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Abstract. Municipal wastewater contains significant amounts of organic substances of both natural and anthropogenic origin. Wastewater treatment removes most of contaminants, however new substances are formed as a result of biochemical changes taking part during the treatment process; some of them remain in the final effluent and may pose a threat to life and health of living organisms. Humic substances (HS), which include soluble fulvic acids (FA) are contaminants commonly found in wastewater. This is why the research attempted to examine the content of fulvic acids in mechanically treated wastewater at the Płaszów Wastewater Treatment Plant (WWTP) in Kraków. The study was conducted to assess the quantities of the pollution load coming to the plant. FA were separated (isolated) at a hydrophobic ion exchanger, and then subjected to qualitative analysis to determine their elemental composition and degree of contamination with metals and other substances. Studies were also conducted in the infrared spectrum to determine the effects of internal structure of fulvic acids. Humic acids (HA) are precursors of chloroorganic compounds and other carcinogenic, mutagenic and teratogenic substances in oxidation and disinfection processes. Therefore the problem of FA in the final effluent is important, because of their amount and location of a wastewater discharge point.

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Fulvic acids, alpha (α) humic acids and hymatomelanic acids were extracted digested sludge in two Cracow sewage treatment plants: Kujawy and Płaszów. Their elemental composition was examined and micropollution and ash content were determined. Based on the IR and UV-VIS spectrum, their similarities were determined with the occurring interactions with micropollution. Strong correlations between the acids coming from different sources depend on acid type and micropollution accompanying them, depending on concentration, influences to a specific extent their IR and UV-VIS spectra. Absorption analysis in infrared constitutes a simple method for characterizing fulvic and humic acids from wastewater treatment plants. The extracted fulvic acids were characterized by moderate maturity, while humus acids were well developed. In the fermentation process, the N bond increases together with the level of humification of the humus acid. The characteristics of the extracted humus acids comply with other humic substances presented in the literature. Quantitative analysis showed that digested sludge contains, on average: FA from 5.07 to 5.30 g/kg dry matter, αHA from 59.22 to 74.72 g/kg dry matter, HMA from 20.31 to 43.66 g/kg dry matter. It was thus demonstrated that wastewater treatment, in particular digested sludge, constitutes an attractive source of humus acids with a wide range of applications in numerous areas, such as agriculture, ecological rehabilitation, environmental protection, animal breeding, aquaculture, veterinary as well as medicine and is a precious source of soil fertilizers.