Production of Biosolids by Autothermal Thermophilic Aerobic Digestion (ATAD) from a Municipal Sewage Sludge: The Polish Case Study

This manuscript analyzed the process of autothermal thermophilic aerobic digestion (ATAD) used in installations of municipal sewage treatment plants in Poland. Additionally, solutions for sludge management and the parameters of operating installations were presented. Attention was also put to the energy consumption of the process, where the energy consumption for 1 m(3) of sludge treated was between 18.4 and 27.79 kWh. The amount of sewage flowing into the analyzed plants was between 1500 and 14,000 m(3)/d. On the basis of research carried out in the years 2003-2019 in the selected plants, the characteristics of sludge after the ATAD process were presented. The parameters that determine the usefulness of the sludge as an organic fertilizer were indicated above all. The content of total nitrogen, which was from 2.4 to 8.1% of dry matter, ammonium nitrogen, which was from 0.8 to 1.8% of dry matter, and total phosphorus, which was from 1.1 to 4.2% of dry matter, recommended using sludge for fertilization. It was also pointed out that sewage sludge should be regularly tested for the dynamics of changes in chemical composition and biological parameters. These are the factors that increase risk and limit the use of sludge for fertilization.