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A proposed abiotic reaction scheme for hydroxylamine and monochloramine under chloramination relevant drinking water conditions
Citation:
Wahman, D. G., G. E. Speitel, Jr, AND M. V. Machavaram. A proposed abiotic reaction scheme for hydroxylamine and monochloramine under chloramination relevant drinking water conditions. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 60:218-227, (2014).
Impact/Purpose:
Research to understand nitrification in chloraminated distribution systems.
Description:
Drinking water monochloramine (NH2Cl) use may promote ammonia–oxidizing bacteria (AOB) growth. For biological ammonia (NH3) oxidation, AOB use (i) ammonia monooxygenase for NH3 oxidation to hydroxylamine (NH2OH) and (ii) hydroxylamine oxidoreductase for NH2OH oxidation to nitrite. NH2Cl also inactivates AOB but rates vary, depending on inactivation criterion (metabolic activity, culturability, cell membrane integrity). One mechanism for the fastest inactivation (metabolic activity basis) would be the direct NH2OH/NH2Cl reaction. Because biological NH2OH oxidation supplies the electrons required for biological NH3 oxidation, the NH2OH/NH2Cl reaction provides a direct mechanism for NH2Cl to inhibit NH3 oxidation, starving the cell of reductant. The present study conducted a detailed literature evaluation and proposed a NH2OH/NH2Cl reaction scheme (RS) under chloraminated drinking water (CDW) relevant conditions (μM concentrations, air saturation, and pH 7–9). Next, the RS was evaluated experimentally at a mid–range pH (8.3) and somewhat lower pH (7.7) and then refined using experimental data and an AQUASIM kinetic model. Finally, simulations investigated RS relevance on AOB activity under representative CDW conditions. Overall, simulations indicated that the proposed RS kinetics are relevant under CDW conditions and provide a possible additional mechanism for biological NH3 oxidation inhibition and NH2Cl demand with subsequent NH3 release.
