Performance and life cycle environmental benefits of recycling spent ion exchange brines by catalytic treatment of nitrate

Citation:

J. K. Choe, Bergquist, A. M., Jeong, S., Guest, J. S., Werth, C. J., and Strathmann, T. J., “Performance and life cycle environmental benefits of recycling spent ion exchange brines by catalytic treatment of nitrate,” Water Research, vol. 80, pp. 267-280, 2015.

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&#x2212;">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&#x2212;">NO3/(min − gPd) 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.

Notes:

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