Heavy Metal Removal And Phosphorus Recovery In Sewage Sludge Ash Through Rotary Kiln Calcination Treatment

Due to the decreasing quality of mineral phosphate resources and the amount of the phosphate rock, new substitutes for phosphate fertilisers used in agriculture must be found.The enhanced biological phosphorus removal（EBPR） or Fe²⁺, Fe³⁺, Ca²⁺or Al³⁺salts are using by the wastewater treatment plant to avoid the P-eutrophication and ends up phosphate in the sewage sludge. Thus, Sewage sludge（SS） is a significant potential source of P as its huge amount and large P content. However, direct application of SS in agriculture as a P-fertiliser cannot be achieved in the presence of organic pollutants and heavy metals. Thus,the studies in this paper involved the influence of different technological conditions, including temperature（900℃, 950℃, 1000℃, 1050℃, 1100℃）, type of furnace（tube furnace and rotary kiln） and additives（MgCl2, CaO, K2O）, on the removal characteristics of heavy metals and the fixed rate of P in PSSA through calcination.The research of addition influence on the removal of heavy metals and the fixed rate of P in PSSA through calcination demonstrates that: With the amount（<100 g-Cl/kg-ash） of MgCl2, the removal of Cu, Zn is more effective at the temperature 1000°C than 1100°C.However, the situation was reversed for both Cu and Zn if Cl-addition is more than 100g-Cl/kg-ash. Ca has an apparent promoting effect on the removal of heavy metals. However,K should be avoided high content in calcination because it is unfavourable for Zn removal. In addition, the higher temperature of 1100°C contributes to P fixation, which the highest fixation rate is 98.33%.The research of temperature influence on the removal of heavy metals and the fixed rate of P in PSSA through calcination demonstrates that: Higher removal rates of heavy metals can be achieved with higher temperatures. This tendency was especially prominent for Cu and Zn,where those removals increased by 55.36% and 52.88%, respectively from 900°C to 1100°C.With increasing calcination temperatures, the metal speciation distributions differed significantly between the heavy metal elements in treated PSSA; while the micro-appearance of treated PSSA particles was also significantly altered; in addition, the composition in treatedPSSA became simple, where the crystalline compound species were decreased from night compounds at 900°C to four compounds at 1100°C. Finally, the mass fractions and fixation rates of P are both increased with increasing temperature. 98.33% of P-fixed rate in treated PSSA was achieved with 15%Cl addition at 1100°C.