3 research outputs found
Monochloramine Cometabolism by Mixed-Culture Nitrifiers under Drinking Water Conditions
Chloramines
are the second most used secondary disinfectant by
United States water utilities. However, chloramination may promote
nitrifying bacteria. Recently, monochloramine cometabolism by the
pure culture ammonia-oxidizing bacteria, <i>Nitrosomonas europaea</i>, was shown to increase monochloramine demand. The current research
investigated monochloramine cometabolism by nitrifying mixed cultures
grown under more relevant drinking water conditions and harvested
from sand-packed reactors before conducting suspended growth batch
kinetic experiments. Four types of batch kinetic experiments were
conducted: (1) positive controls to estimate ammonia kinetic parameters,
(2) negative controls to account for biomass reactivity, (3) utilization
associated product (UAP) controls to account for UAP reactivity, and
(4) cometabolism experiments to estimate cometabolism kinetic parameters.
Kinetic parameters were estimated in AQUASIM with a simultaneous fit
to the experimental data. Cometabolism kinetics were best described
by a first-order model. Monochloramine cometabolism kinetics were
similar to those of ammonia metabolism, and monochloramine cometabolism
accounted for 30% of the observed monochloramine loss. These results
demonstrated that monochloramine cometabolism occurred in mixed cultures
similar to those found in drinking water distribution systems; therefore,
monochloramine cometabolism may be a significant contribution to monochloramine
loss during nitrification episodes in drinking water distribution
systems
Bromamine Decomposition Revisited: A Holistic Approach for Analyzing Acid and Base Catalysis Kinetics
Chloramine chemistry is complex,
with a variety of reactions occurring
in series and parallel and many that are acid or base catalyzed, resulting
in numerous rate constants. Bromide presence increases system complexity
even further with possible bromamine and bromochloramine formation.
Therefore, techniques for parameter estimation must address this complexity
through thoughtful experimental design and robust data analysis approaches.
The current research outlines a rational basis for constrained data
fitting using Brønsted theory, application of the microscopic
reversibility principle to reversible acid or base catalyzed reactions,
and characterization of the relative significance of parallel reactions
using fictive product tracking. This holistic approach was used on
a comprehensive and well-documented data set for bromamine decomposition,
allowing new interpretations of existing data by revealing that a
previously published reaction scheme was not robust; it was not able
to describe monobromamine or dibromamine decay outside of the conditions
for which it was calibrated. The current research’s simplified
model (3 reactions, 17 constants) represented the experimental data
better than the previously published model (4 reactions, 28 constants).
A final model evaluation was conducted based on representative drinking
water conditions to determine a minimal model (3 reactions, 8 constants)
applicable for drinking water conditions
Calibration Curve Raw Data.xlsx
In this research PTR-ToF-MS was used to measure the concentration of five haloamines (monochloramine, dichloramine, monobromamine, dibromamine, and bromochloramine) in aqueous standards and during kinetic experiments that simulate drinking water disinfection. Gas phase sampling was performed and correlated to aqueous concentrations.</p