The aim of the work was to develop a mathematical model using equations of fluid mechanics that describe the dynamics of air flow in a part of the compost aerating system integrated with a stationary reactor. The results of the simulation show that adjusting the flow resistance along the entire length of the compost aerating duct, depending on the distance from the connection of the duct with the fan's pressure conduit pipe through gradually increasing the air outflow area by increasing the number of repeatable gaps, yields a uniform pressure distribution above the grate. The process parameters used for computation were relevant to composting a subscreen fraction separated from mixed municipal waste using 80 mm mesh screen (Fr<80 mm) under real conditions. Microsoft EXCEL 2010 software and STATISTICA version 13.3 by StatSoft were used for numerical and statistical analysis of the test results. The research results are presented in four tables and five figures and discussed in the text of the article. During tests performed in real conditions, various variants were tested for reactor filling level and air outflow active surfaces in subsequent grate parts (Fc (i)). It was found that the target waste layer thickness i.e. 3.0 m and Fc (i) changes, in accordance with the values of the developed model, result in a stable pressure distribution pd, amounting to 1506 Pa and 1495 Pa at the grate front and end part.

This paper presents the concentrations of the polycyclic aromatic hydrocarbons (PAH) and heavy metals in leachates from the autothermal thermophilic aerobic digestion (ATAD). The leachates from ATAD installations (Dąbrowa Białostocka, Hajnówka, Pisz, Olecko, Giżycko, Wysokie Mazowieckie) located in Poland were tested. The concentrations of PAHs in samples from Pisz, Giżycko, Wysokie Mazowieckie and Hajnówka were similar to those in industrial wastewater. The cluster analysis confirmed that in sites with a higher polyethylene (p.e.) input from the industrial sector, the leachates were more contaminated with PAH compounds. In samples from Dąbrowa Białostocka, Olecko, Pisz and Hajnówka, the heavy fraction of PAHs compounds prevailed over the light fraction. Concentrations of heavy metals in leachates from ATAD varied. The Ward’s method isolated the wastewater treatment plant in Giżycko. The p.e. from the industrial sector was the highest for this facility. Also, the samples from ATAD had the highest total concentration of heavy metals (5.87 mg/l). The leachates from ATAD are returned to biological systems of municipal sewage treatment plants, where they can be combined into more toxic compounds. Biological wastewater treatment processes do not ensure the removal of PAHs and heavy metals from the wastewater. As a result, harmful compounds can get into the water or ground, polluting the environment.