Chemically enhanced biological NOx removal from flue gases : nitric oxide and ferric EDTA reduction in BioDeNox reactors

P.M.F. van der Maas

Research output: Thesisinternal PhD, WU

Abstract

The emission of nitrogen oxides (NOx) to the atmosphere is a major environmental problem. To abate NOx emissions from industrial flue gases, to date, mainly chemical processes like selective catalytic reduction (SCR) are applied. All these processes require high temperatures (>300 °C) and expensive catalysts. Therefore, biological NOx removal techniques using denitrification may represent promising alternatives for the conventional SCR techniques. However, water based biofiltration requires relatively long scrubber/bioreactor retention times, i.e. big reactor volumes, due to the slow mass transfer of NO from the gas into the liquid phase. BioDeNOx is in principle a welcome alternative for conventional NOx removal techniques like SCR and water-based biofiltration, since it does not need high temperatures and catalysts, while scrubber retention times can be very short (<10 seconds) due to the chemically enhanced NO absorption. In this thesis, the BioDeNOx concept was investigated with special attention to the bioreactor key conversions: NO and Fe(III)EDTA- reduction. This study showed stable NO removal from the gas phase with efficiencies up to 80 %. It was found that the NO removal from the gas phase is primary determined by NO absorption kinetics. Therefore, a high Fe(II)EDTA2- concentration is required, i.e. the FeEDTA absorption liquor should be in the reduced state. However, a totally reduced system should be avoided, since this will induce sulfide accumulation. The latter process is unwanted, since already low sulfide concentrations showed an incomplete NO reduction due to inhibition of N2O reduction to N2. To achieve satisfying NO removal from the gas and to avoid sulfdogenic conditions, the redox potential of BioDeNOx reactors should be steered between -180 and -200 mV versus Ag/AgCl (pH 7.2±0.2). An ethanol dosing system that is controlled by the redox potential signal was shown to be a proper manner to do so
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Lettinga, Gatze, Promotor
  • Lens, Piet, Co-promotor
Award date19 Dec 2005
Place of PublicationWageningen
Print ISBNs9789085043164
Publication statusPublished - 2005

Keywords

  • nitrogen oxides
  • edta
  • redox reactions
  • air pollution
  • flue gases

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