Chloramination has replaced free chlorine as a secondary
disinfectant at many utilities because of regulations
limiting trihalomethanes (THMs) and haloacetic
acids (HAAs) in the distribution system. Chloramine
use is advantageous because it forms substantially
lower concentrations of THMs and HAAs than free
chlorine. However, the potential for nitrification,
which is the bacterially mediated conversion of ammonia
to nitrite and nitrate, is a trade-off that utilities
must consider in their monitoring and maintenance
practices.
Although many theoretical aspects of nitrification are
understood, practical management of the chloraminated
distribution system still poses a challenge to utility managers.
The absence of adequate data collection to assess
nitrifying conditions and the absence of a comprehensive
framework for analyzing this data contribute to the
difficulties in effectively managing a chloraminated distribution
system to eliminate or minimize nitrification.
In this article, nitrification potential curves are introduced
as a possible operational strategy to prevent nitrification
in chloraminated distribution systems. Nitrification
potential curves are constructed based on the parameters
that define growth and inactivation kinetics of
ammonia-oxidizing bacteria (AOB) in environments
that contain chloramine and ammonia. To demonstrate
the applicability of nitrification potential curves, the
authors conducted long-term, pilot-scale studies that
covered a range of chlorine-to-ammonia application
ratios and chloramine residual concentrations that are
typical of full-scale chloraminated systems.
Results indicate that the total chlorine and free
ammonia concentrations associated with the presence
or absence of nitrification are closely linked to the
growth and inactivation kinetics of AOB in the distribution
system. These growth and inactivation kinetics
can be estimated to produce a nitrification potential
curve that predicts whether the system's operating
conditions are likely to lead to nitrification. The
straightforward methodology outlined may be useful
for full-scale system assessment to explain the presence
and absence of nitrification. Includes 33 references, tables, figures.
| Edition : | Vol. 97 - No. 8 |
| File Size : | 1
file
, 310 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 10 |
| Published : | 08/01/2005 |
