Ammonia- and nitrite-oxidizing bacterial communities in a pilot-scale chloraminated drinking water distribution system

Abstract

Nitrification in drinking water distribution systems is a common operational problem for many utilities that use chloramines for secondary disinfection. The diversity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in the distribution systems of a pilot-scale chloraminated drinking water treatment system was characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis and 16S rRNA gene (ribosomal DNA [rDNA]) cloning and sequencing. For ammonia oxidizers, 16S rDNA-targeted T-RFLP indicated the presence of Nitrosomonas in each of the distribution systems, with a considerably smaller peak attributable to Nitrosospira-like AOB. Sequences of AOB amplification products aligned within the Nitrosomonas oligotropha cluster and were closely related to N. oligotropha and Nitrosomonas ureae. The nitrite-oxidizing communities were comprised primarily of Nitrospira, although Nitrobacter was detected in some samples. These results suggest a possible selection of AOB related to N. oligotropha and N. ureae in chloraminated systems and demonstrate the presence of NOB, indicating a biological mechanism for nitrite loss that contributes to a reduction in nitrite-associated chloramine decay.

FIG. 1.

Pilot plant flow diagram. Two parallel systems were continuously operated, one with conventional alum coagulation and the other with enhanced coagulation. Each treatment train had three distribution systems maintained at pH 7, 8, and 9.

FIG. 2.

Nitrite concentration in the 4-day retention tanks of the conventional coagulation treatment train: pH 7 (⧫), pH 8 (◊), and pH 9 (▵).

FIG. 3.

Nitrite concentration in the 4-day retention tanks of the enhanced coagulation treatment train: pH 7 (⧫), pH 8 (◊), and pH 9 (▵).

FIG. 4.

Ammonia-oxidizing bacteria (⧫) and heterotrophic bacteria (◊) enumeration by MPN and heterotrophic plate counts, respectively, for the 4-day retention tank of the pH 8 conventional coagulation system. The dilution series used in the MPN test imposed a maximum AOB quantitation level of 448 MPN ml⁻¹.

FIG. 5.

AOB-targeted T-RFLP electropherograms for liquid samples collected from the 4-day retention tanks (A to D) and a biofilm sample from the pH 8 conventional coagulation system (E). Panel A is for the pH 8 conventional coagulation system, and panels B through D are for the pH 7, 8, and 9 enhanced coagulation systems, respectively.

FIG. 6.

Neighbor-joining tree generated from an alignment of 16S rDNA sequences from AOB and other Proteobacteria. AOB genus abbreviations are Nm for Nitrosomonas, Nc for Nitrosococcus, and Ns for Nitrosospira. Clones recovered from the drinking water distribution systems are designated DW Nso, followed by B for biofilm or C and E for conventional and enhanced coagulation, respectively; the nominal pH of the distribution system; and the clone number. Bootstrap values above 50 are shown at each node. Scale bar represents 10% sequence difference. Redundant clone sequences are not shown.

FIG. 7.

NOB-targeted T-RFLP electropherograms for liquid samples collected from the 4-day retention tanks (A to D) and a biofilm sample from the pH 8 conventional coagulation system (E). Panel A is for the pH 8 conventional coagulation system, and panels B through D are for the pH 7, 8, and 9 enhanced coagulation systems, respectively. Data from Nitrobacter- and Nitrospira-specific T-RFLP are superimposed.

FIG. 8.

Neighbor-joining tree generated from an alignment of 16S rDNA sequences from NOB and several Proteobacteria representatives. NOB genus abbreviations are Nb for Nitrobacter, Nc for Nitrococcus, Nsr for Nitrospira, and Nsn for Nitrospina. Clone designations are the same as in Fig. 6 except for a prefix of Nb or Nsr for Nitrobacter- or Nitrospira-specific PCR, respectively. Bootstrap values above 50 are shown at each node. Scale bar represents 10% sequence difference. Redundant clone sequences are not shown.