Study on the fate of phosphorus, fluorine and chlorine in sludge during incineration

Sludge is often incinerated to achieve complete harmlessness and maximum capacity reduction, but the utilization of P (phosphorus) and the environmental pollution of F (fluorine) and Cl (chlorine) released from sludge incineration are usually ignored. In this paper, a series of experiments were employed to inquire into the conversion of various forms of P and the release of various forms of F and Cl after sludge incineration at different temperatures; the agriculture application prospect of P in sludge incineration ash and the environmental pollution caused by the release of F and Cl were discussed. The results show that P in sludge mainly exists as NAIP (non-apatite inorganic P) which biological effect was small. In the process of sludge incineration, InorgP (inorganic P) began to volatilize at 900 degrees C, and the remaining P in sludge ash was 30.96 % at 1100 degrees C. The forms of P in sludge incinerated at different temperatures varied considerably: a small amount of OrgP (organic P) in the sludge was converted into InorgP at 400 degrees C; with the increase of incineration temperature, AP (apatite P) increased gradually, with 3.00 x 103-7.98 x 103 g/t in sludge ash at 700-1100 degrees C. At 900 degrees C, the content of AP in incineration ash was the highest, accounting for 58.98 % of Total P, which was the most suitable for slowrelease phosphate fertilizer. At 600-1100 degrees C, more Cl release, with a release rate of 50.61-92.70 %, among which the Cl for HCl (ClHCl) was 1.64 x 103-1.95 x 103 g/t at 700-1100 degrees C. The F release rate was 1.52-37.39 %, among which the InorgF (inorganic F: mainly refers to F in HF and SiF4) was 1.13-27.91 g/t at 300-1100 degrees C, the release amount of OrgF (organic F) was 1.59-1.86 g/t at 600-800 degrees C. It can be seen that after incineration above 700 degrees C, the sludge incineration ash may be used as a slow-release phosphate fertilizer, the release of Cl has greater environmental pollution and instrument corrosion than that of F, and the exhaust gas from sludge incineration cannot be discharged directly into the atmosphere.

Automated summary

This paper investigates the conversion of P and the release of F and Cl after sludge incineration, and discusses the agricultural application and environmental pollution caused by sludge incineration ash.