Nitrite Oxidizing Bacteria Activity Research Articles

Differentiating two partial nitrification mechanisms: Inhibiting nitrite oxidizing bacteria activity or promoting ammonium oxidizing bacteria activity

Partial nitrification is usually more easily achieved for high NH4+ concentration wastewater. In this study, a two-compartment aerobic nitrification reactor was used to raise the NH4+ concentration in the first aerobic compartment and to enhance partial nitrification for low NH4+ concentration wastewater. In addition to the regular sludge wastage to maintain sludge retention time (SRT), extra sludge wastage was used to increase the specific biomass NH4+ load. The experimental results indicated that partial nitrification was closely associated to the specific biomass NH4+ load. The modelling results indicated that a low SRT was needed to maintain the low biomass concentration and high specific biomass NH4+ load. The increased AOB (ammonium oxidizing bacteria) activity, instead of the free ammonia (FA) inhibition of NOB (nitrite oxidizing bacteria) was identified to be the main mechanism for partial nitrification in low NH4+ concentration wastewater treatment with high specific biomass NH4+ load.

Methods for increasing the rate of anammox attachment in a sidestream deammonification MBBR.

Deammonification (partial nitritation-anammox) is a proven process for the treatment of high-nitrogen waste streams, but long startup time is a known drawback of this technology. In a deammonification moving bed biofilm reactor (MBBR), startup time could potentially be decreased by increasing the attachment rate of anammox bacteria (AMX) on virgin plastic media. Previous studies have shown that bacterial adhesion rates can be increased by surface modification or by the development of a preliminary biofilm. This is the first study on increasing AMX attachment rates in a deammonification MBBR using these methods. Experimental media consisted of three different wet-chemical surface treatments, and also media transferred from a full-scale mainstream fully nitrifying integrated fixed-film activated sludge (IFAS) reactor. Following startup of a full-scale deammonification reactor, the experimental media were placed in the full-scale reactor and removed for activity rate measurements and biomass testing after 1 and 2 months. The media transferred from the IFAS process exhibited a rapid increase in AMX activity rates (1.1 g/m(2)/day NH(4)(+) removal and 1.4 g/m(2)/day NO(2)(-) removal) as compared to the control (0.2 g/m(2)/day NH(4)(+) removal and 0.1 g/m(2)/day NO(2)(-) removal) after 1 month. Two out of three of the surface modifications resulted in significantly higher AMX activity than the control at 1 and 2 months. No nitrite oxidizing bacteria activity was detected in either the surface modified media or IFAS media batch tests. The results indicate that startup time of a deammonification MBBR could potentially be decreased through surface modification of the plastic media or through the transfer of media from a mature IFAS process.

Experimentation and mathematical models for partial nitrification in aerobic granular sludge process

In this study, the characteristics partial nitrifying biomass in the Sequencing Batch Reactor (SBR) for aerobic granulation was investigated based on experiments and simulation modeling. The reactor operation was carried out at high concentration of ammonium (200~850 mg N/L) which favored Ammonia-Oxidizing Bacteria (AOB) growth over Nitrite-Oxidizing Bacteria (NOB) growth. In partial nitrifying granulation, both Free Ammonia (FA) and Free Nitrous Acid (FNA) simultaneously influenced the activity of NOB much more than that of AOB. According to the simulation results, thE Dissolved Oxygen (DO) concentration and oxygen affinity affect the growth competition and can influence the species that are predominant in the reactor. Both AOB and NOB can have growth potential under toxicants (FA and FNA) inhibition and limited oxygen condition. The AOB growth forms inner part of granule's biofilm, but the NOB growth does not engage in the formation of granules.

Response of nitrite accumulation and microbial community to free ammonia and dissolved oxygen treatment of high ammonium wastewater.

The effects of free ammonia (FA) and dissolved oxygen (DO) on nitrite accumulation in the treatment of high ammonium wastewater and on the evolution of the microbial community were investigated. Under high DO conditions (3.75 ± 0.49mg/L), FA as high as 10.61 ± 2.89mg NH3/L maintained stable nitrite accumulation rate (NAR) of 84% with NH4 (+)-N load of 2.05kg N/(m(3)day) at sludge retention time (SRT) of 15-18days. After 56days of operation, Proteobacteria and Nitrosomonas were the dominant phylum and genus, respectively; Nitrosomonas increased from 21.14 to 54.57%. By contrast, under relative low DO and low FA, nitrite-oxidizing bacteria (NOB) were nearly eliminated (NOB/AOB of 0; ammonium-oxidizing bacteria (AOB)), and NAR of 94% was achieved with lower NH4 (+)-N load of 0.48kg N/(m(3)day). DO correlated with AOB and NOB abundance, and FA decreased NOB activity and the NOB/AOB ratio. In conclusion, high FA and high DO conditions are optimal for efficient nitrite accumulation.

The Effect of Some Thai Medicinal Herb Extracts on Nitrification Inhibition

This study aimed to determine the effect on nitrification inhibition of some Thai medicinal herb extracts. The experimental design was completely randomized design, consisted 33 treatments with 4 replications. The experiments were performed in a laboratory, using surface soil of Yang Talat soil series as media. In each treatment, soil sample (100 g) was mixed thoroughly with 1 ml of herbal extract and 50 mg kg-1 of ammonium sulphate. The mixture was then incubated at ambient temperature. Ammonium oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), ammonium-N (NH4+-N), nitrate-N (NO3--N), and soil pH were determined at week 1 to 4 after incubation. The results showed that the numbers of AOB in soil sample mixed with galanga stem decreased during the first 2 weeks. It was obvious that after the first week of incubation, the activity of NOB in soil samples mixed with extracts of ringworm bush leaf, heart- leaved moonseed stem, mangosteen fruit, kariyat leaf and galanga rhizome was suppressed. Soil samples containing herbal extracts had higher concentraions of NH4+-N and lower concentraions of NO3--N than those of control. The highest amount of NH4+-N was found in clove flower treated soil during the first 2 weeks of incubation. Kariyat leaf treated and cinnamon bark treated soil samples contained the highest amount of NH4+-N in weeks 3 and 4, respectively. Samples with extracts of ringworm bush leaf, mangosteen fruit, Thai copper pod leaf, Indian mulberry leaf, lemon grass leaf, bitter cucumber fruit, egg woman stem, fingerroot stem, fingerroot rhizome and hog plum leaf contained the lowest amount of NO3--N during the first 3 weeks. The concentraion of NO3--N in heart- leaved moonseed stem treated soil was the lowest in the last 3 weeks. The highest ratio of NH4+-N (100 %) and the lowest ratio of NO3--N (0.0 %) to inorganic N were found in samples with extracts of ringworm bush leaf, mangosteen fruit, Thai copper pod leaf, Indian mulberry leaf, lemon grass leaf, bitter cucumber fruit, egg woman stem, fingerroot stem, fingerroot rhizome, hog plum leaf and heart-leaved moonseed stem for 3 weeks. At early stages of incubation, low pH of herbal soil samples were observed. The pH of those samples, however, increased over time.

Long-term nitritation performance of ammonium-rich landfill leachate

This study presents a biological system combined upflow anaerobic sludge bed (UASB) with sequencing batch reactor (SBR) to treat ammonium-rich landfill leachate. The start-up and operation of the nitritation at low temperatures were investigated. The synergetic interaction of free ammonia (FA) inhibition on nitrite-oxidizing bacteria (NOB) and process control was used to achieve nitritation in the SBR. It is demonstrated that nitritation was successfully started up in the SBR at low temperatures (14.0°C–18.2°C) by using FA inhibition coupled with process control, and then was maintained for 482days at normal/low temperature. Although ammonia-oxidizing bacteria (AOB) and NOB co-existed within bacterial clusters in the SBR sludge, AOB were confirmed to be dominant nitrifying population species by scanning electron microscopic (SEM) observation and fluorescence in situ hybridization (FISH) analysis. This confirmation not only emphasized that cultivating the appropriate bacteria is essential for achieving stable nitritation performance, but it also revealed that NOB activity was strongly inhibited by FA rather than being eliminated altogether from the system.

Rapid achievement of nitrification in CSTR and SBR treating reject water at high ammonia levels

The ability of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) to carry out nitrification in an environment with high ammonia levels was evaluated with the aim to suggest a suitable strategy for a quick start-up of nitrifying reactors treating reject water. It was proved that nitrification could be initiated even without any inoculation of nitrifying biomass. The nitritation was achieved faster (23 d after beginning of reactor operation) than nitratation (after 180 d) due to the presence of AOB and the absence of NOB in raw reject water. Free ammonia (FA) concentration reaching up to 160 mg N L−1 strongly inhibited nitrifying bacteria during the initial phase of reactor operation. Consequently, free nitrous acid (FNA) with a concentration up to 1.25 mg N L−1 supported NOB inhibition after the initiation of AOB activity. High AOB, as well as NOB, activity was observed even during the first day of the operation in a completely stirred tank reactor (CSTR, nitrogen loading rate—NLR 0.5 kg N (m3 d)−1, nitrogen oxidation rate—NOR 0.25±0.05 kg N (m3 d)−1) as well as a sequencing batch reactor (SBR, NLR 0.3 kg N (m3 d)−1, NOR 0.14±0.01 kg N (m3 d)−1) inoculated with common activated sludge at a zero initial total ammonium nitrogen concentration. It was proved that temporary inhibition of NOB activity induced by FA concentration elevated to 88 mg N L−1 may lead to the permanent transformation of standard nitrification into shortcut nitrification in SBRs, thanks to periodical exposition of NOB to high FA and FNA concentration during SBR cycle. Thus, it was demonstrated that the possibility to initiate this process very quickly is essential as a first stage for subsequent anaerobic oxidations of ammonium or shortcut denitrification.

Characterization and mitigation of nitrous oxide (N2 O) emissions from partial and full-nitrification BNR processes based on post-anoxic aeration control.

It has been reported that a directional change from anoxic to aerobic conditions is a common trigger for nitrous oxide (N2 O) production by ammonia oxidizing bacteria (AOB). By extension, during anoxic-aerobic cycling, post-anoxic dissolved oxygen (DO) concentrations might likely play a role in the magnitude of N2 O emissions observed. The overall goal of this study was to determine the impact of three select post-anoxic DO concentrations (0.8, 2.0, and 3.0 mg O2 /L) on N2 O emissions from partial-nitrification (PN) and full-nitrification (FN) reactors subjected to anoxic-aerobic cycling and, ultimately, to explore the development of strategies to minimize N2 O emissions from PN and FN based biological nitrogen removal (BNR) processes. Statistically similar N2 O emissions were observed during anoxia for both PN (0.62 ± 0.21% N load) and FN (0.61 ± 0.070% N load) processes. In contrast, N2 O emissions were statistically lower for PN (0.86 ± 0.25% N load) than for FN (4.6 ± 2.8% N load), during the post-anoxic aerobic phase, when compared together for all three post-anoxic DO concentrations. Further, for PN, the highest N2 O emissions were observed at the highest post-anoxic DO concentration of 3.0 mg O2 /L (1.2% N load), likely due to the highest corresponding AOB specific growth rate. In contrast, for FN, the highest N2 O emissions were at the lowest post-anoxic DO concentration of 0.8 mg O2 /L (8.5% N load). The higher emissions from FN process at low DO concentrations were associated with a lag in nitrite oxidizing bacteria activity upon recovery to aerobic conditions. This lag phase contributed to transient nitrite accumulation, and in turn correlated positively to the observed N2 O emissions. Based on our findings, a gradual ramp up in post-anoxic DO concentrations can minimize N2 O emissions during PN-based BNR, whereas a completely different strategy, entailing a rapid increase in post-anoxic DO concentrations can minimize emissions during FN-based BNR operations.

Resistance and resilience of nitrifying bacteria in aerobic granules to pH shock

To investigate the response difference between flocculent sludge and granular sludge in unfavourable environmental conditions, 1-h pH shock was exerted to both granular sludge and flocculent sludge with the same biomass concentration and the same population sizes of nitrifying bacteria. It was found that nitrite-oxidizing bacteria (NOB) were more sensitive to pH than ammonia-oxidizing bacteria (AOB). In addition, the deviation of 3 pH units to alkaline from the optimal pH was much more detrimental to AOB and NOB in both flocculent sludge and granular sludge compared with the deviation of 3 pH units to acidic. However, respirometric activities of both AOB and NOB in granular sludge after pH shock at 5 and 11 were much higher than those in the flocculent sludge. The recovery of nitrifying activities by only one batch culture indicated that nitrifying bacteria in granular sludge experienced a much less irreversible loss compared with flocculent sludge. The results in this study showed that compact structure and the big size of granules could play a buffering role to unfavourable conditions which resulted in a much higher resistance and resilience to shock. This study aims to provide some guidance to the application of aerobic granular sludge to real wastewater which might experience fluctuated pH. The findings in this study indicate that resistance and resilience of nitrifying bacteria in mature granules to pH shock at steady state is much better than flocculent sludge, suggesting more robust and flexible operation of granular sludge compared with traditional flocculent sludge. In addition, the results in this study underlined a more serious inhibition from free ammonia at high pH than free nitrous acid at low pH as well as the inaccuracy of reported bell-shaped modelling of pH effect on nitrification.

Enrichment of Nitrifiers and the Influence of Antimicrobials on Nitrification during Batch Experiment

The enrichment of nitrifying bacteria was realized and sludge yield was calculated for the batch experiment period. The influence of four kinds of antimicrobials on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was investigated using batch experiments. The specific ammonia-oxidizing activity (SAA) was 0.44 gN/gVSS/d and the specific nitrite-oxidizing activity (SNA) was 0.64 gN/gVSS/d. Below 400 mg/L antimicrobials, Cefalexin (CLX) almost has no adverse effect on nitrification and the highest inhibition caused by Sulfamethoxazole (SMX) was 15.4% and 23.9% to SAA and SNA respectively. Azithromycin (AZI) exhibited the most intense inhibitory effect. The relative activity of AOB and NOB were 39.0% and 29.8% respectively when AZI was 400 mg/L. Due to the complexation of Tetracycline (TC) with Ca and Mg, biomass showed obvious reduction with the foam on water surface. With the addition of 400 mg/L TC, only 76.9%, 13.7% and 8.1% of sludge remained when the substrate contained calcium or magnesium ions or both of them respectively.

Effect of alkalinity on nitrite accumulation in treatment of coal chemical industry wastewater using moving bed biofilm reactor

Nitrogen removal via nitrite (the nitrite pathway) is more suitable for carbon-limited industrial wastewater. Partial nitrification to nitrite is the primary step to achieve nitrogen removal via nitrite. The effect of alkalinity on nitrite accumulation in a continuous process was investigated by progressively increasing the alkalinity dosage ratio (amount of alkalinity to ammonia ratio, mol/mol). There is a close relationship among alkalinity, pH and the state of matter present in aqueous solution. When alkalinity was insufficient (compared to the theoretical alkalinity amount), ammonia removal efficiency increased first and then decreased at each alkalinity dosage ratio, with an abrupt removal efficiency peak. Generally, ammonia removal efficiency rose with increasing alkalinity dosage ratio. Ammonia removal efficiency reached to 88% from 23% when alkalinity addition was sufficient. Nitrite accumulation could be achieved by inhibiting nitrite oxidizing bacteria (NOB) by free ammonia (FA) in the early period and free nitrous acid in the later period of nitrification when alkalinity was not adequate. Only FA worked to inhibit the activity of NOB when alkalinity addition was sufficient.

Control of aeration, aerobic SRT and COD input for mainstream nitritation/denitritation

This work describes the development of an intermittently aerated pilot-scale process (V = 0.34 m3) operated without oxidized nitrogen recycle and supplemental carbon addition optimized for nitrogen removal via nitritation/denitritation. The aeration pattern was controlled using a novel aeration strategy based on set-points for reactor ammonia, nitrite and nitrate concentrations with the aim of maintaining equal effluent ammonia and nitrate + nitrite (NOx) concentrations. Further, unique operational and process control strategies were developed to facilitate the out-selection of nitrite oxidizing bacteria (NOB) based on optimizing the chemical oxygen demand (COD) input, imposing transient anoxia, aggressive solids retention time (SRT) operation towards ammonia oxidizing bacteria (AOB) washout and high dissolved oxygen (DO) (>1.5 mg/L). Sustained nitrite accumulation (NO2–N/NOx–N = 0.36 ± 0.27) was observed while AOB activity was greater than NOB activity (AOB: 391 ± 124 mgN/L/d, NOB: 233 ± 151 mgN/L/d, p < 0.001) during the entire study. The reactor demonstrated total inorganic nitrogen (TIN) removal rate of 151 ± 74 mgN/L/d at an influent COD/NH4+–N ratio of 10.4 ± 1.9 at 25 °C. The TIN removal efficiency was 57 ± 25% within the hydraulic retention time (HRT) of 3 h and within an SRT of 4–8 days. Therefore, this pilot-scale study demonstrates that application of the proposed online aeration control is able to out-select NOB in mainstream conditions providing relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT.

Increased salinity improves the thermotolerance of mesophilic nitrification

Nitrification is a well-studied and established process to treat ammonia in wastewater. Although thermophilic nitrification could avoid cooling costs for the treatment of warm wastewaters, applications above 40 °C remain a significant challenge. This study tested the effect of salinity on the thermotolerance of mesophilic nitrifying sludge (34 °C). In batch tests, 5 g NaCl L(-1) increased the activity of aerobic ammonia-oxidizing bacteria (AerAOB) by 20-21 % at 40 and 45 °C. For nitrite-oxidizing bacteria (NOB), the activity remained unaltered at 40 °C, yet decreased by 83 % at 45 °C. In a subsequent long-term continuous reactor test, temperature was increased from 34 to 40, 42.5, 45, 47.5 and 50 °C. The AerAOB activity showed 65 and 37 % higher immediate resilience in the salt reactor (7.5 g NaCl L(-1)) for the first two temperature transitions and lost activity from 45 °C onwards. NOB activity, in contrast to the batch tests, was 37 and 21 % more resilient in the salt reactor for the first two transitions, while no difference was observed for the third temperature transition. The control reactor lost NOB activity at 47.5 °C, while the salt reactor only lost activity at 50 °C. Overall, this study demonstrates salt amendment as a tool for a more efficient temperature transition for mesophilic sludge (34 °C) and eventually higher nitrification temperatures.

The impact of influent total ammonium nitrogen concentration on nitrite-oxidizing bacteria inhibition in moving bed biofilm reactor

The application of nitrification-denitrification over nitrite (nitritation-denitritation) with municipal (i.e. diluted and cold (or low-temperature)) wastewater can substantially improve the energy balance of municipal wastewater treatment plants. For the accumulation of nitrite, it is crucial to inhibit nitrite-oxidizing bacteria (NOB) with simultaneous proliferation of ammonium-oxidizing bacteria (AOB). The present study describes the effect of the influent total ammonium nitrogen (TAN) concentration on AOB and NOB activity in two moving bed biofilm reactors operated as sequencing batch reactors (SBR) at 15 °C (SBR I) and 21 °C (SBR II). The reactors were fed with diluted reject water containing 600, 300, 150 and 75 mg TAN L(-1). The only factor limiting NOB activity in these reactors was the high concentrations of free ammonia and/or free nitrous acid (FNA) during the SBR cycles. Nitrite accumulation was observed with influents containing 600, 300 and 150 mg TAN L(-1) in SBR I and 600 and 300 in SBR II. Once nitrate production established in the reactors, the increase of influent TAN concentration up to the original 600 mg TAN L(-1) did not limit NOB activity. This was due to the massive development of NOB clusters throughout the biofilm that were able to cope with faster formation of FNA. The results of the fluorescence in situ hybridization analysis preliminarily showed the stratification of bacteria in the biofilm.

Enhanced ammonia removal at room temperature by pH controlled partial nitrification and subsequent anaerobic ammonium oxidation

The Anammox-based processes are suitable for the treatment of wastewaters characterized by a low carbon to nitrogen (C/N) ratio. The application of the Anammox process requires the availability of an effluent with a NO 2−‒ N/NH 4+‒ N ratio composition around 1 g g−1, which involves the necessity of a previous step where the partial nitrification is performed. In this step, the inhibition of the nitrite-oxidizing bacteria (NOB) is crucial. In the present work, a combined partial nitrification-ANaerobic AMmonia OXidation (Anammox) two-units system operated at room temperature (20°C) has been tested for the nitrogen removal of pre-treated pig slurry. To achieve the successful partial nitrification and inhibit the NOB activity, different ammonium/inorganic carbon (NH 4+/IC ) ratios were assayed from 1.19 to 0.82 g NH 4+-N g−1 HCO3‒ C. This procedure provoked a decrease of the pH value to 6.0 to regulate the inhibitory effect over ammonia-oxidizing bacteria caused by free ammonia. Simultaneously, the NOB experienced the inhibitory effect of free nitrous acid which avoided the presence of nitrate in the effluent. The NH 4+/IC ratio which allowed the obtaining of the desired effluent composition (50% of both ammonium and nitrite) was 0.82±0.02 g NH 4+‒ N g−1 HCO 3−‒ C. The Anammox reactor was fed with the effluent of the partial nitrification unit containing a NO 2−‒ N/NH 4+‒ N ratio of 1 g g−1 where a nitrogen loading rate of 0.1 g N L−1 d−1 was efficiently removed.

Cultivation and characterization of thermophilicNitrospiraspecies from geothermal springs in the US Great Basin, China, and Armenia

Despite its importance in the nitrogen cycle, little is known about nitrite oxidation at high temperatures. To bridge this gap, enrichment cultures were inoculated with sediment slurries from a variety of geothermal springs. While nitrite-oxidizing bacteria (NOB) were successfully enriched from seven hot springs located in US Great Basin, south-western China, and Armenia at ≤ 57.9 °C, all attempts to enrich NOB from > 10 hot springs at ≥ 61 °C failed. The stoichiometric conversion of nitrite to nitrate, chlorate sensitivity, and sensitivity to autoclaving all confirmed biological nitrite oxidation. Regardless of origin, all successful enrichments contained organisms with high 16S rRNA gene sequence identity (≥ 97%) with Nitrospira calida. In addition, Armenian enrichments also contained close relatives of Nitrospira moscoviensis. Physiological properties of all enrichments were similar, with a temperature optimum of 45-50 °C, yielding nitrite oxidation rates of 7.53 ± 1.20 to 23.0 ± 2.73 fmoles cell(-1) h(-1), and an upper temperature limit between 60 and 65 °C. The highest rates of NOB activity occurred with initial NO2 - concentrations of 0.5-0.75 mM; however, lower initial nitrite concentrations resulted in shorter lag times. The results presented here suggest a possible upper temperature limit of 60-65 °C for Nitrospira and demonstrate the wide geographic range of Nitrospira species in geothermal environments.

Microbial activity of suspended biomass from a nitritation–anammox SBR in dependence of operational condition and size fraction

Single-stage nitritation-anammox combines the growth of aerobic ammonium-oxidizing bacteria (AOB) and anaerobic ammonium oxidizing bacteria (AnAOB) in one reactor. The necessary compromise of their milieu conditions often leads to the growth of nitrite-oxidizing bacteria (NOB). For this study, a sequencing batch reactor (SBR) for nitritation-anammox was operated for 180days with sewage sludge reject water (removal capacity, 0.4kg N m(-3) day(-1)). The growth of NOB was favored by enhanced oxygen supply rather than extended aerobic phases. Suspended-type biomass from this SBR was taken regularly and sieved into three size fractions (all of them <1,000μm). Batch experiments as well as fluorescence in situ hybridization were performed to study the distribution and activity of AnAOB, AOB, and NOB within those size fractions. Both the measured conversion rates and detected abundances decreased with increasing size fraction. The highest anammox conversion rates (15g NH4 (+)-N per kilogram VSS per hour) and the highest abundances of Brocadia fulgida were found in the medium size fraction (100-315μm). The batch experiments proved to be accurate tools for the monitoring of multiple processes in the reactor. The results were representative for reactor performance during the 6months of reactor operation.

Highly efficient partial nitrification by polyvinyl alcohol–alginate immobilized cells

Partial nitrification (oxidation of ammonium to nitrite by ammonium-oxidizing bacteria (AOB)) is a critical step in the process of removing biological nitrogen from nitrite. However, nitrite is unstable and easily oxidized to nitrate by nitrite-oxidizing bacteria (NOB) under aerobic conditions. In this study, a polyvinyl alcohol–alginate immobilization technique was utilized to entrap nitrifying bacteria for partial nitrification. The experimental results demonstrated that such immobilization limited the diffusion of dissolved oxygen (DO) into the immobilized cells to inhibit the activity of NOB. In this manner, stable and highly efficient partial nitrification was achieved. Nearly all of the ammonium was converted to nitrite rather than nitrate when the concentration of DO was between 0.5 and 2.0 mg L−1. Partial nitrification was also easily achieved at various concentrations of ammonium. Fluorescence in situ hybridization analysis indicated that AOB was the dominant bacteria in the immobilized cells (representing approximately 96% of the total microbial population).

Evaluating a strategy for maintaining nitrifier activity during long-term starvation in a moving bed biofilm reactor (MBBR) treating reverse osmosis concentrate

A two-stage moving bed biofilm reactor (MBBR) was applied at the Bundamba advanced water treatment plant (AWTP) (Queensland, Australia) to treat the reverse osmosis concentrate (ROC) for inorganic nutrient removal. One of the operational challenges for the system was to cope with the large fluctuations of the ROC flow. This study investigated the decay rates of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) and biofilm detachment in MBBR during starvation for up to one month. An intermittent aeration strategy of 15 min aeration every 6 h was applied. This study also evaluated the activity recovery of both AOB and NOB after normal operation was resumed. The results showed that the activity loss of AOB and NOB was relatively minor (<20%) within 10 days of starvation, which ensured relatively quick recovery of ammonium removal when normal operation resumed. In contrast, the AOB and NOB activity loss reached 60-80% when the starvation time was longer than 20 days, resulting in slower recovery of ammonium removal after starvation. Starvation for less than 20 days didn't result in an apparent biomass detachment from carriers.

Influence of Free Ammonia on Completely Autotrophic Nitrogen Removal over Nitrite (CANON) Process

Free ammonia (FA) plays a significant role in the stable, long-term, completely autotrophic nitrogen removal over nitrite (CANON) system operation. The influence of FA on the CANON process in a sequencing batch biofilm reactor was explored. Under controlled FA concentrations of 5.0 mg L(-1) to 10.0 mg L(-1), nitrite-oxidizing bacteria (NOB) was inhibited and achieved partial nitrification, which was important for a successful and quick start-up of the CANON process from activated sludge. However, NOB was acclimated to the condition after the process start-up. Ammonia-oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing bacteria (AnAOB) activities were unaffected when FA concentration was increased from 10 mg L(-1) to 17 mg L(-1), but NOB was completely inhibited only for a short time. The AOB and AnAOB activities were inhibited and the CANON system was deteriorated when FA concentration reached 30 mg L(-1) to 32.5 mg L(-1) at pH 8.5, whereas NOB activity was unaffected. Correlation analysis showed that FA concentration higher than 20 mg L(-1) resulted in the deterioration of the system.