This work presents a model to predict the alkalinity, pH, and Langelier Saturation Index (LSI) in heterotrophic and H2-based autotrophic denitrification systems. The model can also be used to estimate the amount of acid, e.g. HCl, added to the influent (method 1) or the pH set point in the reactor (method 2: pH can be maintained stable by CO2-sparge using a pH-control loop) to prevent the pH from exceeding the optimal range for denitrification and to prevent precipitation from occurring. The model was tested with two pilot plants carrying out denitrification of groundwater with high hardness: a heterotrophic system using ethanol as the electron donor and an H2-based autotrophic system. The measured alkalinity, pH, and LSI were consistent with the model for both systems. This work also quantifies: (1) how the alkalinity and pH in Stage-1 significantly differ from those in Stage-2; (2) how the pH and LSI differ significantly in the two denitrification systems while the alkalinity increase is about the same; and (3) why CO2 addition is the preferred method for autotrophic system, while HCl addition is the preferred method for the heterotrophic system.

Original languageEnglish (US)
Pages (from-to)232-240
Number of pages9
JournalWater Research
Issue number1
StatePublished - Jan 2011


  • Denitrification
  • Groundwater treatment
  • Model
  • PH control
  • Precipitation prevention

ASJC Scopus subject areas

  • Ecological Modeling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution


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