Effect of free ammonia and free nitrous acid concentration on the anabolic and catabolic processes of an enriched Nitrosomonas culture

The effects of free ammonia (FA; NH(3)) and free nitrous acid (FNA; HNO(2)) concentrations on the metabolisms of an enriched ammonia oxidizing bacteria (AOB) culture were investigated using a method allowing the decoupling of growth and energy generation processes. A lab-scale sequencing batch reactor (SBR) was operated for the enrichment of an AOB culture. Fluorescent in-situ hybridization (FISH) analysis showed that 82% of the bacterial population in the SBR bound to the NEU probe specifically designed for Nitrosomonas europaea. Batch tests were carried out to measure the oxygen and ammonium consumption rates by the culture at various FA and FNA levels, in the presence or absence of inorganic carbon (CO(2), HCO(3) (-), and CO(3) (2-)). It was revealed that FA of up to 16.0 mgNH(3)-N . L(-1), which was the highest concentration used in this study, did not have any inhibitory effect on either the catabolic or anabolic processes of the Nitrosomonas culture. In contrast, FNA inhibited both the growth and energy production capabilities of the Nitrosomonas culture. The inhibition on growth initiated at approximately 0.10 mgHNO(2)-N . L(-1), and the data suggested that the biosynthesis was completely stopped at an FNA concentration of 0.40 mgHNO(2)-N . L(-1). The inhibition on energy generation initiated at a slightly lower level but the Nitrosomonas culture was still oxidizing ammonia at half of the maximum rate at an FNA concentration of 0.50-0.63 mgHNO(2)-N . L(-1). The affinity constant of the Nitrosomonas culture with respect to ammonia was determined to be 0.36 mgNH(3)-N . L(-1), independent of the presence or absence of inorganic carbon.     

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.     

Shortcut biological nitrogen removal in hybrid biofilm/suspended growth reactors

A shortcut biological nitrogen removal (SBNR) process converts ammonium directly through nitrite to nitrogen gas, thus requiring less aeration and carbon. We evaluated a hybrid SBNR (HSBNR) reactor containing an anoxic tank followed by an aerobic tank and a settling tank. The aerobic tank was filled with polyvinyl alcohol sponge media (20%, v/v) to attach and retain ammonium oxidizers. Two configurations of the HSBNR reactor were tested for treating a wastewater with high strength ammonium and organic electron donor. The HSNBR reactors accumulated nitrite stably for 1.5 years and maintained a high free ammonia (FA) concentration (20–25 mg/L) and a low dissolved oxygen (DO) concentration (<1 mg/L) in the aerobic tank. Apparently, the biofilm carriers increased the solids retention time (SRT) for ammonium oxidizers, while high FA and low DO selected against nitrite oxidizers and promoted direct denitrification of nitrite in the aerobic tank. The significant amount of chemical oxygen demand (COD) was removed by shortcut denitrification of nitrite in the anoxic tank.     

Effect of pH and nitrite concentration on nitrite oxidation rate

The effect of pH and nitrite concentration on the activity of the nitrite oxidizing bacteria (NOB) in an activated sludge reactor has been determined by means of laboratory batch experiments based on respirometric techniques. The bacterial activity was measured at different pH and at different total nitrite concentrations (TNO?). The experimental results showed that the nitrite oxidation rate (NOR) depends on the TNO? concentration independently of the free nitrous acid (FNA) concentration, so FNA cannot be considered as the real substrate for NOB. NOB were strongly affected by low pH values (no activity was detected at pH 6.5) but no inhibition was observed at high pH values (activity was nearly the same for the pH range 7.5-9.95). A kinetic expression for nitrite oxidation process including switch functions to model the effect of TNO? concentration and pH inhibition is proposed. Substrate half saturation constant and pH inhibition constants have been obtained.     

Optimization of free ammonia concentration for nitrite accumulation in shortcut biological nitrogen removal process

A shortcut biological nitrogen removal (SBNR) utilizes the concept of a direct conversion of ammonium to nitrite and then to nitrogen gas. A successful SBNR requires accumulation of nitrite in the system and inhibition of the activity of nitrite oxidizers. A high concentration of free ammonia (FA) inhibits nitrite oxidizers, but unfortunately decreases the ammonium removal rate as well. Therefore, the optimal range of FA concentration is necessary not only to stabilize nitrite accumulation but also to achieve maximum ammonium removal. In order to derive such optimal FA concentrations, the specific substrate utilization rates of ammonium and nitrite oxidizers were measured. The optimal FA concentration range appeared to be 5–10 mg/L for the adapted sludge. The simulated results from the modified inhibition model expressed by FA and ammonium/nitrite concentrations were shown very similar to the experimental results.     

Activated sludge under free ammonia treatment using gel immobilization technology for long-term partial nitrification with different initial biomass

To achieve stable partial nitrification, activated sludge from a wastewater treatment plant using free ammonia (FA) inhibition was immobilized in a polyvinyl alcohol carrier. After FA treatment at 16.44 mg L⁻¹ for 1 day, due to the increased growth rate gap between ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), AOB enrichment and NOB inhibition were achieved within 12 days, with AOB and NOB accounting for 65.61 and 0.05%, respectively. Subsequently, with dissolved oxygen concentrations of 4−5 mg L⁻¹, pH of 7.6–7.8 and temperature of 25 ± 1 °C, the immobilized carrier made of activated sludge achieved more than 90% and more than 86% of nitrite accumulation rate at the influent ammonia concentration of 90−110 mg L⁻¹ and 35−50 mg L⁻¹, respectively. After 50 days operation, the NOB content was 0.10%, indicating the immobilized carrier provided favorable conditions for maintaining the low NOB content. Furthermore, due to the low NOB content in the inoculum and the oxygen-limited environment formed by the increase in the AOB numbers in the carrier, immobilized carrier with different initial biomass (1, 2.5 and 5%) can achieve stable partial nitrification.     

Identification of novel small molecule enhancers of protein production by cultured mammalian cells

Shortcut nitrogen removal, that is, removal via formation and reduction of nitrite rather than nitrate, has been observed in membrane-aerated biofilms (MABs), but the extent, the controlling factors, and the kinetics of nitrite formation in MABs are poorly understood. We used a special MAB reactor to systematically study the effects of the dissolved oxygen (DO) concentration at the membrane surface, which is the biofilm base, on nitrification rates, extent of shortcut nitrification, and microbial community structure. The focus was on anoxic bulk liquids, which is typical in MAB used for total nitrogen (TN) removal, although aerobic bulk liquids were also studied. Nitrifying MABs were grown on a hollow-fiber membrane exposed to 3 mg N/L ammonium. The MAB intra-membrane air pressure was varied to achieve different DO concentrations at the biofilm base, and the bulk liquid was anoxic or with 2 g m(-3) DO. With 2.2 and 3.5 g m(-3) DO at the biofilm base, and with an anoxic bulk-liquid, the ammonium fluxes were 0.75 and 1.0 g N m(-2) day(-1), respectively, and nitrite was the main oxidized nitrogen product. However, with membrane DO of 5.5 g m(-3), and either zero or 2 g m(-3) DO in the bulk, the ammonium flux was around 1.3 g N m(-2) day(-1), and nitrate flux increased significantly. For all experiments, the cell density of ammonium oxidizing bacteria (AOB) was relatively uniform throughout the biofilm, but the density of nitrite oxidizing bacteria (NOB) decreased with decreasing biofilm DO. Among NOB, Nitrobacter spp. were dominant in biofilm regions with 2 g m(-3) DO or greater, while Nitrospira spp. were dominant in regions with less than 2 g m(-3) DO. A biofilm model, including AOB, Nitrobacter spp., and Nitrospira spp., was developed and calibrated with the experimental results. The model predicted the greatest extent of nitrite formation (95%) and the lowest ammonium oxidation flux (0.91 g N m(-2) day(-1)) when the membrane DO was 2 g m(-3) and the bulk liquid was anoxic. Conversely, the model predicted the lowest extent of nitrite formation (40%) and the highest ammonium oxidation flux (1.5 g N m(-2) day(-1)) when the membrane-DO and bulk-DO were 8 g m(-3) and 2 g m(-3), respectively. The estimated kinetic parameters for Nitrospira spp., revealed a high affinity for nitrite and oxygen. This explains the dominance of Nitrospira spp. over Nitrobacter spp. in regions with low nitrite and oxygen concentrations. Our results suggest that shortcut nitrification can effectively be controlled by manipulating the DO at the membrane surface. A tradeoff is made between increased nitrite accumulation at lower DO, and higher nitrification rates at higher DO.     

Relationship between respirometric activity and community of entrapped nitrifying bacteria: Implications for partial nitrification

Activated sludge obtained from two municipal wastewater treatment facilities (WWTF) was used as seed sludge for enriched nitrifiers, which were later entrapped in polyvinyl alcohol. Seed sludge from one WWTF was acclimated to high ammonia level (1813 mg NH₃-N l^?1) through the return of sludge digester supernatant back to primary clarifier while seed sludge from the other WWTF was un-acclimated. To elucidate on how to control partial nitrification by entrapped cells, which could be different from suspended cells, kinetics of entrapped enriched nitrifiers were studied using a respirometric assay. The community of nitrifiers within the entrapment matrix, which was observed by fluorescence in situ hybridization (FISH) technique, was related to the nitritation and nitratation kinetics based on oxygen uptake rate. Maximum oxygen uptake rate, and substrate and oxygen affinities of both ammonia oxidizing bacteria (AOB) for nitritation and nitrite oxidizing bacteria (NOB) for nitratation in entrapped cells were lower than those of corresponding suspended cells. Under dissolved oxygen (DO) limiting conditions, nitratation was more suppressed than nitritation for suspended cells, while for the entrapped cells, the results were the contrary. A free ammonia (FA) inhibition affected only the un-acclimated sludge. Either FA inhibition or DO limitation might not be a sole effective control parameter to achieve partial nitrification by entrapped cells. FISH results revealed that Nitrosomonas europaea was the dominant AOB while Nitrobacter species was the dominant NOB in all cases. Heterotrophs were also present in the entrapment at 22.8 ± 18.6% and 41.5 ± 4.3% of total bacteria for acclimated and un-acclimated originated sludge. The availability of substrate and oxygen governed the distributions of AOB, NOB and heterotrophs within the entrapment and nitritation kinetics of entrapped nitrifiers.     

好氧和缺氧条件下游离亚硝酸对氨氧化菌和亚硝酸盐氧化菌的选择性抑制

【背景】稳定短程硝化是实现城市污水厌氧氨氧化技术的瓶颈,目前国内外关于游离亚硝酸(Free nitrous acid,FNA)对硝化菌活性的影响大多是在曝气条件下进行研究,鲜有关于缺氧条件下FNA对硝化菌活性影响的报道。【目的】探究好氧和缺氧下FNA对氨氧化菌(Ammonia oxidizing bacteria,AOB)和亚硝酸盐氧化菌(Nitrite oxidizing bacteria,NOB:Nitrospira和Nitrobacter)活性的抑制影响。【方法】采用序批式反应器(Sequencing batch reactor,SBR),基于混合液悬浮固体浓度(Mixed liquid suspended solids,MLSS)为8 300 mg/L的全程硝化污泥条件,通过批次试验分别考察好氧和缺氧下FNA(初始浓度为1.16 mg/L)处理48 h后,AOB和NOB活性的变化情况。【结果】好氧FNA处理活性污泥48 h后,FNA浓度维持在1.16-1.17 mg/L,游离氨(Free ammonia,FA)浓度小于0.017 mg/L,AOB、Nitrospira、Nitrobacter丰度均未发生明显变化;过曝气至99 h时,与空白组相比,比氨氮氧化速率(r~+_(NH4-N))、比亚硝酸盐氮氧化速率(r_(NO2-N))均出现小幅下降,分别由3.5、4.828 mg N/(g VSS·h)降至3.3、4.668 mg N/(g VSS·h),且亚硝酸盐氮累积率(Nitrite accumulation rate,NAR)始终低于33.2%。缺氧FNA处理活性污泥48 h后,FNA浓度维持在0.64-1.16 mg/L,FA浓度低于0.039 mg/L,AOB丰度变化较小,而Nitrospira、Nitrobacter丰度均明显下降,分别由3.002 9×10~9、4.245×10~8 copies/g VSS降至1.666 5×10~8、5.163 8×10~7 copies/g VSS;过曝气至99 h时,与空白组相比,r~+_(NH4-N)值下降幅度较小,而r_(NO2-N)值明显降低,由4.828 mg N/(g VSS·h)降至0.007 mg N/(g VSS·h),且在过曝气0-292 h内,NAR均大于94%。【结论】好氧FNA处理活性污泥48 h后对AOB和NOB无明显抑制作用,但缺氧FNA处理活性污泥48 h后对AOB具有轻微抑制作用,而对NOB具有强烈的抑制作用,可以实现稳定的短程硝化。     

The effect of pH on the efficiency of an SBR processing piggery wastewater

To treat piggery wastewater efficiently, the hydrolysis of urea (mainly derived from swine urine) in piggery wastewater with the change of sewage pH must be considered. Using activated sludge, piggery wastewater was treated in a sequencing batch reactor (SBR), and the effects of influent pH on SBR processing efficiency, sludge settle ability, and sludge activity were investigated. The results showed that a high influent pH value contributed to the improvement of the removal rate of ammonia nitrogen and reduction of the chemical oxygen demand (COD). When the influent pH was between 9.0 and 9.5, the removal rate of ammonia nitrogen was higher than 90%, and the reduction of COD from its original value was 80%. The influent pH had a greater influence on sludge concentration and sludge activity. When the influent pH increased from 7.0 to 9.5, the sludge concentration increased from 2,350 to 3,947 mg/L in the reactor, and the activities of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) first increased and then decreased. When the influent pH was 9.0 and 8.0, the maximum values (0.48 g O₂/(g MLSS/day) and 0.080 g O₂/(g MLSS/day)) were reached, and the sludge settling ratio was nearly steady between 20 and 35% in each reactor.     

Modeling kinetics of ammonium oxidation and nitrite oxidation under simultaneous inhibition by free ammonia and free nitrous acid

Inhibition of ammonium oxidation and nitrite oxidation by free ammonia (FA) and free nitrous acid (FNA) was studied using three different sludges. An uncompetitive inhibition model fit the experimental data well when the reactions were under FA inhibition, whereas a noncompetitive model fit well under FNA inhibition. The estimates of the inhibition constant (K_I) of nitrite oxidation were 46 μM for FA and 1.7–6.8 μM for FNA, each of which was significantly smaller than that of ammonium oxidation, which were 290–1600 μM for FA and 12 μM for FNA. The much smaller values of K_I for nitrite oxidation reflected the susceptibility of that reaction to inhibition by FA and FNA, which could lead to accumulation of nitrite during nitrification. A kinetic model for simultaneous inhibition by FA and FNA was derived. The model predicted that nitrite oxidation should be affected more seriously than ammonium oxidation by the simultaneous inhibition, which would accelerate the accumulation of nitrite in a strong nitrogenous wastewater treatment. It also indicated that a complete removal of ammonia could be achieved with high accumulation of nitrite in a sequencing batch reactor, which is impossible in a continuous-flow reactor.     

Nitrite reduction by a mixed culture under conditions relevant to shortcut biological nitrogen removal

Dissimilative reduction of nitrite by nitrite-acclimated cellswas investigated in a batch reactor under various environmental conditions that can beencountered in shortcut biological nitrogen removal (SBNR: ammonia to nitrite andnitrite to nitrogen gas). The maximum specific nitrite reduction rate was as much as 4.3 times faster than the rate of nitrate reduction when individually tested, but the reaction was inhibited in the presence of nitrate when the initial nitrate concentration was greater than approximately 25 mg-N/l or the initialNO ₃ ^- N/NO ₂ ^- N ratio was larger than 0.5. Nitrite reduction was also inhibited by nitrite itself when theconcentration was higher than that to which the cells had been acclimated. Therefore, it was desirable to avoid excessively high nitrite and nitrate concentrations in a denitrification reactor. Nitrite reduction, however, was not affected by an alkaline pH (in the range of 7–9) or a high concentration of FA (in the range of 16–39 mg/l), which can be common in SBNR processes. The chemical oxygen demand (COD) requirement for nitrite reduction was approximately 22–38% lower than that for nitrate reduction, demonstrating that the SBNR process can be economical. The specific consumption,measured as the ratio of COD consumed to nitrogen removed, was affected by the availability of COD and the physiological state of the cells. The ratio increased when the cells grew rapidly and were storing carbon and electrons.     

Inhibitory effects of free ammonia on Anammox bacteria

Anammox bacteria can effectively treat high ammonia and nitrite concentrations under anoxic environments. However, the presence of high ammonia and nitrite concentrations may cause free ammonia and nitrous acid inhibition at high pH and temperature environments. In this study, the inhibitory effect of free ammonia on Anammox bacteria was investigated in a lab-scale upflow fixed-bed reactor with Kaldnes biofilm carriers. Results of continuous operation showed that inhibition was not observed in the Anammox reactor when the free ammonia concentration gradually increased up to 150?mg/L. However, Anammox activity suddenly dropped to 10 % when the free ammonia concentration reached to 190?mg/L. Nevertheless, high influent ammonia and nitrite concentrations up to 1,500 and 500?mg/L, respectively, did not noticeably inhibit the Anammox activity. Gradually decreasing Anammox activity was also supported by fluorescent in situ hybridization (FISH) analysis. FISH and 16S rRNA gene analysis results revealed that main Anammox organisms were phylogenetically related to Candidatus Kuenenia stuttgartiensis, Candidatus Jettenia asiatica and Candidatus Brocadia anammoxidans.     

Modelling of inhibition of nitrite oxidation in biological nitritation processes by free ammonia

To understand nitrite build-up in the nitritation process, the inhibition kinetics of free ammonia (FA) on nitrite oxidation were investigated. FA inhibition on nitrite oxidation was the key factor of nitrite build-up and its type was mixed inhibition. Therefore, the mixed inhibition model should be adapted to a Michaelis–Menten equation to set up a process rate equation for nitrite oxidation in the nitritation process.     

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.     

Sequentially aerated membrane biofilm reactors for autotrophic nitrogen removal: microbial community composition and dynamics

Membrane‐aerated biofilm reactors performing autotrophic nitrogen removal can be successfully applied to treat concentrated nitrogen streams. However, their process performance is seriously hampered by the growth of nitrite oxidizing bacteria (NOB). In this work we document how sequential aeration can bring the rapid and long‐term suppression of NOB and the onset of the activity of anaerobic ammonium oxidizing bacteria (AnAOB). Real‐time quantitative polymerase chain reaction analyses confirmed that such shift in performance was mirrored by a change in population densities, with a very drastic reduction of the NOB Nitrospira and Nitrobacter and a 10‐fold increase in AnAOB numbers. The study of biofilm sections with relevant 16S rRNA fluorescent probes revealed strongly stratified biofilm structures fostering aerobic ammonium oxidizing bacteria (AOB) in biofilm areas close to the membrane surface (rich in oxygen) and AnAOB in regions neighbouring the liquid phase. Both communities were separated by a transition region potentially populated by denitrifying heterotrophic bacteria. AOB and AnAOB bacterial groups were more abundant and diverse than NOB, and dominated by the r‐strategists Nitrosomonas europaea and Ca. Brocadia anammoxidans, respectively. Taken together, the present work presents tools to better engineer, monitor and control the microbial communities that support robust, sustainable and efficient nitrogen removal.     

Achieving the nitrite pathway using aeration phase length control and step-feed in an SBR removing nutrients from abattoir wastewater

Aeration phase length control and step-feed of wastewater are used to achieve nitrogen removal from wastewater via nitrite in sequencing batch reactors (SBR). Aeration is switched off as soon as ammonia oxidation is completed, which is followed by the addition of a fraction of the wastewater that the SBR receives over a cycle to facilitate denitrification. The end-point of ammonia oxidation is detected from the on-line measured pH and oxygen uptake rate (OUR). The method was implemented in an SBR achieving biological nitrogen and phosphorus removal from anaerobically pre-treated abattoir wastewater. The degree of nitrite accumulation during the aeration period was monitored along with the variation in the nitrite oxidizing bacteria (NOB) population using fluorescence in situ hybridization (FISH) techniques. It is demonstrated that the nitrite pathway could be repeatedly and reliably achieved, which significantly reduced the carbon requirement for nutrient removal. Model-based studies show that the establishment of the nitrite pathway was primarily the result of a gradual reduction of the amount of nitrite that is available to provide energy for the growth of NOB, eventually leading to the elimination of NOB from the system.     

短程硝化启动运行中功能菌群变化研究

【目的】短程硝化-厌氧氨氧化是可实现的最短生物脱氮工艺,短程硝化是实现该工艺的重要环节和必要条件。【方法】采用序批式反应器(SBR)来实现短程硝化过程的启动和稳定运行,并对该过程中的相关功能菌群变化进行检测分析。【结果】通过控制低DO浓度(<1 mg/L)和逐步提高氨氮进水负荷,可抑制氨氧化细菌(NOB)菌群增殖并促进亚硝酸氧化菌(AOB)菌群规模显著扩大,实现短程硝化过程的启动和稳定运行。在氨氮进水负荷为0.055 kg/(m3.d)时,平均氨氮去除容积负荷和污泥负荷可达到0.043kg/(m3.d)和0.16 kg/(kg.d),平均亚硝酸盐积累率可达到83.4%。在短程硝化启动和稳定运行过程中,NOB菌群密度从2.0×105CFU/mL降至1.5×104CFU/mL,相对丰度从5.51%降至2.14%;AOB菌群密度从4.5×104CFU/mL增加至1.5×107CFU/mL,相对丰度从0.18%增加至7.25%。【结论】AOB菌群规模的扩大是实现短程硝化和氨氮去除能力提高的主要原因,同时较高的进水氨氮浓度和负荷也会造成亚硝化活性的抑制。     

Partial nitrification to nitrite using low dissolved oxygen concentration as the main selection factor

Partial nitrification to nitrite (nitritation) can be achieved in a continuous process without sludge retention by wash out of nitrite oxidising bacteria (NOB) while retaining ammonia oxidising bacteria (AOB), at elevated temperatures (the SHARON process) and, as demonstrated in this paper, also at low dissolved oxygen (DO) concentrations. Enriched AOB was attained at a low DO concentration (0.4 mg l⁻¹) and a dilution rate of 0.42 day⁻¹ in a continuous process. A higher oxygen affinity of AOB compared to NOB seemed critical to achieving this. This was verified by determining the oxygen half saturation constant, K _o, with similar oxygen mass transfer resistances for enriched AOB and NOB as 0.033 ± 0.003 mg l⁻¹ and 0.43 ± 0.08 mg l⁻¹, respectively. However, the extent of nitritation attained was found to be highly sensitive to process upsets.     

Nitrification in hybrid bioreactors treating simulated domestic wastewater

Aim

To provide deeper insights into nitrification process within aerobic bioreactors containing supplemental physical support media (hybrid bioreactors).

Methods and Results

Three bench‐scale hybrid bioreactors with different media size and one control bioreactor were operated to assess how biofilm integrity influences microbial community conditions and bioreactor performance. The systems were operated initially at a 5‐day hydraulic retention time (HRT), and all reactors displayed efficient nitrification and chemical oxygen demand (COD) removal (>95%). However, when HRT was reduced to 2·5 days, COD removal rates remained high, but nitrification efficiencies declined in all reactors after 19 days. To explain reduced performance, nitrifying bacterial communities (ammonia‐oxidizing bacteria, AOB; nitrite‐oxidizing bacteria, NOB) were examined in the liquid phase and also on the beads using qPCR, FISH and DGGE. Overall, the presence of the beads in a reactor promoted bacterial abundances and diversity, but as bead size was increased, biofilms with active coupled AOB–NOB activity were less apparent, resulting in incomplete nitrification.

Conclusions

Hybrid bioreactors have potential to sustain effective nitrification at low HRTs, but support media size and configuration type must be optimized to ensure coupled AOB and NOB activity in nitrification.

Significance and Impact of the Study

This study shows that AOB and NOB coupling must be accomplished to minimize nitrification failure.