Effect of the Aeration Strategy on NOB Suppression in Activated Sludge and Biofilm in a Hybrid Reactor with Nitrification/Denitrification

Abstract

The purpose of the study was to analyse the impact of aeration strategies defined by the changes in the duration of aerated sub-phases, the ratio between non-aerated and aerated sub-phase times (R), and dissolved oxygen concentrations (DO) on the suppression of nitrite-oxidizing bacteria (NOB) in activated sludge and biofilm developing in a hybrid reactor with nitrification/denitrification. The primary factor causing NOB suppression both in biofilm and in activated sludge was an increase in the R-value (from 0 to 1/4 and from 1/4 to 1/3). After reducing the DO from 3 to 2 mg O2/L, there were no changes in the frequency of NOB occurrence, and no reduction in the nitrite oxidation rate was recorded. The abundance of Comammox bacteria was considerably affected by the change from continuous to intermittent aeration. Activated sludge showed a substantial increase in the quantity of clade A and B, whereas the quantity considerably decreased in biofilm.

Changes in Nitrification Kinetics and Diversity of Canonical Nitrifiers and Comammox Bacteria in a Moving Bed Sequencing Batch Biofilm Reactor—A Long-Term Study

“…S.II.1.). This aligns with the observations made for the biofilm from hybrid systems [17,18]. Data presented in Figure 5 also suggest that irrespective of the research stage, nitriteoxidizing bacteria showed greater activity, which is consistent with qPCR results, where NOB were the predominant bacterial group in all samples.…”

“…), the abundance of all studied bacteria increased by 6.9-fold, 8.1-fold, and 2.7-fold, for AOB, NOB, and Comammox bacteria, respectively. The same trend was observed in the biofilm from the aforementioned hybrid reactor, where, upon introducing intermittent aeration in the same regime, the abundance of these bacteria increased, despite the DO concentration being half as low as that in the mentioned study [17]. Each time, shortening the duration of subphases with aeration (increase in R) led to a drop in the activity of bacteria capable of oxidizing ammonia nitrogen by approximately 20% (from S.I.1.…”

“…The analysis of the data collected from batch tests shows that changes introduced in MBSBBR operation parameters had a greater effect on the activity of ammonia-oxidizing bacteria. Previous studies also reported that the activity of ammonia oxidizers was more susceptible to changes in system operation than those capable of oxidizing nitrite [17,18]. It is worth emphasizing that in that case, the biofilm came from a hybrid reactor, where, next to this form of biomass, also activated sludge developed.…”

“…The determined AOR and NitOR values indicate changes in the activity of specific groups of nitrifying microorganisms. A detailed methodology of AUR and NitUR batch tests was presented in our previous paper [17], with the difference that in this work, tests were performed only for biomass immobilized on moving carriers (because the reactor worked as a pure moving bed technology).…”

“…In our previous studies, we explored the presence of Comammox bacteria and canonical nitrifiers. However, these studies were conducted in a moving bed sequencing batch biofilm reactor operating as a hybrid technology with biomass in the form of activated sludge and biofilm [17,18]. The focus was on analyzing how changes in aeration strategy and DO concentration affected the size of their populations and activities.…”