Bioaugmentation as a tool for improving the start-up and stability of a pilot-scale partial nitrification biofilm airlift reactor

The effectiveness of bioaugmentation in the improvement of the start-up of a biofilm airlift reactor to perform partial nitrification was investigated. Two identical biofilm airlift reactors were inoculated. The non-bioaugmented reactor (NB-reactor) was inoculated with conventional activated sludge, whereas the bioaugmented reactor (B-reactor) was seeded with the same conventional activated sludge but bioaugmented with nitrifying activated sludge from a pilot plant performing full nitritation under stable conditions (100% oxidation of influent ammonium to nitrite). The fraction of specialized nitrifying activated sludge in the inoculum of the B-reactor was only 6% (measured as dry matter). To simplify comparison of the results, operational parameters were equivalent for both reactors. Partial nitrification was achieved significantly faster in the B-reactor, showing a very stable operation. The results obtained by fluorescence in situ hybridization assays showed that the specialized nitrifying biomass added to the B-reactor remained in the biofilm throughout the start-up period.     

Bioaugmentation as a Tool To Protect the Structure and Function of an Activated-Sludge Microbial Community against a 3-Chloroaniline Shock Load

Bioaugmentation of bioreactors focuses on the removal of xenobiotics, with little attention typically paid to the recovery of disrupted reactor functions such as ammonium-nitrogen removal. Chloroanilines are widely used in industry as a precursor to a variety of products and are occasionally released into wastewater streams. This work evaluated the effects on activated-sludge reactor functions of a 3-chloroaniline (3-CA) pulse and bioaugmentation by inoculation with the 3-CA-degrading strain Comamonas testosteroni I2 gfp. Changes in functions such as nitrification, carbon removal, and sludge compaction were studied in relation to the sludge community structure, in particular the nitrifying populations. Denaturing gradient gel electrophoresis (DGGE), real-time PCR, and fluorescent in situ hybridization (FISH) were used to characterize and enumerate the ammonia-oxidizing microbial community immediately after a 3-CA shock load. Two days after the 3-CA shock, ammonium accumulated, and the nitrification activity did not recover over a 12-day period in the nonbioaugmented reactors. In contrast, nitrification in the bioaugmented reactor started to recover on day 4. The DGGE patterns and the FISH and real-time PCR data showed that the ammonia-oxidizing microbial community of the bioaugmented reactor recovered in structure, activity, and abundance, while the number of ribosomes of the ammonia oxidizers in the nonbioaugmented reactor decreased drastically and the community composition changed and did not recover. The settleability of the activated sludge was negatively influenced by the 3-CA addition, with the sludge volume index increasing by a factor of 2.3. Two days after the 3-CA shock in the nonbioaugmented reactor, chemical oxygen demand (COD) removal efficiency decreased by 36% but recovered fully by day 4. In contrast, in the bioaugmented reactor, no decrease of the COD removal efficiency was observed. This study demonstrates that bioaugmentation of wastewater reactors to accelerate the degradation of toxic chlorinated organics such as 3-CA protected the nitrifying bacterial community, thereby allowing faster recovery from toxic shocks.     

Bioaugmentation as a tool to protect the structure and function of an activated-sludge microbial community against a 3-chloroaniline shock load

Bioaugmentation of bioreactors focuses on the removal of xenobiotics, with little attention typically paid to the recovery of disrupted reactor functions such as ammonium-nitrogen removal. Chloroanilines are widely used in industry as a precursor to a variety of products and are occasionally released into wastewater streams. This work evaluated the effects on activated-sludge reactor functions of a 3-chloroaniline (3-CA) pulse and bioaugmentation by inoculation with the 3-CA-degrading strain Comamonas testosteroni I2 gfp. Changes in functions such as nitrification, carbon removal, and sludge compaction were studied in relation to the sludge community structure, in particular the nitrifying populations. Denaturing gradient gel electrophoresis (DGGE), real-time PCR, and fluorescent in situ hybridization (FISH) were used to characterize and enumerate the ammonia-oxidizing microbial community immediately after a 3-CA shock load. Two days after the 3-CA shock, ammonium accumulated, and the nitrification activity did not recover over a 12-day period in the nonbioaugmented reactors. In contrast, nitrification in the bioaugmented reactor started to recover on day 4. The DGGE patterns and the FISH and real-time PCR data showed that the ammonia-oxidizing microbial community of the bioaugmented reactor recovered in structure, activity, and abundance, while the number of ribosomes of the ammonia oxidizers in the nonbioaugmented reactor decreased drastically and the community composition changed and did not recover. The settleability of the activated sludge was negatively influenced by the 3-CA addition, with the sludge volume index increasing by a factor of 2.3. Two days after the 3-CA shock in the nonbioaugmented reactor, chemical oxygen demand (COD) removal efficiency decreased by 36% but recovered fully by day 4. In contrast, in the bioaugmented reactor, no decrease of the COD removal efficiency was observed. This study demonstrates that bioaugmentation of wastewater reactors to accelerate the degradation of toxic chlorinated organics such as 3-CA protected the nitrifying bacterial community, thereby allowing faster recovery from toxic shocks.     

Microscale distribution of populations and activities of Nitrosospira and Nitrospira spp. along a macroscale gradient in a nitrifying bioreactor: quantification by in situ hybridization and the use of microsensors.

The change of activity and abundance of Nitrosospira and Nitrospira spp. along a bulk water gradient in a nitrifying fluidized bed reactor was analyzed by a combination of microsensor measurements and fluorescence in situ hybridization. Nitrifying bacteria were immobilized in bacterial aggregates that remained in fixed positions within the reactor column due to the flow regimen. Nitrification occurred in a narrow zone of 100 to 150 microm on the surface of these aggregates, the same layer that contained an extremely dense community of nitrifying bacteria. The central part of the aggregates was inactive, and significantly fewer nitrifiers were found there. Under conditions prevailing in the reactor, i.e., when ammonium was limiting, ammonium was completely oxidized to nitrate within the active layer of the aggregates, the rates decreasing with increasing reactor height. To analyze the nitrification potential, profiles were also recorded in aggregates subjected to a short-term incubation under elevated substrate concentrations. This led to a shift in activity from ammonium to nitrite oxidation along the reactor and correlated well with the distribution of the nitrifying population. Along the whole reactor, the numbers of ammonia-oxidizing bacteria decreased, while the numbers of nitrite-oxidizing bacteria increased. Finally, volumetric reaction rates were calculated from microprofiles and related to cell numbers of nitrifying bacteria in the active shell. Therefore, it was possible for the first time to estimate the cell-specific activity of Nitrosospira spp. and hitherto-uncultured Nitrospira-like bacteria in situ.     

Microscale Distribution of Populations and Activities of Nitrosospira and Nitrospira spp. along a Macroscale Gradient in a Nitrifying Bioreactor: Quantification by In Situ Hybridization and the Use of Microsensors

The change of activity and abundance of Nitrosospira and Nitrospira spp. along a bulk water gradient in a nitrifying fluidized bed reactor was analyzed by a combination of microsensor measurements and fluorescence in situ hybridization. Nitrifying bacteria were immobilized in bacterial aggregates that remained in fixed positions within the reactor column due to the flow regimen. Nitrification occurred in a narrow zone of 100 to 150 μm on the surface of these aggregates, the same layer that contained an extremely dense community of nitrifying bacteria. The central part of the aggregates was inactive, and significantly fewer nitrifiers were found there. Under conditions prevailing in the reactor, i.e., when ammonium was limiting, ammonium was completely oxidized to nitrate within the active layer of the aggregates, the rates decreasing with increasing reactor height. To analyze the nitrification potential, profiles were also recorded in aggregates subjected to a short-term incubation under elevated substrate concentrations. This led to a shift in activity from ammonium to nitrite oxidation along the reactor and correlated well with the distribution of the nitrifying population. Along the whole reactor, the numbers of ammonia-oxidizing bacteria decreased, while the numbers of nitrite-oxidizing bacteria increased. Finally, volumetric reaction rates were calculated from microprofiles and related to cell numbers of nitrifying bacteria in the active shell. Therefore, it was possible for the first time to estimate the cell-specific activity of Nitrosospira spp. and hitherto-uncultured Nitrospira-like bacteria in situ.     

Analysis of Microbial Population Dynamics in a Partial Nitrifying SBR at Ambient Temperature

In this study, a lab-scale partial nitrifying sequencing batch reactor (SBR) was developed to investigate partial nitrification at ambient temperature (16–22 °C). Techniques of denaturing gradient gel electrophoresis (DGGE), cloning, and fluorescence in situ hybridization (FISH) were utilized simultaneously to study microbial population dynamics. Partial nitrification was effectively achieved in response to shifts of influent ammonium concentrations. DGGE results showed that higher ammonia concentration referred to lower ammonia-oxidizing bacteria (AOB) diversity in the SBR. Phylogenetic analysis revealed that all the predominant AOB was affiliated with Nitrosomonas genus. FISH analysis illustrated AOB was the predominant nitrifying bacteria of microbial compositions when SBR achieved partial nitrification (PN) at ambient temperature.     

High-rate nitrification at low pH in suspended- and attached-biomass reactors

This article reports on high-rate nitrification at low pH in biofilm and suspended-biomass reactors by known chemolithotrophic bacteria. In the biofilm reactor, at low pH (4.3 +/- 0.1) and low bulk ammonium concentrations (9.3 +/- 3.3 mg.liter(-1)), a very high nitrification rate of 5.6 g of N oxidized.liter(-1).day(-1) was achieved. The specific nitrification rate (0.55 g of N.g of biomass(-1).day(-1)) was similar to values reported for nitrifying reactors at optimal pH. In the suspended-biomass reactor, the average pH was significantly lower than that in the biofilm reactor (pH 3.8 +/- 0.3), and values as low as pH 3.2 were found. In addition, measurements in the suspended-biomass reactor, using isotope-labeled ammonium (15N), showed that in spite of the very low pH, biomass growth occurred with a yield of 0.1 g of biomass.g of N oxidized(-1). Fluorescence in situ hybridization using existing rRNA-targeted oligonucleotide probes showed that the nitrifying bacteria were from the monophyletic genus Nitrosomonas, suggesting that autotrophic nitrification at low pH is more widespread than previously thought. The results presented in this paper clearly show that autotrophic nitrifying bacteria have the ability to nitrify at a high rate at low pH and in the presence of only a negligible free ammonia concentration, suggesting the presence of an efficient ammonium uptake system and the means to cope with low pH.     

Assessment of a bioaugmentation strategy with polyphosphate accumulating organisms in a nitrification/denitrification sequencing batch reactor

Different alternative configurations and strategies for the simultaneous biological removal of organic matter and nutrients (N and P) in wastewater have been proposed in the literature. This work demonstrates a new successful strategy to bring in enhanced biological phosphorus removal (EBPR) to a conventional nitrification/denitrification system by means of bioaugmentation with an enriched culture of phosphorus accumulating organisms (PAO). This strategy was tested in a sequencing batch reactor (SBR), where an 8 h configuration with 3 h anoxic, 4.5 h aerobic and 25 min of settling confirmed that nitrification, denitrification and PAO activity could be maintained for a minimum of 60 days of operation after the bioaugmentation step. The successful bioaugmentation strategy opens new possibilities for retrofitting full-scale WWTP originally designed for only nitrification/denitrification. These systems could remove P simultaneously to COD and N if they were bioaugmented with waste purge of an anaerobic/aerobic SBR operated in parallel treating part of the influent wastewater.     

Effective and robust partial nitrification to nitrite by real-time aeration duration control in an SBR treating domestic wastewater

Achieving sustainable partial nitrification to nitrite has been proven difficult in treating low strength nitrogenous wastewater. Real-time aeration duration control was used to achieve efficient partial nitrification to nitrite in a sequencing batch reactor (SBR) to treat low strength domestic wastewater. Above 90% nitrite accumulation ratio was maintained for long-term operation at normal condition, or even lower water temperature in winter. Partial nitrification established by controlling aeration duration showed good performance and robustness even though encountering long-term extended aeration and starvation period. Process control enhanced the successful accumulation of ammonia oxidizing bacteria (AOB) and washout of nitrite oxidizing bacteria (NOB). Scanning electron microscope observations indicated that the microbial morphology showed a shift towards small rod-shaped clusters. Fluorescence in situ hybridization (FISH) results demonstrated AOB were the dominant nitrifying bacteria, up to 8.3 ± 1.1% of the total bacteria; on the contrary, the density of NOB decreased to be negligible after 135 days operation since adopting process control.     

Achieving nitrite accumulation in a continuous system treating low-strength domestic wastewater: switchover from batch start-up to continuous operation with process control

Although biological nitrogen removal via nitrite is recognized as one of the cost-effective and sustainable biological nitrogen removal processes, nitrite accumulation has proven difficult to achieve in continuous processes treating low-strength nitrogenous wastewater. Partial nitrification to nitrite was achieved and maintained in a lab-scale completely stirred tank reactor (CSTR) treating real domestic wastewater. During the start-up period, sludge with ammonia-oxidizing bacteria (AOB) but no nitrite-oxidizing bacteria (NOB) was obtained by batch operation with aeration time control. The nitrifying sludge with the dominance of AOB was then directly switched into continuous operation. It was demonstrated that partial nitrification to nitrite in the continuous system could be repeatedly and reliably achieved using this start-up strategy. The ratio of dissolved oxygen to ammonium loading rate (DO/ALR) was critical to maintain high ammonium removal efficiency and nitrite accumulation ratio. Over 85% of nitrite accumulation ratio and more than 95% of ammonium removal efficiency were achieved at DO/ALR ratios in an optimal range of 4.0–6.0 mg O₂/g N d, even under the disturbances of ammonium loading rate. Microbial population shift was investigated, and fluorescence in situ hybridization analysis indicated that AOB were the dominant nitrifying bacteria over NOB when stable partial nitrification was established.     

Long-term effect of dissolved oxygen on partial nitrification performance and microbial community structure

In this study, the performance of partial nitrification via nitrite and microbial community structure were investigated and compared in two sequencing batch reactors (SBR) with different dissolved oxygen (DO) levels. Both reactors achieved stable partial nitrification with nitrite accumulation ratio of above 95% by using real-time aeration duration control. Compared with high DO (above 3 mg/l on average) SBR, simultaneous nitrification and denitrification (SND) via nitrite was carried out in low DO (0.4–0.8 mg/l) SBR. The average efficiencies of SND in high DO and low DO reactor were 7.7% and 44.9%, and the specific SND rates were 0.20 and 0.83 mg N/(mg MLSS h), respectively. Low DO did not produce sludge with poorer settling properties but attained lower turbidities of the effluent than high DO. Fluorescence in situ hybridization (FISH) analysis in both the reactors showed that ammonia-oxidizing bacteria (AOB) were the dominant nitrifying bacteria and nitrite-oxidizing bacteria (NOB) did not be recovered in spite of exposing nitrifying sludge to high DO. The morphology of the sludge from both two reactors according to scanning electron microscope indicated that small rod-shaped and spherical clusters were dominant, although filamentous bacteria and few long rod-shaped coexisted in the low DO reactor. By selecting properly DO level and adopting process control method is not only of benefit to the achievement of novel biological nitrogen removal technology, but also favorable to sludge population optimization.     

Effect of temperature and free ammonia on nitrification and nitrite accumulation in landfill leachate and analysis of its nitrifying bacterial community by FISH

The cause of seasonal failure of a nitrifying municipal landfill leachate treatment plant utilizing a fixed biofilm was investigated by wastewater analyses and batch respirometric tests at every treatment stage. Nitrification of the leachate treatment plant was severely affected by the seasonal temperature variation. High free ammonia (NH3-N) inhibited not only nitrite oxidizing bacteria (NOB) but also ammonia oxidizing bacteria (AOB). In addition, high pH also increased free ammonia concentration to inhibit nitrifying activity especially when the NH4-N level was high. The effects of temperature and free ammonia of landfill leachate on nitrification and nitrite accumulation were investigated with a semi-pilot scale biofilm airlift reactor. Nitrification rate of landfill leachate increased with temperature when free ammonia in the reactor was below the inhibition level for nitrifiers. Leachate was completely nitrified up to a load of 1.5 kg NH4-N m(-3)d(-1) at 28 degrees C. The activity of NOB was inhibited by NH3-N resulting in accumulation of nitrite. NOB activity decreased more than 50% at 0.7 mg NH3-N L(-1). Fluorescence in situ hybridization (FISH) was carried out to analyze the population of AOB and NOB in the nitrite accumulating nitrifying biofilm. NOB were located close to AOB by forming small clusters. A significant fraction of AOB identified by probe Nso1225 specifically also hybridized with the Nitrosomonas specific probe Nsm156. The main NOB were Nitrobacter and Nitrospira which were present in almost equal amounts in the biofilm as identified by simultaneous hybridization with Nitrobacter specific probe Nit3 and Nitrospira specific probe Ntspa662.     

Effect of different salt adaptation strategies on the microbial diversity, activity, and settling of nitrifying sludge in sequencing batch reactors

The effect of salinity on the activity of nitrifying bacteria, floc characteristics, and microbial community structure accessed by fluorescent in situ hybridization and polymerase chain reaction–denaturing gradient gel electrophoresis techniques was investigated. Two sequencing batch reactors (SRB₁ and SBR₂) treating synthetic wastewater were subjected to increasing salt concentrations. In SBR₁, four salt concentrations (5, 10, 15, and 20 g NaCl/L) were tested, while in SBR₂, only two salt concentrations (10 and 20 g NaCl/L) were applied in a more shock-wise manner. The two different salt adaptation strategies caused different changes in microbial community structure, but did not change the nitrification performance, suggesting that regardless of the different nitrifying bacterial community present in the reactor, the nitrification process can be maintained stable within the salt range tested. Specific ammonium oxidation rates were more affected when salt increase was performed more rapidly and dropped 50% and 60% at 20 g NaCl/L for SBR₁ and SBR₂, respectively. A gradual increase in NaCl concentration had a positive effect on the settling properties (i.e., reduction of sludge volume index), although it caused a higher amount of suspended solids in the effluent. Higher organisms (e.g., protozoa, nematodes, and rotifers) as well as filamentous bacteria could not withstand the high salt concentrations.     

Microbial community structure in autotrophic nitrifying granules characterized by experimental and simulation analyses

This study evaluates the community structure in nitrifying granules (average diameter of 1600 μm) produced in an aerobic reactor fed with ammonia as the sole energy source by a multivalent approach combining molecular techniques, microelectrode measurements and mathematical modelling. Fluorescence in situ hybridization revealed that ammonia-oxidizing bacteria dominated within the first 200 μm below the granule surface, nitrite-oxidizing bacteria a deeper layer between 200 and 300 μm, while heterotrophic bacteria were present in the core of the nitrifying granule. Presence of these groups also became evident from a 16S rRNA clone library. Microprofiles of NH₄⁺, NO₂^–, NO₃^– and O₂ concentrations measured with microelectrodes showed good agreement with the spatial organization of nitrifying bacteria. One- and two-dimensional numerical biofilm models were constructed to explain the observed granule development as a result of the multiple bacteria–substrate interactions. The interaction between nitrifying and heterotrophic bacteria was evaluated by assuming three types of heterotrophic bacterial growth on soluble microbial products from nitrifying bacteria. The models described well the bacterial distribution obtained by fluorescence in situ hybridization analysis, as well as the measured oxygen, nitrite, nitrate and ammonium concentration profiles. Results of this study are important because they show that a combination of simulation and experimental techniques can better explain the interaction between nitrifying bacteria and heterotrophic bacteria in the granules than individual approaches alone.     

Community structures and activities of nitrifying and denitrifying bacteria in industrial wastewater-treating biofilms

The bacterial community structure, in situ spatial distributions and activities of nitrifying and denitrifying bacteria in biofilms treating industrial wastewater were investigated by combination of the 16S rRNA gene clone analysis, fluorescence in situ hybridization (FISH) and microelectrodes. These results were compared with the nitrogen removal capacity of the industrial wastewater treatment plant (IWTP). Both nitrification and denitrification occurred in the primary denitrification (PD) tank and denitrification occurred in the secondary denitrification (SD) tank. In contrast, nitrification and denitrification rates were very low in the nitrification (N) tank. 16S rRNA gene clone sequence analysis revealed that the bacteria affiliated with Alphaproteobacteria, followed by Betaproteobacteria, were numerically important microbial groups in three tanks. The many clones affiliated with Alphaproteobacteria were closely related to the denitrifying bacteria (e.g., Hyphomicrobium spp., Rhodopseudomonas palustris, and Rhodobacter spp.). In addition, Methylophilus leisingeri affiliated with Betaproteobacteria, which favorably utilized methanol, was detected only in the SD-tank to which methanol was added. Nitrosomonas europaea and Nitrosomonas marina were detected as the ammonia-oxidizing bacteria affiliated with Betaproteobacteria throughout this plant, although the dominant species of them was different among three tanks. Nitrifying bacteria were mainly detected in the upper parts of the PD-biofilm whereas their populations were low in the upper parts of the N-biofilm. The presence of denitrifying bacteria affiliated with Hyphomicrobium spp. in SD- and N-biofilms was verified by FISH analysis. Microelectrode measurements showed that the nitrifying bacteria present in the N- and PD-biofilms were active and the bacteria present in the SD-biofilm could denitrify.     

Structure and activity of multiple nitrifying bacterial populations co-existing in a biofilm

A biofilm from a nitrifying pilot-scale sequencing batch reactor was investigated for effects of varying process conditions on its microscale activity and structure. Microsensor measurements of oxygen, substrates and products of nitrification were applied under incubation at different ammonium and oxygen concentrations which reflected various situations during a treatment cycle. A high net N loss was observed under high ammonium (HA) concentrations in contrast to low ones. Additionally, results indicated inhibition of nitrite-oxidizing bacteria (NOB), but not of ammonia-oxidizing bacteria (AOB) by free ammonia under HA conditions. Diversity, spatial distribution, and abundance of nitrifying bacteria as analysed by fluorescence in situ hybridization (FISH) revealed six different nitrifying populations with heterogeneous distributions. Nitrosococcus mobilis formed conspicuous microcolonies locally surrounded by cells of the dominating N. europaea/eutropha-related AOB population. A third less abundant population was affiliated to N. oligotropha. Nitrite-oxidizing bacteria of the genera Nitrobacter and Nitrospira (with at least two distinct populations) showed a large scale heterogeneity in their distribution. Nitrospira spp. were also found in deeper inactive layers where they might persist rather than thrive, and act as seed population when detached. Results of functional and structural analyses are discussed with respect to specific niches of individual populations in this system.     

Development of a simultaneous partial nitrification and anaerobic ammonia oxidation process in a single reactor

Up-flow oxygen-controlled biofilm reactors equipped with a non-woven fabric support were used as a single reactor system for autotrophic nitrogen removal based on a combined partial nitrification and anaerobic ammonium oxidation (anammox) reaction. The up-flow biofilm reactors were initiated as either a partial nitrifying reactor or an anammox reactor, respectively, and simultaneous partial nitrification and anammox was established by careful control of the aeration rate. The combined partial nitrification and anammox reaction was successfully developed in both biofilm reactors without additional biomass inoculation. The reactor initiated as the anammox reactor gave a slightly higher and more stable mean nitrogen removal rate of 0.35 (± 0.19) kg-N m⁻³ d⁻¹ than the reactor initiated as the partial nitrifying reactor (0.23 (± 0.16) kg-N m⁻³ d⁻¹). FISH analysis revealed that the biofilm in the reactor started as the anammox reactor were composed of anammox bacteria located in inner anoxic layers that were surrounded by surface aerobic AOB layers, whereas AOB and anammox bacteria were mixed without a distinguishable niche in the biofilm in the reactor started as the partial nitrifying reactor. However, it was difficult to efficiently maintain the stable partial nitrification owing to inefficient aeration in the reactor, which is a key to development of the combined partial nitrification and anammox reaction in a single biofilm reactor.     

Bioaugmentation accelerates the shift of bacterial community structure against shock load: a case study of coking wastewater treatment by zeolite-sequencing batch reactor

Bioaugmentation with degrading bacteria is an effective method to improve the treatment of refractory industrial wastewater; nevertheless there were controversial opinions about the fate of inoculated bacteria and microbial community dynamics. In this study, two lab-scale sequencing batch reactors filled with modified zeolite were used to treat a coking wastewater with pyridine and quinoline shock load, and a bacterial consortium containing three degrading strains was added in one reactor for bioaugmentation. During 120-day operation, the bioaugmented reactor removed over 99 % pyridine, 99 % quinoline, 85 % TOC, 65 % COD, and 95 % NO₃ ^?-N with higher resistance to the shock load than the non-bioaugmented reactor. Based on the terminal restriction fragment length polymorphism of 16S rDNA, bacterial community diversity increased in the bioaugmented reactor. Principal component analysis revealed that, to cope with the shock load, the indigenous bacterial community recovered to the initial structure by acclimatizing itself constantly to the inhospitable environment; but bioaugmentation accelerated the shift of whole bacterial community, resulting in a far different structure from the initial one. Canonical correspondence analysis indicated that the environmental parameters of pyridine, quinoline, TOC, and NO₃ ^?-N had close negative correlations with bioaugmentation; and NH₃-N and COD were the main parameters to impact on the bacterial community changes and treatment efficiency.     

Analysis of factors affecting the performance of partial nitrification in a sequencing batch reactor

The objective of this study was to analyze the factors affecting the performance of partial nitrification in a sequencing batch reactor. During a 140-day long-term operation, influent pH value, dissolved oxygen (DO), and chemical oxygen demand/nitrogen (COD/N) ratio were selected as operating factors to evaluate the maintenance and recovery of nitrite accumulation. Results showed that high DO concentration (2–4 mg/L) could damage nitrite accumulation immediately. However, nitrite accumulation ratio (NAR) could be increased from 1.68?±?1.51 to 35.46?±?7.86 % when increasing the pH values from 7.5 to 8.3 due to the increased free ammonia concentration. Afterwards, stable partial nitrification and high NAR could be recovered when the reactor operated under low DO concentration (0.5–1.0 mg/L). However, it required a long time to recover the partial nitrification of the reactor when the influent COD/N ratios were altered. Fluorescence in situ hybridization analysis implied that ammonium oxidizing bacteria were completely recovered to the dominant nitrifying bacteria in the system. Meanwhile, sludge volumetric index of the reactor gradually decreased from 115.6 to 56.6 mL/g, while the mean diameter of sludge improved from74.57 to 428.8 μm by using the strategy of reducing settling time. The obtained results could provide useful information between the operational conditions and the performance of partial nitrification when treating nitrogen-rich industrial wastewater.     

In situ distribution and activity of nitrifying bacteria in freshwater sediment

Nitrification was investigated in a model freshwater sediment by the combined use of microsensors and fluorescence in situ hybridization with rRNA-targeted oligonucleotide probes. In situ nitrification activity was restricted mainly to the upper 2 mm of the sediment and coincided with the maximum abundance of nitrifying bacteria, i.e. 1.5 x 107 cells cm-3 for ammonia-oxidizing Beta-proteobacteria (AOB) and 8.6 x 107 cells cm-3 for Nitrospira-like nitrite-oxidizing bacteria (NOB). Cell numbers of AOB decreased more rapidly with depth than numbers of NOB. For the first time, Nitrospira-like bacteria could be quantified and correlated with in situ nitrite oxidation rates in a sediment. Estimated cell-specific nitrite oxidation rates were 1.2-2.7 fmol NO2- cell-1 h-1.