Slow complexation kinetics for ferric iron and EDTA complexes make EDTA non-biodegradable

Anna I. Willet, Bruce E. Rittmann

Research output: Contribution to journalReview articlepeer-review

18 Scopus citations


Published experimental data on ethylenediaminetetraacetic acid (EDTA) biodegradation in the presence of ferric iron (Fe(III)) showed that rapid biodegradation of EDTA suddenly stopped, leaving a residual of unbiodegraded EDTA that was equal to the concentration of dissolved Fe(III). We hypothesize that slow kinetics for the dissociation of two iron-EDTA complexes - FeEDTA- and FeOHEDTA2- - sequestered the EDTA in a form that is biologically unavailable. To evaluate this hypothesis, we added to the biogeochemical model CCBATCH a new sub-model for kinetically controlled complexation. CCBATCH simulations with kinetically controlled complexation for FeEDTA- and FeOHEDTA2- and the observed concentration of total dissolved Fe(III) accurately predicted the sudden cessation of EDTA biodegradation at the exact time shown experimentally. Our simulations also correctly predicted the observed residual EDTA concentration and the amounts of biomass and NH4+. Alternate explanations for the experimental results - strong equilibrium complexation of ferric iron and EDTA and precipitation of calcium and magnesium solids - could not capture the observed trends. This analysis using CCBATCH's new sub-model for kinetically controlled complexation shows that EDTA, once it becomes complexed with Fe(III), becomes biologically unavailable.

Original languageEnglish (US)
Pages (from-to)105-121
Number of pages17
Issue number2
StatePublished - 2003
Externally publishedYes


  • Aerobic
  • BNC1
  • Biodegradation
  • Biogeochemical modeling
  • EDTA

ASJC Scopus subject areas

  • Pollution
  • Bioengineering
  • Environmental Engineering
  • Microbiology
  • Environmental Chemistry


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