Completely Autotrophic Nitrogen Removal Over Nitrite Research Articles

Implementing a completely autotrophic nitrogen removal over nitrite process using a novel umbrella basalt fiber carrier.

The completely autotrophic nitrogen removal over nitrite (CANON) process is significantly hindered by prolonged start-up periods and unstable nitrogen removal efficiency. In this study, a novel umbrella basalt fiber (BF) carrier with good biological affinity and adsorption performance was used to initiate the CANON process. The CANON process was initiated on day 64 in a sequencing batch reactor equipped with umbrella BF carriers. During this period, the influent NH4+-N concentration gradually increased from 100 to 200 mg·L-1, and the dissolved oxygen was controlled below 0.8 mg L-1. Consequently, an average ammonia nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (TNRE) of ∼90 and 80% were achieved, respectively. After 130 days, ARE and TNRE remained stable at 92 and 81.1%, respectively. This indicates a reliable method for achieving rapid start-up and stable operation of the CANON process. Moreover, Candidatus Kuenenia and Candidatus Brocadia were identified as dominant anammox genera on the carrier. Nitrosomonas was the predominant genus among ammonia-oxidizing bacteria. Spatial differences were observed in the microbial population of umbrella BF carriers. This arrangement facilitated autotrophic nitrogen removal in a single reactor. This study indicates that the novel umbrella BF carrier is a highly suitable biocarrier for the CANON process.

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.

Micro-aeration and low influent C/N are key environmental factors for achieving ANAMMOX in livestock farming wastewater treatment plants

Anaerobic ammonium oxidation (ANAMMOX)-mediated system is a cost-effective green nitrogen removal process. However, there are few examples of successful application of this advanced wastewater denitrification process in wastewater treatment plants, and the understanding of how to implement anaerobic ammonia oxidation process in full-scale is still limited. In this study, it was found that the abundance of anaerobic ammonia-oxidizing bacteria (AnAOB) in the two livestock wastewater plants named J1 and J2, respectively, showed diametrically opposed trends of waxing and waning with time. The microbial communities of the activated sludge in the two plants at different time were sampled and analyzed by high-throughput sequencing of 16S rRNA genes. Structural equation models (SEMs) were used to reveal the key factors affecting the realization of the ANAMMOX. Changes in the concentration of dissolved oxygen and C/N had a significant effect on the relative abundance of anaerobic ammonia oxidation bacteria (AnAOB). The low concentration of DO (0.2∼0.5 mg/L) could inhibit the activity of nitrifying bacteria (NOB) to achieve partial oxidation of ammonia nitrogen and provide sufficient substrate for the growth of AnAOB, similar to the CANON (Completely Autotrophic Nitrogen removal Over Nitrite). Unlike CANON, heterotrophic denitrification is also a particularly critical part of the livestock wastewater treatment, and a suitable C/N of about 0.6 could reduce the competition risk of heterotrophic microorganisms to AnAOB and ensure a good ecological niche for AnAOB. Based on the results of 16S rRNA and microbial co-occurrence networks, it was discovered that microorganisms in the sludge not only had a richer network interaction, but also achieved a mutually beneficial symbiotic interaction network among denitrifying bacteria (Pseudomonas sp., Terrimonas sp., Dokdonella sp.), AnAOB (Candidatus Brocadia sp.) at DO of 0.2∼0.5 mg/L and C/N of 0.6. Among the top 20 in abundance of genus level, AnAOB had a high relative abundance of 27.66%, followed by denitrifying bacteria of 3.67%, AOB of 0.64% and NOB of 0.26%, which is an essential indicator for the emergence of an AnAOB-dominated nitrogen removal cycle. In conclusion, this study highlights the importance of dissolved oxygen and C/N regulation by analyzing the mechanism of ANAMMOX sludge extinction and growth in two plants under anthropogenic regulation of AnAOB in full-scale wastewater treatment systems.

Performance and microbial characteristics of completely autotrophic nitrogen removal over nitrite process in different types of reactors

There are various types of reactors for completely autotrophic nitrogen removal over nitrite (CANON) process, but the advantages and disadvantages of different types of reactors and their scope of application still need to be studied. In this paper, high-throughput sequencing technology was used to analyze the microbial characteristics of four CANON reactors with similar and stable influent water quality conditions, and the applicable scenarios of different types of CANON reactors was clarified. At the gene level, the proportions of aerobic ammonia oxidizing bacteria (AerAOB), anaerobic ammonia oxidation bacteria (AnAOB) and denitrifying bacteria in a flocculent sludge sequencing batch reactor (FSBR), a membrane bioreactor (MBR), a biological aerated filter (BAF) and a granular sludge sequencing batch reactor (GSBR) were 16.88 %, 3.49 %, 19.36 % and 29.67 %; 9.51 %, 4.72 %, 5 % and 27.75 %; 7.12 %, 11.5 %, 6.81 % and 13.6 %. The results showed that FSBR was low nitrogen removal load and low stability in practical application. MBR can treat different concentrations of ammonia nitrogen wastewater by controlling the influent load. BAF can treat ammonia nitrogen wastewater with moderate influent load. GSBR has high removal load and can treat high ammonia nitrogen 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.

Efficiency of hybrid systems enhanced with different sludge ratios in improving resistance to short-term low temperatures

Complete autotrophic nitrogen removal over nitrite (CANON) is used in wastewater treatment. However, the performance of the CANON system significantly decreases at low temperatures; thus, a new strategy to improve the resistance of the CANON system is required. To investigate the impact of sludge ratio control (high-granule, equivalent, and high-floc systems) on the resistance of CANON to low temperatures, and their recovery after restoring to normal temperature, the nitrogen removal performance of hybrid systems with different ratios was evaluated. The equivalent system had the lowest nitrite accumulation rate and highest nitrogen removal rate. Anaerobic ammonia oxidation was the rate-limiting step of each system, and hzs was the rate-limiting gene. The higher anaerobic ammonium oxidizing bacteria (AAOB) abundance and hzs expression levels resulted in an equivalent system with better resistance and recovery to short-term low temperatures at the gene level.

Achieving biogas production and efficient pollutants removal from nitrogenous fertilizer wastewater using combined anaerobic digestion and autotrophic nitrogen removal process

Nitrogenous fertilizer was massively utilized during agricultural production process, which led to the discharge of large amount of nitrogenous wastewater with low C/N ratio. In this study, anaerobic digestion combined with subsequent Completely autotrophic nitrogen removal over nitrite (CANON) process was adopted for treating nitrogenous fertilizer wastewater. The reactor performances and the microbial community structure were analyzed. Results showed that COD was mainly removed by anaerobic digestion, with the COD removal efficiency as 98.4%, and nitrogen was effectively removed via CANON integrating with partial denitrification, with the removal efficiency as 96.3%. The COD, ammonia and total nitrogen in the effluent of the combined process were 3.7, 2.9 and 7.4 mg L−1, respectively. Methanothrix (43.2%) and Methanomassiliicoccus (34.0%) were detected as the dominant methane production archaea, while Nitrosomanas (10.4%), Candidatus Kuenenia (13.8%) and Truepera (2.8%) were detected as the functional bacteria for nitrogen removal, when treated the nitrogenous fertilizer wastewater.

Nitrogen removal performance and microbiological characteristics of a three-stage series of vertical flow constructed wetlands.

In this study, the treatment performance and underlying molecular mechanisms of nitrogen transformation in a three-stage series of vertical flow constructed wetlands (T-VFCWs) treating rural domestic sewage were investigated at three different hydraulic loading rates (HLRs). Specifi-cally, the T-VFCWs composed of three sequential vertical flow constructed wetlands (termed V-1, V-2 and V-3), which were built according to the topography. The results showed that high pollutant removal rates could be achieved when the T-VFCWs was operated to treat rural domestic sewage, even though the HLR increased from 0.10 to 0.20 m3·m-2·d-1. Effluent quality of the T-VFCWs could reach Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) class A standard. Regarding to the T-VFCWs operated under the oxygen-limiting conditions, three different pathways for nitrogen transformation could be respectively formed in V-1, V-2 and V-3, owing to the specific influent quality of each subunit. Consequently, the T-VFCWs were effective in nitrogen removal as a result of the collaboration of the three subunits. When the T-VFCWs ran constantly during the test, nitrogen removal in V-1, V-2, and V-3 respectively relied on the nitritation/denitrification process, the completely autotrophic nitrogen removal over nitrite (CANON) process, and the denitrification process. The contributions of three subunits for total nitrogen (TN) and NH4+-N removal were (51.3±4.4)% and (63.7±2.6)%, (30.9±4.8)% and (35.5±4.5)%, (17.8±5.0)% and (0.8±0.1)%, respectively. This study could provide scientific basis and technical support for the research and the engineering application of hybrid constructed wetlands.

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.

Analysis of Rapid Start-up and Mixed Nutritional Nitrogen Removal Performance of Complete Autotrophic Granular Sludge

A rapid start of the completely autotrophic nitrogen removal over nitrite (CANON) process based on granular sludge and efficient nitrogen removal under mixotrophic conditions are important steps in a continuous flow reactor for CANON engineering applications. In this study, an aged CANON granular sludge was mechanically crushed to 0.3 mm as inoculum in an airlift internal-loop reactor (AIR) to achieve simultaneous COD removal and mixotrophic denitrification of the single-stage granular sludge. The system achieved stable partial nitrification by controlling DO after 26 days of startup. Granulation and anaerobic ammonia oxidation were then promoted by shortening the HRT to increase the ammonia nitrogen load to 5.65 kg ·(m3 ·d)-1. The total nitrogen removal rate reached 58% on the 68th day. Subsequently, the C/N ratio of influent was increased from 0 to 0.25 and 0.5, which promoted the synergistic growth of AOB, AMX, and heterotrophic microorganisms. The removal rates of ammonia and total nitrogen were 95% and 85% respectively, and the removal of COD reached approximately 80%. The activity of NOB such as Nitrospira was effectively inhibited as the COD concentration was increased. q(NH4+-N) and q(TN) were stable at 0.4 g ·(g ·h)-1 and 0.34 g ·(g ·h)-1, respectively, while q(NO3--N) was approximately 0.02 g ·(g ·h)-1. Microbial diversity was observed using MiSeq high-throughput sequencing. It showed that organic carbon had no significant effect on the abundance of Nitrosomomas and Candidutus_Kuenenia, while increasing the abundance of Candidutus_Brocadia and Denitratisoma in the sludge. This study provides ideas for the rapid start of continuous flow CANON granular sludge process to treat wastewater with low C/N ratio.

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%.