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Characterising and modelling free ammonia and ammonium inhibition in anaerobic systems.

Authors
  • Astals, S1
  • Peces, M2
  • Batstone, D J3
  • Jensen, P D3
  • Tait, S3
  • 1 Advanced Water Management Centre, The University of Queensland, Brisbane, 4072, QLD, Australia. Electronic address: [email protected] , (Australia)
  • 2 Centre for Solid Waste Bioprocessing, Schools of Civil and Chemical Engineering, The University of Queensland, 4072, QLD, Australia. , (Australia)
  • 3 Advanced Water Management Centre, The University of Queensland, Brisbane, 4072, QLD, Australia. , (Australia)
Type
Published Article
Journal
Water research
Publication Date
Oct 15, 2018
Volume
143
Pages
127–135
Identifiers
DOI: 10.1016/j.watres.2018.06.021
PMID: 29940358
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Inhibition by ammoniacal nitrogen, consisting of free ammonia (NH3) and ammonium ion (NH4+), has been widely investigated for anaerobic digestion. However, despite the large amount of research on the subject, ammoniacal nitrogen inhibition still threatens many anaerobic digesters. This paper presents (i) a method to reliably characterise ammoniacal nitrogen inhibition and (ii) a robust inhibition modelling approach. Results showed that NH3 and NH4+ inhibition need to be jointly determined, which can only be done by performing inhibition tests at various total ammoniacal nitrogen (TAN) concentrations and pH values. These test conditions were reliably achieved using the salts NH4HCO3 and NH4Cl without pH adjustment, rather than by using NH4Cl with pH adjustment. The use of only salts showed a lower pH change during the inhibition test (∼1.5 days), thereby decreasing the uncertainty in TAN speciation and strengthening the test and model outputs. A threshold inhibition function satisfactorily described (R2 > 0.99) the joint inhibition of NH3 and NH4+ on three distinct inocula, and provided a better description of the inhibition testing results than a non-competitive inhibition function (R2 ∼0.70). The key advantage of the proposed threshold inhibition function is its capacity to identify the inhibition lower limit (concentration where inhibition starts; KImin) and upper limit (concentration where inhibition is complete; KImax). The threshold inhibition function also identifies the 50% inhibition concentration (KI50) at the midpoint of KImin and KImax. Finally, experimental and model results show that at pH 7.3-7.7 and TAN concentrations above 2000 mgN·L-1, both NH3 and NH4+ contribute significantly to overall inhibition. Copyright © 2018 Elsevier Ltd. All rights reserved.

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