Molecular analysis of ammonia-oxidizing bacterial populations in aerated-anoxic Orbal processes

Abstract

Aerated-anoxic processes operate under the principle that small additions of oxygen to an anoxic reactor induce simultaneous nitrification and denitrification. In these systems, ammonia oxidation in the anoxic zone can easily account for 30-50% of the total nitrification in the reactor, even though the dissolve oxygen concentration is usually below detection limit. To investigate whether the nitrification efficiency in aerated-anoxic processes was due to the presence of specialized ammonia-oxidizing bacteria (AOB), an analysis of the AOB population in an aerated-anoxic Orbal process and a conventional nitrogen removal process was carried out using phylogenetic analyses based on the ammonia monooxygenase A (amoA) gene. Terminal restriction fragment length polymorphism (TRFLP) analyses revealed that Nitrosospira-like organisms were one of the major contributors to ammonia oxidation in a full-scale aerated-anoxic Orbal reactor. However, the relative populations of Nitrosospira-like and Nitrosomonas-like AOB were not constant and appeared to have seasonal variability. Cloning and sequence comparison of amoA gene fragments demonstrated that most of the AOB in the aerated-anoxic Orbal process belonged to the Nitrosospira sp. and Nitrosomonas oligotropha lineages. The abundance of Nitrosospira-like organisms in aerated-anoxic reactors is significant, since this group of AOB has not been usually associated with nitrification in wastewater treatment plants.

Identification and evaluation of SND in a full-scale multi-channel oxidation ditch system under different aeration modes

“…Therefore, nitrogen leaving from the system was in the form of the gaseous nitrogen mainly through nitrification and denitrification within each single aerated channel. Based on estimated results, although the lost nitrogen in an OD without internal recycling of mixed liquor was attributed by the sum of SND from three channels, the percentages of removed nitrogen mass via SND in the mass of influent nitrogen gradually dropped from the outer to the inner channel at each mode except for Mode 1 due to no nitrification along with little produced NO x À -N. The largest aerated-anoxic channel optimized by oxygen supply offered a favorable co-existed environment for both nitrifying bacteria adapted to low oxygen and aerobic denitrifiers for promoting SND [16,20], while higher oxygen had an adverse effect on denitrification in the other channels, causing the failure of SND. In the same outer channel, the highest percentage of influent nitrogen mass via SND was achieved at Mode 3 with 44.1%, about twice as much at Mode 2 or Mode 4.…”

“…There were some principal explanations or presumptions for nitrogen removal via SND in oxidation ditches: (1) repeatedly swift alternation is between aerobic (after aerators) and anoxic zones (before aerators) of the mixed liquor in the same aerated channel based on inhomogeneous oxygen distribution [18]; (2) low-oxygen nitrification occurs at low sludge loading rate or long HRT and SRT [14,16,17], despite its nitrification rate is generally maximum value at DO of above 2.0 mg L À1 ; (3) anoxic zones are developed inside the activated-sludge flocs under aerobic conditions [14,19]; (4) novel microbes such as aerobic denitrifiers and nitrifiers adapted to low-oxygen conditions [16,20] are capable of performing SND. Nevertheless, behavior and property of SND in ODs were not deeply understood, especially for micro-environment characteristics related to sludge characteristics and bacterial composition for SND.…”

Involvement of Rhodocyclus -Related Organisms in Phosphorus Removal in Full-Scale Wastewater Treatment Plants

“…Operation of the Nine Springs WWTP as a University of Cape Town process without nitrate recycling optimizes the separation of anaerobic, anoxic, and aerobic stages in the reactor. In contrast, the Dane-Iowa WWTP operates as an aerated-anoxic process plant in which simultaneous nitrification and denitrification are promoted and a strictly anaerobic environment is not observed (20). Under these circumstances, competition between PAO and denitrifying bacteria for volatile fatty acids might create less favorable conditions for enrichment of Rhodocyclus-related bacteria and favor enrichment of PAO not related to Rhodocyclus.…”

Ammonia- and Nitrite-Oxidizing Bacterial Communities in a Pilot-Scale Chloraminated Drinking Water Distribution System

“…oligotropha cluster representatives have been isolated from soil, freshwater, estuary sediments, industrial sewage, and laboratory-activated sludge systems (16,39,41). They have also been detected by molecular methods in freshwater and sediments (38), shallow soil samples over a pH range of 3.9 to 6.6 (40), full-scale activated sludge treatment plants (30), and a phosphate-removing lab-scale biofilm reactor (7). While Kowalchuk et al (17) reported the detection of cluster 6 AOB (nomenclature by Stephen et al [40]) from pig and chicken manure compost and a calf-slurry-activated sludge system, the presence of N. oligotropha representatives could not be determined unequivocally in their study because the initial probe designed for this cluster (40) also targets Nitrosococcus mobilis, which belongs to the N. europaea cluster (cluster 7).…”