Effects of Aeration Cycles on Nitrifying Bacterial Populations and Nitrogen Removal in Intermittently Aerated Reactors

Abstract

The effects of the lengths of aeration and nonaeration periods on nitrogen removal and the nitrifying bacterial community structure were assessed in intermittently aerated (IA) reactors treating digested swine wastewater. Five IA reactors were operated in parallel with different aeration-to-nonaeration time ratios (ANA). Populations of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were monitored using 16S rRNA slot blot hybridizations. AOB species diversity was assessed using amoA gene denaturant gradient gel electrophoresis. Nitrosomonas and Nitrosococcus mobilis were the dominant AOB and Nitrospira spp. were the dominant NOB in all reactors, although Nitrosospira and Nitrobacter were also detected at lower levels. Reactors operated with the shortest aeration time (30 min) showed the highest Nitrosospira rRNA levels, and reactors operated with the longest anoxic periods (3 and 4 h) showed the lowest levels of Nitrobacter, compared to the other reactors. Nitrosomonas sp. strain Nm107 was detected in all reactors, regardless of the reactor's performance. Close relatives of Nitrosomonas europaea, Nitrosomonas sp. strain ENI-11, and Nitrosospira multiformis were occasionally detected in all reactors. Biomass fractions of AOB and effluent ammonia concentrations were not significantly different among the reactors. NOB were more sensitive than AOB to long nonaeration periods, as nitrite accumulation and lower total NOB rRNA levels were observed for an ANA of 1 h:4 h. The reactor with the longest nonaeration time of 4 h performed partial nitrification, followed by denitrification via nitrite, whereas the other reactors removed nitrogen through traditional nitrification and denitrification via nitrate. Superior ammonia removal efficiencies were not associated with levels of specific AOB species or with higher AOB species diversity.There is increasing interest in biological nitrogen removal technologies that use low levels of oxygen to achieve partial nitrification, the oxidation of ammonia to nitrite by ammonia-oxidizing bacteria (AOB), and subsequent denitrification via nitrite, the reduction of nitrite to dinitrogen gas by heterotrophic denitrifiers. Alkalinity and oxygen demands are lower for partial nitrification, and organic substrate requirements are lower for denitrification via nitrite, than the traditional nitrification/denitrification process, resulting in substantial operational savings (2). Partial nitrification relies on the selection of AOB over nitrite-oxidizing bacteria (NOB), which allows the accumulation of nitrite. Sustained nitrite accumulation can be accomplished by controlling solids retention time, temperature, free ammonia and hydroxylamine concentrations, or dissolved oxygen (DO) conditions (2,12,15,19,23,42).The key to efficient and robust biological wastewater treatment relies on knowing the microorganisms involved and how they respond to different operating conditions (41). Several microbial diversity studies of activated sludge and biofilms based on 16S rRNA gene libr...

Effect of Sewage and Industrial Effluents on Bacterial and Archaeal Communities of Creek Sediments in the Taihu Basin

“…Previous studies indicated that Chloroflexia was suited to live under brackish, nutrient-rich conditions [78]. Nitrospira, which was found to be more abundant at sites far away from the pollution source (D2, D3, J2, and J3), has often been found in freshwater ecosystems [79,80], sewage treatment systems [81], and anoxic environments as nitrite oxidizers [82]. Based on the results of RDA (Figure 9a), Nitrospira was positively correlated with NH 4 + -N, NO 3 Cl − -N, TOC, and TSI, but negatively correlated with RI.…”

Low-Dissolved-Oxygen Nitrifying Systems Exploit Ammonia-Oxidizing Bacteria with Unusually High Yields

“…However, there is evidence that complete nitrification can also occur at low DO levels (Ͻ0.5 mg/liter) (35) or with intermittent aeration (30). Also, a recent theoretical study modeling the risk of failure in nitrification based on the overall oxygen transfer coefficient (K L a) suggested that the risk of failure increases at intermediate aeration rates, while high (K L a Ͼ 35 day Ϫ1 ) and relatively low (4 day Ϫ1 Ͻ K L a Ͻ 10 day Ϫ1 ) aeration rates promote process stability (33).…”

“…These studies are promising, for though it may take many years to renew the physical assets of the water industry to meet the challenge of a lowenergy and low-carbon footprint, in principle, the less efficient biological assets could be replaced in a few weeks. Studies investigating the type of AOB in both activated sludge flocs and biofilms, where low oxygen was available, have been performed already using culture-independent techniques (12,25,30,34,35), but the results are sometimes conflicting. For example, Park and Noguera (34,35) reported that AOB communities in activated sludge were dominated by members of the Nitrosomonas europaea lineage and the Nitrosomonas oligotropha lineage under low-DO conditions (Ͻ0.24 mg/liter), while members of the N. oligotropha lineage were dominant at higher DO concentrations.…”

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

“…Moreover, the AC process is a low-cost solution because it only requires an automatic control system. Nevertheless, because both autotrophic (nitrifying) and heterotrophic (denitrifying) microorganisms will grow in one reactor, many authors (among others Lim et al [12] and Mota et al [13]) noted that an incorrect aeration/non aeration ratio could promote an unbalanced growth of heterotrophic and autotrophic bacteria and worsen the removal efficiencies. Referring in particular to nitrogen removal, previous studies revealed a partial nitrification to nitrite under limiting oxygen condition [14,15].…”