research project details
Project Title: A Rapid Ammonia-Oxidizing Bacteria Measurement Method as an Early-Warning Indicator of Nitrification Episodes
Investigator(s): John (Jay) Regan
Sponsor: American Water Works Association Research Foundation
Environmental Problem Addressed:
Water quality treatment/detection for nitrification episodes.
Research Project Objectives:
This research project aims to improve the reliability of chloramination via the prediction and early detection of nitrification episodes. The specific objectives of the project are to:
- Adapt existing molecular-based analysis techniques to provide a protocol that rapidly determines ammonia-oxidizing bacteria concentrations in drinking water samples; and
- Evaluate the hypothesis that an increase in ammonia oxidizer numbers in chloraminated systems indicates the pending onset of a nitrification episode, prior to the observed changes in other water quality parameters typically associated with nitrification.
Summary:
Chloramination offers the drinking water industry a secondary disinfection alternative to chlorination, and its use has increased in the United States over the past decade. Much of this switch to chloramines has been prompted by the increasingly stringent regulations on chlorinated disinfection byproducts and the need to reduce biological regrowth. Chloroamines have been shown to produce lower concentrations of trihalomethanes and haloacetic acids than free chlorine, facilitating the compliance with Stage I Disinfectants and Disinfection By-Products Rule.
Despite these advantages, chloramination has some potential drawbacks. Nitrification episodes are a common operational problem observed in chloraminated distribution systems. While nitrifying bacteria do not pose a direct threat to public health, nitrification episodes are marked by a decline in several water quality parameters that may have public health implications. The growth of nitrifiers, which is promoted by the free ammonia associated with chloramination, is typically accompanied by a deterioration in water quality parameters such as an increase in heterotrophic bacteria, nitrite and nitrate, and a decrease in total chlorine residual.
Once a nitrification episode is underway, increasing chloramine dose is an ineffective means of correcting the problem, requiring utilities to implement alternative control strategies. Therefore, it would be advantageous to detect and respond to the pending onset of a nitrification episode prior to the full establishment of a nitrifying community and the associated water quality impacts.
A number of researchers have recognized the benefit that would be realized by the drinking water industry with the establishment of an early warning nitrification indicator. The direct enumeration of ammonia-oxidizing bacteria (AOB) presents a reasonable candidate for such an indicator, as AOB growth may be the catalyst that gives rise to the broader symptoms associated with nitrification outbreaks. The recent development of rapid, culture-independent molecular measurement tools offers the prospect of overcoming the limitations of culture-based AOB enumeration techniques and investigating the direct use of AOB numbers as an early warning indicator. This research project will develop quantitative molecular methods to monitor AOB community development, which would allow a rigorous evaluation of the relationships between nitrifier growth and water quality operational parameters.
Anticipated Results:
The desired outcome of this project is the development of a rapid and sensitive technique for quantifying ammonia-oxidizing bacteria concentrations in drinking water supplies. This will provide a marked improvement over the culture-based technique presently used by the water industry by reducing the turnaround time from at least three weeks to one or two days. This work will also show whether a measurable increase in ammonia oxidizer concentration preceeds the onset of a nitrification episode as determined by other water quality indicators.