Pilot‐scale studies of Hexavalent Chromium Removal from drinking water

Abstract

The goal of this research was the initial evaluation of several pilot‐scale treatment technologies for hexavalent chromium removal to <5 μg/L (i.e., 95% removal). A major focus was to assess manufacturer‐provided pilot systems with media that were effective in bench‐scale studies as well as technologies that were promising but could not be appropriately tested at bench scale. The technologies tested included ion exchange systems (i.e., column strong‐base and weak‐base anion exchange and reactor‐based strong‐base anion exchange), a reduction/filtration unit using sodium sulfite, and proprietary adsorptive media systems (zeolite and granular activated carbon). In vendor‐independent tests, reduction with ferrous sulfate, coagulation, and filtration was also evaluated. Regeneration efficiency was determined for the best‐performing strong‐base anion exchange resin, including the effect of recycling brine to minimize residuals. Technologies able to consistently treat to concentrations <5 μg/L included column strong‐base anion exchange, weak‐base anion exchange, and reduction–coagulation–filtration using ferrous sulfate.

Hexavalent chromium review, part 2: Chemistry, occurrence, and treatment

“…This reduction is the first step in many effective water treatment strategies that is followed by conversion of the soluble Cr(III) to particulate Cr(OH) 3 or sorbed solids that can be settled or filtered from the water. The most common reductant is Fe(II), with reaction times on the order of seconds to hours, depending on pH (Blute, 2010; McGuire et al, 2006; Qin et al, 2005; Lee & Hering, 2003; Schlautman & Han, 2001; Buerge & Hug, 1999; El‐Shoubary et al, 1998; Pettine et al, 1998b; Buerge & Hug, 1997; Sedlak & Chan, 1997; Fendorf & Li, 1996; Henderson, 1994; Lin et al, 1992; Eary & Rai, 1988; Philipot et al, 1984). The presence of dissolved oxygen does not significantly interfere with reduction of Cr(VI) by Fe(II) (Schlautman & Han, 2001; Eary & Rai, 1988).…”

“…A comprehensive review of Cr(VI) removal via engineered treatment processes was recently conducted (Sharma et al, 2008), and some comprehensive evaluations of viable treatment processes and cost evaluations have also been completed for Cr(VI) removal at California utilites (Blute & Wu, 2012; Blute et al, 2010; Blute, 2010; McGuire, 2010; McGuire et al, 2007, 2006; Qin et al, 2005; Lee & Hering, 2003; Drago, 2001). These have confirmed that treatment via reductive coagulation can easily obtain very low levels (< 5 µg/L) of Cr(VI) in water leaving the treatment plant.…”

“…These have confirmed that treatment via reductive coagulation can easily obtain very low levels (< 5 µg/L) of Cr(VI) in water leaving the treatment plant. Other techniques, including membranes, weak base anion (WBA) exchange, and strong base anion (SBA) exchange, are also effective, with some performance sensitivities related to water chemistry, and at relatively higher cost, residuals handling, and water losses (McGuire et al, 2006; Drago, 2001). WBA treatment consists of polymeric resin that must be used at pH 6 for effective Cr(VI) removal; therefore, pH readjustment is often necessary.…”

“…There is limited work showing that Cr(III) can be removed during conventional alum or ferric coagulation via co‐precipitation with aluminum hydroxide or Fe(OH) 3 , but this is not effective for removing Cr(VI) (Sharma et al, 2008). Sorptive media are promising but to date have never acheived the selectivity or capacity necessary to be reliable or cost‐effective (Sharma et al, 2008; McGuire et al, 2006; Edwards & Benjamin, 1989).…”

Highly efficient removal of hexavalent chromium in aqueous solutionsviachemical reduction of plate-like micro/nanostructured zero valent iron

“…5 Cr(VI) pollution can increase the risk of catching dermatitis, rhinitis, and even cancer. 6 Many methods, such as physicochemical adsorption, 7 bioremediation, 6 chemical reduction, 8 precipitation, 9 membrane separation, 10 and ion exchange, 11 have been developed to remediate Cr(VI) contamination. Among them, physicochemical adsorption is an efficient way to remove Cr(VI).…”