The inevitable consequence of the operation of landfills is the emission of leachate, which is considered to be one of the main polluters of the ground and water environment. The leachate contains soluble organic compounds, inorganic contaminants, suspended solids, heavy metals and dangerous substances. The selection of the leachate disposal method requires a comprehensive assessment of its properties. Therefore, the physicochemical parameters and toxicity tests were chosen for a comprehensive assessment of the properties of leachate. Four municipal waste landfills (operational and non-operational) were selected for the study, for which multidimensional statistical analyses were carried out. The study was conducted between the period of April 2018 and December 2019. The comprehensive assessment showed that pollutants in leachate from the analyzed landfills remained at a level which did not allow them to be discharged to water or soil. The presence of substances particularly harmful to the aquatic environment (e.g AN, chromium, copper) may hinder their treatment together with household sewage, as it involves obtaining a permit required under laws. Toxicity of leachate may also be a problem, as it may persist after the treatment process is completed. The values of pH, EC and the concentrations of ON, TDS, TSS, chloride, iron and manganese had the strongest influence on the properties of leachate from all landfills. For operational landfills, these were also calcium concentrations, for non-operational ones COD, TU and the concentrations of TKN, AN, TS, sodium, potassium and magnesium. The mentioned parameters also showed strong correlation with other physicochemical properties of the leachate, which indicate their suitability for the monitoring of leachate and the aquatic environment in the vicinity of municipal waste landfills.

Leachate formation is one of the many environmental hazards associated with landfilling. The leachate may migrate from the landfill to surface water and groundwater, posing a potential threat to aquatic ecosystems. Moreover, its harmful effect on human health and life has been proven. Due to the risks that landfill leachates may pose, it is necessary to control the state of the environment in their surroundings. The paper presents an example of the application of selected statistical methods (basic statistics, statistical tests, principal component analysis) to assess the impact of individual pollution indicators on the quality of landfill leachates. The conducted analysis showed the existence of significant differences between the surveyed active (Legnica, Jawor) and non-operational (Wrocław, Bielawa) landfills in Poland. These differences were especially visible in the cases of the following: electric conductivity (EC) (non-operational landfills 1915–5075 μS/cm, active 5093–11,370 μS/cm), concentrations of total Kjeldahl nitrogen (TKN) (non-operational landfills 0.18–294.5 mg N/dm³, active 167.56–907.4 mg N/dm³), chemical oxygen demand (COD), organic nitrogen (ON), ammonium nitrogen (AN), total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), sulfates, chlorides, sodium, potassium, calcium, magnesium and nickel. Selected indicators should help to determine the progress of decomposition processes inside the landfill and the potential impact of leachate on the environment, and should be used in the mandatory monitoring of landfills.

The formation of leachate is one of the inevitable consequences associated with the operation of landfills. In addition to the study of physicochemical composition, toxicity is an important parameter taken into account, among others because of the need to subject leachate to treatment before discharge into the environment. The aim of this study was to determine the degree of leachate contamination using LPI and toxicity index. An analysis of the relationship between the toxic effect on plants and the calculated LPI values was also carried out to assess whether they could provide a measure of leachate toxicity when selecting a treatment method. The research conducted was to determine the degree of leachate contamination using LPI and toxicity index. An analysis of the relationship between the toxic effect on plants and the calculated LPI values was also carried out to assess whether they could provide a measure of leachate toxicity when selecting a treatment method. Calculated values of the leachate pollution index showed that leachates from selected Polish landfills are characterized by low and medium levels of LPI values. The variation in index values obtained was particularly evident between active and closed landfills and was related to the physicochemical composition of leachates. In closed landfills this value ranged from 7.4 to 11.1, while in active landfills from 12.9 to 15.9. The variation in index values obtained was particularly evident between active and inactive landfills and was related to the physicochemical composition of leachates. Phytotoxicity tests showed that leachate at low concentrations can promote plant growth. At higher concentrations (50 and 100%), leachates caused inhibition of root and shoot growth, which correlated with high LPI values. The results confirmed the relationship between the toxic effect on plants and the LPI values, so it can be considered as a reliable indicator of leachate toxicity.

Constructed wetlands (CW) with vertical flow were used to treat leachate from municipal landfills (active and closed, at different concentrations) using a combination of substrates, i.e., gravel, sand and an exchangeable layer, depending on a variant: organic substrate (pine bark) or mineral substrate (zeolite, expanded clay). The systems were planted with Phragmites australis. The aim of this study was to compare the efficiency of removal of selected pollutants from landfill leachate in CW using different types of filling. For most parameters, the best reductions were obtained on zeolite substrates. In the investigated CW, reductions were achieved at the levels of: AN 96%-99%; TKN 75%-88.5%; TN 62.5%-70%, TP 84-88% and heavy metals (Zn, Ni, Cu, Cr) 41%-56%.

Composting the municipal organic fraction of waste results in a valuable product in the form of compost, which could be used instead of other forms of fertilisation. The organic waste stream may contain oxo-biodegradable and biodegradable plastics used for waste collection. Their components and decomposition residues may contaminate the compost chemically and physically. In this paper, the results of studies on the content of selected macro- and microelements in new and composted plastics have been analysed. Statistical analyses were carried out in order to determine the most characteristic components of plastics and to determine the character of chemical composition changes. The analysis of the test results showed that multidirectional changes in the content of macro- and microelements occur during composting, and they may be the source of contamination of the fertiliser produced. Contaminants in the form of microplastics may also be released into the environment, which may pose a threat to many elements of the environment, including animals and humans.