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Single‐step nitrification models erroneously describe batch ammonia oxidation profiles when nitrite oxidation becomes rate limiting
Author(s) -
Chandran Kartik,
Smets Barth F.
Publication year - 2000
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/(sici)1097-0290(20000520)68:4<396::aid-bit5>3.0.co;2-s
Subject(s) - chemistry , nitrification , nitrite , nitrogen , ammonia , ammonium , stoichiometry , inorganic chemistry , nitrate , oxygen , sodium azide , nuclear chemistry , redox , organic chemistry
Nitrification involves the sequential biological oxidation of reduced nitrogen species such as ammonium‐nitrogen (NH 4 + ‐N) to nitrite‐nitrogen (NO 2 − ‐N) and nitrate‐nitrogen (NO 3 − ‐N). The adequacy of modeling NH 4 + ‐N to NO 3 − ‐N oxidation as one composite biochemical reaction was examined at different relative dynamics of NH 4 + ‐N to NO 2 − ‐N and NO 2 − ‐N to NO 3 − ‐N oxidation. NH 4 + ‐N to NO 2 − ‐N oxidation and NO 2 − ‐N to NO 3 − ‐N oxidation by a mixed nitrifying consortium were uncoupled using selective inhibitors allylthiourea and sodium azide. The kinetic parameters of NH 4 + ‐N to NO 2 − ‐N oxidation ( q max,ns and K S,ns ) and NO 2 − ‐N to NO 3 − ‐N oxidation ( q max,nb and K S,nb ) were determined by a rapid extant respirometric technique. The stoichiometric coefficients relating nitrogen removal, oxygen uptake and biomass synthesis were derived from an electron balanced equation. NH 4 + ‐N to NO 2 − ‐N oxidation was not affected by NO 2 − ‐N concentrations up to 100 mg NO 2 − ‐N L −1 . NO 2 − ‐N to NO 3 − ‐N oxidation was noncompetitively inhibited by NH 4 + ‐N but was not inhibited by NO 3 − ‐N concentrations up to 250 mg NO 3 − ‐N L −1 . When NH 4 + ‐N to NO 2 − ‐N oxidation was the sole rate‐limiting step, complete NH 4 + ‐N to NO 3 − ‐N oxidation was adequately modeled as one composite process. However, when NH 4 + ‐N to NO 2 − ‐N oxidation and NO 2 − ‐N to NO 3 − ‐N oxidation were both rate limiting, the estimated lumped kinetic parameter estimates describing NH 4 + ‐N to NO 3 − ‐N oxidation were unrealistically high and correlated. These findings indicate that the use of single‐step models to describe batch NH 4 + oxidation yields erroneous kinetic parameters when NH 4 + ‐to‐NO 2 − oxidation is not the sole rate‐limiting process throughout the assay. Under such circumstances, it is necessary to quantify NH 4 + ‐N to NO 2 − ‐N oxidation and NO 2 − ‐N to NO 3 − ‐N oxidation, independently. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 68: 396–406, 2000.