Anaerobic Ammonium-oxidizing Bacteria Research Articles

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.

Effect of exogenous hydrazine on metabolic process of anammox bacteria.

The effect of N2H4 (hydrazine) on AnAOB (anaerobic ammonia oxidizing bacteria) metabolic pattern is unknown. Therefore, the main purpose of this paper was to explore the effects of exogenous N2H4 on the SAA (specific anammox activity), characteristics and metabolic pathway of AnAOB. The results showed that low N2H4 concentration (1-5mg/L) continuous dosing can promote SAA. The promoting effect was found to be more obvious within the dosage of 3-5mg/L N2H4. It was also indicated that high N2H4 concentration dosing (5-10mg/L) can trigger the self-protection mechanism of AnAOB granular sludge by secreting a large amount of B-PN (binding polymeric protein). Intermittent addition of N2H4 at low concentration is conducive to the long-term stable operation of anammox process. Exogenous N2H4 can be directly oxidized by AnAOB to promote the consumption of NO2--N and NH4+-N. In addition, excess electrons can also drive the process of NO3--N reduction and NO2--N disproportionation. Theoretically, these reaction processes need two and ten extra electrons respectively, which is not easy to occur compared with the anammox process.

Inorganic quantum dots - anammox consortia hybrid for stable nitrogen elimination under high-intensity solar-simulated irradiation

External stimulus such as light irradiation is able to deteriorate intracellular redox homeostasis and induce photooxidative damage to non-photogenic bacteria. Exploiting effective strategies to help bacteria resisting infaust stress is meaningful for achieving a stable operation of biological treatment system. In this work, selenium-doped carbon quantum dots (Se-CQDs) were blended into anaerobic ammonia oxidation (anammox) bacteria and an inorganic nanoparticle-microbe hybrid was successfully fabricated to evaluate its nitrogen removal performance under solar-simulated irradiation. It was found that the specific anammox activity decreased by 29.7 ± 5.2% and reactive oxygen species (ROS) content increased by 134.8 ± 4.1% under 50,000 lux light. Sludge activity could be completely recovered under the optimum dosage of 0.42 mL·(g volatile suspended solid) -1 Se-CQDs. Hydroxyl radical (·OH) and superoxide anion radical (·O2−) were identified as the leading ROS inducing lipid peroxidation and antioxidase function detriment. Also, the structure of ladderane lipids located on anammoxosome was destroyed by ROS and functional genes abundances declined accordingly. Although cell surface coated Se-CQDs could absorb ultraviolet light and partially mitigated the photoinhibition, the direct scavenging of ROS by intracellular Se-CQDs primarily contributed to the cellular redox homeostasis, antioxidase activity recovery and sludge activity improvement. The findings of this work provide in-depth understanding the metabolic response mechanism of anammox consortia to light irradiation and might be valuable for a more stable and sustainable nitrogen removal technology, i.e., algal-bacterial symbiotic system, development.

Rapid proliferation of anaerobic ammonium oxidizing bacteria using anammox-hydroxyapatite technology in a pilot-scale expanded granular sludge bed reactor

The practical application of anaerobic ammonium oxidation (anammox) technology was seriously limited by lack of anammox seeding sludge. In this work, a pilot-scale expanded granular sludge bed (EGSB) reactor was used for rapid proliferation of anaerobic ammonium oxidizing bacteria (AnAOB) using anammox-hydroxyapatite (anammox-HAP) technology. The excellent settleability of anammox-HAP granular sludge (with an excellent settling velocity of 395 m/h) supported the up-flow velocity of 9.6 m/h with recirculation ratio of 19. A high nitrogen loading rate (NLR) of 26.4 g N/L/d was achieved in the pilot-scale reactor, with a cell yield of 0.23 g VSS/g NH4+-N. The high recirculation ratio and up-flow velocity brought about the efficient mass transfer for anammox, eliminating free ammonia inhibition, resulting in the high NLR and cell yield. Results of microbial community revealed that the relative abundance of unclassified Brocadiaceae increased from 18.55% to 82.80%, illustrating the rapid proliferation of AnAOB.

Responses of microbial interactions to polyvinyl chloride microplastics in anammox system

Polyvinyl chloride microplastics (PVC MPs) have attracted a lot of attention regarding their potential environmental and health risks. However, their effects on the microbial interaction in anammox process are still unclear. In this study, the long-term effects of different concentrations of PVC MPs (i.e., 0, 1, 15, 50 mg/L) on anammox process were investigated. The results showed that only high concentration of PVC MPs (50 mg/L) induced the performance fluctuation of nitrogen removal but it quickly returned to normal. The rise of the PVC MPs concentration led to a gradual decrease in the particle size of the sludge granules and an increase in the Proteins (PN)/polysaccharides (PS) ratio in extracellular polymeric substances (EPS). PVC MPs significantly reduced the microbial diversity and altered the overall microbial community structure. Network analysis showed that low concentration of PVC MPs (1 mg/L) could increase the network size and complexity, while high concentration of PVC MPs (50 mg/L) reduced the network complexity as the number of nodes and links decreased significantly (P < 0.05). Also, 50 mg/L PVC MPs promoted the communication efficiency among the microbial network in terms of the low path distances, which might be the strategy of microbial community to resist the external environment perturbation and further maintain the system performance stability. Similar trend was found in the subnetwork of Planctomycetota, an important phylum of anaerobic ammonium oxidizing bacteria (AnAOB). This study enriches our understanding of the response of microbial interaction among anammox microorganisms under the stress of PVC MPs.

Phylogenomic Evidence for the Origin of Obligate Anaerobic Anammox Bacteria Around the Great Oxidation Event.

The anaerobic ammonium oxidation (anammox) bacteria can transform ammonium and nitrite to dinitrogen gas, and this obligate anaerobic process accounts for up to half of the global nitrogen loss in surface environments. Yet its origin and evolution, which may give important insights into the biogeochemistry of early Earth, remain enigmatic. Here, we performed a comprehensive phylogenomic and molecular clock analysis of anammox bacteria within the phylum Planctomycetes. After accommodating the uncertainties and factors influencing time estimates, which include implementing both a traditional cyanobacteria-based and a recently developed mitochondria-based molecular dating approach, we estimated a consistent origin of anammox bacteria at early Proterozoic and most likely around the so-called Great Oxidation Event (GOE; 2.32–2.5 Ga) which fundamentally changed global biogeochemical cycles. We further showed that during the origin of anammox bacteria, genes involved in oxidative stress adaptation, bioenergetics, and anammox granules formation were recruited, which might have contributed to their survival on an increasingly oxic Earth. Our findings suggest the rising levels of atmospheric oxygen, which made nitrite increasingly available, was a potential driving force for the emergence of anammox bacteria. This is one of the first studies that link the GOE to the evolution of obligate anaerobic bacteria.

Mainstream partial Anammox for improving nitrogen removal from municipal wastewater after organic recovery via magnetic separation

Total nitrogen (TN) removal from municipal wastewater after organic recovery is challenging because of the low ratio of chemical oxygen demand (COD) to TN. Anaerobic ammonium oxidation (Anammox) is promising because it has no organic requirement, but its performance in treating effluents following COD captured remains unclear. This study used mainstream partial Anammox to remove nitrogen from effluent following magnetic separation within a continuous-flow anoxic–oxic reactor. Compared with traditional nitrification and denitrification, partial Anammox increased TN removal efficiency by 15.0% and contributed 23.6% of TN removal. Quantitative polymerase chain reaction revealed that the copy number of the Anammox gene (hzsB) increased substantially, while those of the nitrite oxidation (nxrA) and denitrification (narG and nirS) genes decreased. High-throughput sequencing identified Candidatus Brocadia as the dominant genus of anaerobic ammonium-oxidizing bacteria. These findings demonstrate the effectiveness of mainstream partial Anammox for treating COD-captured effluents and its potential in municipal wastewater treatment.

Coexistence and competition of the nitrifying and anammox bacteria in SMBBR reactor with partial nitritation/anammox process treating synthetic low-strength ammonium wastewater

The nitrite-oxidizing bacteria (NOB) suppression largely restricts the implementation of partial-nitritation and anammox (PN/A) process for low-strength ammonium wastewater treatment. The main goal of the present study was to verify the feasibility of sequencing moving bed biofilm reactor (SMBBR) treating synthetic low-strength ammonium wastewater and the influence of operating conditions and microbial competitions on NOB suppression. The reactor was operated in sequencing batch reactor (SBR) mode with influent ammonium of 50 mg/L, in which the seeded biofilm harvested from an existing similar PN/A reactor treating high-ammonium synthetic wastewater. After increasing the dissolved oxygen (DO) from 0.50 to 1.25 mg/L-with hydraulic retention time (HRT) gradually decreasing from 15 to 5 h-stable nitrogen removal through PN/A was obtained. The long-term operation results showed nitrogen removal efficiencies of 66.23 ± 7.78 % were stably obtained at a relatively low filling ratio of 25 %. The reactor operated in SBR mode allowed NOB suppression and low effluent ammonium due to the ammonium gradient created in cycles. Further, the activity of NOB was controlled at a low level at medium DO concentration. Both ammonium-oxidizing bacteria (AOB) competition acting as DO-cut and anaerobic ammonium-oxidizing bacteria (anammox, AMX) competition acting as nitrite-sink were found to be essential for NOB suppression, and DO-cut played a dominated role. A simple hypothetical microstructure of one-stage PN/A biofilm, assuming AOB layered in the surface of the biofilm while AMX and NOB in the interior, was proposed to define the mechanism of DO-cut and Nitrite-sink. The obtained results demonstrated SMBBR could be regarded as an alternative guideline for successful operation of mainstream PN/A as compared to the integrated fixed film activated sludge (IFAS) systems.

Activity enhancement and the anammox mechanism under low temperature via PVA-SA and nano Fe2O3-PVA-SA entrapped beads

Anaerobic ammonia-oxidizing bacteria (AAOB) have a long growth time and low activity at low temperatures. In suspended systems, sludge is easily lost, which limits the mainstream application of anaerobic ammonia oxidation (anammox).Entrapment provides effective ideas for solving these problems. In this study, polyvinyl‑sodium alginate (PVA-SA) and nano Fe2O3-PVA-SA entrapment beads were prepared to discuss the effectiveness of entrapment enhanced anammox sludge at low temperatures. The differences in the entrapped beads and granules were compared to analyze the strengthening mechanism. The results show that the nitrogen removal performance of granules, PVA-SA and nano Fe2O3-PVA-SA entrapped beads, first decreased and then increased during the cooling and low-temperature operation. Nano Fe2O3-PVA-SA entrapped beads showed the smallest decline and the highest degree of recovery. Reaction metering ratio (△NO2−-N/△NH4+-N and △NO3−-N/△NH4+-N) showed that entrapment could realize Nitrite oxidizing bacteria (NOB) inhibition and improve the activity of denitrifying bacteria (DNB) to promote the removal of total nitrogen by providing a strict anaerobic environment. The results demonstrate that entrapment is beneficial for maintaining the content of heme c, specifically, nano Fe2O3 can stimulate its production, and is beneficial for alleviating the reduction of hydrazine dehydrogenase (HDH) enzyme activity. The extracellular polymeric substances (EPS) content and analysis showed that entrapment does not change the composition of EPS, and can maintain the EPS content. Nano Fe2O3 can stimulate AAOB to secrete more EPS to maintain sludge stability. From a molecular perspective, entrapment can maintain the expression of functional genes, promote the enrichment of AAOB, thus improving the nitrogen removal performance from the dual perspectives of “quality” and “quantity”.

Nitrous Oxide Emission from Full-Scale Anammox-Driven Wastewater Treatment Systems.

Wastewater treatment plants (WWTPs) are important contributors to global greenhouse gas (GHG) emissions, partly due to their huge emission of nitrous oxide (N2O), which has a global warming potential of 298 CO2 equivalents. Anaerobic ammonium-oxidizing (anammox) bacteria provide a shortcut in the nitrogen removal pathway by directly transforming ammonium and nitrite to nitrogen gas (N2). Due to its energy efficiency, the anammox-driven treatment has been applied worldwide for the removal of inorganic nitrogen from ammonium-rich wastewater. Although direct evidence of the metabolic production of N2O by anammox bacteria is lacking, the microorganisms coexisting in anammox-driven WWTPs could produce a considerable amount of N2O and hence affect the sustainability of wastewater treatment. Thus, N2O emission is still one of the downsides of anammox-driven wastewater treatment, and efforts are required to understand the mechanisms of N2O emission from anammox-driven WWTPs using different nitrogen removal strategies and develop effective mitigation strategies. Here, three main N2O production processes, namely, hydroxylamine oxidation, nitrifier denitrification, and heterotrophic denitrification, and the unique N2O consumption process termed nosZ-dominated N2O degradation, occurring in anammox-driven wastewater treatment systems, are summarized and discussed. The key factors influencing N2O emission and mitigation strategies are discussed in detail, and areas in which further research is urgently required are identified.

Enhanced nitrogen removal of single stage partial nitritation anammox system by glycine betaine addition at low temperature: Performance and mechanism

Low activity of anaerobic ammonia oxidizing bacteria (AnAOB) at low temperature is still an obstacle to the application of a single stage partial nitritation anammox (SPNA) process. In order to improve the performance of nitrogen removal of this system at low ambient temperature, the glycine betaine (GB) was added into a continuous stirred tank reactor (CSTR) at 13–15 °C. At 15 °C, the nitrogen removal rate (NRR) was increased from 0.48 to 0.62 g N/(L·d) by adding 1 mM GB with the nitrogen loading rate of 0.81 g N/(L·d). The activity of hydrazine oxidase (HZO) was enhanced from 15.78 to 19.81 μmol Cyt-c/(g VSS·min), while the extracellular polymeric substances (EPS) production was reduced from 290.31 to 109.06 mg/g VSS after exogenous GB. When the temperature was <15 °C, however, the promoting effect of 1 mM GB was weakened, and the NRR was 0.43 g N/(L·d) at 13 °C. Increasing the addition of GB to 1.5 mM did not improve nitrogen removal performance at 13 °C, whereas it promoted the enrichment of heterotrophic bacteria (HB). Overall, results suggested GB had the potential to enhance the metabolic capability of AnAOB, which provided a novel strategy for improving the nitrogen removal performance of SPNA system at low temperature.

Influence of low air pressure on combined nitritation and anaerobic ammonium oxidation process

At high altitude, wastewater aeration efficiency is low, which is detrimental to nitrification in conventional biological nitrogen removal. The combined partial nitritation and anaerobic ammonium oxidation (CPNA) process requires little oxygen and can be appropriate in low-pressure conditions. As such, in this study, we investigated the effect of air pressure on CPNA using a laboratory-scale reactor. We found that low air pressure promoted the removal of total inorganic nitrogen (TIN), achieving a TIN removal rate of 43,000 mg·N/(kg·VSS·d). The secretion of extracellular polymeric substances under low air pressure was not significantly different from that under ordinary air pressure, indicating no adverse effects on microbial aggregation ability, stability, or settleability. The abundance of aerobic ammonia-oxidizing bacteria (AeAOB) increased from 0.2% to 5.6%, and the activity of anaerobic ammonia-oxidizing bacteria (AnAOB) enhanced, giving AeAOB and AnAOB a competitive advantage over nitrite-oxidizing bacteria, thus forming a microbial community structure favorable to the CPNA process. Our further analysis of the results of batch tests in serum bottles confirmed the positive effect of low air pressure on the anaerobic ammonium oxidation (anammox) process, with a 28.5% ± 1.9% improvement in the specific anammox rate at 70 kPa compared with 100 kPa. AnAOB activity increased, which was reflected in the intracellular heme content increasing from 0.56 ± 0.18 μmol/(g·VSS) at 100 kPa to 2.56 ± 0.20 μmol/(g·VSS) at 70 kPa. We clarified the CPNA-process-promoting effect of low air pressure, which shows potential for nitrogen removal in high-altitude regions.

Simulation and experimental verification of nitrite-oxidizing bacteria inhibition by alternating aerobic/anoxic strategy

Anaerobic ammonium oxidation (ANAMMOX) is a promising technology for sewage treatment. Alternating aerobic/anoxic conditions have been widely adopted to achieve partial nitrification (PN), so as to provide substrates for ANAMMOX. In this study, the feasibility of PN with the strategy of intermittent aeration was investigated under mainstream conditions. At a low dissolved oxygen (DO) concentration, the nitrogen conversion characteristic under different intermittent aeration modes was evaluated by mathematical simulation and experimental method with (1) ordinary activated sludge, (2) mixed sludge with anaerobic ammonia-oxidizing bacteria (AnAOB), and (3) PN sludge, as seed sludge. The existence of functional microorganisms, such as AnAOB and denitrifying bacteria, which can utilize nitrites, was the prerequisite for NOB activity inhibition in the alternating aerobic/anoxic condition. Therefore, low nitrite may be an important factor in NOB activity inhibition under alternating aerobic/anoxic conditions. This study demonstrated a key controlling factor for NOB activity inhibition with alternating aerobic/anoxic condition.

Application of the EGSB-CMBR Process to High-Concentration Organic Wastewater Treatment

To decrease the cost of wastewater treatment at the plant, the Wuzhou Shenguan Protein Enteric Coating Production Plant designed and built an expanded granular sludge bed (EGSB)-ceramic membrane bioreactor reactor (CMBR) process for treating high-concentration organic wastewater with a capacity of 25 m3/d. The EGSB is divided into anaerobic and microaerobic sections. The purpose of the anaerobic section is to substantially degrade COD, and the main functions of the microaerobic section are to coordinate the relationship between hydrolytic acid-producing bacteria, methanogenic bacteria (MBP), and sulfate-reducing bacteria (SRB) and to mitigate the inhibitory effects between them to simultaneously remove COD and sulfate. Anaerobic ammonia-oxidizing bacteria were added to the CMBR reactor to remove both COD and ammonia nitrogen. The results of the operation showed that more than 99% of the COD was removed by the EGSB-CMBR process, while the removal rates of NH4+-N and SS were greater than 70% and 90%, respectively. In addition, the effluent met the requirements of the secondary standard of the Comprehensive Wastewater Discharge Standard (8978-1996). Economic and technical analyses showed that the modified EGSB-CMBR reactor has a high treatment efficiency, which greatly saves on the cost of the “commissioned treatment” of high-concentration organic waste liquid in the plant. Specifically, it can save more than 800,000 CNY for the plant annually.

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.

Nitrite and nitrate reduction drive sediment microbial nitrogen cycling in a eutrophic lake

The anaerobic microbial nitrogen (N) removal in lake sediments is one of the most important processes driving the nitrogen cycling in lake ecosystems. However, the N removal and its underlying mechanisms regulated by denitrifying and anaerobic ammonia oxidation (anammox) bacteria in lake sediments remain poorly understood. With the field sediments collected from different areas of Lake Donghu (a shallow eutrophic lake), we examined the denitrifying and anammox bacterial communities by sequencing the nirS/K and hzsB genes, respectively. The results indicated that denitrifiers in sediments were affiliated to nine clusters, which are involved in both heterotrophic and autotrophic denitrification. However, anammox bacteria were only dominated by Candidatus Brocadia. We found that NO3− and NO2− concentrations, as well as Nar enzyme activity were the key factors affecting denitrifying and anammox communities in this eutrophic lake. The enrichment experiments in bioreactors confirmed the divergence of denitrification and anammox rates with an additional complement of NO2−, especially under a condition low nitrate reductase activity. The coupled denitrification and anammox may play significant roles in N removal, and the availability of electronic acceptors (i.e., NO2− and NO3−) strongly influenced the N loss in lake sediments. Further path analysis indicated that NO2−, NO3− and some N-related enzymes were the key factors affecting microbial N removal in lake sediments. This study advances our understanding of the mechanisms driving the of denitrification and anammox in lake sediments, which also provides new insights into coupled denitrification-anammox N removal in eutrophic lake ecosystems.

The performance and microbial communities of Anammox and Sulfide-dependent autotrophic denitrification coupling system based on the gel immobilization

Anammox and sulfide-dependent autotrophic denitrification (ASDAD) coupling system can improve the nitrogen removal, but high sulfide concentration will affect the activity of anaerobic ammonia-oxidizing bacteria (AnAOB). Gel immobilization technology can enhance the survivability of microorganisms in unsuitable environments. Therefore, in this investigation, gel immobilization technology was applied into the ASDAD coupling system to explore the removal performance and microbial communities. The results showed that the optimal S2−/NO3– was 0.6, under which the best TN removal efficiency was 85.69%. The removal performance of ASDAD coupling system was stable under rapid variations of nitrogen loading rate and sulfide loading rate. Immobilized sludge cubes could attenuate the effects of temperature on AnAOB and sulfide-oxidizing bacteria. Observations of SEM and stereoscope suggested that AnAOB was more likely to exist on the surface of the sludge cubes. Thiobacillus, Candidatus Brocadia, and Candidatus Kuenenia were the main functional bacteria in the coupling system.

Novel strategy for rapid start-up and stable operation of anammox: Negative pressure coupled with the direct-current electric field

An application challenge of anaerobic ammonia oxidation (anammox) is the slow proliferation rate of anaerobic ammonium oxidation bacteria (AnAOB). This study adopted negative pressure coupled with the direct-current electric field (NP–DCEF) to evaluate system nitrogen removal performance. Results showed that the total nitrogen removal rate (TNRR) of the NP–DCEF system was stable at 88.6% after seven days. Compared with that of the ordinary operating system (45.4%), the relative abundance of Candidatus–kuenenia considerably increased from 51.9% to 57.6%. Under transient and long-term influent fluctuation, the NP–DCEF system showed high nitrogen removal performance. The specific activity of AnAOB (SAA) reached 11.0 mg N∙g Vss−1 h−1 under load fluctuation, and it was 8.7 mg N∙g Vss−1 h−1 under ordinary operational conditions. In addition, the specific activities of hydrazine dehydrogenase (HDH) and hydrazine synthetase (HZS) reached 32.66 and 92.95 U∙L−1, which are considerably higher than those under the ordinary operating conditions (18.41 and 63.20 U∙L−1). These results indicated that the novel operation strategy has specific feasibility and potential for the start-up and long-term operation of anammox.

Microbial response on the first full-scale DEMON® biomass transfer for mainstream deammonification

Sidestream partial nitritation and deammonification (pN/A) of high-strength ammonia wastewater is a well-established technology. Its expansion to the mainstream is, however mainly impeded by poor retention of anaerobic ammonia oxidizing bacteria (AnAOB), insufficient repression of nitrite oxidizing bacteria (NOB) and difficult control of soluble chemical oxygen demand and nitrite levels.At the municipal wastewater treatment plant in Strass (Austria) the microbial consortium was exhaustively monitored at full-scale over one and a half year with regular transfer of sidestream DEMON® biomass and further retention and enrichment of granular anammox biomass via hydrocyclone operation.Routine process parameters were surveyed and the response and evolution of the microbiota was followed by molecular tools, ex-situ activity tests and further, AnAOB quantification through particle tracking and heme measurement.After eight months of operation, the first anaerobic, simultaneous depletion of ammonia and nitrite was observed ex-situ, together with a direction to higher nitrite generation (68% of total NOx-N) as compared to nitrate under aerobic conditions. Our dissolved oxygen (DO) scheme allowed for transient anoxic conditions and had a strong influence on nitrite levels and the NOB community, where Nitrobacter eventually dominated Nitrospira. The establishment of a minor but stable AnAOB biomass was accompanied by the rise of Chloroflexi and distinct emergence of Chlorobi, a trend not seen in the sidestream system. Interestingly, the most pronounced switch in the microbial community and noticeable NOB repression occurred during unfavorable conditions, i.e. the cold winter season and high organic load. Further abatement of NOB was achieved through bioaugmentation of aerobic ammonia oxidizing bacteria (AerAOB) from the sidestream-DEMON® tank. Performance of the sidestream pN/A was not impaired by this operational scheme and the average volumetric nitrogen removal rate of the mainstream even doubled in the second half of the monitoring campaign. We conclude that a combination of both, regular sidestream-DEMON® biomass transfer and granular SRT increase via hydrocyclone operation was crucial for AnAOB establishment within the mainstream.

Promoting Nitrogen Removal in ANAMMOX Biofilm Reactor by Fe2+ Under Low Nitrogen Concentration

The feasibility for nitrogen removal in a two-stage ANAMMOX biofilm reactor promoted by Fe2+ under low nitrogen concentration was investigated. The results showed that the ANAMMOX reaction could be effectively promoted by a ρ(Fe2+) of 5, 10, and 15 mg·L-1. A ρ(Fe2+) of 10 mg·L-1 presented the highest promotion for the ANAMMOX reaction, with the highest nitrogen removal efficiency (NRE) of 81.71% under a ρ(TN) of 150 mg·L-1and a nitrogen loading rate (NLR) of 0.62 kg·(m3·d)-1. Fe2+ promoted the secretion of extracellular polymeric substance (EPS) and the synthesis of heme c in the ANAMMOX system. Batch test results further verified the positive effects by Fe2+on the activity of anaerobic ammonium oxidizing bacteria (AnAOB). The specific ANAMMOX activity (SAA) of 10 mg·L-1 ρ(Fe2+) was 3.6 times as high as that of the control group[ρ(Fe2+)=0 mg·L-1], whereas the activity of AnAOB was significantly inhibited with ρ(Fe2+) increased to 20 mg·L-1. High-throughput sequencing results showed that the addition of Fe2+ increased the abundance of Candidatus_Kuenenia. When ρ(Fe2+) was 10 mg·L-1, the relative abundance of Candidatus_Kuenenia in reactor 1 and reactor 2 increased to 16.18% and 4.22%, respectively. The stable operation of the two-stage ANAMMOX biofilm process promoted by Fe2+provides an alternative technology for low-strength nitrogen wastewater.