To solve the bottleneck of the unstable accumulation of nitrite in the partial nitrification (PN)-anammox (AMX) in municipal wastewater treatment, a novel process called partial denitrification ...(PD)-AMX has been developed. PD-AMX, which is known for cost-efficiency and environmental friendliness, has currently exhibited a promising potential for the removal of biological nitrogen from municipal wastewater and has attracted much research interest regarding its process mechanisms, as well as its practical applications. Here, we review the recent advances in the PD process and its coupling to the anammox process, including the development, basic principles, main characteristics, and critical process parameters of the stable operation of the PD-AMX process. We also explore the microbial community and its characteristics in the system and summarize the knowledge of the dominant bacteria to clarify the key factors affecting PD-AMX. Then, we introduce the engineering feasibility and economic feasibility as well as the potential challenges of the process. The induction and implementation of partial denitrification and maintenance of mainstream anammox are critical issues to be urgently solved. Meanwhile, the implementation of a full mainstream anammox application remains burdensome, while the mechanism of partial denitrification coupled to anammox needs to be further studied. Additionally, stable operation performance and process control1 methods need to be optimized or developed for the PD-AMX system for better engineering practice. This review can help to accelerate the research and application of the PD-AMX process for municipal wastewater treatment.
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•PD-AMX provides a promising alternative for N removal from municipal wastewater.•Several strategies have been intensively developed to enrich PD and AMX microbes.•DO, pH, T, and C/N ratio are the main factors affecting PD-AMX process.•AMX biomass retention can be fulfilled by sludge granulation and biofilm formation.
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•An NRR of 0.85 kg-N/m3/d was obtained by a PNA-AIPBR with 250-mg NH4/L influent.•The TNRE of the PNA-AIPBR increased to > 85% within 38 days.•Dual inner circulation and aeration ...regulation are crucial for nitrogen removal.•Spatial distribution of autotrophic N removal biochemical reaction was optimized.•Dual inner circulation/multi-partition promote AOB and AnAOB enrichment/synergism.
The single-stage autotrophic nitrogen removal (ANR) process is impeded by a long start-up cycle and unstable operation performance. In this study, an airlift inner-circulation partition bioreactor (AIPBR) was operated continuously for 215 days to explore methods of strengthening the performance and stable operation of the single-stage ANR system. AIPBR start-up period took around 38 days, the total nitrogen removal efficiency was > 85% on day 35. With the decrease of hydraulic retention time and the increase of aeration rate, the nitrogen removal rate increased to 0.85 ± 0.02 kg-N/m3/day. The sludge morphology gradually changed into dark-red floc-coupled granular sludge. Nitrosomonas (9.95%) and Candidatus Brocadia (6.41%) were dominant in the sludge. During long-term operation, AIPBR achieved the dual inner circulation of sewage and sludge and then formed effective dissolved oxygen and sludge partitions to provide a suitable growth environment for various functional bacteria, promote synergy between them, and strengthen the ANR performance.
•Efficient NREs were achieved in PNA-S and PNA-B systems with low-ammonia influent.•PNA-S system showed good adaptability during start-up time.•Enrichment and protection of biofilm improve ...performance stability.•Biofilm formation inhibits recovery from shock due to the growth of NOB.
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.
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•DO partition was obtained in a single-stage PNA system.•A high TNRE of 82.6% was achieved, and the NRR reached 1.24 kg-N/m3/d.•The synergy between different functional microbes was ...enhanced via DO partition.•Sludge granulation enriched the functional microbes and promoted the synergy.
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.
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•A high NRE of 70% was obtained by a PNA-AICB with 50 mg-NH4/L influent.•Control of DO and aeration rate were the key factors for the stable operation.•A long time was needed for ...performance recovery via aeration adjustment.•Candidatus Brocadia and Nitrosomonas were dominant after the recovery.•Activated AOB, dominated AMX, suppressed NOB & controlled HB were vitally important.
A one-stage airlift internal circulation biofilm reactor was continuously operated for 668 days to treat 50 mg/L of ammonia wastewater to pursue the long-term stability of partial nitritation and anammox (PNA) process. The operational performance and microbial community structure of the biofilm and the flocs were investigated. A nitrogen removal efficiency (NRE) of 70% was obtained successfully at a dissolved oxygen (DO) of 0.05–0.15 mg/L by regulating aeration rate. The microbial analysis indicated Candidatus Brocadia (29.5%) and Nitrosomonas (6.8%) were dominant in both biofilms and flocs. It was found that DO control and aeration rate were the key factors in performance stability, and a stable performance could be recovered and maintained under oxygen-limiting conditions. Further, the achievement of activated ammonia oxidation bacteria (AOB), dominated anammox bacteria (AMX), suppressed NOB, and controlled heterotrophic bacteria (HB) in the biofilms played a major role in the long-term stable operation.
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.
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•TN removal efficiency reached 95.1 % at the optimum influent C/N ratio of 2.0•Efficient nitrogen removal was achieved via PNA coupled with denitrification•AnAOB activity and abundance declined persistently with the increase in C/N ratio•Metabolisms involving material exchange and organic degradation were enhanced
Autotrophic nitrogen removal (ANR) processes have not been widely applied in wastewater treatment due to their long start-up time and unstable performance. In this study, a novel dissolved ...oxygen-differentiated airlift internal circulation reactor was developed to enhance ANR from wastewater. During 200 days of continuous operation, the reactor start-up was achieved within 30 days; a high total nitrogen removal efficiency of 80% was achieved and stably maintained under an aeration rate of 0.90 L/min and hydraulic retention time of 6 h. Additionally, the color of sludge went from a light yellow to dark red, and the amount and size of the micro-granules increased obviously. Medium-sized (1.0–2.5 mm) micro-granules accounted for 72.4% on day 190. The specific anammox activity increased from 0.53 to 1.43 g-N/g-VSS/d, while the SNOA decreased from 0.93 to 0.08 g-N/g-VSS/d. Furthermore, the microbial analysis showed that the Nitrosomonas (4.2%) and Candidatus Brocadia (22.6%) were enriched and formed the micro-granules after the reactor's long-term operation. The results indicate that novel configuration realizes the partitioning of dissolved oxygen (DO), optimizes nitritation and anammox reactions, and accelerates biochemical reactions, thereby enhancing ANR performance. This study provides a practical alternative to enhance ANR performance and a scientific basis for the development and application of novel nitrogen removal reactors.
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•A novel reactor for autotrophic nitrogen removal process was developed.•A high TNRE of 80% was achieved and maintained stable.•The effective partition of DO was realized.•The functional bacteria were enriched and formed the micro-granules successfully.•Partition control and granulation are effective pathways for enhancing performance.
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•The deteriorated AIPBR was successfully recovered with an TNRE of 71.93%.•Flexible use of FNA and FA to inhibit NOB and reduce the toxic effects of FNA.•AR regulation and DO ...partitioning are critical for PNA systems to recover.•Recovery was by reconstructing granular sludge and functional microbes synergy.
Partial nitritation-anammox (PNA) deteriorates easily and is difficult to recover. After an airlift inner-circulation partition bioreactor was impacted by low NH4+–N wastewater containing organic matter, Nitrospira and Denitratisoma propagated rapidly, granular sludge disintegrated, and the total nitrogen removal efficiency (TNRE) decreased from 68.27 % to 5.97 %. This study used a unique strategy to recover deteriorated single-stage PNA systems and explored the mechanism of rapid performance recovery. The TNRE of the system recovered up to 61.77 % in 43 days. The high nitrogen loading rate and hydraulic shear force from the airlift caused the sludge in the reactor to granulate again. The microbial community structure recovered, with a decrease in the abundance of Nitrospira (0.05 %) and enrichment of Candidatus Brocadia (8.82 %). A favorable synergy among functional microbes in the reactor was thus re-established, promoting the rapid recovery of the nitrogen removal performance. This study provides a feasible recovery strategy for PNA processes.
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•UASB–AnMBR was applied for practical swine wastewater (SW) treatment.•A 96 % COD removal, 63 % TP removal, and 0.4 L/g-CODadd biogas yield were achieved.•AnMBR was operated for 53 d ...without severe membrane fouling.•Aceticlastic degradation pathway dominated in the SW treatment.•Microbial enrichment/synergism during anaerobic digestion was optimized.
To address the existing economic and environmental issues associated with swine wastewater (SW) treatment, a process combining up-flow anaerobic sludge blanket (UASB) and anaerobic membrane bioreactor (AnMBR) was developed and continuously operated for 137 d. Bioreactor conversion and microbial community dynamics in reactors were analyzed. The UASB–AnMBR process yielded excellent pollutants removal efficiencies of 96% and 63% for chemical oxygen demand (COD) and total phosphorous (TP), respectively. More than 60% of Firmicutes (Terrisporobacter, Turicibacter, and Clostridium sensu stricto 1), which were dominated by Methanosaeta and Methanobacterium with relative abundances of 58.6% and 36.8% in the UASB and 22.5% and 40.3% in the AnMBR, respectively, converted complex compounds into organic acids for methanogenesis. This research presented an analysis of pollutants removal and microbial dynamics of UASB–AnMBR, which significantly affected the large-scale application of UASB–AnMBR process.
