Completely Autotrophic Nitrogen Removal Over Nitrite Process Research Articles

Effect of aeration on low-substrate CANON process

The completely autotrophic nitrogen removal over nitrite (CANON) is a new type of nitrogen removal process developed in recent years. The control of dissolved oxygen (DO) in this process is relatively stringent, especially in low-substrate wastewater treatment. However, the results of studies on the operation of the process in different aeration modes are still controversial, and investigations on biofilm type CANON reactors are limited. In this study, a pilot-scale CANON bioreactor filled with suspended carriers was investigated on the treatment of wastewater at low ammonium concentrations, and the effect of the aeration mode on autotrophic nitrogen removal was evaluated. Seven conditions with various aeration on/off times and DO levels were tested. The results showed that an intermittent aeration with a 20-min/20-min aeration on/off time and DO concentrations of 1.0–1.3 mg/L at the end of the aeration period was appropriate, potentially inhibiting nitrite oxidizing bacteria (NOB) and keeping the total nitrogen (TN) removal rate at a relatively high level of 76.7% ± 2.5%. In the optimal aeration mode, the reactor achieved effluent TN and NH4+-N concentrations of (11.1 ± 3.3) mg/L and (3.6 ± 2.3) mg/L, respectively, with a hydraulic retention time of 12 h and an influent NH4+-N concentration of (48.6 ± 9.4) mg/L at 30.1°C ± 2.2°C. The results of metagenomic sequencing for microorganisms on carriers indicated that the main nitrogen removal bacteria in the reactor were Proteobacteria, Planctomycetes, and Nitrospirae. The NOB genus Nitrospira was completely inhibited by intermittent aeration. Candidatus Kuenenia had strong adaptability to low-concentration wastewater.

The rapid start-up of CANON process through adding partial nitration sludge to ANAMMOX system

This study aimed to start up the completely autotrophic nitrogen removal over nitrite (CANON) process after adding partial nitration (PN) sludge to the ANAMMOX reactor, so as to help the rapid start-up and stable operation of the CANON process in practical engineering applications. There were three steps in the research: cultivating the PN sludge, building a reliable ANAMMMOX system, and finally starting and running the CANON process. The PN sludge was successfully cultivated in less than 45 days with around 90% nitrite accumulation rate. The ANAMMOX reactor enriched a significant quantity of red granular sludge within 70 days, achieving the maximum nitrogen removal rate of 1.74 kg/(m3·d). Eventually, the CANON reactor was started up successfully, which achieved 95.08% of average ammonium removal efficiency and 84.51% of average total nitrogen removal efficiency in 60 days. The residual recalcitrant nitrite-oxidizing bacteria in the CANON process was successfully inhibited by intermittent aeration and 12 mg/L free ammonia in UASB reactor. Besides, Candidatus Kuenenia, Candidatus Brocadia and Nitrosomonas were the main functional microorganisms involved in the CANON process.

Integrated effects of operational temperature, HRT, and influent ammonium concentration on a CANON coupling with denitrification process treating for digested piggery wastewater: performance and microbial community.

In this study, an improved system called the completely autotrophic nitrogen removal over nitrite (CANON) process was presented and coupled with denitrification for the treatment of digested piggery wastewater (DPW). The effects of operating parameters, including hydraulic retention time (HRT) (1.6d → 1.0d), influent NH4+-N concentration (350mgL-1 → 600mgL-1), and temperature (41℃ → 17℃), on the nitrogen removal performance and response characteristics of microbial population were investigated. Results showed that all considered parameters caused a remarkable effect on NH4+-N and total nitrogen removal efficiencies, and the chemical oxygen demand was more markedly affected by temperature. Candidatus_Kuenenia, Candidatus_Brocadia, Denitratisoma, norank_o_Xanthmonadales, norank_p_WWE3, and SM1A02 were the dominant genera influencing nitrogen removal in the improved CANON system for treating DPW. Redundancy discriminant analysis showed that the biological structure was positively correlated with the influent ammonium concentration, temperature, and HRT. The relative abundance of Candidatus_Kuenenia was perfectly correlated with HRT and temperature. However, environmental factors did not affect Candidatus_Brocadia and norank_p_WWE3. norank_c_Ardenticatenia, SM1A02, and norank_f_SJA-28 were all positively correlated with influent ammonium nitrogen concentration, but not correlated with HRT and temperature. The improved CANON process realized the nitrogen removal under high ammonium (NH4+-N) concentration and low C/N wastewater.

Decoding the response of complete autotrophic nitrogen removal over nitrite (CANON) performance and microbial succession to hydrazine and hydroxylamine: Linking performance to mechanism

The influence of hydrazine (N2H4) and hydroxylamine (NH2OH) on performance and microbial community structures of complete autotrophic nitrogen removal over nitrite (CANON) process were assessed in this study. Experimental results demonstrated that CANON process was successfully started up and got total nitrogen removal efficiency (TNRE) of 53.6 % ± 9.8 % and 56.4 % ± 6.5 % under 1.0 and 0.5 mg L−1 N2H4 and NH2OH, respectively. N2H4 and NH2OH promoted activity of ammonia-oxidizing bacteria (AOB) and anaerobic ammonium oxidation bacteria (AnAOB), and inhibited activity of nitrite-oxidizing bacteria (NOB). Meanwhile, the stable operation of CANON process could be maintained without N2H4 auxiliary. While, performance assisted by NH2OH was fluctuated without NH2OH addition, suggesting that both N2H4 and NH2OH had a persistent and reversible inhibition on NOB. This study reveals new insights into influence of N2H4 and NH2OH on CANON performance.

Efficient pollutant removal from deodorization wastewater during sludge composting using MBR-CANON process

Sludge composting is one of the most economical and effective sludge disposal method at present. However, the composting process releases massive odorous gas, and the gas removal process produces a large amount of deodorizing wastewater with low C/N ratio (named as composting wastewater). In this study, completely autotrophic nitrogen removal over nitrite (CANON) process was adopted for treating composting wastewater. After treated, the ammonia decreased to 0–5 mg L−1, and the total nitrogen removal achieved to 0.200 kg m−3 d−1. Although the introduction of composting wastewater reduced the hydroxylamine oxidoreductase enzyme activity, heme-c, and hzo gene, all of them could be recovered. Microorganisms secreted more extracellular polymeric substances to counteract the cell-damage caused by harmful substances. Chloroflexi, Proteobacteria, and Planctomycetota were detected as the dominant phyla in the system, and the relative abundances of Candidatus_Kuenenia and Nitrosomonas reached 19.8% and 2.8%, respectively. CANON process could be used for treating composting wastewater.

Effects of hydroxylamine and ammonia concentration on the stability of CANON process

This study investigated the effects of hydroxylamine (NH2OH) dosage and duration on the restoration of the deteriorated completely autotrophic nitrogen removal over nitrite (CANON) process due to the overgrowth of nitrite oxidizing bacteria (NOB) under conditions of low and high ammonia concentration. The results showed that the nitrogen removal efficiency of CANON process could be restored to more than 80% in 5 days after 5 mg/L NH2OH addition. However, once the NH2OH was inexistence in the reactor under the low ammonia concentration, the NOB was restored and thus producing nitrate. Upon shock by 133 mg/L nitrite and low temperature, the activity of the functional consortium was inhibited and then recovers under the assist of NH2OH. Compared to low ammonia concentration, the NO3−-Nproduced/NH4+-Nconsumed ratio was more stable and closer to 0.11 under high ammonia concentration after stopping NH2OH addition due to NOB was also inhibited by free ammonia (FA). The analysis for microbial community showed that the relative abundance of anaerobic ammonia oxidation bacteria (AAOB) increased from 6.11% to 12.7% with the enhancement of NH2OH dosage, while barely affected by ammonia concentration. However, the relative abundance of ammonium oxidizing bacteria (AOB) increased slightly from 2.96% to 3.62%, and 3.62% to 4.25%, respectively, under the improvement of NH2OH dosage and ammonia concentration. The relative abundance of NOB was less affected by NH2OH dosage, while it decreased from 1.45% to 0.78% when influent NH4+-N increased from 50 mg/L to 200 mg/L.

Effects of alkalinity addition with different strategies on CANON process: Start‐up, performance, and microbial community

AbstractThe effects of alkalinity addition with different strategies on the start‐up, performance, and microbial community of completely autotrophic nitrogen removal over nitrite (CANON) were investigated over 450 days. In phase I, the alkalinity was increased gradually from 300 to 2,000 mg/L to obtain the optimal range. In phase II, the reactor was restarted to verify the appropriate alkalinity value of 1,600 mg/L. The fact that it only took 90 days (phase I: 170 days) to complete the start‐up of CANON in phase II demonstrated that an alkalinity value of 1,600 mg/L was suitable when the influent NH4+‐N concentration was 200 mg/L (alkalinity/NH4+‐N = 8:1). The slope (k = 2.00) of NH4+‐N concentration decrease in phase II during the start‐up process was significantly higher than that in phase I (k = 1.50). High removal efficiencies of NH4+‐N (98%) and TN (80%) were attained in both phases. Specific anaerobic ammonium oxidation (anammox) activity tests showed that the anammox activity of the two phases reached 3.31 and 5.31 mg TN/(g VSS·h), respectively. High‐throughput sequencing analysis revealed that appropriate alkalinity could promote the enrichment of Candidatus Brocadia, C. Jettenia, and C. Kuenenia (total abundance of 31.96%) while effectively inhibiting Nitrospira (abundance of less than 0.50%).Practitioner Points An alkalinity/NH4+‐N ratio of 8 promoted the rapid start‐up and stable performance of CANON. NH4+‐N and TN removal efficiencies of 98% and 80%, respectively, were obtained. High alkalinity promoted the enrichment of Candidatus Brocadia, Candidatus Jettenia, Candidatus Kuenenia and inhibited Nitrospira.

Effects of fulvic acid on the denitrification performance of completely autotrophic nitrogen removal over nitrite (CANON) process for the treatment of landfill leachate

Ammonia reduction treatment in landfill leachate is primarily necessary to prevent toxic impacts for environmental concerns on aquatic life in surface waters. Fulvic acid (FA) is one of the refractory organic humus in landfill leachate. In this present study, the potential effects of FA on completely autotrophic nitrogen removal over nitrite (CANON) systems were studied. This study focuses on the CANON reaction startup in a short time. Effects of FA on denitrification performance, sludge properties and microbial community of CANON process. The CANON process was started in a short period of time. Ammonia nitrogen (NH4+-N) and total nitrogen (TN) removal efficiency was 98% and 80%, respectively. In the CANON process, part of the nitrification and anaerobic ammonia oxidation reaction proceed simultaneously and reach the maximum rate in the aerobic aeration stage at the initial stage of the reaction. After reaching the stable operation stage, FA was added 50 mg/L, 100 mg/L, 150 mg/L and 200 mg/L, respectively. As the FA concentration reached 200 mg/L, FA addition was stopped and the recovery was observed for a period of time. Nitrogen removal performance, sludge properties and microbial communities of the CANON process, was becoming more and more obvious with the stepwise increase in Humic acid (HA) and FA concentration. With the FA concentration increased from 50 mg/L to 200 mg/L, NH4+-N and TN removal efficiency decreased from 98.00% to 80.00%–71.32% and 48.18%, respectively. Sludge concentration decreased from 3.291 g/L to 2.245 g/L. Abundance of both ammonia-oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing bacteria (AnAOB) decreased gradually, while nitrite-oxidizing bacteria (NOB) increased. After the addition of FA was stopped, the denitrification performance and granular sludge activity of CANON process were evaluated. This study can be used for application of CANON process for the treatment of landfill leachate.

Evaluation of the joint effects of Cu2+, Zn2+ and Mn2+ on completely autotrophic nitrogen-removal over nitrite (CANON) process

The completely autotrophic nitrogen-removal over nitrite (CANON) process has merits in energy saving and consumption reducing, thus being considered as an attractive alternative over the common denitrification technology. In this study, the effects of three common heavy metals (Cu2+, Zn2+ and Mn2+) in wastewater to the CANON process were evaluated comprehensively. A central composite design with response surface methodology was utilized to investigate the joint effect of these three metal ions on the nitrogen removal performance of CANON process. In accordance with the determined optimal dosage in batch tests, four bioreactors were established with different amounts of heavy metal dosage in long-term operation, which determined the optimal concentrations for Cu2+, Zn2+ and Mn2+ to be 0.25, 0.81 and 1.00 mg/L, respectively. However, the optimal dosing level determined in batch tests showed no promotion during long-term experiment. This indicated that the actual concentration of heavy metals in bioreactors during long-term operation could be higher than expectation, leading to the difference between short-term tests and long-term experiment. The distribution of metal ions revealed that Mn2+ was mainly absorbed in anammox bacteria cells while Cu2+ and Zn2+ were mostly identified inside AOB cells. Moreover, the addition of heavy metals consistently showed positive effects for the relative abundance of AOB, while only a low level of dosage could promote the abundance of anammox bacteria. Furthermore, a mathematical model was established to simulate the CANON system considering the impacts of heavy metals, which was calibrated and validated using independent dataset in this study.

Enhancing the in-situ enrichment of anammox bacteria in aerobic granules to achieve high-rate CANON at low temperatures

In this study, a high-rate CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) process was started up successfully by enhancing the in-situ enrichment of anammox bacteria in aerobic granules at conditions relevant for mainstream wastewater treatment. Firstly, to provide nitrite for anammox bacteria growth efficient nitrite-oxidizing bacteria (NOB) repression was rapidly achieved and stably maintained. Both low dissolved oxygen (DO) and ammonium concentrations ratio (DO/NH4+ <0.15) and selective washing-out of NOB-preferred smaller particles at short hydraulic retention time (HRT, 25-15 min) contributed to the NOB repression. Then the stepwise down-regulating DO concentrations from 2.8 to 1.2 mg/L enhanced the enrichment of anammox bacteria in the aerobic granules. The enriched anammox species was dominated by Ca. Brocadia sapporoensis with the estimated growth rate of 0.008–0.013 d−1 at 15 °C. Chloroflexi and Chlorobi-affiliated bacteria were also significantly enriched in the granules, which may benefit the anammox bacteria activity and growth. At the end of this study, the average total nitrogen removal rate and efficiency of the granular CANON process respectively reached 1.26 kg N·m−3·d−1 and 68% treating low-strength ammonium (∼50 mg N·L−1) wastewater under such aggressive conditions (DO = 0.8–1.5 mg/L, HRT< 1.0 h, and T = 15 °C). Overall, the aerobic granules provided a habitable niche for the proliferation and almost complete retention of the anammox bacteria. This study provides a roadmap for in-situ starting up of high-rate CANON process for mainstream wastewater treatment with aerobic granules as inoculum.

Effect of Filter Medium on the Enhancement of Complete Autotrophic Nitrogen Removal over Nitrite Process in a Tidal Flow Constructed Wetland

This study attempted to shorten the time wasted at the startup of a complete autotrophic nitrogen removal over nitrite (CANON) process in a tidal flow constructed wetland (TFCW) to achieve higher nitrogen removal rates. Thus, the starting performance and the related microbiological characteristics of different kinds of filter media filling the TFCW were explored at an appropriate drainage rate. The results showed that the physicochemical properties of the filter medium could significantly affect the quantity and activity of the functional microbes (especially ANAMMOX bacteria) enriched in the TFCWs, leading to fluctuations of the starting time and nitrogen transformation rates of the systems filled with five different kinds of filter media. Compared with that of gravel, the quantity and activity of ANAMMOX bacteria in the bed could be enhanced to different degrees as the TFCW was filled with ceramsite, zeolite, broken bricks, and lobster shells. Correspondingly, the starting times of the TFCWs with the CANON process were shortened, and their nitrogen removal performances could also be optimized. When the hydraulic loading rate of the TFCW was 0.96 m3·(m2·d)-1, the initiation of the CANON process could be accomplished successfully in the system filled with lobster shells within 300 cycles, since AOB and ANAMMOX bacteria could become dominant quickly in the packing bed. Moreover, the TN and NH4+-N removal rates could reach up to (88.37±1.19)% and (91.03±0.66)%, respectively, followed by those of broken bricks, zeolite, ceramsite, and gravel.

Nitrogen removal and microbial community characteristics of CANON process enhanced by static magnetic field at ambient temperature

In this study, a completely autotrophic nitrogen-removal over nitrite (CANON) process was started in a membrane bioreactor at ambient temperature, to which a static magnetic field (SMF) at a 20 ​mT intensity was applied to evaluate the enhancement of the CANON process by SMF. The results indicated that the SMF was capable of enhancing the nitrogen removal rate and shortening the start-up period of the CANON process. After running for about 8 months, the average nitrogen removal rate of the CANON process with SMF exposure was 324.8 ​± ​64.8 gN/m3/d, which was 30.4% higher than that of the control. Moreover, the SMF has the potential to protect the CANON process from being inhibited by low temperatures. Importantly, the SMF induced the synthesis and secretion of the extracellular polymeric substance (EPS) of the activated sludge and simultaneously reduced the zeta potential. This was conducive to the aggregation of the sludge material and the formation of an oxygen gradient in the sludge flocs, which promoted the coexistence of ammonium-oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing bacteria (AnAOB). The high-throughput 16S rRNA gene sequence analysis confirmed that the abundances of the Nitrosomonas and Candidatus Brocadia genera, respectively the main AOB and AnAOB, were enhanced by SMF exposure.

Modeling of completely autotrophic nitrogen removal process with salt and glycine betaine addition

The susceptibility of the completely autotrophic nitrogen removal over nitrite (CANON) process to high salinity limits its widespread application. The addition of glycine betaine (GB), a type of compatible solutes that could resist osmotic stress, could be an effective strategy to enhance the salt tolerance ability of aerobic and anaerobic ammonium oxidizing bacteria (AOB and anammox bacteria) involved in the CANON process. This study aims to make use of mathematical modeling to systematically investigate the effects of salt and GB addition on the activities of AOB and anammox bacteria and the treatment performance of the CANON process. To this end, a series of dedicated batch tests and long-term experiments for the CANON process with salt and GB additions were conducted and the data was used to calibrate and validate the model established to consider the relationships between salt and GB concentrations and bacterial growth in the CANON process. The calibrated/validated CANON process model was then applied to simulate the long-term impacts of GB addition concentration and sludge retention time (SRT) on the CANON process. The results showed that 1 mM GB addition and a SRT of 50 days would be sufficient to protect AOB and anammox bacteria under the high salinity (30 g/L NaCl) conditions studied and therefore reduce the time needed to recover the treatment performance of the CANON process from exposure to salt inhibition by 35%–40%.

New insights into nitrous oxide emissions in a single-stage CANON process coupled with denitrification: thermodynamics and nitrogen transformation.

The dynamic characteristics of N2O emissions and nitrogen transformation in a sequencing batch biofilm reactor (SBBR) using the completely autotrophic nitrogen removal over nitrite (CANON) process coupled with denitrification were investigated via 15N isotope tracing and thermodynamic analysis. The results indicate that the Gibbs free energy (ΔG) values of N2O production by the nitrifier denitrification and heterotrophic denitrification reactions were greater than that of NH2OH oxidation, indicating that N2O was easier to produce via either nitrifier and heterotrophic denitrification than via NH2OH oxidation. Ammonia-oxidizing bacteria (AOB) denitrification exhibited a higher fs 0 (the fraction of electron-donor electrons utilized for cell synthesis) than NH2OH oxidation. Therefore, AOB preferred the denitrification pathway because of its growth advantage when N2O was produced by the AOB. The N2O emissions by hydroxylamine oxidation, AOB denitrification and heterotrophic denitrification in the SBBRs using different C/N ratios account for 5.4-7.6%, 45.2-60.8% and 33.8-47.2% of the N2O produced, respectively. The total N2O emission with C/N ratios of 0, 0.67 and 1 was 228.04, 205.57 and 190.4 μg N2O-N·g-1VSS, respectively. The certain carbon sources aid in the reduction of N2O emissions in the process.

Feasibility of CANON process for treating nitrogenous wastewater containing heavy metals

AbstractThe appearance of heavy metals in wastewater brings a major burden to wastewater treatment plants, due to the high toxicity to microorganisms. Several commonly used heavy metals, including Zn(II), Cd(II), Hg(II), and Pb(II) were adopted to clear the individual and joint toxicity to the completely autotrophic nitrogen removal over nitrite (CANON) process in six sequencing batch reactors. The obtained results suggested that the nitrogen removal performances were transiently inhibited, but rapidly recovered. The restoration period under the stress of Hg(II) and Pb(II) was shorter than that under Zn(II), Cd(II), and the joint heavy metals. During the long‐term exposure, Cd(II) in 1mg L−1 slightly inhibited the nitrogen removal, while Zn(II), Hg(II), Pb(II), and mixture showed a negligible impact on CANON process. The defense of extracellular polymeric substances (EPS), the good adaptability of functional bacteria, and the inducement of resistant genera by heavy metals all contributed to the robustness and stability of CANON process. Therefore, it is feasible to treat nitrogenous wastewater containing low heavy metals using CANON process. © 2020 Society of Chemical Industry

Response and Adaptation of Microbial Community in a CANON Reactor Exposed to an Extreme Alkaline Shock

Responses of a microbial community in the completely autotrophic nitrogen removal over nitrite (CANON) process, which was shocked by a pH of 11.0 for 12 h, were investigated. During the recovery phase, the performance, anaerobic ammonia oxidation (anammox) activity, microbial community, and correlation of bacteria as well as the influencing factors were evaluated synchronously. The performance of the CANON process deteriorated rapidly with a nitrogen removal rate (NRR) of 0.13 kg·m−3·d−1, and Firmicutes, spore-forming bacteria, were the dominant phyla after alkaline shock. However, it could self-restore within 107 days after undergoing four stages, at which Planctomycetes became dominant with a relative abundance of 64.62%. Network analysis showed that anammox bacteria (Candidatus Jettenia, Kuenenia, and Brocadia) were positively related to some functional bacteria such as Nitrosomonas, SM1A02, and Calorithrix. Canonical correspondence analysis presented a strong correlation between the microbial community and influencing factors during the recovery phase. With the increase of nitrogen loading rate, the decrease of free nitrous acid and the synergistic effects, heme c content, specific anammox activity (SAA), NRR, and the abundance of dominant genus increased correspondingly. The increase of heme c content regulates the quorum sensing system, promotes the secretion of extracellular polymeric substances, and further improves SAA, NRR, and the relative abundance of the dominant genus. This study highlights some implications for the recovery of the CANON reactor after being exposed to an alkaline shock.

Effects of seasonal temperature variation on nitrogen removal from a tidal flow constructed wetland system with CANON process

We investigated the effects of seasonal temperature variation on the treatment perfor-mance and underlying mechanisms of nitrogen transformation in a tidal flow constructed wetland (TFCW) with the complete autotrophic nitrogen removal over nitrite (CANON) process. Different temperatures resulted in periodical variations in nitrogen transformation pathways and removal performance of the TFCW with CANON process, which was mainly due to the changes of dominant bacterial communities for nitrogen removal in the system. When temperature was higher than 20.0 ℃, nitrogen transformation and associated microbial characteristics in the TFCW were significantly affected, and the CANON process remained to be the principal pathway for nitrogen removal. The abundance and activity of anammox bacteria experienced different degrees of reduction when temperature dropped below 20.0 ℃. At the temperature of 9.3-20.0 ℃, the proliferation and increased activities of nitrite oxidizing bacteria (NOB) made the nitrification/denitrification process instead of the CANON process became the primary total nitrogen (TN) removal route in the TFCW, and the TN removal efficiency of the system declined to 34.8%±13.0%. Under the temperature range of 2.2-9.0 ℃, anammox bacteria, which was inhibited at the low temperatures, presented competitive advantage in comparison with NOB and denitrifiers, resulting that nitrogen removal in the TFCW relied on the CANON process again. Correspondingly, nitrogen removal rate of the system was 54.8%±4.8%. This study was conductive to the optimization of the TFCW with CANON process, as well as its engineering application.

Start-up of CANON Process and Short-cut Nitrification in a Pilot-scale MBBR Reactor

Using a 150 L moving bed biofilm reactor (MBBR), with the temperature controlled at 28℃ and high NH4+-N concentration (average concentration 350 mg·L-1), inorganic wastewater was used as an influent to start the completely autotrophic nitrogen removal over nitrite (CANON) process. Meanwhile, the flocculent sludge was taken into a 5 L sequencing batch reactor, and the influent NH4+-N concentration was maintained at 90-200 mg·L-1 for the recovery of short-cut nitrification. The results showed that in the MBBR reactor, when the average hydraulic retention time (HRT) was 12 h, short-cut nitrification and total nitrogen (TN) removal rate were mutually constrained, the average TN removal rate was 38.2%, and the average δNO3--N/TN value was 0.274; when the HRT dropped to 6 h, the δNO3--N/TN value decreased from 0.347 to 0.146. The sequencing batch reactor (SBR) maintained aeration and anoxic time for 30 min and 20 min, respectively, by intermittent aeration, while the dissolved oxygen concentration during the aerobic process was 0.5 mg·L-1 to 0.6 mg·L-1, the free nitrous acid concentration was higher than 0.18 mg·L-1 at the end of each cycle, NAR increased from 0 to 99.2% after 12 days, NUR decreased to 0 from an initial 24.8 mg·(g·h)-1, and the TN removal rate decreased from 13% to 3%; the system successfully converted to short-range nitrification. High-throughput sequencing results showed that the abundance of Candidatus Kuenenia in the flocculent sludge and biofilm in the MBBR reactor were 7.91% and 17.38% respectively, Nitrosomonas accounted for 27.43% and 2.55%, respectively, while Nitrospira accounted for 0.30% and 0.28%, respectively. After the recovery of short-cut nitrification in the SBR, the abundance of ammonia-oxidizing bacteria and anaerobic ammonia oxidation decreased to 1.18% and 0.01%, respectively, and the abundance of Nitrospira increased to 1.39%.

N2O profiles in the enhanced CANON process via long-term N2H4 addition: minimized N2O production and the influence of exogenous N2H4 on N2O sources.

Production of the greenhouse gas nitrous oxide (N2O) from the completely autotrophic nitrogen removal over nitrite (CANON) process is of growing concern. In this study, the effect of added hydrazine (N2H4) on N2O production during the CANON process was investigated. Long-term trace N2H4 addition minimized N2O production (0.018% ± 0.013% per unit total nitrogen removed) and maintaining high nitrogen removal capacity of CANON process (nitrogen removal rate and TN removal efficiency was 450 ± 60 mg N/L/day and 71 ± 8%, respectively). Ammonium oxidizing bacteria (AOB) was the main N2O producer. AOB activity inhibition by N2H4 decreased N2O production during aeration, and the N2H4 concentration was negatively correlated with N2O production rate in NH4+ oxidation via AOB, whereas N2O production was facilitated under anaerobic conditions because hydroxylamine (NH2OH) production was accelerated due to anammox bacteria (AnAOB) activity strengthen via N2H4. Added N2H4 completely degraded in the initial aeration phases of the CANON SBR, during which some N2H4 intensified anammox for total nitrogen removal to eliminate N2O production from nitrifier denitrification (ND) by anammox-associated, while the remaining N2H4 competed with NH2OH for hydroxylamine oxidoreductase (HAO) in AOB to inhibit intermediates formation that result in N2O production via NH2OH oxidation (HO) pathway, consequently decreasing total N2O production.

Application of CANON-SBR process for ammonium removal from old municipal old landfill leachate

CANON (Completely Autotrophic Nitrogen-removal Over Nitrite) is the process combined Partial Nitritation and Anammox in a single reactor to remove ammonium from wastewater. This study used a lab-scale SBR Sequencing Bach Reactor for CANON process (CANON-SBR) to treat ammonium from old municipal solid waste landfill leachate. The reactor was run at two phases: (i) In adaptation phase, the synthetic wastewater containing 139 9 mg/l as NH4 +-N was fed into the reactor, and (ii) In operation phase, the reactor was fed with leachate taken from the Go Cat municipal lanfill which was closed since 2007. The reactor was run at ammonium loading rate of 0.2 kgN/m3.day and HRT of 0.6 day in the adaptation phase. pH and DO values in the reactor were controled in the ranges of 7.4 – 7.6 and 0.1 – 0.2 mg/l, respectively. After 15 days of adaptation, total nitrogen removal of 72% was obtained. Then, the leachate containing 3,000 mg/l NH4 +-N and 100 mg/l TSS was fed into the SBR. DO and pH were the key operation parameters for CANON process control. CANON-SBR obtained stable treatment efficiciency at DO ranging from 0.05-0.2 mg/l and pH values of 7.5 – 7.6. The obtained TN and COD removals were above 93% and 40%, respectively, when SBR was run at nitrogen loading rate of 0,4 kgN/m3.day and HRT of 7.43 day. TN concentration of the final batch was 34 mg/l that is met with column B1 QCVN 25:2009/BTNMT (TN&lt; 60 mg/l), while nitrite and nitrate were not detected in the supernatant. This shows that co-existence of denitrifiers which consume nitrate produced from Anammox was available in biomass of the reactor. Numerous Anammox granules in dark red color happened after 20 days of running with leachate. Size of Anammox granules ranged from 5 - 800 μm, among that 73% of granule with size of 20 - 200 μm. The average granule diameter was 97.57 μm.&#x0D;