Effect of trace hydrazine addition on the functional bacterial community of a sequencing batch reactor performing completely autotrophic nitrogen removal over nitrite

Effect of long-term dosage of hydrazine on mainstream anammox process: Biofilm characteristics and microbial community

The impact of the long-term trace hydrazine (N2H4) exogenous supplementation on activity of the anaerobic ammonium oxidation (anammox) biofilm was investigated in a moving bed biofilm reactor (MBBR) for mainstream wastewater treatment. The results of this study demonstrated that the addition of 2-5 mg/L N2H4 enhanced anammox biofilm activity, as evidenced by the augmented nitrogen removal rate (NRR), which increased from 113.4 g/(m3·d) to 126.7 g/(m3·d) with the introduction of 2 mg/L N2H4. However, a higher concentration of N2H4 (10 mg/L) suppressed anammox activity, leading to a reduced NRR of 91.5 g/(m3·d). Bioindicators revealed that the long-term addition of 2 mg/L N2H4 fostered the accumulation of anammox bacteria (AnAOB) biomass, elevating the volatile suspended solids (VSS) content by 12%. Moreover, the structural composition of extracellular polymeric substances (EPS) within the biofilm was altered, resulting in enhanced biofilm strength within the reactor. The protective mechanism of the biofilm was activated, and EPS secretion was stimulated by the continuous N2H4 supplementation. The introduction of an excess dosage of N2H4 led to alterations in the microbial communities, ultimately resulting in a decline in the performance of the reactor. These findings collectively illustrate that N2H4, as an intermediate product, can effectively enhance anammox activity within the MBBR for mainstream wastewater treatment. This study contributes to the understanding of the optimization strategies for anammox processes in wastewater treatment systems.

Enhancement of hydrazine accumulation in anammox bioreactors

The role of hydrazine (N2H4) in anammox metabolism has been widely studied; however, studies on N2H4 biosynthesis by anammox bacteria are limited in the literature. In this context, the current research aims to investigate the enhancement of biological N2H4 production in the anammox process in a long-term manner. The experimental studies started with the optimization of the operating conditions to achieve maximum N2H4 accumulation. Under favorable conditions (pH = 8.97 ± 0.08; T = 35.5 ± 0.5 °C; initial hydroxylamine dose = 1.46 ± 0.01 mM), 17.16 ± 0.64 mg L-1 of N2H4 accumulated in the batch systems. The continuity of N2H4 bioproduction was then evaluated by long-term observations. A continuous flow bioreactor was operated in four consecutive manipulated periods under optimized conditions. In the long-term operated bioreactor, 55.10 ± 0.30 mg L-1 N2H4 was accumulated at optimal conditions, which was 2.5 times higher than reported in the literature. Although manipulation of the bioreactor operating conditions initially resulted in a significant increase in N2H4 bioaccumulation, it subsequently caused a severe deterioration in anammox activity. However, this could be mitigated by increasing the biomass concentration in the anammox systems. In addition, the relative abundance of Candidatus Kuenenia decreased by 1.88% throughout the long-term operation.

Recovery strategies and mechanisms of anammox reaction following inhibition by environmental factors: A review

Anaerobic ammonium oxidation (anammox) is a promising biological method for treating nitrogen-rich, low-carbon wastewater. However, the application of anammox technology in actual engineering is easily limited by environmental factors. Considerable progress has been investigated in recent years in anammox restoration strategies, significantly addressing the challenge of poor reaction performance following inhibition. This review systematically outlines the strategies employed to recover anammox performance following inhibition by conventional environmental factors and emerging pollutants. Additionally, comprehensive summaries of strategies aimed at promoting anammox activity and enhancing nitrogen removal performance provide valuable insights into the current research landscape in this field. The review contributes to a comprehensive understanding of restoration strategies of anammox-based technologies.

Regulation mechanism of hydrazine and hydroxylamine in nitrogen removal processes: A Comprehensive review

As the new fashioned nitrogen removal process, short-cut nitrification and denitrification (SHARON) process, anaerobic ammonium oxidation (anammox) process, completely autotrophic nitrogen removal over nitrite (CANON) process, partial nitrification and anammox (PN/A) process and partial denitrification and anammox (PD/A) process entered into the public eye due to its advantages of high nitrogen removal efficiency (NRE) and low energy consumption. However, the above process also be limited by long-term start-up time, unstable operation, complicated process regulation and so on. As intermediates or by-metabolites of functional microorganisms in above processes, hydroxylamine (NH2OH) and hydrazine (N2H4) improved NRE of the above processes by promoting functional enzyme activity, accelerating electron transport efficiency and regulating distribution of microbial communities. Therefore, this review discussed effects of NH2OH and N2H4 on stability and NRE of above processes, analyzed regulatory mechanism from functional enzyme activity, electron transport efficiency and microbial community distribution. Finally, the challenges and limitations for nitric oxide (NO) and nitrous oxide (N2O) produced from regulation of NH2OH and N2H4 are discussed. In additional, perspectives on future trends in technology development are proposed.

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 (1-5 mg/L) continuous dosing can promote SAA. The promoting effect was found to be more obvious within the dosage of 3-5 mg/L N₂H₄. It was also indicated that high N₂H₄ concentration dosing (5-10 mg/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.

Unveiling performance stability and its recovery mechanisms of one-stage partial nitritation-anammox process with airlift enhanced micro-granules

The performance stability and its recovery mechanisms of a partial nitritation-anammox process were investigated. A one-stage airlift enhanced micro-granules (AEM) system was operated for 650 days continuously to treat 50 mg-NH₄/L wastewater. During the stable stage, a high nitrogen removal efficiency of 72.7 ± 8.4% lasting for 230 days was successfully achieved under 0.28 L/min aeration rate and 0.10-0.20 mg/L dissolved oxygen (DO) concentration. A microbial consortium with good granularity appeared in red. The specific activity of anammox and ammonia oxidation increased to 1.02 and 0.93 g-N/g-VSS/d, respectively. Meanwhile, the microbial analysis showed the AEM system shifted the dominant microflora from Proteobacteria to Planctomycetes in which Candidatus Brocadia abundance reached a high of 35.0%. The results reveal that the long-term airlift-aeration promoted granulation and further enhanced activities, the abundances of anammox bacteria, and suppressed nitrite-oxidizing bacteria. Optimizing the DO control is also critical for stability increment and process recovery.

Sequencing batch reactor technology for landfill leachate treatment: A state-of-the-art review

Landfill has become an underlying source of surface and groundwater pollution if not efficiently managed, due to the risk of leachate infiltration into to land and aquifers. The generated leachate is considered a serious environmental threat for the public health, because of the toxic and recalcitrant nature of its constituents. Thus, it must be collected and appropriately treated before being discharged into the environment. At present, there is no single unit process available for proper leachate treatment as conventional wastewater treatment processes cannot achieve a satisfactory level for degrading toxic substances present. Therefore, there is a growing interest in examination of different leachate treatment processes for maximum operational flexibility. Based on leachate characteristics, discharge requirements, technical possibilities, regulatory requirements and financial considerations, several techniques have been applied for its degradation, presenting varying degrees of efficiency. Therefore, this article presents a comprehensive review of existing research articles on the pros and cons of various leachate degradation methods. In line with environmental sustainability, the article stressed on the application and efficiency of sequencing batch reactor (SBR) system treating landfill leachate due to its operational flexibility, resistance to shock loads and high biomass retention. Contributions of integrated leachate treatment technologies with SBR were also discussed. The article further analyzed the effect of different adopted materials, processes, strategies and configurations on leachate treatment. Environmental and operational parameters that affect SBR system were critically discussed. It is believed that information contained in this review will increase readers fundamental knowledge, guide future researchers and be incorporated into future works on experimentally-based SBR studies for leachate treatment.

Start-Up of Anammox SBR from Non-Specific Inoculum and Process Acceleration Methods by Hydrazine

Biological nutrient removal from wastewater to reach acceptable levels is needed to protect water resources and avoid eutrophication. The start-up of an anaerobic ammonium oxidation (anammox) process from scratch was investigated in a 20 L sequence batch reactor (SBR) inoculated with a mixture of aerobic and anaerobic sludge at 30 ± 0.5 °C with a hydraulic retention time (HRT) of 2–3 days. The use of NH4Cl, NaNO2, and reject water as nitrogen sources created different salinity periods, in which the anammox process performance was assessed: low (<0.2 g of Cl−/L), high (18.2 g of Cl−/L), or optimum salinity (0.5–2 g of Cl−/L). Reject water feeding gave the optimum salinity, with an average nitrogen removal efficiency of 80%, and a TNRR of 0.08 kg N/m3/d being achieved after 193 days. The main aim was to show the effect of a hydrazine addition on the specific anammox activity (SAA) and denitrification activity in the start-up process to boost the autotrophic nitrogen removal from scratch. The effect of the anammox intermediate hydrazine addition was tested to assess its concentration effect (range of 2–12.5 mg of N2H4/L) on diminishing denitrifier activity and accelerating anammox activity at the same time. Heterotrophic denitrifiers’ activity was diminished by all hydrazine additions compared to the control; 5 mg of N2H4/L added enhanced SAA compared to the control, achieving an SAA of 0.72 (±0.01) mg N/g MLSS/h, while the test with 7.5 mg of N2H4/L reached the highest overall SAA of 0.98 (±0.09) mg N g/MLSS/h. The addition of trace amounts of hydrazine for 6 h was also able to enhance SAA after inhibition by organic carbon source sodium acetate addition at a high C/N ratio of 10/1. The start-up of anammox bacteria from the aerobic–anaerobic suspended biomass was successful, with hydrazine significantly accelerating anammox activity and decreasing denitrifier activity, making the method applicable for side-stream as well as mainstream treatment.

A novel technology with precise oxygen-input control: Application of the partial nitritation-anammox process

Reliable and accurate oxygen-input control, which is critical to maintaining efficient nitrogen removal performance for partial nitritation-anammox (PN-A) process, remains one of the main operational difficulties. In this study, a novel, yet simple system (a simple process for autotrophic nitrogen-removal, SPAN) with precise oxygen-input control was developed to treat ammonium-rich wastewater via PN-A process. SPAN brings oxygen to biomass by circulating water and creating water spray (shower) at the water-air interface, and effectively balances the activities of core functional microorganisms through precise oxygen-input control. The oxygen-input rate is decided by the water circulation rate and shower rate and is measurable and predictable. Therefore, the required amount of oxygen for ammonium oxidation can be precisely delivered to the biomass by adjusting the circulation rate and shower rate. The results of two parallel SPAN reactors demonstrated that during long-term operation, the required oxygen input was precisely and reliably controlled. More than 99% of NH₄⁺-N and 81% - 85% of total nitrogen were stably removed, with anammox bacteria contributing to more than 96% of total nitrogen removal. Anammox bacteria were efficiently enriched to the highest level among the key nitrogen-converting microbial groups, both in terms of abundance (8.17%) and nitrogen-conversion capacity, while ammonium oxidizing bacteria were well controlled to provide sufficient ammonium-oxidizing capacity. Nitrite oxidizing bacteria were maintained stable (relative abundance of 1.08%-1.88%) and their activity was effectively suppressed. This study provided a novel technology, SPAN, to precisely control oxygen input in PN-A system, and proved that SPAN was effective and reliable in achieving long-term high-efficiency nitrogen removal.

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.

Roles of hydroxylamine and hydrazine in the in-situ recovery of one-stage partial nitritation-anammox process: Characteristics and mechanisms

Nitrate built-up is a serious operational difficulty in one-stage partial nitritation anammox (PN/A) process. To investigate an effective method for in-situ restoration, hydroxylamine (NH₂OH) and hydrazine (N₂H₄) of 2 mgN/L were dosed in PN/A process with nitrate built-up in a comparative study. NH₂OH treatment showed better performances on TN removal and nitrate reduction than N₂H₄ and blank control. Through 104 days' addition of NH₂OH, MRNN (mole ratio of NO₃^--N production to NH₄⁺-N removal) was decreased from 70% to 19.91%; TN removal was increased from 0.01 to 0.18 kgN/(m³ d). After stopping the chemical addition, nitrate rebounded for N₂H₄ treatment, but the restoration effect was stable and persistent for NH₂OH. NH₂OH addition resulted in a low reductive potential (-250 mV) and exerted strong inhibitions on nitrite oxidizing bacteria activities. Additionally, rapid enhancement of ammonia oxidizing bacteria activities, functional gene (hao) and Nitrosomonas gave rise to the restoration of PN/A with NH₂OH addition.

Nitrite accumulation stability evaluation for low-strength ammonium wastewater by adsorption and biological desorption of zeolite under different operational temperature

How to achieve stable nitrite accumulation was still a huge challenge for low-carbon and energy-saving biological nitrogen removal of low-strength ammonium wastewater. This study proposed a new way to solve this problem with zeolite biological fixed bed (ZBFB) by cycle operation of adsorption and biological desorption. In order to evaluate nitritation performance of this reactor, the influence of operational temperature on nitrite accumulation stability was investigated by 126 cycles operation in four parallel ZBFB reactors for low-strength ammonium wastewater (50 mg/L NH₄⁺-N). It was found that higher operational temperature (i.e., 36.0 °C), rather than other temperature (i.e., 27.0 °C, 30.0 °C, 33.0 °C), could maintain stable nitrite accumulation with nitrite production rate of 0.312 kg NO₂^--N·m^-3 zeolite·day^-1 and nitrite accumulation ratio higher than 95.0% after biological desorption. High-throughput sequencing analysis results showed that bacterial structure significantly changed in ZBFB under different operational temperature, and obvious enrichment of genus Nitrosomonas (AOB) and gradually enhanced free ammonia (FA) inhibition on genus Nitrospira and Nitrobacter (NOB) were found by elevation of operational temperature, leading to different nitrite accumulation performance in ZBFB reactors. The mechanism for stable nitrite accumulation performance by ZBFB might be attributed to overwhelming growth rate of AOB than NOB, faster ammonium desorption and enhanced FA inhibition on NOB under operational temperature (i.e., 36.0 °C). All in all, keeping high temperature for biological desorption step should be extremely crucial for stable nitrite accumulation by ZBFB, which could facilitate further low-carbon and energy-saving biological nitrogen removal for low-strength ammonium wastewater treatment.

Investigation of the process stability of different anammox configurations and assessment of the simulation validity of various anammox-based kinetic models

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world. Various reactor configurations were investigated for the anammox process. However, the construction of the anammox process is a delicate topic in regards to the high sensitivity of the biological reaction. To better understand the effects of configurations on the anammox performance, process-kinetic models and activity kinetic models were critically overviewed, respectively. A significant difference in the denitrification capabilities was observed even with similar dominated functional species of anammox with different configurations. Although the kinetic analysis gained insight into the feasibility of both batch and continuous processes, most models were often applied to match the kinetic data in an unsuitable manner. The validity assessment illustrated that the Grau second-order model and Stover–Kincannon model were the most appropriate and shareable reactor-kinetic models for different anammox configurations. This review plays an important role in the anammox process performance assessment and augmentation of the process control.

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world.

Sugar sources as Co-substrates promoting the degradation of refractory dye: A comparative study

Four sugar sources were used as co-substrates to promote the degradation of a selected refractory dye reactive black 5 (RB5) by the natural bacterial flora DDMZ1. The boosting performance of the four sugar sources on RB5 decolorization ranked as: fructose > sucrose > glucose > glucose + fructose. Kinetic results of these four co-metabolism systems agreed well with a first-order kinetic model. Four sugar sources stimulated the extracellular azoreductase secretion causing enhanced enzyme activity. An increased formation of low molecular weight intermediates was caused by the addition of sugar sources. The toxicity of RB5 degradation products was significantly reduced in the presence of sugar sources. The bacterial community structure differed remarkably as a result of sugar sources addition. For a fructose addition, a considerably enriched population of the functional species Burkholderia-Paraburkholderia and Klebsiella was noted. The results enlarge our knowledge of the microkinetic and microbiological mechanisms of co-metabolic degradation of refractory pollutants.

Comparing two hydrazine addition strategies to stabilize mainstream deammonification: Performance and microbial community analysis

In this study, an expanded granular sludge blanket reactor (EGSB) was proposed to achieve stable mainstream deammonification process by adding hydrazine (N₂H₄). Two N₂H₄ addition methods consisted of constant concentration (strategy A) and variable concentration (strategy B) both can inhibit nitrite oxidizing bacteria. A efficient performance was achieved with higher total nitrogen removal efficiency (82 ± 6%) and nitrogen removal rate (0.32 ± 0.02 kg N/(m³·d)) under strategy B. For strategy A, anaerobic ammonia oxidizing bacteria (AnAOB) in-situ activity was decreased from 2.76 to 0.68 mg N/(g VSS·h) at 42 mg/L NH₄⁺-N. Candidatus Brocadia abundance increase from 14.62% to 20.07% under the strategy may indicated the self-regulate mechanism of AnAOB. Aerobic ammonia oxidizing bacteria (AOB, mainly Nitrosomonas) and AnAOB (mainly Candidatus Brocadia) were always dominated under two strategies. Strategy B provided better environment for most microorganisms (mainly Chloroflexri, Planctomycetes, Proteobacteria and Chlorobi).

Effect of external hydrazine addition on anammox reactor start-up time

Hydrazine is an intermediate product of the anaerobic ammonium oxidation (Anammox) process where both ammonium and nitrite in wastewater are converted to nitrogen gas by bacteria. In this study the effect of external hydrazine addition (5, 10, 15, and 20 mg/L) on the start-up period of the Anammox process was studied using sequencing batch reactors (SBRs). The SBR with an addition of 10 mg/L hydrazine took only 7 weeks to stabilize and achieve the maximum removal of ammonium and nitrite, whereas the SBR without the addition of hydrazine took 12 weeks. The amount of Heme C extracted from the biomass indicated that externally added hydrazine accelerated the growth of Anammox bacteria and reduced the release of nitrous oxide gas from the reactors.

Attachment of anaerobic ammonium-oxidizing bacteria to augmented carrier material

The formation of stable and highly active anammox biofilm is a lengthy process leading to long start-up times of deammonifying reactors of several months or more. This study aims to provide a quick solution to the problem of long start-up periods by pretreating the surface of carrier material. Two different techniques were investigated. The first one focused on growing a layer of heterotrophic biofilm on the surface of the plastic carriers prior to inoculation with anammox biomass. Specific anammox activity increased by almost 400% as compared to seed values and was equal to 250 mg NH₄-N/gVSS/L•d. In the second technique, the carrier material was coated with a layer of granular-activated carbon to provide a higher surface area. The anammox activity increased by approximately 50%. In comparison, the control reactor did not develop any biofilm and no anammox activity was detected. Rapid attachment of the anammox biomass was achieved in a reactor with media that had a predeveloped layer of a biofilm. In a way, this approach is analogous to a primer or an undercoat that is put on materials before painting to ensure better adhesion of paint to the surface, hence the suggested name - bioprimer.

Nitritation of real sewage: start-up and maintenance by the side-stream heat-shock treatment

In this study, the side-stream heat-shock treatment was used to start up and maintain the nitritation of real sewage. Complete nitrification was obtained when the real sewage was treated in a sequencing batch reactor (SBR). Then, about 50% of the mixed sludge was collected from the SBR and treated with the heat-shock treatment at 60 °C for 40 min in another reactor every 2 weeks. After providing the heat-shock treatment for four times, the effluent nitrate in the SBR gradually decreased from 22.5 to 3.2 mg/L, while the nitrite accumulation rate increased from 4.4% to 81.8%, indicating a successful start-up of nitritation. Further, the sewage nitritation was stable with the regular side-steam heat-shock treatment for 91 days, and the ammonium removal efficiency of 80.6% and nitrite accumulation rate of 91.2% were achieved. This study suggests that the side-stream heat-shock treatment could be used to start up sewage nitritation and maintain stability for a long-term operation.

Start up of partial nitritation-anammox process using intermittently aerated sequencing batch reactor: Performance and microbial community dynamics

This study investigated the performance and microbial community dynamics of a start-up method for the partial nitritation-anammox (PN-A) process: start-up from return sludge in an intermittently aerated sequencing batch reactor (IASBR). The robustness of this PN-A IASBR system in achieving long-term efficient nitrogen removal was also investigated. Stable partial nitritation with nitrite accumulation ratio of about 80% was firstly achieved in the IASBR. Then, PN-A process with total nitrogen removal of up to 81.5% was established due to the thriving of anammox bacteria Candidatus Kuenenia resulting from the reduction of the aeration rate. Molecular analysis showed that both bacterial and archaeal communities shifted greatly throughout the start-up stage and the PN-A stage. Besides bacterial genus Nitrosomonas, ammonium-oxidizing archaea (AOA) Candidatus Nitrososphaera with a high abundance of 3.44% also contributed to partial nitritation. Nitrospira was effectively restrained (abundance <1.6%) while methanogens co-existed with the aerobic and anaerobic nitrogen-conversion microorganisms. This study showed that IASBR configuration was efficient in starting up the PN-A process from return sludge, maintaining long-term efficient nitrogen removal and triggering the thrive of AOA.

Restoration of real sewage partial nitritation-anammox process from nitrate accumulation using free nitrous acid treatment

This study presented a strategy for recovering partial nitritation-anammox (PN/A) of real sewage from nitrate accumulation using free nitrous acid (FNA) treatment. Sewage PN/A was successfully achieved in an integrated fixed-film activated sludge (IFAS) reactor but effluent nitrate gradually increased. For recovering the system performance, flocculent sludge of the reactor was collected and treated with FNA of 1.35 mg/L for 24 h. After FNA treatment, effluent nitrate decreased from 17.6 to 6.1 mg/L with an increase of total nitrogen removal efficiency from 29.1% to 63.1% within 32 days. The improvement of nitrogen removal was mainly due to the selective suppression of FNA on nitrite-oxidizing bacteria. Its relative abundance decreased from 0.32% to 0.08% and the activity declined from 9.05 to 2.42 mg N/(g MLSS·h). Meanwhile, ammonium-oxidizing bacteria and anammox bacteria were barely affected. Overall, IFAS reactor combined with FNA treatment potentially provided a promising technology for stable operation of one-stage sewage PN/A.

The transformation from anammox granules to deammonification granules in micro-aerobic system by facilitating indigenous ammonia oxidizing bacteria

Granular deammonification process is a good way to retain aerobic and anaerobic ammonia oxidizing bacteria (AOB and anammox bacteria) and exhaust flocculent nitrite oxidizing bacteria (NOB). In this study, to facilitate indigenous AOB growth on anammox granules, by stepwise reducing influent nitrite, anammox granules were effectively transformed into deammonification granules in a micro-aerobic EGSB in 100 days. Total nitrogen removal efficiency of 90% and nitrogen removal rate of 2.3 g N/L/d were reached at stable deammonification stage. High influent FA and limited oxygen supply contributed suppression for Nitrospira-like NOB. In transition stages, Proteobacteria and Chloroflexi were always dominated. Anammox abundance decreased, while AOB abundance grew fast. Anammox bacteria and AOB were dominated by Brocadia fulgida and Nitrosomonas europaea, respectively. Denitrification activity and bacteria existed although without influent organic. The final AOB abundance was about 4.55-13.8 times more than anammox bacteria abundance, with almost equal potential activities.

In-situ restoration of one-stage partial nitritation-anammox process deteriorated by nitrate build-up via elevated substrate levels

The one-stage partial nitritation and anammox process (PN/A) has been a promising microbial process to remove ammonia from wastewater especially with low carbon/nitrogen ratio. The main breakdown was the deterioration caused by overgrowth of nitrite oxidizing bacteria (NOB) resulting effluent nitrate build-up in the PN/A process. This study presented an in-situ restoring strategy for suppressing NOB activity in a one-stage granular PN/A system deteriorated over 2 months, using elevated concentrations of substrates (ammonia and nitrite) under limited dissolved oxygen level. The results showed that the NOB activity was successfully suppressed after 56 days of restoration, and finally the ratio of produced nitrate/consumed ammonium was reduced from 36.8% to 7%. On day 66 the nitrogen removal rate obtained as 1.2 kg N/(m³·d). The high FA level (5-40 mg/L) and low dissolved oxygen (<0.13 mg/L) were responsible for NOB suppression. From quantitative PCR (qPCR) analysis, after this restoration, anammox bacteria had a widely growth, and AOB stay stable, but Nitrospira increase and Nitrobacter declined. High amount of NOB was still persistent in the granules, which was not easy to wash-out and threaten the deammonification performance.

Stoichiometry and kinetics of the anaerobic ammonium oxidation (Anammox) with trace hydrazine addition

Purpose of this study is to investigate the stoichiometry and kinetics of anaerobic ammonium oxidation (Anammox) with trace hydrazine addition. The stoichiometry was established based on the electron balance of Anammox process with trace N2H4 addition. The stoichiometric coefficients were determined by the proton consumption and the changes in substrates and products. It was found that trace N2H4 addition can increase the yield of Anammox bacteria (AnAOB) and reduce NO3(-) yield, which enhances the Anammox. Subsequently, kinetic model of Anammox with trace N2H4 addition was developed, and the parameters of the anaerobic degradation model of N2H4 were obtained for the first time. The maximum specific substrate utilization rate, half-saturation constant and inhibition constant of N2H4 were 25.09mgN/g VSS/d, 10.42mgN/L and 1393.88mgN/L, respectively. These kinetic parameters might provide important information for the engineering applications of Anammox with trace N2H4 addition.