Impact of dissolved oxygen and pH on the removal of selenium from water by iron electrocoagulation

Yeunook Bae; Nyssa M Crompton; Neha Sharma; Yihang Yuan; Jeffrey G Catalano; Daniel E Giammar

doi:10.1016/j.watres.2022.118159

Impact of dissolved oxygen and pH on the removal of selenium from water by iron electrocoagulation

Water Res. 2022 Apr 15:213:118159. doi: 10.1016/j.watres.2022.118159. Epub 2022 Feb 4.

Authors

Yeunook Bae¹, Nyssa M Crompton², Neha Sharma³, Yihang Yuan³, Jeffrey G Catalano⁴, Daniel E Giammar⁵

Affiliations

¹ Department of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, Brauer Hall, Room 1023, St. Louis, MO 63130, United States; Department of Preventive Medicine, Northwestern University, Chicago, IL 60611, United States.
² Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, United States; Department of Chemistry, Joliet Junior College, Joliet, IL 60431, United States.
³ Department of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, Brauer Hall, Room 1023, St. Louis, MO 63130, United States.
⁴ Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, United States.
⁵ Department of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, Brauer Hall, Room 1023, St. Louis, MO 63130, United States. Electronic address: giammar@wustl.edu.

PMID: 35172259
DOI: 10.1016/j.watres.2022.118159

Abstract

Removing dissolved selenium (i.e., selenate and selenite) from wastewater is a challenging issue for a range of industries. Iron electrocoagulation can produce Fe(II)-containing solids that can adsorb and chemically reduce dissolved Se. In a series of bench-scale experiments we investigated the effects of dissolved oxygen (fully oxic, partially oxic, and strictly anoxic) and pH (6 and 8) on the rate and extent of dissolved selenate and selenite removal by iron electrocoagulation. These studies combined measurements of the aqueous phase with the direct characterization of the resulting solids. Among the conditions studied the rate and extent of dissolved selenium (Se) removal were highest at pH 8 and strictly anoxic conditions. X-ray absorption spectroscopy demonstrated that in the absence of oxygen, Se was primarily transformed to elemental selenium (Se⁰) and selenide. Green rust that formed in the suspension during electrocoagulation played a key role as a reductant and sorbent of Se. At pH 6 dissolved oxygen did not affect the rates and extents of dissolved Se removal. Under all the conditions studied, dissolved Se removal was more effective with iron electrocoagulation than with the direct addition of pre-synthesized green rust or ferrous hydroxide. The most rapid and substantial dissolved Se removal was achieved by freshly-formed green rust and ferrous hydroxide, which are both Fe(II)-bearing solids. With an improved understanding of the products and mechanisms of the process, iron electrocoagulation can be optimized for removal of Se from wastewater.

Keywords: Dissolved selenium; Green rust; Iron electrocoagulation; pH, Dissolved oxygen.