determined for MSW had similar change trends to those presented in the literature: the hydrolysis constant had the lowest value (2.6 × 10-5 d-1), the highest acid phase constant (4.1 × 10-4 d-1), while the methane phase constant - 2.2 × 10-4 d-1. The PMSW decomposition rate constants in each anaerobic waste degradation phase had similar change trends, though their values were higher, by 21, 11 and 19%, respectively.