Applicability of two-step models in estimating nitrification kinetics from batch respirograms under different relative dynamics of ammonia and nitrite oxidation

Abstract

A mechanistically based nitrification model was formulated to facilitate determination of both NH 4 + -N to NO 2 − -N and NO 2 − -N to NO 3 − -N oxidation kinetics from a single NH 4 + -N to NO 3 −-N batch-oxidation profile by explicitly considering the kinetics of each oxidation step. The developed model incorporated a novel convention for expressing the concentrations of nitrogen species in terms of their nitrogenous oxygen demand (NOD). Stoichiometric coefficients relating nitrogen removal, oxygen uptake, and biomass synthesis were derived from an electron-balanced equation.A parameter identifiability analysis of the developed two-step model revealed a decrease in correlation and an increase in the precision of the kinetic parameter estimates when NO 2 − -N oxidation kinetics became increasingly rate-limiting. These findings demonstrate that twostep models describe nitrification kinetics adequately only when NH 4 + -N to NO 3 − -N oxidation profiles contain sufficient information pertaining to both nitrification steps. Thus, the rate-determining step in overall nitrification must be identified before applying conventionally used models to describe batch nitrification respirograms.

A two-step nitrification model of ammonia and nitrite oxidation under benzene inhibitory and toxic effects in nitrifying batch cultures

“…This is particularly the case considering the heterogeneity of the nitrifying microbial consortium under study. An alternative to the unavailability of X A and X N measurements is to estimate them as fractions of the total biomass concentration according to stoichiometric considerations [1,5] or to consider the nitrification kinetics in terms of volumetric rather than specific oxidation rates. In this work, the volumetric rate of ammonium oxidation r NH 4 = q NH 4 X A , of nitrite oxidation r NO 2 = q NO 2 X N and benzene transformation r BZ,A = q BZ,A X A was introduced.…”

“…Eqs. (5) and (6) correspond to Monod equations when S BZ = 0. Some authors have suggested that this kind of negative effect is probably due to the harmful effect of hydrocarbons on the functioning of biological membranes [18][19][20][21][22][23].…”

“…when nitrite oxidation becomes limiting, single-step models have been shown to erroneously describe batch ammonia oxidation profiles [1]. The use of two-step nitrification models has already been accurately investigated [2][3][4][5][6] and their implementation is especially essential when nitrite accumulation becomes important as a target product or an unwanted limiting intermediate.…”

A New Field Assay for Measuring and Characterizing Nitrification Inhibition

“…The assay also uses custom built graphical user interface software to facilitate respirometric data acquisition and kinetic parameter estimation. A complete description of the laboratory assay is presented by Chandran and Smets (2000). The work described here used a modified assay design to measure nitrification inhibition in actual activated sludge.…”

Using an extended activated sludge model to simulate nitrite and nitrate variations in TNCU2 process

“…The discussion of nitrite (S NO 2 Þ variation was absent in theses models. Of course, some two-stage nitrification models [7][8][9][10][11][12][13][14][15] and some multi-stage denitrification models [8,16] were proposed too. Although these models could predict nitrification or denitrification successfully, the application of these models were merely related to nitrogen removal.…”