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.

The paper describes a new, proprietary method of HS extraction from digested sewage sludge. HS was extracted using the processes of dissolving organic substances and precipitating mineral micropollutants. The obtained substances were tested by determining their IR spectrum, elemental composition, and content of micropollutants and comparing them with HS obtained using the classical method. Using Phytotestkit, it was shown that HSs isolated from digested sewage sludge contain relatively large amounts of the nutrients necessary for plants (including N and P) and are a good component of a biostimulating substance. The obtained HS contains more ammonium and phosphorus ions. During extraction, inorganic impurities (including heavy metals) are reduced, and the humic product does not contain pathogens, parasites, and their spores. The method is simple, economically justified, and can be used on an industrial scale.

Research over several years has shown that municipal engineering is an important source of humic substance formation (HS). Effluents from municipal landfills and digested sludge, due to high concentrations of organic pollutants, including HS and inorganic pollutants, are discharged to a biological treatment plant, where their largely non-biodegradable pollutants constitute a burden on the activated sludge and generate problems related to wastewater treatment. To demonstrate that humic substances, primarily soluble acids, are the carriers of micro-pollutants, their isolation was carried out from samples taken at different municipal management sites. The following analyses were performed: elemental composition, and the content of inorganic micropollutants, including heavy metals. In addition, the sorption affinity of pure HS to selected pharmaceuticals was investigated. The sorbed pharmaceuticals were Diclofenac and Estrone. HS commonly found in municipal engineering have been shown to be carriers of inorganic and organic micropollutants, including pharmaceuticals. Based on the study data, surface water’s primary source of micropollutants is treated municipal wastewater and fulvic acids are the transfer agent. To demonstrate the locations of HS occurrence within municipal engineering and the micropollutants they carry, their isolation was carried out from samples taken at different municipal management sites. Fulvic acids were studied due to their high mobility. Extraction was carried out according to the method recommended by the International Humic Substances Society (IHSS) with the author’s modification. The following analyses were performed: elemental composition (N, C, O, and H); the content of inorganic micropollutants, including heavy metals; and the IR spectrum. In addition, the sorption affinity of pure HS to selected pharmaceuticals was investigated. The sorbed pharmaceuticals were Diclofenac and Estrone. The study confirmed the occurrence of HS in municipal landfill effluents, activated sludge, excess and digested sludge effluents, and treated wastewater. At the same time, HS commonly found in municipal engineering have been shown to be carriers of inorganic and organic micropollutants, including pharmaceuticals.

This work presents the characteristics of humic substances, with particular emphasis on the properties of agricultural importance, i.e., the improvement of soil structure, soil properties and the availability of nutrients. Attention was also paid to the methods of introducing given substances into the soil and the possibility of direct application to the plant surface. The mechanisms responsible for the stimulating and protective effect of humic substances on plant development were explained in detail, including phytohormonal regulation, the mitigation of biotic and abiotic stresses, antioxidant properties and the influence on seed germination and the development of the plant root system. The economic and environmental importance of the application of the substances in question was also emphasized, consisting of maintaining the health of the soil and the quality of plants, while reducing the share of chemical fertilizers and reducing the amount of water used. It should be noted that humic substances, like any agricultural product, should be appropriately selected for the type of cultivation conducted, i.e., the optimal dose and method of application should be determined.

This paper is based on recent articles regarding applications of humic substances (HSs). HSs are natural organic materials, which have a number of potential applications. Furthermore, HSs are cheap, widespread and obtainable from bio-waste materials. HSs can be used as organic compound sorbents or in detoxification. They are applied as organic additives due to their positive effect on soil and plants, even under stress conditions. HSs reduce water consumption and minimise environmental problems. HSs are utilised for the remediation of multi-metal contaminated soils and as substitutes for synthetic washing agents. From an environmental engineering point of view, it is beneficial to remove HSs from municipal management, where they are undesirable (by-products of disinfection) and to utilise them where they are valuable. The aim of this article is to provide a greater insight into research about the applications of HSs.