Partial Nitrification Performance Research Articles

High efficiency and stable partial nitration achieved via gel immobilization

Long-term high efficiency and stable partial nitrification (PN) performance was achieved using gel-immobilized partial nitrifying bacteria. The PN characteristics of the filler under high and low ammonia nitrogen concentrations and low temperature were comprehensively studied and the rapid reactivation was achieved after reactor breakdown or long stagnation period. The results showed that the maximum ammonia oxidation rate was 66.8 mg•(L•h)−1 and the nitrite accumulation rate was above 95 % for the filler. Efficient and stable PN performance depends on the high abundance of ammonia-oxidizing bacteria (AOB) inside the filler and dynamically microbial community. In addition, the oxygen-limited zone and competition between the microorganisms inside the filler effectively inhibited the growth of nitrite oxidizing bacteria, and the sludge outside the filler assisted in this process, which supported the dominant position of AOB in fillers. This study provides a reliable technology for the practical application of the PN nitrogen removal process.

Feasibility of low-intensity ultrasound treatment with hydroxylamine to accelerate the initiation of partial nitrification and allow operation under intermittent aeration

Partial nitrification is a key aspect of efficient nitrogen removal, although practically it suffers from long start-up cycles and unstable long-term operational performance. To address these drawbacks, this study investigated the effect of low intensity ultrasound treatment combined with hydroxylamine (NH2OH) on the performance of partial nitrification. Results show that compared with the control group, low-intensity ultrasound treatment (0.10 W/mL, 15 min) combined with NH2OH (5 mg/L) reduced the time required for partial nitrification initiation by 6 days, increasing the nitrite accumulation rate (NAR) and ammonia nitrogen removal rate (NRR) by 20.4% and 6.7%, respectively, achieving 96.48% NRR. Mechanistic analysis showed that NH2OH enhanced ammonia oxidation, inhibited nitrite-oxidizing bacteria (NOB) activity and shortened the time required for partial nitrification initiation. Furthermore, ultrasonication combined with NH2OH dosing stimulated EPS (extracellular polymeric substances) secretion, increased carbonyl, hydroxyl and amine functional group abundances and enhanced mass transfer. In addition, 16S rRNA gene sequencing results showed that ultrasonication-sensitive Nitrospira disappeared from the ultrasound + NH2OH system, while Nitrosomonas gradually became the dominant group. Collectively, the results of this study provide valuable insight into the enhancement of partial nitrification start-up during the process of wastewater nitrogen removal.

Startup of a large height-diameter ratio bioreactor by alternate feeding: performance of partial nitrification and enrichment of ammonia-oxidizing bacteria (AOB)

ABSTRACT In order to solve the complicated control of dissolved oxygen (DO) for partial nitrification in bioreactors treating high NH 4 + − N wastewater, a large height-diameter ratio anammox pre-reactor system was developed. And in this reactor, NO 2 − − N accumulation rate can reach 85.76% by alternate feeding with high NH 4 + − N wastewater (150 mg NH 4 + − N / L ) and low NH 4 + − N wastewater (50 mg c) with low DO (0.19 mg/L–0.62 mg/L). Based on 16S rRNA identification technology, it was found that Nitrosomonas had a significant effect on NH 4 + − N oxidization in this study. And when the reactor treated higher concentration wastewater (250 mg NH 4 + − N / L ), the growth rate of Nitrosomonas was higher than that of Nitrospira (nitrite-oxidizing bacteria, NOB), which was conducive to improving the NO 2 − − N accumulation rate and realizing partial nitrification stably. It was also found that the material exchange frequency of the microbial flora during alternate feeding with different NH 4 + − N concentration wastewaters was higher than that during feeding with higher NH 4 + − N concentration wastewater (250 mg/L) by Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolism pathways analysis. This study can provide valuable insights and lay the foundation for building anammox pre-reactors.

Enhanced simultaneous partial nitrification and denitrification performance of aerobic granular sludge via tapered aeration in sequencing batch reactor for treating low strength and low COD/TN ratio municipal wastewater

The aerobic granular sludge simultaneous partial nitrification, denitrification and phosphorus removal (AGS-SPNDPR) process was carried out via tapered aeration in sequencing batch reactor (SBR) for treating low strength and low COD/TN ratio municipal wastewater. The results showed that aerobic granular sludge was successfully cultivated with good sedimentation performance when treating the municipal wastewater. Meanwhile, the median granule size increased to 270 (R1) and 257 (R2) μm on day 80. The excellent removal performance of COD (92%) and NH4+-N (95%) were achieved under different aeration modes, while the higher TN removal efficiency (76%) was achieved by tapered aeration. The accumulation of NO2−-N in R2 indicated that the tapered aeration was beneficial to achieve simultaneously partial nitrification and denitrification. Meanwhile, the high-efficiency phosphorus (95%) removal was realized via additional carbon source, and SPNDPR process was formed under tapered aeration. The bacterial community analysis indicated denitrifying glycogen-accumulating organisms (DGAOs) Candidatus_Competibacter and ammonia-oxidizing bacteria (AOB) Nitrosomonas were more effectively enriched via tapered aeration, while phosphorus-accumulating organisms (PAOs) Candidatus_Accumulibacter were effectively enriched under additional organic carbon. AOB, denitrifying bacteria and PAOs were simultaneously enriched by tapered aeration and additional carbon source, which was beneficial to nutrients removal. This study might be conducive to the application of AGS-SPNDPR system for treating low strength and low COD/TN ratio municipal wastewater under tapered aeration.

Partial nitrification coupled with denitrification and anammox to treat landfill leachate in a tower biofilter reactor (TBFR)

This study investigated the performance of partial nitrification (PN), carbon oxidation, denitrification and anammox in a continuous tower biofilter reactor (TBFR) with large height-to-diameter ratio of 13 in treating actual landfill leachate. The nitrogen loading rate (NLR) and organic loading rate (OLR) varied from 0.44 to 1.31 kg-N/(m3·day) and 1.59 to 4.76 kg/(m3·day), respectively. The average removal rates of total nitrogen (TN) and chemical oxygen demand (COD) in the TBFR reached 87.47% and 88.45% at the maximum NLR and OLR of 1.31 kg-N/(m3·day) and 4.76 kg/(m3·day), respectively. Variation of water quality along the TBFR in different operating conditions indicated that approximately 45% - 60% of the influent NH4+-N was converted into NO2−-N, and nearly 55% - 70% of the influent COD was removed in the 0–40 cm zone, which provided suitable conditions for the subsequent anaerobic anammox and denitrification processes in the 40–160 cm zone. Overall, the TBFR with a large height-to-diameter ratio demonstrated an effective technology for the treatment of landfill leachate by creating distinct aerobic and anaerobic zones in a single reactor.

Partial nitrification performance and microbial community evolution in the membrane bioreactor for saline stream treatment

Effects of salinity level and gradient on partial nitrification performance, sludge properties and microbial activities were investigated using partial nitrification membrane bioreactors (PN-MBRs). PN-MBRs obtained stable nitrite accumulation rate of 91.1% and ammonia removal of 64.8% at 10 g/L NaCl. 10 g/L NaCl obtained higher oxygen uptake rate than 5 g/L, and promoted the differentiation of ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria. Salinity increased sludge flocs size, stimulated secretion of extracellular polymeric substances with high carbohydrates contents, but had insignificant impact on sludge settleability and dewaterability. Salt level and gradient were both important for microbial community evolution to salt-tolerant bacteria. PN-MBRs enriched aerobic AOBs (Nitrosomonas and norank_f_Nitrosomonadaceae) and anaerobic AOBs (Candidatus_Kuenenia and Candidatus_Brocadia) for partial nitrification, while salt gradients resulted in different metabolism pathways for nitrification even at the same salinity. Increasing salinity promoted hydroxylamine oxidizer in nitrification process evolving from Candidatus_Kuenenia and Candidatus_Brocadia to aerobic AOBs.

Effect of Different Ratios of Anaerobic Time and Aeration Time on the Operation of a Continuous-Flow Reactor with Partial Nitrification Granules

A continuous flow reactor was inoculated at 25-28℃ with mature partial nitrification granular sludge. In order to avoid the granular sludge being crushed because of the sludge backflow through the peristaltic pump, a built-in sedimentation zone was used for internal backflow. The experiment investigated the influence of the different anaerobic time to aeration time ratio (1:1, 2:1, and 1:2) on the stability of a continuous-flow partial nitrification granular sludge system. The results showed that when the controlled anaerobic time to aeration time ratio was 1:1 and 2:1, the partial nitrification performance was good and the nitrite accumulation rates were 85.2% and 94.5%, respectively. When the controlled anaerobic time to aeration time ratio was 1:2, the partial nitrification performance gradually deteriorated, and the ammonia nitrogen removal rate and nitrite accumulation rate at the end of the stage decreased to 64.1% and 58.7%, respectively. Batch test results showed that intermittent aeration and continuous aeration can better inhibit the relative activity of NOB in the partial nitrification system to a certain extent. The longer the anaerobic time, the better the NOB activity inhibition. However, too long an anaerobic time will also lead to ammonia nitrogen removal rate. In the process of partial nitrification, the long-term stable operation of continuous flow partial nitrification process can be realized by 1:1 and coordinated control of other control conditions. An analysis of sludge performance indicated that in the anaerobic time to aeration time ratio range of 1:1-1:2, the longer the anaerobic time, the more stable the granular sludge structure. The shorter the anaerobic time, the smaller the selection pressure in the reactor, resulting in poor sludge sedimentation performance and partial disintegration of partial nitrification granular sludge. An EPS chemical analysis and a three-dimensional fluorescence spectroscopic analysis showed that the PN content was higher and the PN/PS value was higher when the anaerobic time and aeration time ratio was 2:1.

Impact of influent ammonia concentration on partial nitrification of biological sand filter and kinetics

The impact of influent NH4 +/-N concentration on partial nitrification performance was investigated in a biological sand filter. The removal kinetics model of NH4 +-N in partial nitrification-sand filter was established and its accuracy was verified. The results showed that the NH4 +-N removal rates and NO2 −-N accumulation rates stabled at about 60% and 94% respectively and the effluent NO2 −-N/NH4 +-N ratios were 1.20~1.39 when the hydraulic load was 1.0 m/d and the influent NH4 +-N concentration was 45~50 mg/L, indicating that the sand filter had good partial nitrification effect, and the effluent quality basically met the theoretical influent demand of anaerobic ammonia oxidation. The kinetic model of NH4 +/-N removal in sand filter could be described as Sh /S 0=exp(-1.0033S 0 −1.1337 h) when the influent NH4 +-N concentration was 10.2~61.3 mg/L. The model had high accuracy and could provide scientific guidance for effluent quality prediction and optimization design.

Achieving stable two-stage mainstream partial-nitrification/anammox (PN/A) operation via intermittent aeration.

The mainstream anammox process has attracted extensive attention recently. Compared to single-stage partial-nitrification/anammox (PN/A) system, two-stage PN/A process was more advantageous for achieving mainstream anammox. However, complex control strategy in partial-nitrification reactor (N-SBR) might not be feasible in practical application. The aim of this study was to provide an easy operation strategy to achieve two-stage PN/A process. Firstly, intermittent aeration was investigated to achieve 100% conversion of ammonium to nitrite in N-SBR. The effluent nitrite concentrations increased from 19.96 to 38.62mg/L when intermittent aeration ratio (IAC) varied from 30min/30min-30min/15min. During 125d's operation of N-SBR, stable partial nitrification performance was obtained through intermittent aeration, without coupling with low dissolve oxygen or short sludge retention time. Then, raw municipal wastewater was directly mixed with N-SBR effluent to provide suitable feed to anaerobic sequencing batch reactor (A-SBR).When the mixture ratio between the raw wastewater and the N-SBR effluent was 2.5, the effluent ammonium and total inorganic nitrogen (TIN) was only 0.97 and 2.52mgN/L, respectively. Additionally, carbon-based pollutants was also removed in the proposed system without any pretreatment, which made the process easier to operate in practice.

Effect of cadmium on the performance of partial nitrification using sequencing batch reactor

Partial nitrification (PN) in sequencing batch reactors (SBR) was investigated in the presence of cadmium to simulate treatment of landfill leachate containing heavy metals. Different pH conditions were investigated in the SBR to determine the optimum pH to establish PN, which was 7.5. After successful establishment of the PN process, different concentrations of cadmium (Cd) were added into the SBR to evaluate the heavy metal influence on the PN process. The results showed that PN activities were not affected by low concentrations of Cd (< 5 mg L−1). However, the PN efficiency decreased by more than 30% when Cd influent reached 10 mg L−1. This was mainly due to the toxicity of Cd under high concentrations, which decreased the activity of microorganisms, leading to failure of the PN process. The effects of different Cd concentrations were further investigated toward ammonia oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and heavy metal resistant bacteria (MerA) via quantitative real-time PCR. The overall change in the SBR microbial population was also determined via 16S rRNA metagenomics. The results indicated the AOB and NOB were able to tolerate and function well under concentrations below 5 mg L−1 of Cd. In the Cd augmented reactors, Bacteroidetes and Proteobacteria were the most dominant phyla. At the genus level, Chryseobaterium and Flavobacterium, were the most abundant and tolerated Cd at 5 mg L−1, while some microbial groups, such as Dechloromonas and Citrobacter resisted to 10 mg L−1 Cd but did not contribute to PN.

Impact of temperature reduction on partial nitrification in a batch biofilter

The impact of temperature reduction on the stability and recoverability of partial nitrification in a batch biofilter were investigated in present study. The results showed that NH4+-N removal rate, NO2–N accumulation rate and effluent NO2–N/NH4+-N ratio of the batch biofilter could maintain at about 60%, 95% and 1.3 respectively when the temperature was controlled at 20∼25°C. Within this temperature range, the batch biofilter had good partial nitrification performance and could provide suitable and stable influent conditions for the subsequent anaerobic ammonia oxidation (ANAMMOX). When the biofilter was shocked by low temperature, its COD removal ability and partial nitrification performance could both basically restore to its original level via resuming 25°C for a period of time.

Effective partial nitrification of ammonia in a fluidized bed bioreactor

ABSTRACTA lab-scale fluidized bed bioreactor with high-density polyethylene as biofilm carrier media was operated to study partial nitrification (PN) performance with high ammonia concentrations. The system was run at nitrogen loading rates (NLRs) from 1.2 to 4.8 kg N/(m3 d) with empty bed contact time of 2.0 and 2.7 h and four different influent ammonia concentrations of 100, 200, 300 and 400 mg/L. Dissolved oxygen concentration and temperature were maintained around 1.3 mg/L and 35°C, respectively. Stable PN was successfully achieved during the whole period with low effluent NO3-N concentration at less than 15 mg/L, due to effective suppression of nitrite-oxidizing bacteria activity at high concentrations of free ammonia (5.3–27.3 mg N/L) and low alkalinity-to-ammonia ratio. At the NLR of 3.6 kg N/(m3 d), NH4-N conversion and NO2-N accumulation ratios were 57.8% and 53.9%, respectively, which could be further used in the anaerobic ammonium oxidation process (ANAMMOX) as the effluent NO2-N/NH4-N ratio was 1.27.

Partial nitrification performance and mechanism of zeolite biological aerated filter for ammonium wastewater treatment

A zeolite biological aerated filter (ZBAF) with continuous feeding was successfully applied for achieving stable partial nitrification. Excellent nitrite accumulation (higher than 98.0%) and high nitrite/nitrate production rate (NPR) (approximately 0.760kg/m3/d) were obtained with increase influent ammonium concentration from 250 to 550mg/L within a nitrogen loading rate (NLR) of 0.854–1.200kg/m3/d. Owning to the adsorption of zeolite to ammonium, free ammonia (FA) concentration could remain at an appropriate range for inhibition of nitrite oxidizing bacteria (NOB) and dominance of ammonia-oxidizing bacteria (AOB), which should be responsible for the excellent partial nitrification realized in ZBAF. Kinetic study showed that the production of nitrite in ZBAF followed the zero-order kinetics model and high-throughput sequencing analysis further presented the enrichment of AOB and inhibition of NOB in ZBAF. All the results demonstrated that ZBAF hold a great potential in the application of partial nitrification for ammonium wastewater treatment.

Achievement, performance and characteristics of microbial products in a partial nitrification sequencing batch reactor as a pretreatment for anaerobic ammonium oxidation

This study was carried out to evaluate achievement, performance and characteristics of microbial products in a partial nitrification sequencing batch reactor as a pretreatment for anaerobic ammonium oxidation (anammox). After 100 days long-term operation, the effluent NO2−-N/NH4+N ratio of the reactor was average at 1.3 and NO3−-N concentration was low by controlling low dissolved oxygen (DO) concentration, which was considered as the ideal influent for anammox. Specific oxygen uptake rate (SOUR) implied that (SOUR)NH4 and (SOUR)NO2 of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in sludge changed from 21.73 ± 0.52 and 27.39 ± 0.50 O2/g SS/h to 36.37 ± 0.85 and 12.04 ± 0.17 O2/g SS/h, respectively. The main compositions of extracellular polymeric substances (EPS) and soluble microbial products (SMP), including proteins (PN) and polysaccharides (PS), were both reduced during the achievement of partial nitrification. Three-dimensional excitation-emission matrix (3D-EEM) and synchronous fluorescence spectra revealed that PN-like, fulvic acid-like and humic acid-like substances were identified in both EPS and SMP, and their fluorescence intensities changed significantly after partial nitrification achievement. It was found from typical cycle that free ammonia (FA) may play a significant role on inhibiting the activity of NOB. The obtained results could provide more information on the performance of partial nitrification through the characteristics of microbial products when treating high ammonium wastewater.

Effects of phenol on physicochemical properties and treatment performances of partial nitrifying granules in sequencing batch reactors

This study attempts to investigate the effect of phenol on physicochemical properties and treatment performances of partial nitrifying granules (PNGs). Two sequencing batch reactors (SBRs) fed with synthetic ammonium wastewaters were operated in absence (R1) or presence (R2) of phenol. The PNGs in R1 maintained excellent partial nitrification performance and relatively stable physicochemical properties, and exhibited compact and regular shaped structure with a cocci-dominant surface. However, as phenol concentration was stepwise increased from 0 to 300mg/L in R2, filamentous bacteria appeared and gradually dominated within granules, which in turn resulted in settleability deterioration. Most notably, granules in R2 got easier to agglomerate in the reactor walls and then been washed out with effluent, leading to significant biomass loss, frequent outflow pipe blockage, and eventual system failure. The extracellular polymeric substances (EPS) contents including proteins and polysaccharides in R2 reached 1.8 and 1.7 times of that in R1, respectively, indicating that the presence of phenol played an important role on EPS production. Removal efficiency of ammonium and phenol remained high, but dropped sharply when phenol concentration reached 300mg/L. Moreover, the failed maintenance of partial nitrification was observed due to the revival of nitrite oxidizing bacteria (NOB) within granules after phenol exposure, which was confirmed by quantitative fluorescence in situ hybridization (FISH) analysis. Overall this study demonstrates that phenol had negative effects on PNGs, and pretreatment to eliminate phenolic substances is recommended when using PNGs for wastewater treatment.

Performance and microbial ecology of a nitritation sequencing batch reactor treating high-strength ammonia wastewater.

The partial nitrification (PN) performance and the microbial community variations were evaluated in a sequencing batch reactor (SBR) for 172 days, with the stepwise elevation of ammonium concentration. Free ammonia (FA) and low dissolved oxygen inhibition of nitrite-oxidized bacteria (NOB) were used to achieve nitritation in the SBR. During the 172 days operation, the nitrogen loading rate of the SBR was finally raised to 3.6 kg N/m3/d corresponding the influent ammonium of 1500 mg/L, with the ammonium removal efficiency and nitrite accumulation rate were 94.12% and 83.54%, respectively, indicating that the syntrophic inhibition of FA and low dissolved oxygen contributed substantially to the stable nitrite accumulation. The results of the 16S rRNA high-throughput sequencing revealed that Nitrospira, the only nitrite-oxidizing bacteria in the system, were successively inhibited and eliminated, and the SBR reactor was dominated finally by Nitrosomonas, the ammonium-oxidizing bacteria, which had a relative abundance of 83%, indicating that the Nitrosomonas played the primary roles on the establishment and maintaining of nitritation. Followed by Nitrosomonas, Anaerolineae (7.02%) and Saprospira (1.86%) were the other mainly genera in the biomass.

Operational conditions for successful partial nitrification in a sequencing batch reactor (SBR) based on process kinetics

ABSTRACTThe objective of this study is to analyze the factors affecting the performance of partial nitrification in a sequencing batch reactor (SBR) using kinetic models. During the 4-month operation, dissolved oxygen (DO) and influent ammonia concentration were selected as operating variables to evaluate nitrite accumulation. Stable partial nitrification was observed with two conditions, influent ammonia concentration of 190 mg N/L and a DO of 0.6–3.0 mg/L as well as influent ammonia concentration of 100 mg N/L and a DO of 0.15–2.0 mg/L with intermittent aeration. At a DO of 0.6–3.0 mg O2/L and influent ammonia concentration of 90 mg N/L, nitrite-oxidizing bacteria growth was not suppressed. Kinetic parameters were determined or estimated with batch tests and model simulation. The kinetic model predicted the SBR performance well.

Partial nitrification in an air-lift reactor with long-term feeding of increasing ammonium concentrations

The partial nitrification (PN) performance under high ammonium concentrations was evaluated in an airlift reactor (ALR). The ALR was operated for 253days with stepwise elevation of ammonium concentration to 1400mg/L corresponding nitrogen loading rate of 2.1kg/m3/d. The ammonium removal rate was finally developed to 2.0kg/m3/d with average removal efficiency above 91% and nitrite accumulation percentage of 80%. Results showed that the combined effect of limited DO, high bicarbonate, pH and free ammonia (FA) contributed to the stable nitrite accumulation substantially. The biomass in the ALR was improved with the inception of granulation. Precipitates on biomass surface was unexpectedly experienced which might improve the settleability of PN biomass. Organic functional groups attached to the PN biomass suggested the possible absorbability to different types of pollutant. The results provided important evidence for the possibility of applying an ALR to treat high strength ammonium wastewater.

Kinetics of nitrogen removal in pilot-scale internal-loop airlift bio-particle reactor for simultaneous partial nitrification and anaerobic ammonia oxidation

The pilot-scale internal-loop-airlift bio-particle (ILAB) reactor was a novel configuration adopted to study the performance of simultaneous partial nitrification (PN) and anaerobic ammonia oxidation (ANAMMOX). The ILAB reactor was operated at different nitrogen loading rates and hydraulic retention times to investigate the nitrogen removal kinetics. The reactor showed good tolerance to substrate concentration shock while it was significantly affected by hydraulic shock. Five kinetic models including first-order model, Grau second-order model, Stover–Kincannon model, Monod model and Contois model were applied to steady-state experimental data to evaluate the substrate removal in the reactor. The Grau second-order model and Stover–Kincannon model were found to be more appropriate compared with other models to describe and predict the performance of the reactor. Both the models were evaluated by judging the linearity between experimental data and predicted values which confirmed their validity for the process.

Partial nitrification using aerobic granule continuous-flow reactor: Operations and microbial community

Partial nitrification on ammonia laden wastewater using aerobic granule continuous-flow reactors was studied. Effects of temperature and carbon sources on performance of partial nitrification and characteristics of aerobic granules were reported. High nitrite accumulation ratio (>90%) was observed in all reactors after an acclimation phase of 6 days. Decrease in temperature or inorganic carbon concentration limited nitrite accumulation ratio; while nitrite accumulation was hard to recover once complete nitrification to nitrate was established in granules. The aerobic granules collected at continuous-flow reactor were stronger in strength than the seed granules from sequential batch reactor. Clone libraries revealed that Nitrosomonas europaea and Nitrosomonas sp. were the ammonia-oxidizing bacteria (AOB), whereas Nitrobacter sp. and Nitrospira cf. moscoviensis were nitrite-oxidizing bacteria (NOB). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that temperature and carbon sources shifted the microbial community in granules.