Simultaneous Nitrification And Denitrification Process Research Articles

Partial nitrification and simultaneous denitrification in sequential anaerobic and aerobic reactors: performance and microbial community dynamics

ABSTRACT The removal of organic matter and nitrogen from domestic sewage was evaluated using a system composed of two sequential reactors: an anaerobic reactor (ANR) with suspended sludge and an aerobic (AER) reactor with suspended and adhered sludge to polyurethane foams. Nitrogen removal consisted of AER operating at low dissolved oxygen (DO) concentrations; this favoured the simultaneous nitrification and denitrification (SND) process. The concentration of COD and N were 440 mgO2.L−1 and 37 mgTN.L−1, respectively. The operation was divided into three phases (P), lasting 51, 53, and 46 days, respectively. The initial DO concentrations applied in the AER were: 3.0 (PI) and 1.5 mg.L−1 (PII and PIII). In PIII, the AER effluent was recirculated to the ANR at a ratio of 0.25. Kinetic assays were performed to determine the nitrification and denitrification rates of the biomasses (ANR and AER in PIII). Changes in the microbial community were evaluated throughout phases PI to PIII by massive sequencing. In PIII, the best results obtained for chemical oxygen demand (COD) and total nitrogen (TN-N) removal efficiencies, were close to 94% and 65%, respectively. Under these conditions, system effluent concentrations below 30 mg COD.L−1 and 15 mg TN-N.L−1 were verified. The nitritation and nitration rates were 10.5 and 6.5 mg N.g VSS−1.h−1, while the denitrification via nitrite and nitrate were 6.8 and 5.8 mg N.g VSS−1.h−1, respectively. A mixotrophic community was prevalent, with Rhodococcus, Nitrosomonas, Pseudomnas, and Porphyromonas being dominant or co-dominant in most of the samples, confirming the SND process in the AER sludge.

Irons differently modulate bacterial guilds for leading to varied efficiencies in simultaneous nitrification and denitrification (SND) within four aerobic bioreactors

As a novel biological wastewater nitrogen removal technology, simultaneous nitrification and denitrification (SND) has gained increasing attention. Iron, serving as a viable material, has been shown to influence nitrogen removal. However, the precise impact of iron on the SND process and microbiome remains unclear. In this study, bioreactors amended with iron of varying valences were evaluated for total nitrogen (TN) removal efficiencies under aerobic conditions. The acclimated control reactor without iron addition (NCR) exhibited high ammonia nitrogen (AN) removal efficiency (98.9%), but relatively low TN removal (78.6%) due to limited denitrification. The reactor containing zero-valent iron (Fe0R) demonstrated the highest SND rate of 92.3% with enhanced aerobic denitrification, albeit with lower AN removal (84.1%). Significantly lower SND efficiencies were observed in reactors with ferrous (Fe2R, 66.3%) and ferric (Fe3R, 58.2%) iron. Distinct bacterial communities involved in nitrogen metabolisms were detected in these bioreactors. The presence of complete ammonium oxidation (comammox) genus Nitrospira and anammox bacteria Candidatus Brocadia characterized efficient AN removal in NCR. The relatively low abundance of aerobic denitrifiers in NCR hindered denitrification. Fe0R exhibited highly abundant but low-efficiency methanotrophic ammonium oxidizers, Methylomonas and Methyloparacoccus, along with diverse aerobic denitrifiers, resulting in lower AN removal but an efficient SND process. Conversely, the presence of Fe2+/Fe3+ constrained the denitrifying community, contributing to lower TN removal efficiency via inefficient denitrification. Therefore, different valent irons modulated the strength of nitrification and denitrification through the assembly of key microbial communities, providing insight for microbiome modulation in nitrogen-rich wastewater treatment.

The Influence of Atmospheric Pressure and Organic Loading on the Sustainability of Simultaneous Nitrification and Denitrification

In high-altitude regions, a diminished atmospheric oxygen content significantly impairs the aeration efficiency of municipal wastewater, posing a challenge to sustainable wastewater management. Consequently, conventional biological wastewater treatment methods necessitate elevated energy consumption in high-altitude areas, rendering them economically and environmentally unsustainable. The simultaneous nitrification and denitrification (SND) process, owing to its minimal oxygen requirements, emerges as a promising and sustainable solution in low-pressure environments. Additionally, owing to the unique lifestyle and natural conditions in plateau regions, the organic loading in municipal wastewater is often low. To comprehensively assess the impact of low pressure and organic loading on the SND process, three laboratory-scale reactors were implemented. This study revealed that low pressure and the introduction of organic matter enhanced both nitrogen removal performance and SND efficiency. The sludge volume index decreased by 93.5%, indicating a substantial improvement in the microbial aggregation ability and the formation of a more favorable SND sludge structure. 16S rRNA sequencing results demonstrated alterations in the microbial community structure due to low pressure and the addition of organic matter, leading to a substantial increase in the abundance of nitrifying and denitrifying bacteria. Furthermore, the prediction results of functional genes indicated the upregulation of genes related to the nitrification and denitrification processes with decreasing pressure and the addition of organic matter. This enhancement underlines the improved microbial nitrogen removal function. This study underscores the positive influence of low pressure and organic loading on the SND system, thereby substantially enhancing the economic and environmental sustainability of the SND process in plateau regions.

Nitrite improved nitrification efficiency and enriched ammonia-oxidizing archaea and bacteria in the simultaneous nitrification and denitrification process

Simultaneous nitrification and denitrification (SND) is effective and energy-saving for wastewater treatment. As an inevitable intermediate product in the SND process, nitrite affects the efficiency of ammonia oxidation and the composition of nitrifiers. To investigate the impact of nitrite on ammonia oxidation efficiency, two reactors performing SND were respectively operated without nitrite (R1 as control) and with 20 mg N/L nitrite addition (R2 as experimental). The total nitrogen removal efficiency was 74.5% in R1 while 99.0% in R2. With nitrite addition (i.e., 20 mg N/L), the ammonia removal rate in R2 increased to 4.5 times of that in R1. The ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) contributed to respective around 46.9% and 41.8% ammonia removal in R2 based on the results of experiments with specific inhibitors. The number of respective AOA and AOB ammonia monooxygenase gene (amoA) copies increased by 280 and 30 times due to nitrite addition, according to the qPCR results. The high-throughput sequencing results illustrated the increase of dominant AOB species from 0.40% in R1 to 1.59% in R2 and the phylogenetic tree analysis revealed a close link to Nitrosospira multiformis. These results indicated that the ammonia removal efficiency was improved and AOA/AOB were enriched by nitrite addition. The specific nitrite reductases in AOA and AOB boosted the adaptation of nitrite addition. This study demonstrated the positive impacts of nitrite addition on the ammonia removal efficiency and rate in the SND process.

Ammonia Removal by Simultaneous Nitrification and Denitrification in a Single Dual-Chamber Microbial Electrolysis Cell

Ammonia removal from wastewater was successfully achieved by simultaneous nitrification and denitrification (SND) in a double-chamber microbial electrolysis cell (MEC). The MEC operations at different applied voltages (0.7 to 1.5 V) and initial ammonia concentrations (30 to 150 mg/L) were conducted in order to evaluate their effects on MEC performance in batch mode. The maximum nitrification efficiency of 96.8% was obtained in the anode at 1.5 V, followed by 94.11% at 1.0 V and 87.05% at 0.7. At 1.5 V, the initial ammonia concentration considerably affected the nitrification rate, and the highest nitrification rate constant of 0.1601/h was determined from a first-order linear regression at 30 mg/L ammonium nitrogen. The overall total nitrogen removal efficiency was noted to be 85% via the SND in the MEC operated at an initial ammonium concentration of 50 mg/L and an applied cell voltage of 1.5 V. The MEC operation in continuous mode could remove ammonia (50 mg/L) in a series of anode and cathode chambers at the nitrogen removal rate of 170 g-N/m3.d at an HRT of 15. This study suggests that a standalone dual-chamber MEC can efficiently remove ammonia via the SND process without needing additional organic substrate and aeration, which makes this system viable for field applications.

Simultaneous Nitrification and Denitrification under Aerobic Atmosphere by Newly Isolated Pseudomona aeruginosa LS82

Discharge of wastewater contained high amount of nitrogen would cause eutrophication to water bodies. Simultaneous nitrification and denitrification (SND) has been confirmed as an effective process, the isolation of SND bacteria is crucial for its successful operation. In this study, an SND strain was isolated and identified as Pseudomona aeruginosa LS82, which exhibited a rapid growth rate (0.385 h−1) and good nitrogen removal performance (4.96 mg N·L−1·h−1). Response surface methodology was applied to optimize the TN removal conditions, at which nearly complete nitrogen (99.8 ± 0.9%) removal were obtained within 18 h at the condition: pH 8.47, 100 rpm and the C/N ratio of 19.7. The saddle-shaped contours confirmed that the interaction of pH and inoculum size would influence the removal of total nitrogen significantly. Kinetic analyses indicated that the reduction of nitrite was the rate-limiting step in the SND process. Our research suggested strain LS82 can serve as a promising candidate for the treatment of ammonium rich wastewater, and expended our understanding the nitrogen removal mechanism in the SND process.

Ammonium and hydroxylamine can be preferentially removed during simultaneous nitrification and denitrification by Pseudomonas taiwanensis EN-F2

To overcome a large amount of nitrite accumulation and poor removal rate for hydroxylamine, a simultaneous nitrification and denitrification (SND) bacterium was isolated and identified as Pseudomonas taiwanensis EN-F2 by DNA sequencing. Strain EN-F2 could remove 100% of ammonium (52.90 mg/L), 100% of hydroxylamine (23.32 mg/L), 86.99% of nitrite (56.32 mg/L) and 89.21% of nitrate (56.18 mg/L) with a maximum removal rate of 8.72, 2.12, 4.55 and 5.80 mg/L/h, respectively. Ammonium and hydroxylamine could be preferentially removed during the SND process. The nitrite removal rate and cell growth were substantially enhanced by 2.10 mg/L/h and 0.45 after supplementation of hydroxylamine. The specific activities of ammonia monooxygenase (AMO), hydroxylamine oxidoreductase (HAO), nitrate reductase (NR), nitrite reductase (NIR) were successfully detected as 0.95, 0.31, 0.42 and 0.03 U/mg protein, respectively. All results demonstrated that strain EN-F2 could perform SND to remove multiple nitrogen sources from wastewater.

Role of heterotrophic nitrifiers and aerobic denitrifiers in simultaneous nitrification and denitrification process: a nonconventional nitrogen removal pathway in wastewater treatment.

Bacterial species capable of performing both nitrification and denitrification in a single vessel under similar conditions have gained significance in the wastewater treatment scenario considering their unique character of performing the above reactions under heterotrophic and aerobic conditions respectively. Such a novel strategy often referred to as simultaneous nitrification and denitrification (SND) has a tremendous potential in dealing with various wastewaters having low C:N content, considering that the process needs very little or no external carbon source and oxygen supply thus adding to its cost-effective and environmentally friendly nature. Though like other micro-organisms, heterotrophic nitrifiers and aerobic denitrifiers convert inorganic or organic nitrogen-containing substances into harmless dinitrogen gas in the wastewater, their ecophysiological role in the global nitrogen cycle is still not fully understood. Attempts to highlight the role played by the heterotrophic nitrifiers and aerobic denitrifiers in dealing with nitrogen pollution under various environmental operating conditions will help in developing a mechanistic understanding of the SND process to address the issues faced by the traditional methods of aerobic autotrophic nitrification-anaerobic heterotrophic denitrification.

Heterotrophic nitrification-aerobic denitrification performance in a granular sequencing batch reactor supported by next generation sequencing

Several nitrogen transformation processes occur in wastewater treatment; among them, heterotrophic nitrification-aerobic denitrification (HNAD) has not been adequately quantified. In the present study, a comprehensive analysis of the simultaneous ammonia and organic carbon removal was carried out in an aerobic granular sequencing batch reactor (SBR) operated under feast/famine regime. For this, biological processes, microbial community composition and metabolic pathways were evaluated. Mass balances allowed estimating the ammonia assimilation and simultaneous nitrification and denitrification (SND). Better SND process (55%) was achieved in starvation period involving that denitrification driven by intracellular carbon reserves is more efficiently coupled to the ammonia oxidation with regard to external carbon-driven denitrification. Proton balances and titration monitored the organic carbon and nitrogen removal. High abundance of HNAD bacteria, Diaphorobacter sp. and Flavobacterium sp., and Zoogloea sp. aerobic denitrifier was detected by next generation sequencing (NGS) technology. Bioinformatics analysis predicted enzymes involved in nitrogen transformation pathways present in Phylogenetic investigation PYCRUSt database. Heterotrophic nitrification took place involving detoxification against ammonia. Non-limiting nitrate and high oxygen concentrations were favorable for aerobic denitrifiers. HNAD was the main process responsible for the biological nitrogen removal according to NGS and operational conditions given by high dissolved oxygen and low COD:NO3−-N ratio.

Effect of HRT and BDPs types on nitrogen removal and microbial community of solid carbon source SND process treating low carbon/nitrogen domestic wastewater

A novel simultaneous nitrification and denitrification (SND) process using biodegradable polymers (BDPs) as the biofilm carrier and carbon source was developed to remove nitrogen from low-carbon sewage. The effects of BDPs types and hydraulic retention time (HRT) on nitrogen removal and microbial community composition were investigated. The results suggested that HRT parameters were tested in a range from 40h to 3h, and nitrogen removal performance was significantly worse with short HRT (13h to 3h). The NH4+-N and total nitrogen (TN) removal rates of the polycaprolactone (PCL) reactor reached to 98.40 % and 89.14 % at the optimal HRT (13h), respectively, and polybutylene succinate (PBS) reactor reached to 85.73 % and 81.64 %, respectively. When HRT was decreased from 13h to 3h, the NH4+-N removal rate of the PCL and PBS reactors were reduced to the lowest values of 55.43 % and 33.47 %, and the removal rate of TN also reduced to 55.53 % and 44.88 %. According to Illumina MiSeq sequencing and correlation analyses, the genera Methyloversatilis, Bdellovibrio, and Zoogloea were significantly, positively correlated with nitrogen removal rate and short HRT, and short HRT impacted TN removal through increasing the abundance of these genera. LEfSe analysis revealed that the differences observed between PCL and PBS reactors were dependent on differences in Methyloversatilis, ultimately resulting in differences in microbial communities related to nitrogen removal. KEGG analysis suggested that nitrification-related functional genes (amoA, amoB, amoC, and hao) had the greatest abundance in the 13h HRT condition, and denitrification-related functional genes (napA, napB, nasA, nirS, and nosZ) were generally more abundant in the PBS system than the PCL system.

Electron transfer pathways and kinetic analysis of cathodic simultaneous nitrification and denitrification process in microbial fuel cell system

Microbial fuel cell (MFC) is an innovative bioconversion technology for wastewater treatment accompanied with electricity recovery. In this study, a kinetic model was developed base on Activated Sludge Model No.1 (ASM1) to describe electron transfer pathways during the simultaneous nitrification and denitrification (SND) process in the biocathode system of a dual-chamber MFC. The batch running of the dual-chamber MFC system showed that it produced a power density up to 2.96 W m−3 within 48 h, the achieved SND efficiency and autotrophic denitrification ratio in the cathodic denitrification process were up to 87.3 ± 0.8% and 69.5 ± 6.6%, respectively. Meanwhile, by integrating nitrification, autotrophic denitrification, heterotrophic denitrification, organic carbon oxidation, and oxygen reduction in the cathode, the model was able to precisely fit the concentration variations of NH3–N, dissolved oxygen (DO) and chemical oxygen demand (COD) during the cathodic SND process (R2 ≥ 0.9876). The cathode electrons tended to be completely utilized with the increase of autotrophic denitrification ratio in the cathodic denitrification process. When the nitrification rate was enhanced, the autotrophic denitrification would prevail in the competition with the heterotrophic denitrification. In summary, the developed model was confirmed to be effective and reliable for describing the electron transfer pathways and predicting the performance of the nitrogen removal reactions during the cathodic SND process in a double-chamber MFC.

Nitrogen removal pathway and dynamics of microbial community with the increase of salinity in simultaneous nitrification and denitrification process

In this study, simultaneous nitrification and denitrification (SND) process was successfully established in a hybrid sequencing batch biofilm reactor (HSBBR). High removal efficiency of NH4+-N (98.0±2.4% to 99.8±0.4%) and COD (86.6±4.0% to 91.6±1.8%) was observed in the salinity range of 0.0 to 2.4%. SND via nitrite, replacing SND via nitrate, became the main nitrogen removal pathway at 1.6% and 2.4% salinity. Suspended sludge and biofilm shared similar microbial composition. Dominant genera were substituted by salt-adaptable microbes as salinity increasing. Abundance of autotrophic ammonia-oxidizing bacteria (Nitrosomonas) increased with elevated salinity, while autotrophic nitrite-oxidizing bacteria (Nitrospira) exhibited extreme sensitivity to salinity. The presence of Gemmata demonstrated that heterotrophic nitrification co-existed with autotrophic nitrification in the SND process. Aerobic denitrifiers (Denitratisoma and Thauera) were also identified. Thiothrix, Sedimenticola, Sulfuritalea, Arcobacter (sulfide-based autotrophic denitrifier) and Hydrogenophaga (hydrogen-based autotrophic denitrifier) were detected in both S-sludge and biofilm. The occurrence of ANAMMOX bacteria Pirellula and Planctomyces indicated that ANAMMOX process was another pathway for nitrogen removal. Nitrogen removal in the HSBBR was accomplished via diverse pathways, including traditional autotrophic nitrification/heterotrophic denitrification, heterotrophic nitrification, aerobic and autotrophic denitrification, and ANAMMOX.

Simultaneous nitrification and denitrification without nitrite accumulation by a novel isolated Ochrobactrum anthropic LJ81

Nitrogen contaminants are widespread presence in municipal wastewater, heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria have advantages of dealing with multiple nitrogen. Strain LJ81 was isolated from domestic sludge, identified as Ochrobactrum anthropic, which was oxygen-dependent and could survive in a wide range of pH values. Results showed that strain LJ81 could achieve simultaneous nitrification and denitrification (SND) under aerobic condition, whilst more than 80% of initial nitrogen was converted into gaseous nitrogen. The removal rates of ammonia increased from 3.75 to 3.85 and 5.70 mg-N L−1 h−1 by adding nitrite and nitrate, respectively, while the nitrate denitrification was the rate-limiting step of SND process. Moreover, adding chlorate could inhibit not only the cell growth slightly but also denitrification of nitrate. All results indicated that O. anthropic strain LJ81 exhibited excellent performance on nitrogen removal without nitrite accumulation under aerobic condition.

Improving a compact biofilm reactor to realize efficient nitrogen removal performance: step-feed, intermittent aeration, and immobilization technique.

Purifying tank as a compact biofilm reactor has been widely used to remove organic matter in rural sewage, but its potential for nitrogen removal is rare to be discussed. This study developed a lab-scale compact biofilm reactor to realize an efficient nitrogen removal performance by step-feed, intermittent aeration, and immobilization technique. The results show that an efficient simultaneous nitrification and denitrification (SND) process took place by feeding with synthetic wastewater under high C/N ratio of 2 and with real sewage as well, mainly due to the step-feed. The average removal efficiency of total inorganic nitrogen arrived at 72.7 and 63.3% for synthetic wastewater and real sewage, respectively. Besides the step-feed operation, the intermittent aeration was adopted to enhance SND, which allowed hydraulic behavior of compact biofilm reactor following the model of completely stirred tank reactor. The high-throughput sequencing analysis indicates that Sphaerotilus became the dominant genera with relative abundance of 30.29% under high C/N ratio, and the nitrifiers were not greatly inhibited. Moreover, the immobilization technique helped restore microbial activity under low temperature, promoting the satisfactory nitrogen removal performance of recovered microorganism to be rebuilt by feeding nutrient solution. Overall, the long-term SND process and maintaining effective biofilm activity can be established in the compact biofilm reactor through several improving alternatives.

Accelerated start‐up and microbial community structures of simultaneous nitrification and denitrification using novel suspended carriers

AbstractBACKGROUNDThe integrated free‐floating biofilm and activated sludge (IFFAS) process is an ideal candidate for simultaneous nitrification and denitrification (SND). However, traditional carriers have their inherent drawbacks, such as the weak hydrophilicity and negative charges on the surface. In this study, novel carriers with favorable hydrophilicity and electrophilicity were prepared and implemented in an IFFAS‐based SND reactor.RESULTSCompared with traditional carriers, the water contact angle of the novel carriers dropped to 60.2° and positive charges on the surface (+11.7 mV, pH 7.0) were acquired. Through accurate control of dissolved oxygen (DO), it took only 30 days to start SND, with a total nitrogen (TN) removal efficiency of 80.2%. In contrast, the start‐up period was 42 days with weaker TN removal capacity in a control reactor filled with traditional carriers. Novel carriers provided a favorable niche for more types of bacteria to survive, of which Nitrosomonadales and Nitrospirale were identified as nitrifiers while anoxic denitrifiers, aerobic denitrifiers and anammox bacteria also co‐existed in the system, contributing to TN removal.CONCLUSIONNovel carriers with favorable hydrophilicity and electrophilicity were successfully prepared through a relatively facile approach, and a novel carriers‐based SND process enabled a shorter start‐up period, higher biomass and better TN removal efficiency. © 2017 Society of Chemical Industry

The potential multiple mechanisms and microbial communities in simultaneous nitrification and denitrification process treating high carbon and nitrogen concentration saline wastewater

A simultaneous nitrification and denitrification (SND) process in sequencing batch biofilm reactor (SBBR) was established to treat high carbon and nitrogen saline wastewater in this study. Acetate, glucose and an organic mixture were applied as organic sources in three SBBRs, achieving average total nitrogen removal efficiency of 97.15%, 63.94% and 94.99% during 120days’ operation, respectively. The underlying nitrogen removal mechanisms were investigated by 16S rRNA sequencing and batch tests. Results showed different carbon sources had great impact on microbial communities, and led to different nitrogen removal mechanism. Autotrophic and heterotrophic nitrification together contributed to the well performance of nitrification process. And denitrification was carried out by a combined anoxic and aerobic denitrificans. Furthermore, the SND process was mainly via nitrite not nitrate. Compared with ammonia-oxidizing bacteria, ammonia-oxidizing archaea with a much higher abundance contributed more to autotrophic nitrification. Pseudomonas_stutzeri and Bacillus_cereus were the predominant detected heterotrophic nitrification-aerobic denitrification bacterium.

Greenhouse gas emission and microbial community dynamics during simultaneous nitrification and denitrification process

This study evaluates greenhouse gas emission and the microbial community dynamics during simultaneous nitrification and denitrification (SND) process. Based on CO2 equivalents, the SND reactor released 4.28g of greenhouse gases each cycle. 2.91% of the incoming nitrogen load was emitted as N2O. The CO2 and N2O emissions mainly occurred in the aerobic stage and CH4 emissions were consistently near zero. Extracellular polymeric substance (EPS) contents in activated sludge increased during start-up the SND process. High-throughput sequencing showed increases in bacterial species richness, leading to changes in EPS content and composition observed using 3D-EEM fluorescence spectra. For denitrifying bacteria, the relative abundance of Pseudomonas significantly increased during the SND process, while Paracoccus decreased significantly. For phosphorus-accumulating bacteria, the relative abundance of Rhodocyclaceae also significantly increased. The relative abundance of other functional microbes, such as Nitrosomonadaceae (ammonia oxidizer), Nitrospirales (nitrite oxidizer) and Planctomyces (anammox) decreased significantly during the SND process.

Evaluation of simultaneous nitrification and denitrification under controlled conditions by an aerobic denitrifier culture

Paracoccus versutus LYM was characterized with the ability of simultaneous nitrification and denitrification (SND) in presence of NH4+-N and NO3−-N (140mg/L-N each). However, there was approximate 95.80mg/L NO2−-N left during SND process. Fe2+ was added in the SND medium and it benefited bacterial growth and further converted NO2−-N a little. Besides, remaining NO2−-N could be completely reduced by adding carbon donors in presence of NH4+-N and NO3−-N, whose converting efficiencies also reached 97.09% and 96.34%, respectively. And N2 stayed as the main product of SND process. While NO2−-N and NH4+-N were present simultaneously, strain LYM could also remove nitrogen compounds thoroughly with sufficient carbon source. But there was no NO2−-N reduced as sole nitrogen source in the medium even if C/N ratio reached as high as 30.

N2O emission in short-cut simultaneous nitrification and denitrification process: dynamic emission characteristics and succession of ammonia-oxidizing bacteria.

A sequencing batch airlift reactor was used to investigate the characteristics of nitrous oxide (N2O) emission and the succession of an ammonia-oxidizing bacteria (AOB) community. The bioreactor could successfully switch from the complete simultaneous nitrification and denitrification (SND) process to the short-cut SND process by increasing the influent pH from 7.0-7.3 to 8.0-8.3. The results obtained showed that, compared with the complete SND process, the TN removal rate and SND efficiency were improved in the short-cut SND process by approximately 13 and 11%, respectively, while the amount of N2O emission was nearly three times larger than that in the complete SND process. The N2O emission was closely associated to nitrite accumulation. Analysis of the AOB microbial community showed that nitrifier denitrification by Nitrosomonas-like AOB could be an important pathway for the enhancement of N2O emission in the short-cut SND process.

Tracking composition of microbial communities for simultaneous nitrification and denitrification in polyurethane foam.

The process of simultaneous nitrification and denitrification (SND) of immobilized microorganisms in polyurethane form is discussed. The effect of different positions within the polyurethane carrier on microbial community response for the SND process is investigated by a combination of denaturing gradient gel electrophoresis profiles of the 16S rRNA gene V3 region and scanning electron microscopy. Results show that polyurethane, which consists of a unique porous structure, is an ideal platform for biofilm stratification of aerobe, anaerobe and facultative microorganisms in regard to the SND process. The community structure diversity response to different positions was distinct. The distributions of various functional microbes, detected from the surface aerobic stratification to the interior anaerobic stratification of polyurethane, were mainly nitrifying and denitrifying bacteria. Meanwhile aerobic denitrifying bacteria such as Paracoccus sp., Agrobacterium rubi and Ochrobactrum sp. were also adhered to the interior and surface of polyurethane. The SND process occurring on polyurethane foam was carried out by two independent processes: nitrogen removal and aerobic denitrification.