title: Performance and life cycle environmental benefits of recycling spent ion exchange brines by catalytic treatment of nitrate.
abstract: Salt used to make brines for regeneration of ion exchange (IX) resins is the dominant economic and environmental liability of IX treatment systems for nitrate-contaminated drinking water sources. To reduce salt usage, the applicability and environmental benefits of using a catalytic reduction technology to treat nitrate in spent IX brines and enable their reuse for IX resin regeneration were evaluated. Hybrid IX/catalyst systems were designed and life cycle assessment of process consumables are used to set performance targets for the catalyst reactor. Nitrate reduction was measured in a typical spent brine (i.e., 5000 mg/L NO3(-) and 70,000 mg/L NaCl) using bimetallic Pd-In hydrogenation catalysts with variable Pd (0.2-2.5 wt%) and In (0.0125-0.25 wt%) loadings on pelletized activated carbon support (Pd-In/C). The highest activity of 50 mgNO3(-)/(min - g(Pd)) was obtained with a 0.5 wt%Pd-0.1 wt%In/C catalyst. Catalyst longevity was demonstrated by observing no decrease in catalyst activity over more than 60 days in a packed-bed reactor. Based on catalyst activity measured in batch and packed-bed reactors, environmental impacts of hybrid IX/catalyst systems were evaluated for both sequencing-batch and continuous-flow packed-bed reactor designs and environmental impacts of the sequencing-batch hybrid system were found to be 38-81% of those of conventional IX. Major environmental impact contributors other than salt consumption include Pd metal, hydrogen (electron donor), and carbon dioxide (pH buffer). Sensitivity of environmental impacts of the sequencing-batch hybrid reactor system to sulfate and bicarbonate anions indicate the hybrid system is more sustainable than conventional IX when influent water contains <80 mg/L sulfate (at any bicarbonate level up to 100 mg/L) or <20 mg/L bicarbonate (at any sulfate level up to 100 mg/L) assuming 15 brine reuse cycles. The study showed that hybrid IX/catalyst reactor systems have potential to reduce resource consumption and improve environmental impacts associated with treating nitrate-contaminated water sources.
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Jong Kwon
authors.initials: JK
authors.lastname: Choe
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Allison M
authors.initials: AM
authors.lastname: Bergquist
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Sangjo
authors.initials: S
authors.lastname: Jeong
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Jeremy S
authors.initials: JS
authors.lastname: Guest
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Werth
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. Electronic address: strthmnn@mines.edu.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Strathmann
mesh_terms: D000465:Algorithms; D001639:Bicarbonates / Q000737:chemistry / Q000378:metabolism; D019149:Bioreactors; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D008956:Models, Chemical; D009566:Nitrates / Q000737:chemistry* / Q000378:metabolism; D059027:Recycling; D015203:Reproducibility of Results; D012492:Salts / Q000737:chemistry* / Q000378:metabolism; D012965:Sodium Chloride / Q000737:chemistry / Q000378:metabolism; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000378:metabolism; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*
chemical_list: D001639:Bicarbonates; D009566:Nitrates; D012492:Salts; D013431:Sulfates; D014874:Water Pollutants, Chemical; C017082:brine; D002245:Carbon Dioxide; D012965:Sodium Chloride; D006859:Hydrogen
keywords: Bimetallic catalyst; Brine reuse; Drinking water; Hybrid treatment; Life cycle assessment; Oxyanions