Onset of severe nitrification in mildly nitrifying chloraminated bulk waters and its relation to biostability

Impact of total organic carbon and chlorine to ammonia ratio on nitrification in a bench-scale drinking water distribution system

“…After that, with the symptom of nitrification enhancing, the loss of chloramines was also obvious, owing to the presence of nitrite nitrogen. Several researchers found that nitrification accelerates the chloramine decay [15,20,27]. Although the mechanism of the chloramine loss by nitrification is not very clear, the increase of the nitrite nitrogen level means the presence of biologic oxidation of the AOB.…”

“…The free ammonia released from chloramines can lead to nitrification via a two-step process: initially, the ammoniaoxidizing bacteria (AOB) utilize ammonia as energy and convert it into nitrite, and, subsequently, nitrite-oxidizing bacteria (NOB) convert nitrite into nitrate [6,7]. Usually, partial nitrification takes place in drinking water distribution systems because NOB exhibit slower growth rates than AOB, and they are more sensitive to environmental changes [8].…”

“…Low levels of nitrite can be neglected and no measure need be adopted. However, once severe nitrification occurs, chlorine and ammonia concentrations will decrease to zero levels and the nitrite will increase to a high concentration [7] because the chloramine decay can be accelerated by nitrification in the distribution systems [15]. Researchers reached the conclusion that the microbiologically accelerated chloramine decay rate is mainly controlled by activity of the AOB [16].…”

Effectiveness of breakpoint chlorination to reduce accelerated chemical chloramine decay in severely nitrified bulk waters

“…Initially, ammonia-oxidizing bacteria (AOB) convert free ammonia to nitrite and then nitrite-oxidizing bacteria (NOB) convert nitrite to nitrate. Based on chloramine decay rates and prevailing nitrite levels nitrification in chloraminated distribution systems was defined as mild or severe nitrification (Sathasivan et al, 2008). In the front parts of the system, chloramine was reasonably stable and nitrite production was low (nitrite < 0.01 mg N L À1 ).…”

Bacterial inactivation kinetics of a photo-disinfection system using novel titania-impregnated kaolinite photocatalyst

“…Coleman et al [5] have reported that a low concentration of common DBPs in water, such as haloacetic acid (60 ppb) and trihalomethanes (80 ppb), might cause serious congenital cardiac defects in human beings following prolonged consumption. In addition, poor maintenance of ammonia during chloramination might result in direct nitrification in water which can directly promote algal blooms and treatment costs [6]. For these reasons, various chemical-free water disinfection technologies without the formation of DBPs have become highly sought in recent years.…”