Nitritation-anammox Process Research Articles

Partitioned granular sludge coupling with membrane-aerated biofilm reactor for efficient autotrophic nitrogen removal

The partial nitritation-anammox process based on a membrane-aerated biofilm reactor (MABR) faces several challenges, such as difficulty in suppressing nitrite-oxidizing bacteria (NOB), excessive effluent nitrate, and ineffective synergy between denitrification and anammox bacteria. Therefore, a novel partitioned granular sludge coupling with MABR (G-MABR) was constructed. The chemical oxygen demand (COD) and nitrogen removal efficiency were 88.8 ± 1.8 %–92.6 ± 1.2 % and 88.8 ± 1.5 %–93.6 ± 0.7 %, respectively. The COD was mainly lowered in the lower granular sludge-zone, while nitrogen was removed in the upper MABR-zone. NOB was significantly suppressed in the MABR-zone due to competition for substrate with denitrifying bacteria and anammox bacteria. This partitioned configuration reduced the C/N ratio in the MABR-zone, thus facilitating autotrophic nitrogen removal. Both partial nitrification and denitrification provided nitrite for anammox bacteria in granular sludge, whereas partial nitrification mainly supplied nitrite to the anammox bacteria in membrane biofilms.

Lab-Scale Treatment of Anaerobic Co-Digestion Liquor from Kitchen Waste, Human Feces, and Municipal Sludge Using Partial Nitritation-Anammox Process

Effective nitrogen removal from anaerobic co-digestion is a major challenge to achieving dual-carbon goals. This study explored the acclimatization process of a lab-scale two-stage partial nitritation and anammox process of a stepwise increase in the percentage of raw anaerobic co-digestion liquor from kitchen waste, human feces, and municipal sludge in a venous industrial park in China, which has not been reported yet. Under limited dissolved oxygen (below 0.5 mg/L) and high ammonia levels (200–1500 mg/L), based on adjusting aeration rates, partial nitritation rapidly started up in 50 days. After acclimatization, partial nitritation still performed efficiently and stably, with the final total nitrogen loading rate (TNLR) of 1.24 ± 0.09 gN/L/d, nitrite accumulation rate of 99 ± 4%, and ratio of eff. nitrite/ammonia of 1.32 ± 0.13. In the anammox process, the final total nitrogen removal efficiency, total nitrogen removal rate, and TNLR reached 94 ± 5%, 1.27 ± 0.03 gN/L/d, and 1.36 ± 0.05 gN/L/d, respectively. Chemical oxygen demand (COD) was also reduced in both reactors, with COD removal rates of 0.7 gCOD/L/d in the partial nitritation and 0.4 gCOD/L/d in the anammox process. Overall, the PNA system demonstrated its feasibility in adapting to high ammonia, salinity, and iron levels, when treating anaerobic co-digestion liquor, particularly regarding resource recovery in venous industrial parks.

Enhanced anammox performance under lower nitrite accumulation in modified partial nitritation-anammox (PN/A) process

Higher nitrite accumulation, which is challenging to achieve reliably, is always sought to obtain better nitrogen removal performance in traditional partial nitritation-anammox (PN/A) process. This study developed a modified PN/A process by introducing nitrite-oxidizing bacteria and endogenous metabolism. Advanced nitrogen removal performance of 95.5 % was achieved at a low C/N ratio of 2.7 under nitrite accumulation ratio (NAR) fluctuations. Higher nitrate accumulation at lower NAR (70 ∼ 40 %) resulted in superior anammox contribution (60 ∼ 75 %) and nitrogen removal performance (93 ∼ 98 %). This was attributed to the higher nitrogen removal efficiency of the post-anoxic endogenous partial denitrification coupling anammox process, although the PN/A process occurring first possessed a faster anammox rate of 2.0 mg NH4+-N /(g VSS⋅h). The introduction of nitrate allowed more nitrite flow to anammox, promoting a high enrichment of anammox bacteria (Ca. Brocadia, 0.3 % to 2.8 %). This study provides new insights into the practical application of the PN/A process.

Improving carbon and nitrogen removal efficiency in high-strength nitrogen wastewater via two-stage nitritation-anammox process

Centralized systems employ biological treatments to remove nutrients, whereas decentralized systems, especially in rural areas, face challenges in implementing them. These systems are low flow but high carbon and nitrogen concentrations, and low C/N ratios. Source-separated wastewater (urine + flush) is an extreme example, like confined animal-feeding wastewater. High nutrient concentrations necessitate innovative technologies typically not employed for decentralized systems. This research demonstrates a simple two-stage nitritation-anammox system to treat high N concentration wastewater (pure urine + flush water). The systems consisted of a Membrane Aerated Biological Reactor (MABR) which performed carbon oxidation and nitritation and novel anammox reactors, (Pancopia AnammoX (PAXs)). The MABRs achieved OC removal over 108–198 g-C/m3-day with ∼ 97% removal, TAN oxidation rates up to 156 g-N/m3-day and nitrite/AN ratios were near 1 with no external control (e.g. pH, DO, cell wasting) other than urine loading rate. The PAXs achieved maximum AN removal efficiencies of 85–97%. The main limitation to complete TN removal in the PAXs was insufficient NO2- in the influent (nonideal influent NO2-/AN ratio). This system was not optimized for energy efficiency and had low volumetric conversion rates compared with other systems. However, it demonstrates that source-separated wastewater can be effectively treated with near complete N removal using a system with minimal process control requirements, lack of solid production, and elimination of diffuse aeration preventing odor generation. These attributes are attractive for applications where conditions do not allow for more complex high-rate systems such as developing societies and rural areas.

Resource-efficient nitrogen and salinity removal in a synergistic partial nitritation-anammox bioelectrochemical system

We investigated the performance of a two-stage partial-nitritation-anammox biocathode integrated microbial desalination cell (TNiAmoxMDC) for concurrent nitrogen removal, desalination, and bioelectricity generation at different aeration rates in the nitritation chamber. The TNiAmoxMDC system achieved a maximum total nitrogen removal rate of 50.4 ± 8.2 g-TN/m3/d with 300 mW/m2 of maximum power production utilizing 500 mg/L of glucose chemical oxygen demand (COD) in the anode. The organic removal in the anode chamber showed a good fit to first order reaction model with a rate constant of 0.036 h−1. The biocatalytic activity of anammox bacteria in the biocathode produced a current density of 0.7 A/m2 in the absence of oxygen. More than 98% of the salinity was removed at a rate of 1.48 mg/h. The energy consumption values for nitrogen removal at aeration rates of 0.7, 2.2, and 10 ml/min were 0.022, 0.55, and 0.20 kWh/kg-N, respectively. The maximum energy produced by the TNiAmoxMDC was 0.0157 kWh/m3. Excluding the energy consumption by the system, the net energy recovery was 0.0023 kWh/m3 at an airflow rate of 10 ml/min. Thus, the integration of the partial nitritation-anammox process with microbial desalination cell (MDC) provides energy-and resource-efficient synergy for bioelectrochemical wastewater treatment.

Improved performance of single-stage partial nitritation-anammox membrane bioreactor (PN/A MBR) by adding biofilm carriers: start-up, membrane operation and microbial structure

Serious sludge washout is a bottleneck in the partial nitritation-anammox (PN/A) process that needs to be addressed urgently. A membrane bioreactor (MBR) is suitable for the PN/A process because of its 100 % biomass retention ability. Therefore, this study establishes a single-stage PN/A MBR and a PN/A moving bed membrane reactor (PN/A MB-MBR) for investigating the operation performance, membrane fouling behavior, and effect of biofilm carrier addition. The results demonstrate that the PN/A MB-MBR achieves a significantly shorter start-up time and substantially higher maximum nitrogen removal rate (NRR) of 17 days and 1.02 g N/L/d, respectively, compared to that of PN/A MBR (61 days and 0.19 g N/L/d, respectively). Further, the PN/A MB-MBR exhibits a lower membrane fouling of 0.023 kPa/L compared to that of 0.050 kPa/L in PN/A MBR because of the integration of the biofilm carrier. The biofilm in PN/A MB-MBR shows a higher relative abundance of Candidatus Kuenenia (18.90–25.10 %), which is a major AnAOB, compared to that observed in the suspended sludge of PN/A MB-MBR (10.30–14.32 %). Furthermore, the relative abundance of Candidatus Kuenenia absorbed on the membrane surface of PN/A MB-MBR (8.6 %) was lower than that on PN/A MBR (15.5 %). This study presented a promising method for enhancing the performance of PN/A MBR, which can serve as a valuable reference for its extensive implementation.

Intensifying single-stage denitrogen by a dissolved oxygen-differentiated airlift internal circulation reactor under organic matter stress: Nitrogen removal pathways and microbial interactions

Current research focuses on efficient single-stage nitrogen removal from organic matter wastewater using the partial nitritation-anammox (PNA) process. In this study, we constructed a single-stage partial nitritation-anammox and denitrification (SPNAD) system using a dissolved oxygen-differentiated airlift internal circulation reactor. The system was operated continuously for 364 days at 250 mg/L NH4+–N. During the operation, the COD/NH4+–N ratio (C/N) was increased from 0.5 to 4 (0.5, 1, 2, 3, and 4), and the aeration rate (AR) gradually increased. The results showed that the SPNAD system maintained efficient and stable operation at C/N = 1–2 and AR = 1.4–1.6 L/min, with an average total nitrogen removal efficiency of 87.2%. The removal pathways of pollutants in the system and the interactions between microbes were revealed by analyzing the changes in sludge characteristics and microbial community structure at different phases. As the influent C/N increased, the relative abundance of Nitrosomonas and Candidatus Brocadia decreased, and that of denitrifying bacteria, such as Denitratisoma, increased to 44%. The nitrogen removal pathway of the system gradually changed from autotrophic nitrogen removal to nitrification-denitrification. At the optimum C/N, the SPNAD system synergistically removed nitrogen through PNA and nitrification-denitrification. Overall, the unique reactor configuration facilitated the formation of dissolved oxygen compartments, providing a suitable environment for different microbes. An appropriate organic matter concentration maintained the dynamic stability of microbial growth and interactions. These enhance microbial synergy and enable efficient single-stage nitrogen removal.

Revealing the response of community structure and metabolic pathway to varying organic matter stress in a dissolved oxygen-differentiated airlift internal circulation partial nitritation-anammox system

In practice, the influent organic matter is often pre-treated to reduce the impact on partial nitritation-anammox (PNA) process. However, the influent organics may also drive the denitrification process and improve total nitrogen removal efficiency of the PNA process. Thus, we designed and operated a novel dissolved oxygen-differentiated airlift internal circulation PNA (PNA-DOAIC) system in this study at various influent C/N ratios of 0–4.0. Nitrogen removal performance, microbial activity and community, and metabolic pathways in response to varying organic matter stress were investigated via the continuous experiment combined with batch test. The results showed that the optimum influent C/N ratio was 2.0 in this system, and the efficient and stable operation was still maintained at the C/N ratios of 0–3. At this time, the TN removal efficiency and removal rate could reach 95.1 % and 0.93 kg-N/m3/d, respectively, while COD efficiency remained at 95.4 %. Efficient removal performance was achieved via the PNA coupled with denitrification. However, the anammox bacteria (AnAOB) activity and abundance declined persistently as the influent C/N ratio was further raised, and heterotrophic bacteria gradually replaced AnAOB as dominate genus. Meanwhile, metabolic functions involving the material exchange and organic degradation were significantly enhanced. Nitrogen removal pathways changed from PNA to the nitrification-denitrification process. This study provides deep insights into effects of organic matter on the PNA process and can expand the application scope of this novel PNA-DOAIC bioreactor.

Deciphering the effect of temperature reduction on the biofilm in partial nitritation-anammox system: Insights from microbial community to metabolic pathways

The concept of partial nitritation-anammox (PN/A) process has been proposed for many years, however seasonal temperatures and low ammonia concentrations under mainstream conditions always challenge the application in practical engineering. Thus, we operated a PN/A moving bed biofilm reactor (PN/A-MBBR) for treating 50 mg-NH4/L wastewater at various temperatures of 35 °C, 25 °C, and 15 °C. The effect of temperature reduction on biofilm system was investigated from process performance, microbial community and activity, to metabolic pathways. The results showed that total nitrogen removal efficiency declined from 76.6 % to 48.6 % as the temperature was reduced from 35 °C to 15 °C, while nitrogen removal rate decreased to 0.28 kg-N/m3/d. Low temperature stimulated the secretion of polysaccharide in loosely bound-EPS and protein in tightly bound-EPS. Meanwhile, specific activity of anammox declined from 1.53 to 0.56 g-N/g-VSS/d, and the relative abundance of Candidatus Brocadia dropped from 20.1 % to 9.4 %. Temperature reduction had significant effect on the expression of functional genes (hzsA and hdh) for anammox reaction. Nitrification-denitrification process was enhanced during low temperatures and recovery phases. Biofilm system might respond to temperature reduction by the decline of substance transport and energy consumption, as well as the enhancement of biofilm formation and diversity of nitrogen removal pathways. The findings of this study provide a deep insight into the effect of temperature reduction on PN/A process, also promote the practical applications of mainstream PN/A in the future.

Metagenomics reveals the microbial community and functional metabolism variation in the partial nitritation-anammox process: From collapse to recovery

Mainstream partial nitritation-anammox (PNA) process easily suffers from performance instability and even reactor collapse in application. Thus, it is of great significance to unveil the characteristic of performance recovery, understand the intrinsic mechanism and then propose operational strategy. In this study, we combined long-term reactor operation, batch tests, and metagenomics to reveal the succession of microbial community and functional metabolism variation from system collapse to recovery. Proper aeration control (0.10-0.25 mg O2/L) was critical for performance recovery. It was also found that Candidatus Brocadia became the dominant flora and its abundance increased from 3.5% to 11.0%. Significant enhancements in carbon metabolism and phospholipid biosynthesis were observed during system recovery, and the genes abundance related to signal transduction was dramatically increased. The up-regulation of sdh and suc genes showed the processes of succinate dehydrogenation and succinyl-CoA synthesis might stimulate the production of amino acids and the synthesis of proteins, thereby possibly improving the activity and abundance of AnAOB, which was conducive to the performance recovery. Moreover, the increase in abundance of hzs and hdh genes suggested the enhancement of the anammox process. Changes in the abundance of key genes involved in nitrogen metabolism indicated that nitrogen removal pathway was more diverse after system recovery. The achievement of performance recovery was driven by anammox, nitrification and denitrification coupled with dissimilatory nitrate reduction to ammonium. These results provide deeper insights into the recovery mechanism of PNA system and also provide a potential regulation strategy for the stable operation of the mainstream PNA process.

Benchmarking sidestream shortcut nitrogen removal processes against nitrous oxide recovery from a life cycle perspective

Anaerobic digestion effluent adds significantly to nutrient loading, energy consumption, and emissions of wastewater treatment plants. Sustainably treating this ammonia-rich sidestream requires systematic analysis on environmental impacts of shortcut nitrogen removal processes. Coupled Aerobic–Anoxic Nitrous Decomposition Operation (CANDO) is a novel biotechnology for sidestream nitrogen removal with energy recovery potential from N2O. Nevertheless, the environmental impacts of CANDO remain unknown after initial scale-up studies. In this study, three sidestream treatment processes, namely, nitritation-denitritation, nitritation-anammox, and CANDO, integrated with mainstream anaerobic-anoxic-oxic (A2O) treatment routes, are assessed by process simulation and life cycle assessment (LCA). The results show that the nitritation-anammox process has the smallest effect on human health, ecosystem quality, and resource availability among the three routes. Furthermore, the global warming potential generated from the CANDO-A2O process is 157 kg CO2 eq per cubic meter of anaerobic digestion liquid treated, which is slightly higher than nitritation-anammox-A2O (132 kg CO2 eq) but remarkably lower than nitritation-denitritation-A2O (248 kg CO2 eq). With low carbon emission and promising alternatives for carbon source, the CANDO-A2O route exhibits great potential in achieving carbon neutrality. This work is the first to quantitatively evaluate the potential environmental impacts of CANDO from a life cycle perspective, providing insights on the adoption and optimization of shortcut nitrogen removal processes in sidestream treatment.

Response of partial nitritation-anammox process to substrate concentration and temperature variations in a single-stage airlift circulation system: Performance and microbial community dynamics

Low-strength ammonia and temperature challenge the application of partial nitritation-anammox (PNA) process in the treatment of mainstream wastewater. In this study, we operated a single-stage PNA process under various substrate concentrations (250, 150, and 50 mg/L) and temperatures (32, 25, 15 °C). Changes in nitrogen removal performance, biochemical reaction rate, and specific activity were investigated via the long-term continuous experiment and batch tests. Microbial diversity, community structure, and metabolic pathways in response to the various conditions were explored. When the temperature declined to 15 °C, the nitrogen removal efficiency decreased from 83.9 % to 51.5 % with the influent of 50 mg-NH4/L, while the nitrogen removal rate dropped to 0.33 kg N/m3/d. Meanwhile, the relative abundances of Candidatus Brocadia and Nitrosomonas reached 14.1 % and 1.5 %, respectively. The results showed that the mechanisms of performance degradation caused by low ammonia concentration and low temperature were significantly different. Moreover, the substrate concentration mainly affected the reaction rate and activity of anammox bacteria and hardly affected the relative abundance of functional bacteria. But temperature reduction resulted in a significant decline in the relative abundance of anammox bacteria. Changes in metabolic pathways suggested that this PNA system may respond to low substrate concentrations and low temperatures by facilitating substance transport and reducing energy consumption. These results provide a deep insight into the microbial community dynamics and interactions in the treatment of mainstream wastewater by PNA process.

Endogenous partial denitritation as an efficient remediation to unstable partial nitritation-anammox (PNA) process: Bacteria enrichment and superior robustness

The application of partial nitritation-anammox (PNA) process suffers severe obstacles due to the instability of partial nitritation (PN) process. This study sought to evaluate the feasibility of endogenous partial denitratation (EPD) as a remediation or alternative to supply nitrite for the unstable PNA process. A novel strategy of optimal organics utilization through pre-anaerobic carbon storage and post-anoxic endogenous denitrification coupled with anammox was developed in a single-stage bioreactor treating actual municipal wastewater with low C/N (∼3.2). Specifically, the undesired NO2−/NH4+ ratio (2.4 to 0.04) and nitrate accumulation were obtained by increasing the aeration rate (0.6 to 1.8 L/min) to simulate the PN instability. Delightedly, advanced nitrogen removal efficiency (92.1%) was maintained despite a dramatic decrease in nitrite accumulation ratio from 97.6% to 2.6%. This was attributed to the significant increase in anammox contribution to total nitrogen removal from 30.2% to 80.5%. The steady nitrite flux supplied from EPD coupled with PN (EPD contribution increased from 0 to 97.0%) was assumed to be the main reason for the continually increasing abundance and bioactivity of anammox bacteria. Both the anammox bacteria (1.5%, Ca. Brocadia) and glycogen accumulating organisms (6.0%, responsible for EPD) were enriched and coexisted stably in the single reactor. Our study confirms that coupling EPD with anammox has great potential as a remediation for the unstable mainstream PNA process.

Long term analysis of N2O emission from partial nitritation anammox process under oxygen limitation

Partial nitritation with anammox (PNA) process was achieved during 300 days to investigate the fate of N2O and NO. N2O emission factor increased from 0.4 ± 0.1 % up to 6.1 ± 0.3 % during intensification phase of 5 months and progressively stabilized at 2.0 ± 0.1 % after 10 months without any significant emission of NO. The emission of N2O correlated with the ammonium consumption rate and the oxygen transfer rate. Experiment carried out in anoxic condition suggested that heterotrophic denitrification poorly contributed. Measurements of δ15N, δ18O and SP of N2O demonstrated that its production resulted from the reduction of nitrite. The stimulating effect of nitrite on N2O production was demonstrated with specific tests and observed during transient nitrite accumulation periods. This study highlighted the importance of nitrite and oxygen transfer rate control for future control strategies aiming to mitigate N2O emission in PNA system.

Revealing the effect of biofilm formation in partial nitritation-anammox systems: Start-up, performance stability, and recovery

Successful application of partial nitritation-anammox (PNA) processes is currently and primarily associated with biofilm systems. Biofilm characteristics significantly influence start-up, performance stability, and recovery. Here, two PNA systems with and without carriers were implemented simultaneously for treating wastewater containing 50 mg-NH4/L. The performance characteristics of these two PNA systems were compared. Stable nitrogen removal efficiencies of 76.3 ± 2.8% and 72.9 ± 1.6% were obtained for suspended sludge and biofilm systems, respectively. The slow process of biofilm colonization resulted in a long start-up time in the biofilm system. Biofilm enrichment and protection conferred stable performance when exposed to aeration shock. The suspended sludge system displayed good elasticity during performance recovery after shock compared to the slow recovery in the biofilm system. Moreover, suitable control of dissolved oxygen could improve the activity and abundance of the functional microbes. This study provides new insights into the operation and control of PNA systems for treating mainstream wastewater.

Rapid initiation of a single-stage partial nitritation-anammox process treating low-strength ammonia wastewater: Novel insights into biofilm development on porous polyurethane hydrogel carrier

Media-supported biofilm is a powerful strategy for growth and enrichment of slow-growing microorganisms. In this study, a single-stage nitritation-anammox process treating low-strength wastewater was successfully started to investigate the biofilm development on porous polyurethane hydrogel carrier. Suspended biomass migration into the carrier and being entrapment by its internal interconnected micropores dominated the fast initial colonization stage. Both surface-attached growth and embedded growth of microbes occurred during the following accumulation stage. Fluorescence in situ hybridization analysis of mature biofilm indicated that ammonium-oxidizing bacteria located at the outer layers featured a surface-attached growth, while anammox microcolonies housed in the inner layers proliferated as an embedded-like growth. In this way, the growth rate of anammox bacteria (predominated by Candidatus Kuenenia) could be 0.079 d-1. The anammox potential of the biofilm reactor reached 1.65 ± 0.3 kg/m3/d within two months. This study provides novel insights into nitritation-anammox biofilm formation on the porous polyurethane hydrogel carrier.

Comparison of Different Carriers to Maintain a Stable Partial Nitrification Process for Low-Strength Wastewater Treatment.

Practical application of the partial nitritation–anaerobic ammonium oxidation (anammox) process has attracted increasing attention because of its low operational costs. However, the nitritation process, as a promising way to supply nitrite for anammox, is sensitive to the variations in substrate concentration and dissolved oxygen (DO) concentration. Therefore, a stable supply of nitrite becomes a real bottleneck in partial nitritation–anammox process, limiting their potential for application in mainstream wastewater treatment. In this study, five 18-L sequencing batch reactors were operated in parallel at room temperature (22°C ± 4°C) to explore the nitritation performance with different carrier materials, including sepiolite-nonwoven carrier (R1), zeolite-nonwoven carrier (R2), brucite-nonwoven carrier (R3), polyurethane carrier (R4), and nonwoven carrier (R5). The ammonia oxidation rate (AOR) in R1 reached the highest level of 0.174 g-N L−1 d−1 in phase II, which was 1.4-fold higher than the control reactor (R4). To guarantee a stable supply of nitrite for anammox process, the nitrite accumulation efficiency (NAE) was always higher than 77%, even though the free ammonia (FA) decreases to 0.08 mg-N/L, and the pH decreases to 6.8 ± 0.3. In phase V, the AOR in R1 reached 0.206 g-N L−1 d−1 after the DO content increase from 0.7 ± 0.3 mg/L to 1.7 ± 0.3 mg/L. The NAE in R1 was consistently higher than 68.6%, which was much higher than the other reactor systems (R2: 43.8%, R3: 46.6%, R4: 23.7%, R5: 22.7%). Analysis of 16S rRNA gene sequencing revealed that the relative abundance of Nitrobacter and Nitrospira in R1 was significantly lower than other reactors, indicating that the sepiolite carrier plays an important role in the inhibition of nitrite-oxidizing bacteria. These results indicate that the sepiolite nonwoven composite carrier can effectively improve the nitritation process, which is highly beneficial for the application of partial nitritation–anammox for mainstream wastewater treatment.

Nitrogen Removal from Real Sewage Pretreated with Anaerobic Membrane Bioreactors Using One-Stage Partial Nitritation-Anammox Process with Hydroxyapatite Crystallization and Partial Nitritation-Anammox Granule

Nitrogen Removal from Real Sewage Pretreated with Anaerobic Membrane Bioreactors Using One-Stage Partial Nitritation-Anammox Process with Hydroxyapatite Crystallization and Partial Nitritation-Anammox Granule

Start-up a novel coupling process with partial nitritation, partial denitrification and anaerobic ammonia oxidation in a single sequencing batch reactor

A novel process, named single-stage PNDA, that integrates the partial nitritation, partial denitrification and anaerobic ammonia oxidation in a single lab-scale sequencing batch reactor was developed to treat moderate-strength ammonia wastewater (220 mg N/L). Firstly, a single stage partial nitritation-anammox process was started up with the total nitrogen removal efficiencies of approx. 76.22%, and the remaining free ammonia concentration could produce a more sustained inhibition of nitrite oxidizing bacteria(NOB) than low DO condition. Then, the proposed one-stage PNDA process achieved an average total nitrogen removal efficiency of 85.29% by adding sodium acetate in the influent at a concentration of 50 mg COD/L. Microbial community characterization revealed that ammonia-oxidizing bacteria, anammox bacteria, NOB and partial denitrification bacteria coexist in the suspended sludge. The significant enrichment of Thauera and the dominance of Ca. Anammoxoglobus in the Anammox biomass indicate their important role in the improved nitrogen removal performance. This single-stage PNAD process can potentially be applied to further improve the total nitrogen removal efficiency of PN/A process.

Insights into the synergy between functional microbes and dissolved oxygen partition in the single-stage partial nitritation-anammox granules system

The rapid start-up and stable operation of the single-stage partial nitritation-anammox (PNA) process remains a challenge in practical applications. An integrated investigation of nitrogen removal performance, sludge characteristics, activity and abundance, and microbial dynamics was implemented for 360 days via an airlift internal circulation reactor. During long-term operation, the reactor realized a stable dissolved oxygen (DO) partition and cultivated granular sludge. The nitrogen removal rate increased from 0.15 kg-N/m3/d to 1.24 kg-N/m3/d, and a high nitrogen removal efficiency of 82.6% was obtained. A stable DO partition further accelerated the bioreaction rates and enhanced the activity of functional microbes. The activities of ammonia oxidation and anammox reached 1.21 g-N/g-VSS/d and 1.43 g-N/g-VSS/d, respectively. Sludge granulation efficiently enriched the abundances of Candidatus Brocadia (7.4%) and Nitrosomonas (5.2%). These results demonstrated that efficient DO partition and stable culture of granular sludge could enhance the synergy of functional microbes for autotrophic nitrogen removal.