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Abstract
Nitrite in drinking water is a potentially harmful substance for humans, and controlling nitrite formation in drinking water distribution systems (DWDSs) is highly important. The effect of natural organic matter (NOM) on the formation of nitrite in simulated distribution systems was studied. The objective was to inspect how a reduced NOM concentration affected nitrite development via nitrification, separated from the effects of disinfection. We observed that nitrite formation was noticeably sensitive to the changes in the NOM concentrations. Nitrite declined with reduced NOM (TOC 1.0 mg L-1) but increased with the normal NOM concentration of tap water (TOC 1.6 mg L-1). Ammonium oxidation was not altered by the reduced NOM, however, nitrite oxidation was enhanced significantly according to the pseudo-first order reaction rate model interpretation. The enhanced nitrite oxidation was observed with both ammonium and nitrite as the initial nitrogen source. The theoretical maximum nitrite concentrations were higher with the normal concentration of NOM than with reduced NOM. The results suggest that the role of nitrite oxidation may be quite important in nitrite formation in DWDSs and worth further studies. As a practical result, our study supported enhanced NOM removal in non-disinfected DWDSs.
Highlights
Nitrification and nitrite formation are unwanted, but widely observed occurrences in drinking water distribution with water containing free ammonium or an ammonium source
The nitrite concentrations increased with normal natural organic matter (NOM) by 2.7 mgN L-1 h-1, and decreased with reduced NOM by -2.4 mgN L-1 h-1 as medians
The effects of natural organic matter (NOM) on nitrite formation in the conditions of non-disinfected tap water were studied in simulated distribution systems (SDSs), with an emphasis on both ammonium and nitrite oxidation
Summary
Nitrification and nitrite formation are unwanted, but widely observed occurrences in drinking water distribution with water containing free ammonium or an ammonium source. Autotrophic nitrification is a two-phase microbiological reaction: first, ammonium is oxidized into nitrite (Equation (1)) and, second, nitrite is oxidized into nitrate (Equation (2)) as follows: (1) (2). Equation (1) is called nitritation and Equation (2) is called nitratation. Nitrite is formed as an intermediate product of these two reactions. Nitritation occurs by ammonia oxidizing bacteria (AOB), and nitratation by nitrite oxidizing bacteria (NOB). The most common type of AOB is Nitrosomonas sp., and the most common type of NOB is Nitrospira sp. The AOB and the NOB are aerobic chemolithoautotrophic organisms that consume carbon dioxide and do not need organic matter for their growth
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