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Phosphorus Sorption Characteristics in Aluminum‐based Water Treatment Residuals Reacted with Dairy Wastewater: 1. Isotherms, XRD, and SEM‐EDS Analysis
Author(s) -
Zohar Iris,
Massey Michael S.,
Ippolito James A.,
Litaor M. Iggy
Publication year - 2018
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2017.10.0405
Subject(s) - sorption , chemistry , phosphorus , wastewater , scanning electron microscope , nuclear chemistry , calcite , adsorption , environmental chemistry , mineralogy , materials science , environmental engineering , organic chemistry , engineering , composite material
We examined P sorption characteristics in Al‐based water treatment residuals (Al‐WTR) generated from slightly alkaline surface water and in an organic residual composite (WW‐Al/O‐WTR), produced by using the Al‐WTR to treat organic‐rich and high P concentration dairy wastewater. Solids from both residuals were examined using scanning electron microscopy–energy dispersive spectroscopy (SEM‐EDS) and X‐ray diffraction (XRD), and exposed to P additions of 0 to 4000 mg L −1 in a sorption experiment. The Al‐WTR removed ∼97% of the added P, whereas WW‐Al/O‐WTR removed only 78% of the added P in the addition range of 0 to 100 mg P L −1 . With P additions of ≥100 mg L −1 , the removal rate declined to <38% by Al‐WTR and to 16% by WW‐Al/O‐WTR, possibly implying a change in sorption mechanisms. Analysis by XRD indicated that the major mineral was calcite, with some silica and poorly crystalline Al hydroxides. Analysis by SEM‐EDS, which used three‐element overlay maps of the residual surfaces, indicated that P was sparsely sorbed on both calcic and Al (hydr)oxide surfaces, along with a few clusters, even at low P concentrations of the treated waters. Ternary clusters of P, Al, and Ca were more abundant on the WW‐Al/O‐WTR. Carbon distribution suggested that organic substances covered Al surfaces. Sorption of P onto WW‐Al/O‐WTR may be reversible due to relatively weak Ca‐P and Al‐P bonds induced by the slight alkaline nature and in the presence of organic moieties, enhancing the WW‐Al/O‐WTR potential to act as a P source, rather than a P sink, in agricultural applications. Core Ideas Water treatment residuals displayed two distinct regions in sorption isotherms. Variable P associations and distribution were elucidated by advanced SEM‐EDS mapping. Mixing with wastewater promoted Al‐P, Ca‐P, and Al‐Ca‐P associations closer together. The presence of organic C and slight alkaline nature may enhance P release. Evidence from P K‐edge XANES complemented these findings (see Part II).