*3.2. Physicochemical Analyses*

Apart from the samples taken from Groups No II and No III, which were composed of the components separated at the structural examination stage, samples of mechanically dehydrated sewage sludge taken from the municipal wastewater treatment plant in Koszalin were also subjected to physicochemical tests. The research included recording dry mass (*dm*) according to PN-EN 14346 and organic matter (*om*) according to PN-EN 15169: 2011. The analysis of C and N content was accomplished by Elementar, VarioMax CN. About 10 mg of dried powdered homogenous sample was used to determine the percentage of carbon and nitrogen. The measurement uncertainty of both analytes was the same, i.e., ±0.5%.
