ASSESSMENT OF THE POSSIBILITIES OF AGRICULTURAL USE OF SEWAGE SLUDGE FROM SMALL, MEDIUM AND LARGE WASTEWATER TREATMENT PLANTS

The management of sewage sludge, generated at various stages of wastewater treatment, is still a significant problem. One of the possibilities of using sewage sludge, which is a valuable source of nutrients (carbon, nitrogen, phosphorus), is its use for agricultural purposes. Sludge can be used for fertilising when it meets the requirements with regard to the content of heavy metals, the number of eggs of intestinal parasites and Salmonella bacteria, and when the amount of organic substances and fertilising components is sufficient. That is why it is so important to know exactly the characteristics of sewage sludge. This allows determination of whether it can be used as fertiliser in agriculture. The study assesses the agricultural use of sewage sludge from three mechanical and biological wastewater treatment plants of different PE, produced in 2016-2018. The analysis was carried out on the basis of the physicochemical parameters of the sludge. Particular attention was paid to the fertilisation and sanitary properties, as well as the presence of heavy metals, which were largely influenced by such factors as: the size of the wastewater treatment plant, the method of sewage sludge treatment and sludge management, and the nature of the catchment area. The concentrations of particular substances in sludge from wastewater treatment plants differed from one another, and sometimes these were very large differences. The conducted analysis showed that sewage sludge, from both small and large wastewater treatment plants, has a significant potential as agricultural fertiliser due to the presence of minerals such as nitrogen, phosphorus and calcium.