Aerobic Ammonium-oxidizing Bacteria Research Articles

Unraveling microbial structure and diversity of activated sludge in a full-scale simultaneous nitrogen and phosphorus removal plant using metagenomic sequencing

Activated sludge contains highly complex microbial communities, which play crucial roles in pollutant removal performance in wastewater treatment plants (WWTPs). Metagenomic sequencing was applied to characterize microbial community and functional profiles within activated sludge from a full-scale municipal WWTP carrying out simultaneous nitrogen and phosphorous removal (SNPR). We applied the assembled contigs (N90 of 591bp) and predicted genes to conduct taxonomic and function annotations, respectively. Results revealed the extraordinary microbial diversity of activated sludge, which included detection of minority populations that are difficult to be explored by traditional molecular methods. Taxonomic analysis indicated that the dominant bacterial phyla were Proteobacteria, Nitrospirae, Bacteroidetes, Actinobacteria and Firmicutes. The abundance of the key organisms involved in nitrogen and phosphorous removal were qualified. Aerobic ammonia-oxidizing bacteria distinctly dominate over ammonia-oxidizing archaea and anaerobic ammonium oxidation bacteria. Various key enzymes involved in the global nitrogen cycle were annotated in the activated sludge. High abundance of the known polyphosphate accumulating organisms was detected (approximately 4.89% of the overall population reads), supporting good phosphorous removal performance. This study provides a comprehensive insight into the community structure and diversity of the SNPR system, and will provide foundation for optimal operation of nutrient removal systems.

Faunal Burrows Alter the Diversity, Abundance, and Structure of AOA, AOB, Anammox and n-Damo Communities in Coastal Mangrove Sediments.

In the present work, the diversity, community structures, and abundances of aerobic ammonia-oxidizing archaea (AOA) and bacteria (AOB), anaerobic ammonium-oxidizing (anammox) bacteria, and denitrifying anaerobic methane oxidization (n-damo) bacteria were unraveled in the bioturbated areas of the coastal Mai Po mangrove sediments. Results indicated that the bioturbation by burrowing in mangrove sediments was associated with higher concentration of NH4+ but lower concentrations of both NO2- and NO3-, and increase in diversity and richness of both AOA and AOB, but relatively lower diversity and richness of n-damo bacteria. The phylotypes of anammox bacterial community were significantly increased while their phylogenetic lineages observed in the less bioturbated areas were also maintained. Infauna also showed a great impact on the composition of n-damo bacterial phylotypes and burrowing activity altered the n-damo community structure profoundly in the sampled areas. The communities of n-damo bacteria in the surrounding bulk sediments showed similar structures to marine n-damo communities, but those on the burrow wall and in the ambient surface layer had a freshwater pattern, which was different from previous findings in Mai Po wetland. On the other hand, the abundances of AOA, AOB, and n-damo bacteria were greatly stimulated on burrow walls while the abundance of anammox bacteria remained unchanged. Infaunal burrows and mangrove roots affected the relative abundance of AOA and AOB. The benthic infauna stimulated the abundances of AOA, AOB, anammox, and n-damo bacteria. Furthermore, NH4+ and NO2- were important environmental factors changing the structure of each group. The communities of anammox and n-damo bacteria in bioturbated areas showed a competitive relationship.

Intensive removal efficiency and mechanisms of carbon and ammonium in municipal wastewater treatment plant tail water by ozone oyster shells fix-bed bioreactor − membrane bioreactor combined system

Residual carbon and ammonium in municipal wastewater treatment plant (WWTP) tail water lead to membrane fouling, and prejudice the operation and life time of reverse osmosis (RO) membrane. In this study, a new combined treatment system of ozone oyster shells fix-bed bioreactor (OFBR)-membrane bioreactor (MBR) was developed and pilot scale was tested for 110days to intensify the removal of residual carbon and ammonium in WWTP tail water. This results showed that the mean maximum COD, ammonium and TP removal efficiencies were achieved by 73%, 99% and 43%, under the optimum ozone dosage of 70mgL−1 and HRT of 25h. The single contribution of OFBR and MBR was 62% and 38% to COD removal, 94% and 6% to ammonium removal, 63% and 37% to TP removal, respectively. High throughput sequencing data showed that there were rich bacterial populations (>2800 species), and Deinococcus-Thermus, Firmicutes, Actinobacteria and Planctomyctes were dominant in both reactors. After addition of ozone, Deinococcus-Thermus and Planctomyctes species bacteria increased significantly in OFBR, and Firmicutes, Actinobacteria and Planctomyctes species bacteria increased remarkably in MBR, which might mainly contribute to carbon removal in OFBR and MBR, respectively. Aerobic ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and denitrifying bacteria were all existed in both reactors, which might be the main reasons for high removal efficiency of ammonium in OFBR-MBR system.

Mainstream partial nitritation-anammox in municipal wastewater treatment: status, bottlenecks, and further studies.

Driven by energy neutral/positive of wastewater treatment plants, significant efforts have been made on the research and development of mainstream partial nitritation and anaerobic ammonium oxidation (anammox) (PN/A) (deammonification) process since the early 2010s. To date, feasibility of mainstream PN/A process has been demonstrated and proven by experimental results at various scales although with the low loading rates and elevated nitrogen concentration in the effluent at low temperatures (15-10°C). This review paper provides an overview of the current state of research and development of mainstream PN/A process and critically analyzes the bottlenecks for its full-scale application. The paper discusses the following: (i) the current status of research and development of mainstream PN/A process; (ii) the interactions among aerobic ammonium-oxidizing bacteria, aerobic nitrite-oxidizing bacteria, anammox bacteria, and heterotrophic bacteria; (iii) the suppression of aerobic nitrite-oxidizing bacteria; (iv) process and bioreactors; and (v) suggested further studies including efficient and robust carbon concentrating pretreatment, deepening of understanding competition between autotrophic nitrogen-converting organisms, intensification of biofilm anammox activity, reactor design, and final polishing.

Horizontal gene transfer drives the evolution of Rh50 permeases in prokaryotes

BackgroundRh50 proteins belong to the family of ammonia permeases together with their Amt/MEP homologs. Ammonia permeases increase the permeability of NH3/NH4+ across cell membranes and are believed to be involved in excretion of toxic ammonia and in the maintenance of pH homeostasis. RH50 genes are widespread in eukaryotes but absent in land plants and fungi, and remarkably rare in prokaryotes. The evolutionary history of RH50 genes in prokaryotes is just beginning to be unveiled.ResultsHere, a molecular phylogenetic approach suggests horizontal gene transfer (HGT) as a primary force driving the evolution and spread of RH50 among prokaryotes. In addition, the taxonomic distribution of the RH50 gene among prokaryotes turned out to be very narrow; a single-copy RH50 is present in the genome of only a small proportion of Bacteria, and, first evidence to date, in only three methanogens among Euryarchaea. The coexistence of RH50 and AMT in prokaryotes seems also a rare event. Finally, phylogenetic analyses were used to reconstruct the HGT network along which prokaryotic RH50 evolution has taken place.ConclusionsThe eukaryotic or bacterial “origin” of the RH50 gene remains unsolved. The RH50 prokaryotic HGT network suggests a preferential directionality of transfer from aerobic to anaerobic organisms. The observed HGT events between archaeal methanogens, anaerobic and aerobic ammonia-oxidizing bacteria suggest that syntrophic relationships play a major role in the structuring of the network, and point to oxygen minimum zones as an ecological niche that might be of crucial importance for HGT-driven evolution.

A novel simultaneous partial nitrification Anammox and denitrification (SNAD) with intermittent aeration for cost-effective nitrogen removal from mature landfill leachate

Mature landfill leachate is difficult to be treated due to its complex composition, high concentration of ammonia, and low carbon/nitrogen ratio (C/N). Simultaneous partial nitrification, Anammox and denitrification (SNAD) with intermittent aeration was developed to achieve nitrogen removal from mature landfill leachate. An ammonia conversion efficiency of 99.3±0.3% and total nitrogen (TN) removal efficiency of 99±0.1% were obtained under the influent NH4+-N, SCOD and TN of 1950±250mg/L 1900±200mg/L and 2300±75mg/L, respectively. Full utilization of carbon source and high efficient Anammox were two significant factors in SNAD process. Based on the nitrogen balance, the nitrogen removal contribution was 77.1% for Anammox, and 15.6% for denitrification. Three dimensional excitation-emission matrix (EEM) fluorescence spectroscopy was used to detect dissolved organic matter (DOM) in a typical operation cycle for the first time, demonstrating that DOM increased during the anoxic phase and facilitated the reduction of excess NO3--N by denitrification. Quantitative polymerase chain reaction (QPCR) analysis revealed dominant bacterial groups, aerobic ammonia-oxidizing bacteria (AOB) and anaerobic ammonia oxidizing bacteria (AnAOB), which accounted for 12.99% and 8.32% of total bacteria respectively. As a whole, in the SNAD process, nitrogen and COD are removed from the wastewater simultaneously.

Evaluations of biofilm thickness and dissolved oxygen on single stage anammox process in an up-flow biological aerated filter

The overall influence of dissolved oxygen (DO) concentrations and biofilm thicknesses on single stage anammox process performance has been evaluated in this study. Results indicated the biofilm displayed a rapid initial increase and followed by a relatively slower formation rate during the operational period. The optimal DO concentration could be determined from a variety of biofilm thicknesses and as well the best biofilm thickness was required among different DO levels. In our lab-scale single stage anammox reactor with a constant hydraulic retention time of 1.0h and influent ammonium of 400mgL−1, an optimal nitrogen removal capacity was acquired (TN removal loading of 2.18kg-Nm−3d−1) at the DO level of 0.6mgL−1 and biofilm thickness of 700μm. Species identification showed that Nitrosomonas related aerobic ammonium-oxidizing bacteria (AerAOB) and Candidatus Brocadia fulgida-like anaerobic ammonium-oxidizing bacteria (AnAOB) were the predominant functional bacteria mixed together with each other and exhibited no distinct niche. However, AerAOB exhibited higher biodiversity at the thinner biofilm while AnAOB showed a stable but lower biodiversity. Moreover, the population of AnAOB was smaller along with more scattered cells at the thinner biofilm while they trended to form specific irregular cauliflower-like zooglea as biofilm thickness increased.

Community structure of partial nitritation-anammox biofilms at decreasing substrate concentrations and low temperature.

SummaryPartial nitritation‐anammox (PNA) permits energy effective nitrogen removal. Today PNA is used for treatment of concentrated and warm side streams at wastewater treatment plants, but not the more diluted and colder main stream. To implement PNA in the main stream, better knowledge about microbial communities at the typical environmental conditions is necessary. In order to investigate the response of PNA microbial communities to decreasing substrate availability, we have operated a moving bed biofilm reactor (MBBR) at decreasing reactor concentrations (311–27 mg‐N l−1 of ammonium) and low temperature (13°C) for 302 days and investigated the biofilm community using high throughput amplicon sequencing; quantitative PCR; and fluorescence in situ hybridization. The anammox bacteria (Ca. Brocadia) constituted a large fraction of the biomass with fewer aerobic ammonia oxidizing bacteria (AOB) and even less nitrite oxidizing bacteria (NOB; Nitrotoga, Nitrospira and Nitrobacter). Still, NOB had considerable impact on the process performance. The anammox bacteria, AOB and NOB all harboured more than one population, indicating some diversity, and the heterotrophic bacterial community was diverse (seven phyla). Despite the downshifts in substrate availability, changes in the relative abundance and composition of anammox bacteria, AOB and NOB were small and also the heterotrophic community showed little changes in composition. This indicates stability of PNA MBBR communities towards decreasing substrate availability and suggests that even heterotrophic bacteria are integral components of these communities.

Biochemical characteristic along UBAF in a one-stage autotrophic nitrogen removal reactor.

The Up-flow biological aerated filter (UBAF) based on a one-stage autotrophic nitrogen removal process has been widely investigated nowadays. In this work, the biochemical characteristic along the volcanic-filled UBAF reactor had been studied. The results indicate that short-rod, spherical and elliptical (averaged 0.2-1.0 μm) microorganisms with a specific irregular cauliflower profile existed in the system. Species identification showed Nitrosococcus- and Nitrosomonas-related aerobic ammonium-oxidizing bacteria (AerAOB) and Candidatus Kuenenia stuttgartiensis-like anaerobic ammonium-oxidizing bacteria (AnAOB) were the predominant functional bacteria that mixed with each other and showed no distinct niche in the system. However, the bioactivity of functional microorganisms displayed differently at different filter layers, with a better pollutant-removal activity in the lower parts than in the upper parts of the UBAF. In the lower parts, compact and small zooglea formed, whereas it trended to be larger and looser along the filter. Moreover, there was better biodiversity of AerAOB in the lower part, while AnAOB showed stable and low biodiversity along the filter.

Abundance and Diversity of Aerobic/Anaerobic Ammonia/Ammonium-Oxidizing Microorganisms in an Ammonium-Rich Aquitard in the Pearl River Delta of South China

Natural occurring groundwater with abnormally high ammonium concentrations was discovered in the aquifer-aquitard system in the Pearl River Delta, South China. The community composition and abundance of aerobic/anaerobic ammonia/ammonium-oxidizing microorganisms (AOM) in the aquitard were investigated in this study. The alpha subunit of ammonia monooxygenase gene (amoA) was used as the biomarker for the detection of aerobic ammonia-oxidizing archaea (AOA) and bacteria (AOB), and also partial 16S rRNA gene for Plantomycetes and anaerobic ammonium-oxidizing (anammox) bacteria. Phylogenetic analysis showed that AOA in this aquitard were affiliated with those from water columns and wastewater treatment plants; and AOB were dominated by sequences among the Nitrosomonas marina/Nitrosomonas oligotropha lineage, which were affiliated with environmental sequences from coastal eutrophic bay and subtropical estuary. The richness and diversity of both AOA and AOB communities had very little variations with the depth. Candidatus Scalindua-related sequences dominated the anammox bacterial community. AOB amoA gene abundances were always higher than those of AOA at different depths in this aquitard. The Pearson moment correlation analysis showed that AOA amoA gene abundance positively correlated with pH and ammonium concentration, whereas AOB amoA gene abundance negatively correlated with C/N ratio. This is the first report that highlights the presence with low diversity of AOM communities in natural aquitard of rich ammonium.

Microbial activity balance in size fractionated suspended growth biomass from full-scale sidestream combined nitritation-anammox reactors

The purpose of this study was to determine the abundance, distribution and activity of aerobic ammonia-oxidizing bacteria (AOB) and anammox in size fractionated aggregates from full-scale suspended growth combined nitritation-anammox sidestream reactors. Plants with or without a cyclone device were also studied to assess a purported enrichment of anammox granules. Specific aerobic ammonium oxidation rates (p=0.01) and specific oxygen uptake rates (p=0.02) were significantly greater in flocs than in granules. AOB abundance measured using quantitative FISH was significantly higher in flocs than in granules (p=0.01). Conversely, anammox abundance was significantly greater in granules (p=0.03). The average ratio of anammox/AOB in systems employing hydrocyclone separation devices was 2.4, significantly higher (p=0.02) than the average ratio (0.5) in a system without a hydrocyclone. Our results demonstrate substantial functional and population-level segregation between floccular and granular fractions, and provide a key corroboration that cyclone separation devices can increase anammox levels in such systems.

Impact of carbon to nitrogen ratio and aeration regime on mainstream deammonification.

While deammonification of high-strength wastewater in the sludge line of sewage treatment plants has become well established, the potential cost savings spur the development of this technology for mainstream applications. This study aimed at identifying the effect of aeration and organic carbon on the deammonification process. Two 10 L sequencing bath reactors with different aeration frequencies were operated at 25°C. Real wastewater effluents from chemically enhanced primary treatment and high-rate activated sludge process were fed into the reactors with biodegradable chemical oxygen demand/nitrogen (bCOD/N) of 2.0 and 0.6, respectively. It was found that shorter aerobic solids retention time (SRT) and higher aeration frequency gave more advantages for aerobic ammonium-oxidizing bacteria (AerAOB) than nitrite oxidizing bacteria (NOB) in the system. From the kinetics study, it is shown that the affinity for oxygen is higher for NOB than for AerAOB, and higher dissolved oxygen set-point could decrease the affinity of both AerAOB and NOB communities. After 514 days of operation, it was concluded that lower organic carbon levels enhanced the activity of anoxic ammonium-oxidizing bacteria (AnAOB) over denitrifiers. As a result, the contribution of AnAOB to nitrogen removal increased from 40 to 70%. Overall, a reasonably good total removal efficiency of 66% was reached under a low bCOD/N ratio of 2.0 after adaptation.

Environmental factors affecting the presence of Acidimicrobiaceae and ammonium removal under iron-reducing conditions in soil environments

The oxidation of ammonium (NH4+) under iron reducing conditions, also referred to as Feammox, has been described in recent years by several investigators. The environmental characteristics in which the Feammox process occurs need to be understood in order to determine its contribution to the nitrogen cycle. In this study, through extensive field sampling at various locations in the US (mostly New Jersey) and South China, soil chemical analyses, serial incubation experiments, analysis of microbial communities, and using canonical correspondence analyses, it was determined that the soil pH, as well as its Fe(III) and NH4+ concentration were the most important factors controlling the distribution of Acidimicrobiaceae, which have been linked to the Feammox reaction. Under the conditions that favored the presence of Feammox bacteria and their oxidation of NH4+ under iron reducing conditions, denitrification bacteria were also abundant. However, the presence of known nitrous oxide (N2O) reducers was limited under these conditions, implying that at locations where the Feammox process is active, conditions might favor a higher N2O:N2 ratio for the nitrogen (N) end products. To determine the effect of dissolved oxygen (DO) on NH4+ oxidation under iron reducing conditions, incubations were conducted at two different DO levels. In incubations with DO < 0.02 mg/L, and when NH4+ oxidation was noticeable, the proportion of Acidimicrobiaceae with respect to total bacteria increased, while the proportion of other known NH4+ oxidizing bacteria (aerobic ammonia-oxidizing bacteria and anammox bacteria) decreased. In incubations of the same soil but with DO = 0.8–1.0 mg/L the opposite trend was observed, indicating that Feammox favored very low or no DO in these incubations.

Treatment of semiconductor wastewater using single-stage partial nitrification and anammox in a pilot-scale reactor

Start-up of pilot scale reactor to treat real semiconductor wastewater is reported in this study. Semiconductor industrial wastewater stream was characterized as highly alkaline (pH 10) and contained high concentration of H2O2 of 311 ± 505mg/L, ammonium nitrogen of 318 ± 122 NH4+-Nmg/L and negligible COD of <10mg/L. H2O2 was removed by adding enzyme “REYONET F-35” and H2SO4. Before the H2O2-free wastewater is fed to the biological reactor, the pH is adjusted to ∼7.0. Completely autotrophic nitrogen removal over nitrite (CANON) process was cultivated in a 1.0m3 pilot-scale sequencing batch reactor by using enzyme pretreated semiconductor wastewater without temperature control. The nitrogen loading rate was increased step-wise from 94 to 665g NH4+-N/m3d. The average NH4+-N and total nitrogen removal efficiencies were 85.5 and 75.7%, respectively at NLR of 665g NH4+-N/m3d and HRT of 4d. The pilot reactor was successfully started up and operated for more than 550d. The CANON was evidenced by the ratio of the effluent nitrite and nitrate to ammonium ratio (η) of 0.076 during the steady state operation period. PCR results also confirmed the presence of AOB (aerobic ammonia oxidizing bacteria) and anammox (anaerobic ammonia oxidizing) bacteria in the reactor.

Deammonification for digester supernatant pretreated with thermal hydrolysis: overcoming inhibition through process optimization.

The thermal hydrolysis process (THP) has been proven to be an excellent pretreatment step for an anaerobic digester (AD), increasing biogas yield and decreasing sludge disposal. The goal of this work was to optimize deammonification for efficient nitrogen removal despite the inhibition effects caused by the organics present in the THP-AD sludge filtrate (digestate). Two sequencing batch reactors were studied treating conventional digestate and THP-AD digestate, respectively. Improved process control based on higher dissolved oxygen set-point (1mgO2/L) and longer aeration times could achieve successful treatment of THP-AD digestate. This increased set-point could overcome the inhibition effect on aerobic ammonium-oxidizing bacteria (AerAOB), potentially caused by particulate and colloidal organics. Moreover, based on the mass balance, anoxic ammonium-oxidizing bacteria (AnAOB) contribution to the total nitrogen removal decreased from 97±1% for conventional to 72±5% for THP-AD digestate treatment, but remained stable by selective AnAOB retention using a vibrating screen. Overall, similar total nitrogen removal rates of 520±28mgN/L/day at a loading rate of 600mgN/L/day were achieved in the THP-AD reactor compared to the conventional digestate treatment operating at low dissolved oxygen (DO) (0.38±0.10mgO2/L).

Effect of inorganic carbon on nitrogen removal and microbial communities of CANON process in a membrane bioreactor

In this study, a membrane bioreactor (MBR) was adopted for completely autotrophic nitrogen removal over nitrite (CANON) process. Inorganic carbon (IC) was step-wise decreased to analyze the IC influence on nitrogen removal and microbial communities, finally IC was elevated to study its recovery capability. The bioactivities of functional organisms were detected by batch experiments. Results showed that the bioactivity and biodiversity of aerobic ammonia-oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing bacteria (AAOB) both decreased due to the IC shortage, while nitrite-oxidizing bacteria bioactivity showed a contrary result. When the concentration ratio of IC to nitrogen (IC/N) decreased to 1.0, the nitrogen removal sharply deteriorated, which then recovered when the ratio increased to 2.5. Denaturing gradient gel electrophoresis results showed that Nitrosomonas sp. of AOB and Candidatus Brocadia fulgida of AAOB could survive in the condition of IC deficit. The prominent IC/N ratio for high-rate and stable CANON was between 1.5–2.0.

Exploration of rapid start-up of the CANON process from activated sludge inoculum in a sequencing biofilm batch reactor (SBBR).

In this study, a laboratory-scale sequencing biofilm batch reactor (SBBR) was employed to explore a fast start-up of completely autotrophic nitrogen removal over nitrite (CANON) process. Partial nitrification was achieved by controlling free ammonia concentration and operating at above 30 °C; then the reactor was immediately operated with alternating periods of aerobiosis and anaerobiosis to start the anammox process. The CANON process was successfully achieved in less than 50 d, and the total-nitrogen removal efficiency and the nitrogen removal rate were 81% and 0.14 kg-N m(-3) d(-1) respectively. Afterwards, with the increasing of ammonium loading rate a maximum nitrogen removal rate of 0.39 kg-N m(-3) d(-1) was achieved on day 94. DNA analysis showed that 'Candidatus Brocadia' was the dominant anammox species and Nitrosomonas was the dominant aerobic ammonium-oxidizing bacteria in the CANON reactor. This study revealed that due to shortening the persistent and stable nitrite accumulation period the long start-up time of the CANON process can be significantly reduced.

Effect of temperature on functional bacterial abundance and community structure in CANON process

Completely autotrophic nitrogen-removal over nitrite (CANON) has been considered as a promising nitrogen-removal technology in treating high ammonia and high temperature wastewater. In this study, the exact effect of different temperatures on process performance and microbial features based on two lab-scale CANON reactors was investigated. Results showed extraordinary nitrogen removal performance with mean total nitrogen (TN) removal efficiency of 80.01% and 66.90% under high TN removal loading of 2.09kgm−3d−1 and 1.02kgm−3d−1 at 30°C and ambient temperature (16–23°C) respectively. Biodiversity analysis indicated Nitrosomonas-related aerobic ammonia oxidizing bacteria (AerAOB) and Candidatus Brocadia-like anaerobic ammonia oxidizing bacteria (AnAOB) were predominant functional microorganisms that coexisted without distinguishable niche on the volcanic carriers in both two CANON reactors. Temperature could noticeably impact functional bacterial population: the population of AerAOB and AnAOB decreased to one to two orders of magnitude whereas Nitrospira and Nitrobacter increased at ambient temperature. Based on the bacterial experimental results, some feasible strategies have been discussed to improve the bioactivity and increase the function bacterial population, aiming at enhancing nitrogen-removal capacity at ambient temperature.

Microprofiles of activated sludge aggregates using microelectrodes in completely autotrophic nitrogen removal over nitrite (CANON) reactor

Microsensor measurements and fluorescence in situ hybridization (FISH) analysis were combined to investigate the microbial populations and activities in a laboratory-scale sequencing batch reactor (SBR) for completely autotrophic nitrogen removal over nitrite (CANON). Fed with synthetic wastewater rich in ammonia, the SBR removed 82.5±5.4% of influent nitrogen and a maximum nitrogen-removal rate of 0.52 kgN∙m–3∙d–1 was achieved. The FISH analysis revealed that aerobic ammonium-oxidizing bacteria (AerAOB) Nitrosomonas and anaerobic ammonium-oxidizing bacteria (AnAOB) dominated the community. To quantify the microbial activities inside the sludge aggregates, microprofiles were measured using pH, dissolved oxygen (DO), NH 4+, NO 2- and NO3- microelectrodes. In the outer layer of sludge aggregates (0–700 μm), nitrite-oxidizing bacteria (NOB) showed high activity with 4.1 μmol∙cm–3∙h–1 of maximum nitrate production rate under the condition of DO concentration higher than 3.3 mg∙L–1. Maximum AerAOB activity was detected in the middle layer (depths around 1700 μm) where DO concentration was 1.1 mg∙L–1. In the inner layer (2200–3500 μm), where DO concentration was below 0.9 mg∙L–1, AnAOB activity was detected. We thus showed that information obtained from microscopic views can be helpful in optimizing the SBR performance.

Reactor performance and microbial characteristics of CANON process with step-wise increasing of C/N ratio

In this study, the nitrogen removal performance and microbial characteristics of completely autotrophic nitrogen removal over nitrite (CANON) process was investigated with a step-wise increasing of C/N ratio (0.5, 1, 2 and 4) in a membrane bioreactor. The microbial distribution of aerobic ammonia-oxidizing bacteria (AOB) and anaerobic AOB (AAOB) was analysed by fluorescence in situ hybridization (FISH). Results showed that the denitrification ratio rose up correspondingly with the increase of influent C/N, and nitrogen removal rate (NRR) reached the maximum when C/N was 1 due to the harmonious work of denitrification and CANON. However, NRR decreased when influent C/N was more than 2. The threshold C/N ratio of CANON process was 2.2; so the sewage with a high C/N ratio should be pretreated by combining with pre-oxidation of organics or anaerobic-energy-producing process. FISH results showed decreasing numbers of both AOB and AAOB with the addition of organics.