Case Study on the Use of Sewage Sludge for the Reclamation of Mining Sites Contaminated with Heavy Metals

The aim of the study was to determine the heavy metal content of soils after sewage sludge application and to calculate the costs associated with fertilising the soil with sewage sludge, which have not been analysed in the available literature so far. The soil for the pot experiments came from villages where the soil was contaminated with heavy metals. Sewage sludge was proposed as a material for the reclamation of land degraded by the mining industry in the aforementioned settlements, and its effect on improving the physical and chemical properties of the soil after application was demonstrated. The cost of applying three doses of municipal sludge to restore areas damaged (degraded) by human activity was estimated. The calculation was carried out on the basis of KNR (National Contractors Estimator) No. 2–21 Tereny Zieleni (Green Areas) and the current prices from Sekocendbud Bulletin 5/2023 (2145), 1st quarter 2023. The cost of fertilising with stabilised sewage sludge for category II land is relatively low. The cost difference between the lowest sludge application of 50 Mg•ha-1 and the highest of 200 Mg•ha-1 is 85%. Therefore, it is cost-effective to apply the highest possible sludge dose per unit area. The study used sewage sludge that was suitable for natural purposes, including agricultural use, and that met the requirements [Journal of Laws 2015, item 257]. In Karniowice, no contamination of the soil with copper, cadmium, zinc and lead was found, although the content of these metals clearly increased after sludge application at the aforementioned sludge doses. The application of sludge, even in multiple doses, had no influence on exceeding the permissible concentration for these metals according to the Regulation of the Minister of the Environment of 2015, which allowed the area to be classified as uncontaminated after sludge application. In Lgota, soil contamination standards were exceeded for cadmium, lead and zinc after sludge application. In the case of copper after sludge application, the results were in line with the regulation.