Activity Of Ammonia-oxidizing Bacteria Research Articles

Successful start-up of pilot-scale single-stage ANAMMOX reactor through cultivation of ammonia oxidizing and ANAMMOX bacteria

The lack of seed sludges for Ammonium Oxidizing Bacteria (AOB) and slow-growing ANaerobic AMMonium OXidation (ANAMMOX) bacteria is one of the major problem for large-scale application. In this study, 24m3 of single-stage SBR (Sequencing Batch Reactor) was operated to remove nitrogen from reject water using AOB and ANAMMOX bacteria cultivated from activated sludge in the field. The ANAMMOX activity was found after 44 days of cultivation in the ANAMMOX cultivation reactor, and then 0.66 kg N/m3/d of the nitrogen removal rate was achieved at 0.78 kg N/m3/d of the nitrogen loading rate at 153 days of cultivation. The AOB cultivation reactor showed 0.2 kg N/m3/d of nitrite production rate at 0.4 kg N/m3/d of nitrogen loading rate after 36 days of operation. The cultivated ANAMMOX bacteria and AOB was mixed into the single-stage SBR. The feed distribution was applied to remove total nitrogen stably in the single-stage SBR. The nitrogen removal rate in the single-stage SBR was gradually enhanced with an increase of specific activities of both AOB and ANAMMOX bacteria by showing 0.49 kg N/m3/d of the nitrogen removal rate at 0.56 kg N/m3/d of the nitrogen loading rate at 54 days of operation.

Startup strategy for nitrogen removal via nitrite in a BAF system.

A biological aerated filter (BAF) pilot plant consisting of two reactors (aerobic and anoxic one) was used to determine a strategy to remove nitrogen via nitrite. RNA/DNA analysis was performed to assess microbial activity and support chemical results. In less than 13 days the pilot plant was able to remove COD and suspended solids. Nitrogen removal via nitrite pathway could not be observed until day 130 when the empty bed contact time (EBCT) was set at 0.71h. Nitrite was detected in the aerated BAF effluent but never nitrate. qPCR of amoA gene from RNA and DNA extracts of the aerobic biofilm confirmed that ammonia oxidizing bacteria (AOB) were present from the beginning of the operation but not active. AOB activity increased with time, reaching stability from operational day 124. The combination of both, low EBCT together with high OLR, has been demonstrated to be a feasible strategy to startup a BAF to achieve nitrogen removal via nitrite.

Stable and efficient partial nitritation granular sludge reactor treating domestic sewage at low temperature

The success of combined partial nitritation (PN) and anammox process treating low-strength domestic wastewater depends on achieving a stable and efficient PN. In this study, desirable PN for domestic sewage with low temperature of 11.8–16.9 °C was achieved in a granular sludge reactor operated in anaerobic/aerobic (A/O) mode. Average nitrite accumulation ratio of 97.3% was obtained with an effluent nitrite/ammonium ratio of 1.2 for influent ammonium of 39.3–78.7 mg·L−1. Quantitative microbial analysis and activity batch test showed that nitrite oxidizing bacteria (NOB) were effectively suppressed, while ammonium oxidizing bacteria (AOB) were dominant. For the efficient suppression of NOB, A/O mode, aerobic phosphorus uptake and granular sludge could play important roles. Furthermore, high AOB activity was obtained with an average ammonium oxidation rate of 11.6 mg N·L−1·h−1, which could be due to the abundant psychrotolerant microorganisms, increased content of extracellular polymeric substances and relatively high dissolved oxygen condition of the reactor.

Nitrous oxide emissions from biofilm processes for wastewater treatment.

This paper discusses the microbial basis and the latest research on nitrous oxide (N2O) emissions from biofilms processes for wastewater treatment. Conditions that generally promote N2O formation in biofilms include (1) low DO values, or spatial DO transitions from high to low within the biofilm; (2) DO fluctuations within biofilm due to varying bulk DO concentrations or varying substrate concentrations; (3) conditions with high reaction rates, which lead to greater formation of intermediates, e.g., hydroxylamine (NH2OH) and nitrite (NO2-), that promote N2O formation; and (4) electron donor limitation for denitrification. Formation of N2O directly results from the activities of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and heterotrophic denitrifying bacteria. More research is needed on the roles of AOA, comammox, and specialized denitrifying microorganisms. In nitrifying biofilms, higher bulk ammonia (NH3) concentrations, higher nitrite (NO2-) concentrations, lower dissolved oxygen (DO), and greater biofilm thicknesses result in higher N2O emissions. In denitrifying biofilms, N2O accumulates at low levels as an intermediate and at higher levels at the oxic/anoxic transition regions of the biofilms and where COD becomes limiting. N2O formed in the outer regions can be consumed in the inner regions if COD penetrates sufficiently. In membrane-aerated biofilms, where nitrification takes place in the inner, aerobic biofilm region, the exterior anoxic biofilm can serve as a N2O sink. Reactors that include variable aeration or air scouring, such as denitrifying filters, trickling filters, or rotating biological contactors (RBCs), can form peaks of N2O emissions during or following a scouring or aeration event. N2O emissions from biofilm processes depend on the microbial composition, biofilm thickness, substrate concentrations and variability, and reactor type and operation. Given the complexity and difficulty in quantifying many of these factors, it may be difficult to accurately predict emissions for full-scale treatment plants. However, a better understanding of the mechanisms and the impacts of process configurations can help minimize N2O emission from biofilm processes for wastewater treatment.

Inhibitory Kinetics of Free Ammonia (FA) on Ammonia-oxidizing Bacteria (AOB)

In this study, a sequencing batch reactor (SBR) was operated to investigate the inhibitory kinetics of free ammonia (FA) on ammonia-oxidizing bacteria (AOB). At the beginning of the experiment, FA concentrations in influent were altered to achieve stable short-cut nitrification and enrich AOB. Nitritation sludge was then employed to study variations in the specific nitrite production rate (SNiPR) during the ammonia oxidation process of batch tests. Furthermore, a kinetic model of FA inhibition on AOB activity was fitted for statistical analysis. Results showed that SNiPR increased rapidly with increase in FA concentration (0.7 mg·L-1 ≤ FA ≤ 50.2 mg·L-1) but decreased with an increase in FA concentration (FA ≥ 50.2 mg·L-1). SNiPR was maintained at 0 g·(g·d)-1 when FA concentration was higher than 687.1 mg·L-1, implying that AOB activity was completely inhibited. Statistical analysis showed that, compared to Haldane, Edwards-1#, Edwards-2#, and Luong inhibition kinetics models, the Aiba model was the most suitable for describing the inhibitory effect of FA on AOB activity. The statistical constants, i.e., residual square sum (RSS) correlation coefficient (R2), F value of the fitting equation, and confidence degree (P) were 0.005, 0.932, 181.7, and 1.06×10-9, respectively. The dynamic constant values, i.e., maximum specific nitrite production rate (rmax), half saturation constant (KS), and inhibition constant (KI) were 0.37 g·(g·d)-1, 11.78 mg·L-1, and 153.74 mg·L-1, respectively.

An innovative U-shaped sludge bed anammox process for nitrogen removal

In this study, we proposed an innovative U-shaped sludge bed reactor which could be a cost effective and simplified approach for the operation of an anammox reactor. The performance for nitrogen removal and the composition of bacterial communities were investigated for about 500 days of operation. The nitrogen removal rate could be approximately 85% when the total nitrogen loading rate was about 0.54 kg N/m3/d. The 16S rRNA gene pyrosequencing analysis of the bacterial community determined that Betaproteobacteria (class level) of the ammonia-oxidizing bacteria (AOB) community, Nitrospira (genus level) of the nitrite-oxidizing bacteria (NOB) community, and Brocadia (genus level) of the anammox bacteria community simultaneously coexisted in the reactor sludge. These results demonstrated that simultaneous growth and coexistence of AOB, NOB, and anammox were capable within the reactor. Furthermore, a mathematical modeling system was developed to simulate the nitrification and anammox processes. The model simulation showed that the oxygen was rapidly depleted and that led to a drop in the activity of AOB and NOB, then the growth of anammox bacteria started under anaerobic conditions.

High contribution of ammonia-oxidizing archaea (AOA) to ammonia oxidation related to a potential active AOA species in various arable land soils

Ammonia oxidation is the limiting step in soil nitrification and critical in the global nitrogen cycle. The discovery of ammonia-oxidizing archaea (AOA) has improved our knowledge of microbial mechanisms for ammonia oxidation in complex soil environments. However, the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to ammonia oxidation remain unclear. In this study, through large geographical scale sampling in China, totally nine samples representing various types of arable land soils were selected for analyzing the ammonia oxidation activity. The AOA and AOB activities were separately determined by using the dicyandiamide and 1-octyne inhibition method. High-throughput pyrosequencing and DNA stable-isotope probing (DNA-SIP) analysis were applied to investigate the distribution and activity of Candidatus Nitrosocosmicus franklandus in the arable land soils. In this study, AOA abundance (3.2 × 107–3.4 × 109 copies g−1) and activity (0.01–1.33 mg N kg−1 dry soil day−1) were evaluated for nine selected arable land soils and accounted for 4–100% of ammonia oxidation. By separately determining AOA and AOB rates, we observed that archaeal ammonia oxidation dominated the ammonia oxidation process in six soils, revealing a considerable contribution of AOA in ammonia oxidation in arable land soils. Based on high-throughput pyrosequencing analysis, the AOA species Ca. N. franklandus with relatively low abundance (0.6–13.5% in AOA) was ubiquitously distributed in all the tested samples. Moreover, according to the DNA-SIP analysis for Urumqi sample, the high activity and efficiency of Ca. N. franklandus in using CO2 suggests that this species plays an important role in archaeal ammonia oxidation in arable land soils. Through determining the AOA activity and analyzing the potential predominant functional AOA species, this study greatly improves our understanding of ammonia oxidation in arable land soils.

The relative contribution of nitrifiers to autotrophic nitrification across a pH-gradient in a vegetable cropped soil

Microbial nitrification plays an important role in nitrogen cycling in ecosystems. Nitrification is performed by ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) including complete ammonia oxidizers. However, the relative importance of nitrifiers in autotrophic nitrification in relation to soil pH is still unclear. Combining DNA-based stable isotope probing (SIP) and molecular biological techniques, we investigated the abundance, structure, and activity of AOA, AOB, and NOB along a pH-gradient (3.97–7.04) in a vegetable cropped soil. We found that AOA abundance outnumbered AOB abundance and had a significantly negative relationship with soil pH. The abundances of NOB Nitrospira 16S rRNA, nxrB gene, and Nitrobacter nxrA gene were affected by soil pH. Incubation of soil with 13CO2 and DNA-SIP analysis demonstrated that significant 13CO2 assimilation by AOA rather than by AOB occurred in the acidic soils, whereas the labeled 13C level of AOA was much less in the neutral soil than in the acidic soils. There was no evidence of 13CO2 assimilation by NOB except for Nitrobacter with NxrB gene at pH 3.97. Phylogenetic analysis of AOA amoA gene in the 13C- and 12C-labeled treatments showed that the active AOA mainly belonged to Nitrososphaera in the acidic soils. These results suggested that the main performer of nitrification was AOA in the acidic soils, but both AOA and AOB participated in nitrification in the neutral soil with low nitrification activity. NOB Nitrospira and Nitrobacter did not grow in the soils with pH 4.82–7.04 and other populations of NOB were probably involved in nitrite oxidation in the vegetable cropped soil.

Achieving mainstream nitrogen removal via the nitrite pathway from real municipal wastewater using intermittent ultrasonic treatment

Achieving mainstream nitrogen removal via the nitrite pathway (NH4+ → NO2− → N2) is highly beneficial for energy neutral/positive wastewater treatment. Our previous batch assays revealed that ultrasonic treatment can suppress nitrite-oxidizing bacteria (NOB) while enhancing the activity of ammonia-oxidizing bacteria (AOB). Based on this concept, this study investigated the feasibility of applying ultrasonication to achieve the nitrite pathway in mainstream wastewater treatment. Two lab-scale sequencing batch reactors were set-up in parallel and fed with real municipal wastewater. With 100% of the sludge treated every 12 h at a treatment energy input of 0.066 kJ per mg mixed liquor suspended solids, the nitrite pathway was rapidly (within two weeks) established in the experimental reactor with stable effluent nitrite accumulation ratio (NO2−/(NO2− + NO3−)) of above 80% and significantly decreased NOB population. In comparison, the control reactor always possessed the conventional nitrification and denitrification pathway. Economic analysis indicated that energy consumption is too high for practical applications. However, this technology may be used in conjunction with other technologies, whereby this ultrasonic treatment can be used infrequently (e.g. once every few months) when the nitrite pathway becomes unstable.

The influence of dissolved oxygen on partial nitritation/anammox performance and microbial community of the 200,000 m3/d activated sludge process at the Changi water reclamation plant (2011 to 2016).

Mainstream partial nitritation/anammox (PN/A), coupled with excess biological phosphorus removal, in a 200,000 m3/d step-feed activated sludge process (Train 2) in the Changi Water Reclamation Plant (WRP), Singapore, has been studied and reported. This paper presents an overview of process performance and the microbial community during the period from 2011 to 2016. The site data showed that, along with the reduction of dissolved oxygen (DO) from 1.7 to 1.0 mg O2/L in the aeration zones, the concentrations of ammonium and nitrate of the final effluent increased, while nitrite decreased, resulting in an increase of 2.4 mg N/L of total inorganic nitrogen. Autotrophic nitrogen removal was higher than heterotrophic biological nitrogen removal under higher DO concentration conditions, but decreased under low DO operating condition. These macro-scale changes were caused by shifts of the nitrogen-converting microbial community. The ammonia oxidizing bacteria (AOB) population abundance was reduced by 30 times, while the nitrite oxidizing bacteria (NOB) population abundance and specific activity increased significantly with a shift of dominant genus from Nitrobacter to Nitrospira. The ratio of AOB and NOB specific activities were reduced from 12.8 to 1.6, and the ex situ nitrite accumulation ratio reduced from 76% to 29%. Changes in the microbial community and overall process performance illustrated that, compared to the excellent NOB suppression under high DO conditions, NOB were more active after the DO concentration reduction despite still being partly suppressed. This case study demonstrated, for the first time, the influence of DO reduction on the nitrogen conversion microbial community and PN/A process performance for a suspended growth system. Its relevance to biofilm and hybrid PN/A processes is also discussed.

Performance and recovery of a completely separated partial nitritation and anammox process treating phenol-containing wastewater.

Anammox process is considered as a promising technology for removing total nitrogen from low-strength ammonium and phenol-containing wastewater. However, it is still a challenge for the anammox process to treat high-strength ammonium and phenol-containing wastewater. A completely separated partial nitritation and anammox (CSPN/A) process was developed to remove total nitrogen from high-strength phenol-containing wastewater. About 92% of COD, 100% of phenol, and 82.4% of total nitrogen were successfully removed at a NH4+-N concentration of 200mgL-1 with a phenol/NH4+-N mass ratio of 0.5 in the CSPN/A process. Furthermore, a shock loading of 300mg phenol L-1 with a phenol/NH4+-N mass ratio of 1.5 led to a complete failure of partial nitritation, but the performance was rapidly recovered by the increase of NH4+-N concentration. Although the activities of ammonium-oxidizing bacteria and anammox bacteria were severely inhibited at a phenol/NH4+-N mass ratio of 1.5, the enrichment of efficient phenol degraders in the CSPN stage could strengthen the performance robustness of partial nitritation and anammox process. Therefore, this study presented a new insight on the feasibility of the anammox process for treating high-strength ammonium and phenol-containing wastewater.

Ammonia-oxidizing bacteria are the primary N2 O producers in an ammonia-oxidizing archaea dominated alkaline agricultural soil.

Most agricultural N2 O emissions are a consequence of microbial transformations of nitrogen (N) fertilizer, and mitigating increases in N2 O emission will depend on identifying microbial sources and variables influencing their activities. Here, using controlled microcosm and field studies, we found that synthetic N addition in any tested amount stimulated the production of N2 O from ammonia-oxidizing bacteria (AOB), but not archaea (AOA), from a bioenergy crop soil. The activities of these two populations were differentiated by N treatments, with abundance and activity of AOB increasing as nitrate and N2 O production increased. Moreover, as N2 O production increased, the isotopic composition of N2 O was consistent with an AOB source. Relative N2 O contributions by both populations were quantified using selective inhibitors and varying N availability. Complementary field analyses confirmed a positive correlation between N2 O flux and AOB abundance with N application. Collectively, our data indicate that AOB are the major N2 O producers, even with low N addition, and that better-metered N application, complemented by selective inhibitors, could reduce projected N2 O emissions from agricultural soils.

Different Recovery Processes of Soil Ammonia Oxidizers from Flooding Disturbance

Understanding how microorganisms respond to environmental disturbance is one of the key focuses in microbial ecology. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are responsible for ammonia oxidation which is a crucial step in the nitrogen cycle. Although the physiology, distribution, and activity of AOA and AOB in soil have been extensively investigated, their recovery from a natural disturbance remains largely unknown. To assess the recovery capacities, including resistance and resilience, of AOA and AOB, soil samples were taken from a reservoir riparian zone which experienced periodically water flooding. The samples were classified into three groups (flooding, recovery, and control) for a high-throughput sequencing and quantitative PCR analysis. We used a relative quantitative index of both the resistance (RS) and resilience (RL) to assess the variation of gene abundance, alpha-diversity, and community composition. The AOA generally demonstrated a better recovery capability after the flooding disturbance compared to AOB. In particular, AOA were more resilient after the flooding disturbance. Taxa within the AOA and AOB showed different RS and RL values, with the most abundant taxa showing in general the highest RS indices. Soil NH4+ and Fe2+/Fe3+ were the main variables controlling the key taxa of AOA and AOB and probably influenced the resistance and resilience properties of AOA and AOB communities. The distinct mechanisms of AOA and AOB in maintaining community stability against the flooding disturbance might be linked to the different life-history strategies: the AOA community was more likely to represent r-strategists in contrast to the AOB community following a K-life strategy. Our results indicated that the AOA may play a vital role in ammonia oxidation in a fluctuating habitat and contribute to the stability of riparian ecosystem.

Effect of Potassium Chlorate on the Treatment of Domestic Sewage by Achieving Shortcut Nitrification in a Constructed Rapid Infiltration System

A constructed rapid infiltration (CRI) system is a new type of sewage biofilm treatment technology, but due to its anaerobic zone it lacks the carbon sources and the conditions for nitrate retention, and its nitrogen removal performance is very poor. However, a shortcut nitrification–denitrification process presents distinctive advantages, as it saves oxygen, requires less organic matter, and requires less time for denitrification compared to conventional nitrogen removal methods. Thus, if the shortcut nitrification–denitrification process could be applied to the CRI system properly, a simpler, more economic, and efficient nitrogen removal method will be obtained. However, as its reaction process shows that the first and the most important step of achieving shortcut nitrification–denitrification is to achieve shortcut nitrification, in this study we explored the feasibility to achieve shortcut nitrification, which produces nitrite as the dominant nitrogen species in effluent, by the addition of potassium chlorate (KClO3) to the influent. In an experimental CRI test system, the effects on nitrogen removal, nitrate inhibition, and nitrite accumulation were studied, and the advantages of achieving a shortcut nitrification–denitrification process were also analysed. The results showed that shortcut nitrification was successfully achieved and maintained in a CRI system by adding 5 mM KClO3 to the influent at a constant pH of 8.4. Under these conditions, the nitrite accumulation percentage was increased, while a lower concentration of 3 mM KClO3 had no obvious effect. The addition of 5mM KClO3 in influent presumably inhibited the activity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), but inhibition of nitrite-oxidizing bacteria (NOB) was so strong that it resulted in a maximum nitrite accumulation percentage of up to over 80%. As a result, nitrite became the dominant nitrogen product in the effluent. Moreover, if the shortcut denitrification process will be achieved in the subsequent research, it could save 60.27 mg CH3OH per litre of sewage in the CRI system compared with the full denitrification process.

Potential dual effect of nitrification inhibitor 3,4-dimethylpyrazole phosphate on nitrifier denitrification in the mitigation of peak N2O emission events in North China Plain cropping systems

The winter wheat–summer maize rotation system in the North China Plain is a major source of nitrous oxide (N2O) emissions due to high nitrogen (N) fertilizer and irrigation water inputs. However, a detailed understanding of the contribution of N2O production sources is still limited because of the complexity of N2O generation in soils and a lack of relevant field studies. Moreover, the efficiency and mechanisms of N2O mitigation approaches in this area, i.e. the use of nitrification inhibitors, remains poorly understood. To elucidate the N2O production pathways from this rotation system and to evaluate the effect of a widely used nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on mitigating N2O emissions, we monitored N2O fluxes and analyzed isotopomer ratios of soil-emitted N2O during one rotation year. Results indicate that the application of DMPP significantly reduced N2O emissions by 67% in the winter wheat season and 47% in the summer maize season. Isotopomer analysis revealed that in the N-fertilized treatment, nitrification and/or fungal denitrification accounted for up to 36% of the N2O emission peaks observed after fertilization and irrigation events, whereas the nitrifier denitrification pathway was likely to be the major source, accounting for the remaining N2O emissions. The high effectiveness of the nitrification inhibitor on mitigating N2O emissions at high soil moisture may be attributed to the dual inhibitory effect on nitrifier denitrification, i.e. reducing the supply of nitrite, which is the substrate of nitrifier denitrification and inhibiting ammonia-oxidizing bacteria activities, which carry nitrifier denitrification.

Soil enzyme activities and abundance of microbial functional genes involved in nitrogen transformations in an organic farming system

Organic farming systems receive organic amendments to maintain soil fertility and supply nutrients for plant growth. This study investigated the effect of organic fertilizers (no amendment as control, compost, and manure), and their interaction with cover crops (millet, buckwheat, and black turtle bean) on soil enzyme activities, N transformation rates, and functional gene abundances under an organic production system. Organic N fertilizers had a stronger effect than cover crop type on soil function and functional gene abundances. Soil enzyme activities were increased by both compost and manure, but there were few differences between these treatments. Nitrification potential, nitrite oxidation potential, and denitrification potential were significantly higher in manure-treated than in control and compost-treated soils, indicating application of manure had a higher N loss potential than compost application in this organic farming system. Organic N fertilizers significantly increased the abundance of some genes involved in N mineralization, ammonification, and nitrification (sub, ureC, bacterial amoA and nxrB). The activity of ammonia-oxidizing bacteria and archaea were both increased by organic N fertilizers, and their activities were higher in manure-treated than in compost-treated soils. Overall, the abundance of functional genes was significantly correlated with their corresponding enzyme activity. However, functional gene abundance was less important than soil chemical and microbiological properties in explaining the variation in the corresponding enzyme activity.

Effect of Aeration Rate on Shortcut Nitrification Recovery in Intermittent Aeration Mode

Shortcut nitrification sludge, which was set aside for two months, was recovered using Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ. The aeration rates of Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ were 120, 100, 80, and 60 L·h-1, respectively, while treating real domestic sewage, and the ratio of aerobic/anoxic was 30 min/30 min at the temperature of 25℃. The influent of ammonia was 50-80 mg·L-1, and the concentration of effluent ammonia was stable, at below 5 mg·L-1, after the 12th, 18th, 21st, and 21st cycles. The removal ratio of ammonia nitrogen was about 95%. The highest concentrations of nitrite for Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ were 20.83, 22.81, 21.50, and 20.73 mg·L-1, respectively, which occurred in the 30th, 35th, 38th, and 42nd cycles, respectively. The concentrations of effluent nitrate were lower than 0.5 mg·L-1, and the nitrite accumulation rates were higher than 99%. The activity of ammonia-oxidizing bacteria (AOB) increased gradually and finally stabilized at 100.00%; however, the activity of nitrite-oxidizing bacteria (NOB) was gradually inhibited. The recovery of shortcut nitrification was achieved successfully in the different aeration modes.

Effect of quorum quenching on biofouling and ammonia removal in membrane bioreactor under stressful conditions

Quorum quenching (QQ) has been used to control biofouling in membrane bioreactors (MBRs), but the effect of QQ on the performance of MBR has not been systematically studied. This study investigated the effect of QQ on ammonia removal in MBR especially in some stressful conditions. The results showed that membrane fouling was effectively alleviated by QQ in all conditions. For the short HRT (3.94 h), the ammonia removal in QQ-MBR was fluctuating. In the presence of nitrification inhibitors (acetonitrile and allylthiourea) or at low temperature (10 °C), QQ induced much more significant suppression on nitrification in batch test and MBR. The number of the ammonia oxidizing bacteria (AOB) was not decreasing in these situations, which indicated that QQ only suppressed the activity of AOB. In all, comprehensive considerations should be taken into account when applying a QS tuning strategy to a bioreactor.

Effect of starvation on the nitrification performance of constructed rapid infiltration systems

ABSTRACTThree constructed rapid infiltration (CRI) systems (C1, C2 and C3) were operated under 7, 14 and 21 days of continuous starvation, respectively. The effect of starvation on the ammonia removal efficiency (ARE), nitrite accumulation rate (NAR), bioactivity of nitrifiers and content of extracellular polymeric substances (EPS) was investigated. The results showed that the activity of nitrite-oxidizing bacteria (NOB) was higher than that of ammonia-oxidizing bacteria (AOB) in stabilization periods, leading to a complete nitrification in CRI systems. During starvation periods, the activity decay rates of AOB (kAOB) for C1, C2 and C3 were 0.172 ± 0.008, 0.132 ± 0.009 and 0.128 ± 0.009 d−1, respectively, and those of NOB (kNOB) were 0.159 ± 0.005, 0.152 ± 0.009 and 0.150 ± 0.005 d−1, respectively, implying that kAOB was higher than kNOB in a 7-day starvation period, while showing a contrasting result in a 14- or 21-day starvation period. When resuming wastewater supply, AOB activity as well as the ARE in C1, C2 and C3 gradually restored to their initial levels within 6, 10 and 23 days, respectively. However, NOB activity was unable to fully restore after a 14- or 21-day starvation period, causing the final NAR of C2 and C3 to remain at 25% and 60%, respectively. Furthermore, EPS could be used as the source of carbon and energy for hungry microorganisms to guarantee the metabolic activity of living cells in a starvation environment. These findings could provide a theoretical foundation for operational optimization of CRI systems under starvation conditions.

Stimulating ammonia oxidizing bacteria (AOB) activity drives the ammonium oxidation rate in a constructed wetland (CW)

An integrated approach to document high ammonium oxidation rate in Guanjinggang constructed wetland (GJG-CW) was performed and the results showed that the substantial ammonium oxidation rate could be obtained by enhancing Ammonia Oxidizing Bacteria (AOB) activity rather than Ammonia Oxidizing Archaea (AOA) activity. In the plant-bed/ditch system, ditch center and plant-bed fringe were two active zones for NH4+-N removal with ammonium oxidation rate peaking at 2.98±0.04 and 2.15±0.02mgNkg−1d−1, respectively. The enhanced AOB activity were achieved by increasing water level fluctuations, extending hydraulic retention time (HRT) and stimulating substrate availability, which subsequently enhanced NH4+-N removal by 34.06% in GJG-CW. However, the high AOB activity was not correlated with high AOB abundance, but was instead mostly determined by specific AOB taxa, particularly Nitrosomonas, which dominated in the active AOB. The increased cell-specific AOA activity and high AOA diversity were also achieved using those engineering measures. Although the AOA activity decreased overall with extended HRT and increased NH4+-N contents in GJG-CW, AOA still played a major role on ammonium oxidation in plant-bed soil. The study illustrated that artificially enhancing AOB activity and certain species in anthropogenically polluted water ecosystems would be an effective strategy to improve NH4+-N removal.