## 1 Introduction
Furthermore, recent studies concentrated on deriving biotechnological products from wastewater sludge in the form of biostimulants--substances that enhance plant growth and soil health. For instance, biostimulants have been obtained by fermenting sludge with the bacterium Bacillus licheniformis. This fermentation process produces compounds that when applied to soil, were shown to significantly increase the degradation of the herbicide oxyfluorfen, a widely used pre-emergent herbicide known for its persistence in the environment. The application of these biostimulants not only accelerates oxyfluorfen breakdown but also enhances the relative abundance of specific microbial communities involved in bioremediation. These results demonstrate the fundamental role of sludge-derived biostimulants in the bioremediation of soils contaminated with oxyfluorfen, offering a sustainable approach to mitigate herbicide pollution [12]. However, alongside the development of advanced methods for extracting high-value secondary products from wastewater sludge, it is also essential to consider the potential for producing more traditional and accessible products, but with guaranteed quality that will facilitate their widespread use. A number of contemporary studies focused on modern methods for producing fertilizers from wastewater sludge with assured quality. Wastewater sludge is a heterogeneous mixture of organic and inorganic compounds, as well as microorganisms [13]. The composition and volume of sludge can vary over time and depend on the characteristics of incoming wastewater, while taking into account seasonal fluctuations. For instance, in the European wastewater system, the annual loads of nitrogen and phosphorus are estimated to exceed 3 million and 1 million tons, respectively [14]. Since, after preliminary treatment stages, the organic fraction in sludge comprises over 50%, wastewater sludge can be considered a valuable source of organic carbon [15]. Given the characteristics of wastewater treatment methods, it is noted that the most significant biogenic substance in treated sludge is phosphorus compounds. Extracting even half of the phosphorus contained in European wastewater sludge could satisfy approximately 15% of the global demand for phosphorus in agriculture [16; 17]. The technology for fertilizer production is aimed at enhancing the efficiency of the agricultural sector, which must meet the nutritional needs of the population. Most developed countries import phosphorus and phosphate fertilizers due to the limited availability of these resources. Additionally, conventional fertilizers are primarily produced from non-renewable raw materials, posing certain risks to ecosystems [18; 19]. Therefore, wastewater sludge can be considered a high-potential substitute for chemical fertilizers in agriculture [20; 21]. The extraction of nutrients from waste can contribute to the reduction in environmental pollution and to the decreased depletion of non-renewable resources [22]. In the context of fertilizer production from wastewater sludge, contemporary research typically examines sludge that has undergone anaerobic digestion and sludge resulting from composing. [PERSON] et al. [23] discussed the applicability of wastewater sludge as fertilizer after composing and anaerobic digestion. During the composing process, wastewater sludge undergoes specific physicochemical transformations that yield a stable, humidified product. Among the advantages of this method are low capital and operational costs, as well as the additional stabilization of sludge, including devorming. It was observed that using wastewater sludge and composs derived from it as fertilizers or soil substrates increases the organic matter, nitrogen, phosphorus, and other macro- and micronutrient contents in soils [24; 25]. Under the influence of sludge, soil acidity typically decreases and moisture retention increases, which is particularly important for soils with a light granulometric composition.