Inventory of Polish municipal sewage sludge ash (SSA) - Mass flows, chemical composition, and phosphorus recovery potential

This paper presents an inventory of sewage sludge ashes (SSA) generated in the mono-incineration plants for municipal sewage sludge in Poland. This research focused on the detailed study of mass flows, chemical composition, and phosphorus recovery potential. There are currently 11 sludge mono-incineration plants operated with a total capacity of 160,300 Mg dry weight (d.w.) of sludge annually. Recently, a significant increase in the amount of SSA generated in these plants has been observed, reaching 26,756 Mg in 2018. Chemical composition of SSA showed significant amounts of the main nutrients: calcium (similar to 14%), phosphorus (similar to 13%), magnesium (similar to 3%), and potassium (similar to 1%). Additional main elements were iron (similar to 14.5%), silicon (similar to 13%), and aluminium (similar to 6%). The main trace elements in the SSA were zinc (similar to 3750 mg/kg) and copper (similar to 899 mg/kg). Pollutants, according to fertilizer regulations of different countries, present in Polish SSA were chromium (similar to 703 mg/kg), nickel (similar to 260 mg/kg), lead (similar to 94 mg/kg), and cadmium (similar to 9 mg/kg). The radionuclides, uranium, and thorium often present in higher amounts in commercial phosphate rock-based fertilizers, were only detected in SSA at low levels of 4-9 mg/kg and 2-3 mg/kg, respectively. Theoretical phosphorus recovery potential from the SSA (from plants in Cracow, Lodz, Gdansk, Gdynia, Szczecin, and Kielce) was estimated at 1613.8 Mg, of which 33.9% is bioavailable. Currently, in Poland, the recommended approach is the production of fertilizers as a result of the extraction of phosphorus from the SSA with its use in the production of secondary mineral fertilizers. Further research in this area is required considering Polish conditions and legislation. (C) 2020 Elsevier Ltd. All rights reserved.