A kinetic study of nitrification inhibition in water distribution systems using low levels of chlorite

Abstract

Water utilities use operational strategies such as increasing pH, chlorine-ammonia ratio, and/or chloramine residual, distribution main flushing, and periodic break-point chlorination to control nitrification of chloraminated water in distribution systems. Although these methods are proven to be useful in controlling nitrification, the results are utility dependent and sometimes not effective in controlling the loss of chloramines. In various pilot studies, the direct application of chlorite at 0.1 to 0.8 mg/L is shown to be an effective alternative to control and prevent nitrification. Chlorite inactivates ammonia-oxidizing bacteria (AOB), the root cause of nitrification. In this study, we developed a kinetic model for nitrification inhibition through the addition of chlorite and the observation of residual chloramines and AOB. The important water quality variables examined were: chlorite concentration ranging from 0.02 to 0.4 mg/L, pH ranging from 7 to 9, ammonia concentrations ranging from 0.5 to 2.0 mg/L-N, and temperature ranging from 15 to 35 W C. Instead of measuring the viability of the AOB cells, the production of nitrite and the consumption of ammonia are used as surrogates for cell activity. This information was used to develop a kinetic model (modified Intrinsic Quenching model) that was able to fit the experimental data.

Nitrification inhibitor chlorate and nitrogen substrates differentially affect comammox Nitrospira in a grassland soil

“…The relatively quicker effect chlorate had on AOB abundance may be attributed to the mechanism of its inhibition. DCD is thought to bind to the ammonia monooxygenase active site, while chlorite (produced by the oxidation of chlorate by Nitrospira ) is thought to inactivate the bacterium itself ( Rungvetvuthivitaya et al, 2014 ). Therefore, it is possible that some metabolically diverse members of the AOB community may have persisted under the DCD treatment, thereby reducing its effect on overall community abundance.…”

Review of Nitrification Monitoring and Control Strategies in Drinking Water System

“…According to Karim and LeChevallier [ 55 ], nitrification cannot be effectively controlled by adding up to 0.5 mg of chlorite, especially after long-term application. However, in a pilot study by Rungvetvuthivitaya, et al [ 56 ], they suggested that the direct application of chlorite at a concentration of 0.8 mg can effectively control nitrification. In copper surfaces, application of chlorite at a concentration of 20 ppm can inhibit nitrification, although chlorite can increase copper corrosion [ 45 ].…”

“…Similarly, in an activated sludge system, the use of graphite nanoparticles (GNPs) slows down the nitrification process [ 54 ]. Moreover, some studies suggest that using chlorite ( ) at a concentration of 0.8 mg can effectively inhibit the growth of nitrifying bacteria [ 55 , 56 ]. While some of these strategies have been promising in controlling nitrification, the performance is often site-specific, as the treated water characteristics from water treatment plants (WTPs) vary [ 56 ].…”

“…Moreover, some studies suggest that using chlorite ( ) at a concentration of 0.8 mg can effectively inhibit the growth of nitrifying bacteria [ 55 , 56 ]. While some of these strategies have been promising in controlling nitrification, the performance is often site-specific, as the treated water characteristics from water treatment plants (WTPs) vary [ 56 ]. For example, a long-term use of breakpoint chlorination may increase the chlorinated and nitrogenous DBPs’ levels in such distribution systems where NOM concentration is relatively high [ 57 , 58 ].…”