Fraction Distributions of Phosphorus in Sewage Sludge and Sludge Ash

Abstract

Previous publications on phosphorus (P) in sewage sludge and sludge ash have mostly focused on the total contents, while information on the fraction distribution of P is rarely examined. In this study, P in sewage sludge was, for the first time, fractioned into NH4Cl-P, BD-P, NaOH-P, HCl-P and Res-P via increasing chemical reagents. Its speciation evolution during sludge incineration was also investigated. Results showed that the total P content in sewage sludge had a wide range (0.97–1.74%), and NaOH-P and Res-P were the dominant fractions, which contributed with 67.1–81.2% of sludge P. Sludge incineration process increased the relative proportion of HCl-P from the initial 9.1–11.7% (sewage sludge) to 63.0–78.0% (from ash when sludge was incinerated at 900°C). Furthermore, P in sludge ash was respectively extracted by acid (HCl) and base (NaOH). It was found that the extraction percentage by HCl reached more than 90%, while that by NaOH was less than 30%. The different extraction efficiencies could be explained by the P sequential extraction procedure applied in this study.