Community survey of ammonia-oxidizing bacteria in full-scale activated sludge processes with different solids retention time

Abstract

Aims: To study the effects of different solids retention time (SRT) on the nitrification activity and community composition of ammonia-oxidizing bacteria (AOB) in two full-scale activated sludge processes during a 5-month period. Methods and Results: The AOB community composition was analysed using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE), and the identified populations were enumerated by quantitative FISH. Potential nitrification rates were determined in batch tests and the in situ rates were calculated from mass balances of nitrogen in the plants. Increased SRT reduced the nitrification activity, but neither the number per mixed liquor suspended solids nor community composition of AOB were affected. Two dominant AOB populations related to Nitrosomonas europaea and Nitrosomonas oligotropha were identified by FISH, whereas only the latter could be detected by DGGE. Conclusions: The effect of a longer SRT on the activity was probably because of physiological changes in the AOB community rather than a change in community composition. Significance and Impact of the Study: Physiological alterations of a stable AOB community are possible and may stabilize activated sludge processes. The commonly used FISH probes designed to target all betaproteobacterial AOB does not detect certain Nitrosomonas oligotropha populations, leading to an underestimation of AOB if a wider set of probes is not used.

Transcription levels (amoA mRNA-based) and population dominance (amoA gene-based) of ammonia-oxidizing bacteria

“…Thus, the AOB cells in the 2-day system (with higher amoA mRNA levels) could quickly propagate under short SRT operation, thereby reducing the possible cellular washout and ultimately system failure. These observations are well supported by previous reports that indicate decreased SRT results in an increased substrate loading and oxidation rate when normalized per unit of activated sludge [10,20].…”

Community dynamics of ammonia oxidizing bacteria in a full-scale wastewater treatment system with nitrification stability

“…and not to Nitrosospira spp. This result is consistent with most previous studies [2,[22][23][24][25][26][27][28][29][30] but is in contrast to a few studies that found Nitrosospira spp. to be the dominant AOB [27,31].…”

“…AOB belonging to this cluster are often recovered from freshwater, sediments, soils, wastewater treatment plants, and other environments [22,24,25,32,33]. A study of isolates of the N. oligotropha cluster revealed that they have very low K s values for free ammonia, ranging from 0.027 to 0.059 mg$L -1 [34].…”

“…The strains of this cluster have been widely observed in wastewater treatment plants [1,2,22,25,26,34]. The significant physiologic feature of this cluster is a high ammonia K s value ranging from 0.42 to 0.85 mg$L -1 [22].…”

An innovative respirometric method to assess the autotrophic active fraction: Application to an alternate oxic–anoxic MBR pilot plant

“…The size and morphology of the investigated AOB populations are consistent with those reported in the literature [38,39], although AOB clusters can also be present in larger aggregates depending on the sample age [39,40].…”