Optimized bimetallic ratios for durable membrane catalyst-film reactors in treating nitrate-polluted water

Juliana Levi, Bongyeon Jung, Hunter P. Jacobs, Yihao Luo, Chung Seop Lee, Kiheon Hong, Min Long, Juan Donoso, Sergi Garcia-Segura, Michael S. Wong, Bruce E. Rittmann, Paul Westerhoff

Research output: Contribution to journalArticlepeer-review

Abstract

Nitrate contamination of surface and ground water is a significant global challenge. Most current treatment technologies separate nitrate from water, resulting in concentrated wastestreams that need to be managed. Membrane Catalyst-film Reactors (MCfR), which utilize in-situ produced nanocatalysts attached to hydrogen-gas-permeable hollow-fiber membranes, offer a promising alternative for denitrification without generating a concentrated wastestream. In hydrogen-based MCfRs, bimetallic nano-scale catalysts reduce nitrate to nitrite and then further to di-nitrogen or ammonium. This study first investigated how different molar ratios of indium-to-palladium (In:Pd) catalytic films influenced denitrification rates in batch-mode MCfRs. We evaluated eleven In-Pd bimetallic catalyst films, with In:Pd molar ratios from 0.0029 to 0.28. Nitrate-removal exhibited a volcano-shaped dependence on In content, with the highest nitrate removal (0.19 mgNO3-N-min−1 L−1) occurring at 0.045 mol In/mol Pd. Using MCfRs with the optimal In:Pd loading, we treated nitrate-spiked tap water in continuous-flow for >60 days. Nitrate removal and reduction occurred in three stages: substantial denitrification in the first stage, a decline in denitrification efficiency in the second stage, and stabilized denitrification in the third stage. Factors contributing to the slowdown of denitrification were: loss of Pd and In catalysts from the membrane surface and elevated pH due to hydroxide ion production. Sustained nitrate removal will require that these factors be mitigated.

Original languageEnglish
Article number173711
JournalScience of the Total Environment
Volume943
DOIs
StatePublished - Sep 15 2024
Externally publishedYes

Keywords

  • Catalysis
  • Denitrification
  • Membrane catalytic film reactor
  • Nitrate
  • Water treatment

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