Transport and Transformation of Selenium and Other Constituents of Flue‐Gas Desulfurization Wastewater in Water‐Saturated Soil Materials

Abstract

Constructed wetland treatment systems are used to remove selenium (Se) from flue-gas desulfurization (FGD) wastewater (WW). However, direct confirmation of the mechanism responsible for FGD WW Se retention in soil is lacking. A laboratory-based soil column study was performed to develop an evidence-based mechanism of Se retention and to study the behavior and the retention capacity of FGD WW constituents in water-saturated soil. A deoxygenated 1:1 mixture of FGD WW and raw water was delivered to the columns bottom-up at a flux of 1.68 cm d for 100 d. Some of the columns were flushed with the raw water at the same rate for an additional 100 d. Column effluent was analyzed for constituents of concern. Results showed a complete retention of FGD WW Se in the soil materials. Boron and fluorine were partially retained; however, sulfur, sodium, and chlorine retention was poor, agreeing with field observations. The FGD WW Se was retained in soil near the inlet end of the columns, indicating its limited mobility under reduced conditions. Sequential extraction procedure revealed that retained Se was mainly sequestered as stable/residual forms. Bulk- and micro-X-ray absorption near-edge structure spectroscopy confirmed that Se was mainly retained as reduced/stable species [Se(IV), organic Se, and Se(0)]. This study provides direct evidence for FGD WW Se retention in water-saturated soil via the transformation of oxidized Se into reduced/stable forms.

Iron Oxides Minimize Arsenic Mobility in Soil Material Saturated with Saline Wastewater

“…The untreated soil was as successful as the Fh‐treated soil in retaining Se from the influent under reducing conditions. Our previous study (Galkaduwa et al, 2017) found that Se retention in water‐saturated soil not amended with Fh occurred via transformation of oxidized Se into reduced and stable forms. However, the total dissolved Se in the effluent of the two dried columns was detectable immediately after resuming influent delivery (Fig.…”

“…The synthesized Fh (1.0%, w/w) was thoroughly mixed with the soil prior to wetting. A wet packing procedure (Galkaduwa et al, 2017) was used to pack both the untreated and Fh‐treated soils to a bulk density of 1.0 Mg m −3 . The six columns were saturated from below with the raw water by incrementally raising the water level over a period of 24 h. Syringe pumps (Legato 210, KD Scientific) were then used to deliver deoxygenated (bubbled with N 2 ) raw water at a constant flux of 3.36 cm d −1 in the upward direction.…”

“…The total dissolved As was measured by using a graphite tube atomizer (GTA 120, Varian) equipped with an AA 240 Zeeman Atomic Absorption Spectrometer. The total dissolved Se was measured as described by Galkaduwa et al (2017). An inductively coupled plasma optical emission spectrometer (720 ES, Varian) was used to determine the total dissolved Fe and the other constituents listed in Supplemental Table S2.…”

“…Previous studies have found that removal efficiency of As in FGD WW is relatively low compared with that of Se in CWTSs (Eggert et al, 2008; Mooney and Murray‐Gulde, 2008). Under suboxic and anoxic conditions, Se in FGD WW is immobile and becomes less toxic (Galkaduwa et al, 2017). However, As released from native soil under reducing conditions will create additional complications in terms of the efficiency of CWTSs (Paredez et al, 2017).…”

Application of Synchrotron Radiation‐based Methods for Environmental Biogeochemistry: Introduction to the Special Section

“…Datta et al (2012),Al-Abed et al (2008),Burke et al (2012),Cances et al (2005),Blamey et al (2015),Bodei et al (2007) Bulk-X-ray absorption near-edge structure spectroscopy (XANES) Speciation of elements in numerous environmental samples such as atmospheric aerosols, plants, soils, sediments and various waste materials, etc., especially useful for studies focusing on the oxidation state of elementsTakahashi et al (2006),Burke et al (2012),Galkaduwa et al (2017),Sarret et al (2005) Micro-X-ray absorption spectroscopym-XANES Spatially resolved elemental speciation in numerous environmental samples such as atmospheric aerosols, plants, soils, sediments, and mine wastes, etc., especially useful for studies focusing on the oxidation state of elements Castillo-Michel et al (2011), Smith et al (2009a), Bacquart et al (2007), Arai et al (2003, 2006), Karna et al (2016) Micro-extended XAFS (m-EXAFS) Spatially resolved elemental speciation in numerous environmental samples such as atmospheric aerosols, plants, soils, sediments, and mine wastes, etc. Manceau et al (2004), Mitsunobu et al (2012), Baker et al (2012), Strawn and Baker (2009) Synchrotron radiation-based X-ray photoelectron spectroscopy (XPS) Surface chemistry of minerals and solids and characterization of nanomaterials Papaefthimiou et al (2011) Micro-and nanoscale X-ray fluorescence spectroscopy (XRF) Elemental distribution and associations in soil, sediments, dust, plant tissues, roots, animal tissues, soil aggregates Kyriacou et al (2014), Moore et al (2014), Seyfferth et al (2010), Spielman-Sun et al (2017) Synchrotron radiation-based X-ray diffraction (SR-XRD) Detection of crystalline trace precipitates in environmental mediums due to better collimation and lower spectral overlapping Baker et al (2012), Manceau et al (2004) High-energy resolution XAS (high-energy resolution fluorescence detected [HERFD] XANES; high-energy resolution auger detection [HERAD] XANES) Precise determination of the local structure around the absorbing atom Speciation of XAS nonsensitive elements such as Pb in soils, sediments, etc.…”