Fractionation and identification of iron-phosphorus compounds in sewage sludge

Bingqian Zhang; Lin Wang; Yongmei Li

doi:10.1016/j.chemosphere.2019.02.052

Fractionation and identification of iron-phosphorus compounds in sewage sludge

Chemosphere. 2019 May:223:250-256. doi: 10.1016/j.chemosphere.2019.02.052. Epub 2019 Feb 12.

Authors

Bingqian Zhang¹, Lin Wang², Yongmei Li³

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China.
² State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China.
³ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China. Electronic address: liyongmei@tongji.edu.cn.

PMID: 30784732
DOI: 10.1016/j.chemosphere.2019.02.052

Abstract

Iron (Fe) salts are widely used to remove phosphorus (P) in wastewater treatment plants (WWTPs). Understanding the existing species of iron-phosphorus compounds (FePs) in sludge is conducive to P recovery. In this study, the chemical equilibrium modeling software, sequential chemical extraction methods and instrumental analytical techniques were used to establish a reliable method for fractionation and identification of FePs in sewage sludge. Five FePs-containing sludge samples obtained in the laboratory or from WWTPs were investigated. Modified chemical extraction methods for P and Fe fractionations combined with Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis are preferable for qualitative and quantitative identification of FePs in sewage sludge. The analytical results revealed that more than half of P was bound to Fe in all the sludge samples. Approximately 83% and 14% of Fe was present as iron phosphates in the samples prepared in the laboratory with Fe(III) dosed to a phosphate solution and lab-scale secondary effluent, respectively. Ferrihydrite and hematite were the dominant iron oxides in these two samples, respectively. In the sludge samples collected from WWTPs, Fe bound to iron oxides (71%), mainly hematite, was the dominant Fe fraction in the returned sludge. Mature iron hydroxyphosphate together with some lepidocrocite was the dominant FePs in both the thickened sludge and mixed sludge before digestion.

Keywords: Instrumental analysis; Iron oxides; Iron phosphates; Iron-phosphorus compounds; Sequential chemical extraction; Sewage sludge.

MeSH terms

Chemical Fractionation
Ferric Compounds
Iron / analysis*
Models, Chemical
Phosphorus / analysis*
Sewage / chemistry*
Spectrum Analysis

Substances

Ferric Compounds
Sewage
ferric oxide
Phosphorus
Iron
ferric phosphate