# Municipal Sewage Sludge Disposal in the Republic of Poland
## 5 Methods of Disposal of Sewage Sludge
### Fertilizer Production
This way, a product with a grain size of at least 0.5 mm and a dry matter content of 40-50% is obtained, which is dried at a temperature of 20-105 \({}^{\circ}\)C for 2-3 h.  
An alternative solution developed by the Central Mining Institute in Poland is the production of fertilizer. For this, stabilized sewage sludge with a hydration of 55-90% is mixed with sodium alginate at a concentration of 1-4% and a calcium chloride solution at a concentration of 1-2%. The mixture is then left to harden and dried at a temperature of 20-105 \({}^{\circ}\)C for 2-48 h (patent No. PL 233663B1, Poland [95]). Rzeszow University of Technology in Poland together with Podkarpackie Centrum Innowacji Sp. z o.o. (Poland) developed a method for producing an organic-mineral fertilizer from stabilized sewage sludge mixed with dusty diatomite (patent No. PL 242576B1, 2023, Poland [96]). The procedure consists of preheating the sewage sludge at 55-65 \({}^{\circ}\)C Celsius for 20 to 30 min at a pressure of 0.1 MPa. Then, diatomite is added to the heated sludge, and the whole mixture is mixed. A granulate is formed and dried at a temperature of 60 to 85 \({}^{\circ}\)C.  
Scientists from the Tadeusz Kosciuszko Cracow University of Technology in Poland developed several different multi-component organic-mineral fertilizers with specific applications for rapeseed (patent No. PL 243440B1, 2023 [97]), corn (patent no PL 243439B1, 2023 [98]), sunflower (patent No PL 243441B1, 2023 [99]) and for general use without specifying the type of crop (patent No. PL 243442B1, 2023 [100]). In the case of fertilizers intended for the cultivation of rapeseed and corn, the production process consists of mixing in appropriate proportions dried sewage sludge with a grain size below 0.2 mm, ash from chicken droppings, also with a grain size below 0.2 mm, ammonium nitrate, potassium sulfate, and nitric acid in a bound form in the form of calcium nitrate. Different mixing proportions of the ingredients are used depending on the purpose of the fertilizer. In the case of fertilizers intended for the cultivation of sunflowers (patent No. PL 243441B1, 2023 [99]), the production process uses a mixture (inappropriate weight proportions) of dried sewage sludge with a grain size below 0.2 mm, chicken manure ash also with a grain size below 0.2 mm, ammonium nitrate, potassium sulfate and sulfuric acid in a bound form in the form of calcium sulfate. The production of granulated multi-component organic-mineral fertilizer [100] involves mixing dried sewage sludge with chicken manure ash, ammonium nitrate, potassium chloride, and potassium sulfate. The mixture is then granulated with an aqueous solution of sulfuric or nitric acid, and the whole mixture is dried to a moisture content of 2-5% by weight. A fertilizer designed to improve soil structure in agricultural applications was also developed by the University of Agriculture in Cracow and Paper and Texture Factory Beskidy S.A., and [PERSON] (patent No. PL 228796B1, 2018 [101]). In this solution,-sewage sludge is mixed with flour in a binder, and the whole mixture is mixed. Additionally, quicklime and bentonite are added to this mixture, and after solidification, it is subjected to mechanical granulation and drying with hot gases at a temperature above 50 \({}^{\circ}\)C.  
Another solution for producing fertilizers from sewage sludge (application No. PL 421521A1, 2018 [102]) is a method developed by the West Pomeranian University of Technology in Szczecin (Poland). It consists of mixing sewage sludge from a mechanical-biological sewage treatment plant with incineration by-products with inappropriate weight ratios. Ashes formed after burning straw in fluidized bed boilers, ashes after burning wood in fluidized bed boilers, and slag after burning sewage sludge are added here. In addition, potassium salt or potassium sulfate is added to this mixture.