Influence of increasing anode surface area on nitrite-absent ammonium oxidation in a continuous single-chamber bio-electrochemical system

Reducing energy consumption in conventional nitrogen removal processes is a crucial and urgent requirement. This study proposes an efficient electrode-dependent bio-electrochemical anaerobic ammonium (NH4+-N) oxidation (BE-ANAMMOX) process, employing a carbon brush as the electron acceptor and voltage of 0.8 V. The applied voltage facilitated the removal of NH4+-N with a maximum removal efficiency of 41% and a Coulombic efficiency of 40.92%, without the addition of nitrite (NO2--N). Furthermore, the NH4+-N removal efficiency demonstrated an increase corresponding to the increase in the anodic surface area. The bio-electrochemical NH4+-N removal achieved remarkable reductions, eliminating the need for O2 and NO2--N by 100%, lowering energy consumption by 67%, and reducing CO2 emissions by 66% when treating 1 kg of NH4+-N. An analysis of the microbial community revealed an increase in nitrifiers and denitrifiers, including Exiguobacterium aestuarii, Alishewanella aestuarii, Comamonas granuli, and Acinetobacter baumannii. This intricate process involved the direct conversion of NH4+-N to N2 by ANAMMOX bacteria through extracellular electron transfer, all without NO2--N. Thus, bio-electrochemical NH4+-N removal exhibits promising potential for effective nitrogen removal in wastewater treatment facilities.

Analyzing the nitrogen removal performance and cold adaptation mechanism of immobilized cold-acclimation ANAMMOX granules at low temperatures

To improve the treatment performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, the immobilized cold-acclimation ANAMMOX granules (R3) were prepared and their low-temperature nitrogen removal ability as well as the cold adaptation mechanism were analyzed. The results indicated that the total inorganic nitrogen (TIN) removal efficiency of R3 was significantly higher than that of R2 (cold-acclimation granules without immobilization) and R1 (common granules), especially at 11 ± 2 and 7 ± 2°C (68% and 54%). These were attributed to the remarkable biomass retention capacity of R3, high up to 4.3-4.9 mg/gVSS even at 5-18°C. Besides, higher protein (PN) content of tightly bound extracellular polymeric substances (TB-EPS) also facilitated microbial aggregation in R3. Meanwhile, R3 granules retained higher ANAMMOX activity and heme c content at 5-25°C. The original dominant ANAMMOX genus (Candidatus Kuenenia) in R3 kept higher abundance (49%-57%) at 23 ± 2 and 16 ± 2°C, whereas Candidatus Brocadia became the dominant ANAMMOX genus (25%-32%) in R3 at 11 ± 2 and 7 ± 2°C. Notably, different ANAMMOX genera in R3 may adapt to cold environment by regulating the expression of cold-stress proteins (CspA, CspB, PpiD, and UspA). PRACTITIONER POINTS: Immobilized cold-acclimation ANAMMOX granules showed higher nitrogen removal efficiency at 23°C → 5°C. Immobilization method effectively retained biomass (Candidatus Kuenenia and Candidatus Brocadia). Immobilization facilitated TB-EPS release and biological aggregation in cold-acclimation granules. Expression of cold-stress proteins in immobilized cold-acclimation granules was more active.

Free nitrous acid prediction in ANAMMOX process using hybrid deep neural network model

Free nitrous acid (FNA) is a critical metric for stabilization of ANAMMOX but can not be directly and immediately measured by sensors or chemical measurement method, which hinders the effective management and operation for ANAMMOX. This study focuses on FNA prediction using hybrid model based on temporal convolutional network (TCN) combined with attention mechanism (AM) optimized by multiobjective tree-structured parzen estimator (MOTPE), called MOTPE-TCNA. A case study in an ANAMMOX reactor is carried out. Results show that nitrogen removal rate (NRR) is highly correlated with FNA concentration, indicating that it can forecast the operational status by predicting FNA. Then, MOTPE successfully optimizes the hyperparameters of TCN, helping TCN achieve a high prediction accuracy, and AM furtherly improves model accuracy. MOTPE-TCNA obtains the highest prediction accuracy, whose R2 value gets 0.992, increasing 1.71-11.80% compared to other models. As a deep neural network model, MOTPE-TCNA has more advantages than traditional machine learning methods in FNA prediction, which is beneficial to maintain the stable operation and easy control for ANAMMOX process.

Bioelectrochemical system for nitrogen removal: Fundamentals, current status, trends, and challenges

Biological nitrogen removal (BNR) is essential for the treatment of nitrogen-containing wastewater. However, the requirement for aeration and the addition of external carbon sources, resulting in greenhouse gas emissions and additional costs, are disadvantages of the traditional BNR process. Alternative technologies have been devised to overcome these drawbacks. Bioelectrochemical nitrogen removal (BENR) has been proposed for efficient nitrogen removal, demonstrating flexibility and versatility. BENR can be performed by combining nitrification, denitrification, anaerobic ammonium oxidation (ANAMMOX), or organic carbon oxidation. Bioelectrochemical-ANAMMOX (BE-ANAMMOX) is the most promising method for nitrogen removal, as it can directly convert NH4+ to N2 and H2 in one step when the electrode is arranged as an electron acceptor. High-value-added hydrogen can potentially be recovered with efficient nitrogen removal using this concept, maximizing the benefits of BENR. Using alternative electron acceptors, such as electrodes and metal ions, for complete total nitrogen removal is a promising technology to substitute NO2- production from NH4+ oxidation by aeration. However, the requirement of electron donors for NO3- reduction, low NH4+ removal efficiency, and low competitiveness of exoelectrogenic bacteria still remain the main obstacles. The future direction for successful BENR should aim to achieve complete anaerobic NH4+ oxidation without any electron acceptor and to maximize selectivity in H2 production. Therefore, the bioelectrochemical pathways and balances between efficient nitrogen removal and high-value-added chemical production should be further studied for carbon and energy neutralities.

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.

Improving stability and nitrogen removal performance of pilot-scale autotrophic process for mature landfill leachate treatment utilizing in-situ organics

This study established a stable and efficient pilot-scale denitrification (DN) and partial nitritation (PN) combined with autotrophic nitrogen removal process for mature landfill leachate treatment. A total inorganic nitrogen removal efficiency (TINRE) of 95.3% was achieved without any external carbon source input, including 17.1%, 1.0% and 77.2% of nitrogen removal contributed by the DN, PN and autotrophic processes, respectively. ANAMMOX genus, Ca_Anammoxoglobus (19.4%) was dominant in autotrophic reactor. Moreover, denitrifying bacteria could utilize in-situ organics, including poorly degradable organics, to enhance the nitrogen removal performance of autotrophic process, contributing 3.4% of TINRE. This study provides new insights for the economical, low-carbon, and efficient treatment of mature landfill leachate.

Performance evaluation and microbial community structure of a modified trickling filter and conventional activated sludge process in treating urban sewage

This study compares the performance and microbial composition of a conventional activated sludge process (ASP) with a modified trickling filter (MTF) for urban sewage treatment. MTF (2 h HRT with effluent recycling) and ASP (8 h HRT) showed >60 % removal efficiency for COD, NH₃-N and PO₄^3--P. MTF outperformed ASP in denitrification and 5 mg/L of NO₃^--N was detected in the effluent of MTF. The widespread distribution of nitrogen removal functional genes (amoA, nirK, nirS, napA, narG and nosZ) in MTF indicates simultaneous nitrification and denitrification (SND) as a key process controlling nitrogen removal. In addition, Miseq sequencing was used to examine the microbial community composition in MTF and ASP. The sequencing result revealed that Proteobacteria, Planctomycetes, Chloroflexi and Actinobacteriota were the dominant phyla in both MTF and ASP. Moreover, the co-occurrence of various nitrifiers, denitrifiers, aerobic denitrifiers, and ANAMMOX bacteria in MTF suggested their role in nitrogen removal.

Effect of aerobic microbes' competition for oxygen on nitrogen removal in mainstream nitritation-anammox systems

The effects of C/N ratio in mainstream partial nitritation (PN)-anaerobic ammonia oxidation (ANAMMOX) considering competitive relationship of aerobic microbes competing for oxygen were investigated. Thy system was operated for 501 d with various C/N ratio. Competitive growth of aerobic heterotrophic bacteria (AHB) at ≥ 1 of C/N ratio acted effectively on the selective inhibition of nitrite-oxidizing bacteria (NOB) while contributing to stable PN-A. In-depth kinetic analysis indicated oxygen affinity of aerobic microbes was in the order of AHB > ammonia-oxidizing bacteria (AOB) > NOB. In addition, potential of denitritation by AHB could contributed to improving nitrogen removal up to 87.5 ± 4.3%. AHB was comparatively clustered into two groups with a C/N ratio of 1. Nitrosomonas sp. PY1 became predominant while Nitrospira spp. were the major NOB. The potential of AHB in establishing selective inhibition of NOB was identified, which could be a novel approach to stabilze the mainstream PN-A.

Key enzymes involved in anammox-based processes for wastewater treatment: An applied overview

The anaerobic ammonium oxidation (anammox) process has attracted significant attention as an economic, robustness, and sustainable method for the treatment of nitrogen (N)-rich wastewater. Anammox bacteria (AnAOB) coexist with other microorganisms, and particularly with ammonia-oxidizing bacteria (AOB) and/or heterotrophic bacteria (HB), in symbiosis in favor of the substrate requirement (ammonium and nitrite) of the AnAOB being supplied by these other organisms. The dynamics of these microbial communities have a significant effect on the N-removal performance, but the corresponding metabolic pathways are still not fully understood. These processes involve many common metabolites that may act as key factors to control the symbiotic interactions between these organisms, to maximize N-removal efficiency from wastewater. Therefore, this work overviews the current state of knowledge about the metabolism of these microorganisms including key enzymes and intermediate metabolites and summarizes already reported experiences based on the employment of certain metabolites for the improvement of N-removal using anammox-based processes. PRACTITIONER POINTS: Approaches knowledge about the biochemistry and metabolic pathways involved in anammox-based processes. Some molecular tools can be used to determine enzymatic activity, serving as an optimization in nitrogen removal processes. Enzymatic evaluation allied to the physical-chemical and biomolecular analysis of the nitrogen removal processes expands the application in different effluents.

Biofilm carriers for anaerobic ammonium oxidation: Mechanisms, applications, and roles in mainstream systems

The anaerobic ammonium oxidation (ANAMMOX) process was proposed as the most promising nitrogen removal process. Biofilm carriers were demonstrated to effectively enhance the anaerobic ammonium oxidating bacteria (AnAOB) retention. This paper reviews the effect of carrier properties on the AnAOB biofilm development according to the biofilm development process and the application state-of-art of three major kinds of conventional carriers, organic-based, inorganic-based carriers, and gel carriers, from the view of system performance and functional microorganisms. The carrier modification methods and purpose are thoroughly summarized and classified into three categories corresponding to various carrier defects. Four important aspects of the desirable carrier for the mainstream ANAMMOX process were proposed, including providing spatial configuration, enhancing the biomass retention, reinforcing the activity, and improving the growth environment, which needs to combine the advantages of organic and inorganic materials. Eventually, the future application directions of novel carriers for the ANAMMOX-based process were also highlighted.

Development of long-term dynamic BioWin® model simulation for ANAMMOX UASB micro-granular process

Three different innovative mathematical models were established to assess the volumetric nitrogen conversion rates of a lab-scale ANAMMOX upflow anaerobic sludge blanket reactor. Despite the vast technological and economical advantages of ANAMMOX, major challenges in process implementation call for mathematic simulations of the process, optimization of operating conditions, and kinetic/statistical analysis of the entire process. In this study, all developed mathematical models implemented via BioWin®, were calibrated and validated, with adequate representations of a bench-scale micro-granular ANAMMOX process, to understand the potential setbacks of ANAMMOX process start-up and stabilization. Fundamental calculations of the kinetic and stoichiometric constants were integrated in the BioWin® software, and the adjusted parameters based on experimental analysis were applied for the assessments. Based on the results from the statistical approach, one of the models (Model III) exhibited a precise prognosis of the effluent data for the entire operational phases with a mean relative error (MRE) of approximately 1.96, 4.36 and 2.54% for nitrogen removal efficiency, removal rate and loading rate, respectively. Evaluating alkalinity and pH during the operation, led to identifying an acceptable fit between the experiment and Model III results, with a MRE of -7.19 and -0.35%, correspondingly. This study confirms the reliability of ANAMMOX-based process modeling and high predictive ability with BioWin®. The presented simulation constants and modeling outline, can be further employed in full-scale applications design and development.

[Cultivation and Performance Analysis of Simultaneous Partial Nitrification, ANAMMOX, and Denitratation Granular Sludge]

We cultivated simultaneous partial nitrification, anaerobic ammonium oxidizing(ANAMMOX), and denitratation granular sludge in a novel air-lift internal circulation reactor using low C/N wastewater as the substrate and ANAMMOX sludge matched with ordinary activated sludge as the inoculum. The results showed that the mature and stable granular sludge could be cultivated after 225 d of continuous operation, and the total nitrogen removal rate was as high as 91.4%. Compared with flocculated sludge, the ANAMMOX activity in the granular sludge increased significantly, and the ANAMMOX activity was highest among the four nitrogen removal processes followed by partial nitrification, and the specific denitratation activity was 2.1-times higher than the specific nitrite reduction activity. High-throughput sequencing results showed that the dominant bacteria in partial nitrification and ANAMMOX were Nitrosomonas and Candidatus_Brocadia, respectively, compared to flocculated sludge, with abundances increasing to 0.70% and 0.57%, respectively. Thauera may also be the potential dominant bacteria for denitratation, with an abundance of up to 0.26%. RT-qPCR analysis showed that compared to the inoculation stage, the transcript levels of the amoA and hao genes for partial nitrification increased 3.5-and 1.5-fold, respectively, and the transcript levels of the hzsA gene for ANAMMOX increased 2.1-fold. During denitrataion, the overall abundance of napA and narG transcript levels was 4.8-times higher than that of nirK and nirS. The results of this study provide new insights for the treatment of low C/N wastewater.

[Spatial Differences and Influencing Factors of Denitrification and ANAMMOX Rates in Spring and Summer in Lake Taihu]

Denitrification and ANAMMOX are the main nitrogen removal processes in lakes, which are of great significance for maintaining the nitrogen balance. Lake Taihu is a large, shallow lake. There are great spatial and temporal differences in the nutrient levels and algal blooms, which will affect the rates of denitrification and ANAMMOX. In order to understand the spatial and temporal variations in the denitrification and ANAMMOX rates and their influencing factors in Lake Taihu, undisturbed sediment cores were collected from Meiliang Bay, Gonghu Bay, Zhushan Bay, Dapukou Bay, Xukou Bay, and the center of Lake Taihu in the spring and summer of 2020. The results showed that the spatial distribution of the denitrification and ANAMMOX rates varied greatly in different areas of Lake Taihu in spring. The denitrification and ANAMMOX rates were (27.74±8.45)-(142.43±35.54) μmol·(m²·h)^-1 and (2.35±1.06)-(17.95±8.66) μmol·(m²·h)^-1, respectively. The contribution of ANAMMOX to nitrogen removal was relatively low, ranging from (7.82±1.71)% to (11.20±1.53)%. In summer, the denitrification and ANAMMOX rates were (165.68±62.14) μmol·(m²·h)^-1 and (33.56±10.66) μmol·(m²·h)^-1, respectively. The nitrogen removal rates were relatively low in other areas where the denitrification and ANAMMOX rates were (25.47±10.46)-(42.50±16.46) μmol·(m²·h)^-1 and (2.65±0.94)-(5.95±2.65) μmol·(m²·h)^-1, respectively. The contribution of ANAMMOX to nitrogen removal was (13.62±1.95)%-(7.24±1.78)%. The denitrification rate in summer was generally lower than that in spring, while the ANAMMOX rate did not decrease significantly compared with that in spring. The statistical analysis showed that the denitrification and ANAMMOX rates were significantly correlated with the substrate nitrogen concentration (P<0.01), which indicated that the nitrogen concentration was the main factor causing the difference in the nitrogen removal rates in different lake regions. In addition, there was a significant positive correlation between the contribution rate of ANAMMOX and the concentration of chlorophyll-a (P<0.05), thereby indicating that cyanobacteria blooms have a great influence on the change in the contribution of ANAMMOX to nitrogen removal.

[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.

A new kinetic model to predict substrate inhibition and better efficiency in an airlift reactor on deammonification process

A collection of kinetic models to explore the bacteria pathway inhibition by high-ammonia during deammonification process was fitted. The main goal was to determine the substrate concentration to operate the deammonification with efficiency, performance and low impact to ANAMMOX and ammonia-oxidizing bacteria (AOB) by substrate. A new mathematical model was created to describe the deammonification behavior, since the empirical theoretical models showed inconsistent parameters to describe the process. The proposed model showed significant prediction to the estimable parameters and according to it, until 550 mg NH₃-N L^-1 no inhibitions by ammonia and nitrite were observed. However, concentrations higher than this promote the decrease on specific bacterial activity and nitrite accumulation, since it was not quickly consumed by the bacteria. The proposed model can be applied to predict microorganism affinity and inhibition by substrate over a wide range of ammonia concentrations (<900 mgNH₃-N L^-1) in reactors treating high-ammonia concentration swine wastewater.

[Performance and Microbial Characteristics of Ammonium-limited and Nitrite-limited ANAMMOX Systems]

The performance and microbial characteristics of ammonium-limited and nitrite-limited ANAMMOX reactors were studied in two continuously stirred tank reactors. The influent TN concentrations were controlled below 50 mg·L^-1. The hydraulic retention time and water temperature were maintained at 2.0 h and 20℃, respectively. Results showed that though both ANAMMOX reactors demonstrated similar TN removal loading rates[0.45-0.5 kg·(m³·d)^-1] and TN removal efficiencies (around 70%), the ΔNO₃^-/ΔNH₄⁺ ratio of the ammonium-limited ANAMMOX reactor showed a faster upward trend. Batch tests and high-throughput sequencing results indicated that the ammonium-limited ANAMMOX reactor had more significant functional and population heterogeneity than the nitrite-limited ANAMMOX reactor. Candidatus_Brocadia was the predominant ANAMMOX bacteria in both reactors. The relative abundance of Candidatus_Brocadia in large granules (53.9%) was significantly higher than that in flocs (19.1%) under the ammonium-limited conditions, whereas only a small difference in relative abundance of Candidatus_Brocadia was observed between the granules (28.1%) and flocs (21.3%) in the nitrite-limited ANAMMOX reactor. Nitrospira-like NOB were detected in both ANAMMOX reactors, which primarily inhabited flocs, seemingly driven by the availability of oxygen. Moreover, the ammonium-limited (i.e., excess nitrite) conditions seemingly favored the growth of Nitrospira. Building upon these results, a control strategy for optimal operation of the ammonium-limited ANAMMOX reactor was proposed based on selective floc discharge.

Domestic Sewage Treatment Using a One-Stage ANAMMOX Process

A one-stage anaerobic ammonium oxidation (ANAMMOX) reactor can be quickly started within 40 days by mixing partial nitrifying sludge with ANAMMOX granular sludge with an average temperature of 30 °C. After 70 days of nitrogen load acclimation, Acinetobacter, including Candidatus Kuenenia, became the dominant strain of the system within the reactor, which exhibited high efficiency and a stable nitrogen removal performance. At an influent chemical oxygen demand (COD), NH₄⁺-N content, total nitrogen (TN) content, hydraulic retention time (HRT), temperature, and reactor dissolved oxygen (DO) content of 100, 60, and 70 mg/L, 6 h, 30 ± 1 °C, and below 0.6 mg/L, respectively, the one-stage ANAMMOX reactor could effectively treat domestic sewage on campus. The removal rates of COD, NH₄⁺-N, and TN were approximately 89%, 96.7%, and 70%, respectively.

[Advanced Nitrogen Removal Characteristics of Low Carbon Source Municipal Wastewater Treatment via Partial-denitrification Coupled with ANAMMOX]

Partial-denitrification coupled with ANAMMOX is a novel biological nitrogen removal technology, which is expected to significantly reduce the external carbon source dosage for advanced nitrogen removal from municipal wastewater. In this study, ANAMMOX sludge was inoculated to investigate advanced nitrogen removal performance and sludge characteristics in a partial-denitrification/ANAMMOX reactor. The results showed that inoculation of ANAMMOX sludge could quickly start the partial-denitrification/ANAMMOX reactor. The effluent total nitrogen concentrations were (4.82±1.84) mg·L^-1 with a chemical oxygen demand of 2.19±0.08. Sludge particles larger than 0.20 mm accounted for 86.16% in the reactor. This meant that granular sludge was formed, which was conducive to good retention of ANAMMOX bacteria in the reactor. The external carbon source dosage and the oxygen requirement for nitrification can be reduced by applying partial-denitrification coupled with ANAMMOX to advanced nitrogen removal from the effluent of secondary clarifier in municipal wastewater treatment plants.

Treatment of anaerobically digested effluent from kitchen waste using combined processes of anaerobic digestion-complete nitritation-ANAMMOX based on reflux dilution

In this study, an anaerobically digested effluent from kitchen waste with high concentrations of chemical oxygen demand (COD) and ammonia nitrogen was treated using combined processes of anaerobic digestion (AD), complete nitritation (CN), and anaerobic ammonium oxidation (ANAMMOX). The COD and nitrogen removal efficiency of each treatment unit were investigated. The feasibility of using the final treatment effluent to dilute the original wastewater was also discussed. Findings showed that as a pretreatment step, AD resulted in the decline in biodegradability and increase in NH 4 + - N concentration. CN was successfully and stably achieved for 106 days with an average nitritation rate of 95% by maintaining the dissolved oxygen at 2-3 mg/L and hydraulic retention time of 24 hr under 30 ± 1°C. High NH 4 + - N and NO 2 - - N . removal efficiencies of over 88% and 96% were attained in the following ANAMMOX reactor. The reflux of ANAMMOX-treated effluent for the dilution of raw wastewater or an influent of CN and ANAMMOX ensured the stable operation of the combined system. PRACTITIONER POINTS: Anaerobic digestion effluent of kitchen waste had low COD/ NH 4 + - N ratio and poor biodegradability. Stable and efficient nitritation was realized by controlling DO, HRT and TEMP. High NH 4 + - N and NO 2 - -N removal efficiency were obtained by ANAMMOX process. Average nitrogen removal rate of 0.94 kg N/m³ /day were obtained by ANAMMOX. Reflux dilution with the effluent guaranteed the system's successful operation.

Removal of ametryn and organic matter from wastewater using sequential anaerobic-aerobic batch reactor: A performance evaluation study

The present study was aimed to investigate biodegradation of 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine (ametryn) in a laboratory-scale anaerobic sequential batch reactor (ASBR) and followed by aerobic post-treatment. Co-treatment of ametryn with starch is carried out at ambient environmental conditions. The treatment process lasted up to 150 days of operation at a constant hydraulic retention time (HRT) of 24 h and an organic loading rate (OLR) of 0.21-0.215 kg-COD/m³/d. Ametryn concentration of 4 and 6 mg/L was removed completely within 48-50 days of operation with chemical oxygen demand (COD) removal efficiencies >85% at optimum reactor conditions. Ametryn acted as a nutrient/carbon source rather causing toxicity and contributed to methane gas production and sludge granulation in the anaerobic reactor. Biotransformation products of ametryn to cyanuric acid, biuret, and their further conversion to ammonia nitrogen and CO₂ are monitored during the study. Adsorption of ametryn on to reactor sludge was negligible, sludge granulation, presence of ANAMMOX bacteria, and low MLVSS/MLSS ratio between 0.68 and 0.72. The study revealed that ametryn removal occurred mainly due to biodegradation and co-metabolism processes. Aerobic post-treatment of anaerobic effluent was able to remove COD up to 95%. The results of this study exhibit that anaerobic-aerobic treatment is feasible due to easy operation, economic, and highly efficient.

Optimization of nitrogen removal performance in a single-stage SBR based on partial nitritation and ANAMMOX

A partial nitritation (PN)/anaerobic ammonium oxidation (ANAMMOX) process in sequencing batch reactor (SBR) was successfully developed to treat high-strength ammonium wastewater. The feed distribution in the SBR cycle and sub-cycles was considered as the main operating strategy, and was optimized using a response surface methodology (RSM)-based optimization technique. In the SBR cycle, the maximum nitrogen removal rate (NRR) of 0.79 ± 0.01 kg m^-3 d^-1 was achieved by applying a feed distribution strategy that considered the kinetic characteristics of ANAMMOX and ammonia oxidizing bacteria (AOB). However, this strategy negatively affected the nitrogen removal efficiency (NRE) due to alkalinity loss. Therefore, the feed distribution in the SBR sub-cycles with respect to the NRE and the NRR was further studied. The nitrogen removal performance was optimized in the optimum region and an NRE of 88% and an NRR of 0.84 kg m^-3 d^-1 were achieved. The optimized model was verified in confirmation test. The RSM-based optimization results provide insights into the feed distribution strategy for achieving single-stage PN/ANAMMOX SBR operation.

[Water Bloom Modified Sediment Nitrogen Transformation and Removal]

Water bloom is a notorious and annual reoccurring problem in eutrophic lakes. Understanding the influence of water bloom on lacustrine nitrogen transformation and removal is crucial for predicting ecosystem functions and taking strategies to reduce in-lake nitrogen budgets. In this study, we investigated the impact of water bloom on the levels and transformation of nitrogen in sediments as well as the pathway to influence the nitrogen removal process. The results of structural equation model analysis showed that water bloom can directly elevate the sediment budget of total dissolved nitrogen (TDN) and total organic carbon (TOC), and the gene abundance of anaerobic ammonium oxidation (ANAMMOX), nirS, and nirK and can indirectly enhance sediment concentration of ammonia and nitrate as well as nitrogen removal. Moreover, compared with coupled nitrification-ANAMMOX in Lake Taihu sediment, denitrification was the main path of nitrogen removal, with 42.3% explanation of the total nitrogen removal in the sediments. Water bloom can accelerate nitrogen removal in sediment through enhancement of ANAMMOX and denitrification process.

Toward N2O emission reduction in a single-stage CANON coupled with denitrification: Investigation on nitrite simultaneous production and consumption and nitrogen transformation

A dynamic analysis approach for determining nitrite production and consumption rates was established to systematically investigate the characteristics of nitrogen transformation and N₂O emission of the completely autotrophic nitrogen removal over nitrite (CANON) process coupled with denitrification using a sequencing batch biofilm reactor (SBBR). The results indicate that anaerobic ammonium-oxidizing bacteria was not inhibited significantly by low C/N ratios. There were no obvious differences in the nitrite production rate, nitrite consumption rate or nitrogen removal among reactors operated with C/N ratios of 0, 0.67 and 1.00, which suggested that the certain carbon source did not significantly affect the nitrite conversion and nitrogen removal in the process. More than 60% of total N₂O emission is generated during the initial phase of each period in the SBBR. More than 94.5% of N₂O was generated by NO₂^--N consumption via denitrification in the process. Interestingly, total N₂O production drops by 16.7%, when the C/N ratio increases from 0 to 1. This phenomenon may be caused by the inhibition of N₂O production via AOB denitrification. Therefore, an appropriate carbon source (C/N = 1.00) has the beneficial effect of reducing N₂O emission by CANON coupled with denitrification. The results of this study provide an important empirical foundation for the mitigation of N₂O emission in the CANON process coupled with denitrification.

Comparative study on pilots between ANAMMOX favored conditions in a partially saturated vertical flow constructed wetland and a hybrid system for rural wastewater treatment

The objective of this research was to evaluate the nitrogen removal in a single stage rural wastewater treatment system. It was a modified subsurface vertical flow (SSVF) constructed wetland. The so-called Anaerobic Ammonium Oxidation(ANAMMOX) process is favored by imposing a saturated zone at the bottom of the basin. The nitrogen removal performances of this modified SSVF were compared to those of a conventional hybrid system where the well-known nitrification-denitrification process is performed. This study was carried out using three lab-scale pilots of constructed wetlands during four months: (1) a hybrid constructed wetlands with a reed-Phragmites australis SSVF bed in serial with a cattail-Typha angustofolia SSHF bed (SSVF_p + SSHF). (2) A reed-Phragmites australis SSVF bed partially saturated at 40% of its depth (SSVF_PS); (3) A cattail-Typha angustofolia SSVF bed partially saturated at 40% of its depth (SSVF_TS). The results showed that the three configurations used in this study were efficient for most of the pollutants reduction. In fact, single-stage reactors have achieved similar chemical oxygen demand (COD) removal in comparison to the two-stage reactor independently of the macrophytes species. However, for Total Kjeldahl Nitrogen (TKN), a slightly higher nitrogen removal efficiency was recorded for (SSVF _p + SSHF) with an average removal rate of 53% versus 48% and 51% for SSVF _PS and SSVF_TS respectively. These findings were highlighted with fluorescent in situ hybridization (FISH) analysis, which demonstrated the presence of major differences in the community composition and abundance of the bacteria involved with denitrification and nitrification in the three systems. In fact, SSVF_P of the hybrid system was characterized by highest relative abundance of nitrifying bacteria (13% Nitrosomonas, 11% Nitrosospira, 14% Nitrospira and 10% Nitrobacter). While, the SSHF of hybrid system had larger number of denitrifying species than SSVF, with relative abundances of pseudomonas (3%), Paracoccus (9%), Zoogloea (6%), Thauera (4%), Thiobacillus (2%) and Aeromonas (1%). Interestingly, in the SSVF_ST (planted with Thypha angustofolia) where the relative abundance of nitrifying bacteria was very low (4% Nitrosomonas, 4% Nitrosospira, 4% Nitrospira and 1% Nitrobacter), we have detected the presence of ANAMMOX bacteria (3%). Accordingly SSVF_ST in the presence of Thypha angustofolia have favored the development of ANAMMOX activity in comparison to the other configurations.

Long-term operation and autotrophic nitrogen conversion process analysis in a biofilter that simultaneously removes Fe, Mn and ammonia from low-temperature groundwater

One lab-scale biofilter that simultaneously removes Fe, Mn and ammonia from 4 °C groundwater was established to investigate the nitrogen conversion process. The results showed that 333 days were needed to achieve the required standards for Fe, Mn and ammonia under a filtration rate of 3 m/h. Effluent nitrite concentration was the key factor determining the final operation parameters. Both nitrification and anaerobic ammonium oxidation (ANAMMOX) contributed to nitrogen conversion. The calculation results demonstrated that autotrophic nitrogen removal proportion was about 15.92% in steady operation period. Meanwhile, 7 genera of Mn oxidizing bacteria (MnOB) were detected; Candidatus Brocadia was the only detected ANAMMOX genera. The corresponding functional oxidizing bacteria could be acclimated sufficiently in biofilter treating low-temperature groundwater.

Quick start-up and stable operation of a one-stage deammonification reactor with a low quantity of AOB and ANAMMOX biomass

In this study, a quick start-up of one-stage deammonification in an immobilized aerobic ammonium oxidizing bacteria (AOB) and anoxic ammonium oxidizing (ANAMMOX) bacteria up-flow reactor (IAAR) was successfully achieved. With the aid of gel layers, AOB and ANAMMOX bacteria had excellent spatial distribution, theoretically meeting dissolved oxygen requirements for the simultaneous processes of aerobic and anaerobic ammonium oxidizing. The results indicated that an IAAR containing 0.4 g-VSS L^-1 immobilized biomass achieved a nitrogen removal rate (NRR) of 0.53 kg-N m^-3 d^-1 after only 10 days of operation and subsequently reached a maximum nitrogen removal rate (NRR_max) of 3.73 kg-N m^-3 d^-1. The micro-profiles of DO and pH were measured using microelectrodes to help understand the stratification of the microbial processes inside the gel layers. The distribution of AOB and ANAMMOX bacteria within the gel layers was verified using fluorescence in situ hybridization (FISH) analysis. The community distribution in the FISH three-dimensional images closely corresponded to the micro-profiles of DO concentration and pH, enabling rapid adaptation and stable operation of the reactor seeded with a quite low quantity of biomass.

[Biological Nitrogen Removal Process in a Microbubble-aerated Biofilm Reactor Treating Low C/N Wastewater]

The microbubble-aerated biofilm reactor as a new treatment process combines microbubble aeration technology with aerobic biological treatment. A microbubble aerated biofilm reactor was used in this study to treat low C/N ratio wastewater at a low air/water ratio. The process and performance of biological nitrogen removal were investigated, and the functional bacterial populations for nitrogen removal in the biofilm were analyzed. The results showed that the biological nitrogen removal process was converted from simultaneous nitrification-denitrification to simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) processes when DO concentration was controlled by an air/water ratio of lower than 1:2 and the influent C/N ratio was reduced. As a result, the efficient biological nitrogen removal performance was achieved when treating low C/N ratio wastewater. When the DO concentration was lower than 1.0 mg·L^-1 and the influent C/N ratio was 1:2.8, the SNAD process became dominant for biological nitrogen removal. In this case, the average total nitrogen (TN) removal efficiency was 76.3%, and the average TN loading rate removed was 1.42 kg·(m³·d)^-1. In addition, it was estimated that 86.0% of TN removal was attributed to the ANAMMOX process. The relative abundances of ammonia-oxidizing bacteria populations and ANAMMOX bacteria populations in the biofilm increased gradually, while the relative abundances of nitrite-oxidizing bacteria populations and denitrifying bacteria populations decreased gradually, with a decrease in influent C/N ratio. The variation of functional bacterial populations for nitrogen removal was consistent with the conversion of nitrogen removal process to SNAD process.

Impact of Mn and ammonia on nitrogen conversion in biofilter coupling nitrification and ANAMMOX that simultaneously removes Fe, Mn and ammonia

One lab-scale biofilter coupling nitrification and anaerobic ammonium oxidation (ANAMMOX) that simultaneously removes Fe, Mn and ammonia from simulated groundwater was adopted to investigate the influence of Mn and ammonia on nitrogen conversion and Mn removal kinetics in this study. The results showed that autotrophic nitrogen removal proportion (ANRP) rose slightly with the raise of Mn concentration and declined along with the raise of ammonia; the average ratios were 49.6%, 51.5%, 51.8%, 52.3%, 52.6%, 48.9%, 47.4% and 38.8%, respectively. Relative constant or slight down trend of accumulated ANRP was detected in filter bed which indicated the superiority of nitrification in relevant areas. After reaching a certain value, Mn could promote ANAMMOX in the upper part of the filter bed and shorten the main ammonia conversion area. As ammonia content rising, the maximum accumulated ANRP reduced and the maximum value acquired height went up. Moreover, the ammonia inhibition threshold for ANAMMOX in the biofilter might be different from waste water treatment. Mn removal could be assessed by first order reaction in all the eight periods and the k values were more comparable than those in abiotic Mn oxidation.

Nitrogen removal in pilot-scale partially saturated vertical wetlands with and without an internal source of carbon

The aim was to evaluate and compare total nitrogen (TN) removal in pilot-scale partially saturated vertical wetlands (PSVWs) with and without an internal solid source of organic carbon (corncob) in order to distinguish the role of nitrification-denitrification and ANAMMOX in the removal process. The height of the free-drainage zone (FDZ) was 40 cm and the saturated zone (SZ) was 30 cm in system I (SI) and system II (SII) and 40 cm in system III (SIII) and system IV (SIV). In SII and SIV, approximately 30 kg of dry, 5 cm-length corncob was added. The systems were evaluated during two periods, that is, P1 and P2. Measurements of water quality parameters including BOD₅, COD, organic nitrogen (Org-N), ammonium, nitrate and nitrite were taken in the influent and effluents on a weekly basis; nitrate measurements were also taken at the interface. Measurements of pH, dissolved oxygen (DO) and oxidation-reduction potential (ORP) were taken in the SZ. The height of both SZ (40 cm vs. 30 cm in P1) and FDZ (40 vs. 25 and 30 cm in SI/SIII in P2) did not affect the efficiencies (p > 0.05) but the presence or absence of corn cob did (p < 0.05). Thus, SII and SIV were superior when compared to SI and SIII (p < 0.05) with TN average removal efficiencies of 72.9% and 73.2% in P1, and 59.8% and 64.2% in P2, respectively; showing a tendency to lower values when the biodegradable organics supplied by the corncob diminished. In SI and SIII, TN removals were 47.6% and 40.3% in P1, and 46.1% and 44.1% in P2, respectively. In SII and SIV, denitrification took place in both the lower semi-saturated part of the FDZ (probably also ANAMMOX) and SZ; whereas in SI and SIII, ANAMMOX took place in the lower semi-saturated part of the FDZ.

[High-rate Nitrogen Removal in a Two-stage Partial Nitritation-ANAMMOX Process Under Mainstream Conditions]

A two-stage partial nitritation (PN)-ANAMMOX process was successfully carried out for low-strength NH₄⁺-N (50 mg·L^-1) wastewater treatment at ambient/low temperatures. The results show that an average total nitrogen removal rate and removal efficiency above 0.6 kg·(m³·d)^-1and 80% could be maintained, respectively, at temperatures between 20℃ and 14℃. The two-stage PN-ANAMMOX process was successful both under NO₂^--N-limited and NH₄⁺-N-limited conditions. When the two-stage PN-ANAMMOX process was operated under NH₄⁺-N-limited conditions, the "limit of technology" for nitrogen removal (TN<3 mg·L^-1) could be easily achieved by following anoxic denitrification. Lowering the temperature to 12℃ resulted in the reduction of the total nitrogen removal rate to~0.5 kg·(m³·d)^-1. Due to the low temperature, the anammox reaction became the rate-limiting step for nitrogen removal, while the PN reaction was not impacted. In the temperature range of 10-20℃, the activity-temperature coefficients (θ) of the PN granules and ANAMMOX sludge were 1.056 and 1.172, respectively, suggesting that the anammox bacteria have a higher temperature sensitivity than the ammonium oxidizing bacteria (AOB). Overall, the results clearly indicate that the nitrogen removal loading rate of the two-stage PN-ANAMMOX process is mainly controlled by the activity and quantity of anammox biomass. In contrast, the process nitrogen removal efficiency mainly depends on the performance of the first-stage PN (i.e., effluent NO₂^--N/NH₄⁺-N ratio and NO₃^--N concentration) under a constant nitrogen removal loading rate (no overload). Based on these results, a hierarchically separate control strategy was proposed to obtain a high-rate nitrogen removal during the two-stage mainstream PN-ANAMMOX process.

Microbial community dynamics in an ANAMMOX reactor for piggery wastewater treatment with startup, raising nitrogen load, and stable performance

Bacterial community dynamics of the ANAMMOX reactor of an integrated “UASB + SHARON + ANAMMOX” system for treating piggery wastewater were investigated using the Illumina MiSeq method with samples obtained at ~ 2-week intervals during a 314-day period. With aerobic activated sludge as seeds and low content artificial wastewater (NH₄⁺–N 50 mg/L; NO₂⁻–N 55 mg/L) as influent for the ANAMMOX reactor, nitrogen removal was initially observed on day 38 with a removal rate 1.3 mg N L⁻¹ day⁻¹, and increased to 90.4 mg N L⁻¹ day⁻¹ on day 55 with almost complete removal of ammonia and nitrite, indicating a successful startup of the reactor. Increasing influent load stepwise to NH₄⁺–N 272.7 mg/L/NO₂⁻–N 300 mg/L, nitrogen removal rate increased gradually to 470 mg N L⁻¹ day⁻¹ on day 228, and maintained a stable level (~ 420 mg N L⁻¹ day⁻¹) following introduction of SHARON effluent since day 229. Correlation between microbial community dynamics and nitrogen removal capability was significant (r = 0.489, p < 0.001). Microbial community composition was determined by influent ammonia, influent nitrite, effluent nitrate and some undefined factors. Anammox bacteria, accounting for ~ 98.7% of Planctomycetes, became detectable (0.03% relative abundance) since day 38 and increased to 0.9% on day 58, well consistent with nitrogen removal performance of the reactor. Relative abundance of anammox bacteria gradually increased to 38.4% on day 140 with stepwise increased influent load; decreased to 0.4% on day 169 because of nitrite inhibition; increased to 19.24% on day 233 when the influent load was dropped; kept at ~ 9.0% with SHARON effluent used as influent and dropped to 3.3% finally. Anammox bacteria, only Candidatus Brocadia and Ca. Kuenenia detected, were the most abundant at genus level. Ca. Brocadia related taxa were enriched firstly under low load and detectable during the entire experimental period. Three main groups represented by Ca. Brocadia related OTUs were enriched or eliminated at different loads, but Ca. Kuenenia related taxa were enriched only under high load (NO₂⁻–N > 300 mg/L), suggesting their different niches and application for different loads. These findings improve the understanding of relationships among microbial community/functional taxa, running parameters and reactor performance, and will be useful in optimizing running parameters for rapid startup and high, stable efficiency.

The threshold of influent ammonium concentration for nitrate over-accumulation in a one-stage deammonification system with granular sludge without aeration

Low-strength ammonium is still a challenge for the mainstream deammonification because of nitrate over-accumulation. In this study, the threshold of influent ammonium concentration of one-stage deammonification system with granular sludge was investigated, by stepwise decreasing influent ammonium from high concentrations (280mg/L to 140mg/L) to the low concentration (70mg/L) in 108d at 32°C without aeration. Results showed that, under 70mg/L NH₄⁺-N, ΔNO₃^--N/ΔNH₄⁺-N ratio increased to 0.2, deviated from the theoretical value of 0.11, with ammonium and TN removal efficiencies of 91% and 71%, respectively. However, under both high ammonium concentrations (280mg/L and 140mg/L), nitrate production stabilized at only 13%. Chloroflexi, Planctomycetes and Proteobacteria contributed >70% of the communities under all three ammonium concentrations. As influent ammonium decreasing, the relative abundances of bacteria for anammox, aerobic oxidizing and denitrifying decreased, while NOB (nitrite oxidizing bacteria) abundance increased greatly. So 70mg/L was the threshold of influent ammonium concentration for stable deammonification without organic influent. It was the decrease of functional bacteria and overgrowth of NOB that worsen the deammonification performance under low-strength ammonium.

Increased salinity triggers significant changes in the functional proteins of ANAMMOX bacteria within a biofilm community

Anaerobic ammonium oxidation (ANAMMOX) processes can potentially be influenced by salinity related to variable salinity in water environment. Here, we used 16S rRNA sequencing analysis combining with iTRAQ-based quantitative proteomic approach to reveal the response of microbial community and functional proteins to salinity, which was increased from 0 to 20 g L^-1 with a step of 5 g L^-1 (designed as S5, S10, S15 and S20) compared to control reactor (without salinity stress desined as S0). The 16S rRNA sequencing analysis showed that a high salinity (20 g L^-1, S20) decreased the abundance of genus Candidatus Jettenia but increased that of Candidatus Kuenenia. A total of 1609 differentially expressed proteins were acquired in the three comparison groups (S5:S0, S20:S0 and S20:S5). Of these, 39 proteins co-occurred in the three salt-exposed samples. Hydrazine dehydrogenase (HDH; Q1PW30) and nitrate reductase (Q1PZD8) were up-regulated more than 3-folds in the exposure of 20 g-NaCl/L. The functional enrichment analysis further showed that some proteins responsible for ion binding, catalysis and oxidation-reduction reaction were up-regulated, which explained the physiological resilience of ANAMMOX bacteria under salinity stress. Additionally, ANAMMOX bacteria responded to salinity by modulating the electron transport systems, indicating that the cells retained a high potential for proton pumping, as well as the ATP production. Furthermore, the over-expression of HDH which associated with ANAMMOX metabolism, was potentially related to the increased abundance of halophilic Candidatus Kuenenia. These findings provide a comprehensive baseline for understanding the roles of salinity stresses in shaping the functional proteins of ANAMMOX bacteria.

Key operating parameters affecting nitrogen removal rate in single-stage deammonification

The key operating parameters for improving the nitrogen removal rate (NRR) in a sequencing batch reactor (SBR) for deammonification were investigated. The major operating strategies were the coexistence between deammonification and denitrification with a carbon/nitrogen (C/N) ratio of 0.5 and the control of the number of sub-cycles based on substrate concentration for anaerobic ammonium oxidation (ANAMMOX) and ammonium oxidizing bacteria (AOB). In the study, denitrification with the addition of an organic source was beneficial for improving the NRR from 0.5 ± 0.01 kg N m^-3 d^-1 to 0.53 ± 0.01 kg N m^-3 d^-1 by removing the nitrate produced as a by-product of ANAMMOX. Unlike the gradual increase of the specific activity for AOB, the specific ANAMMOX activity (SAA) was maximized when an ammonium concentration supplied after sub-feeding phase was increased from 20 to 100 mg L^-1, which increased the NRR from 0.53 ± 0.01 kg N m^-3 d^-1 to 0.79 ± 0.01 kg N m^-3 d^-1. This result suggested that the SAA is more important than the specific activity for AOB as a parameter for controlling the NRR in the single-stage deammonification. In the whole experimental period, the granule size smaller than 100 μm accounted for 52.5 ± 0.9%, making the largest contribution to the activity for AOB and denitrifiers. However, the granule size larger than 100 μm made the greatest contribution (83.8 ± 0.5%) to SAA. The feasibility of using the derivate of pH and OPR as indirect parameters to control the NRR was verified.

Modeling and multi-objective optimization for ANAMMOX process under COD disturbance using hybrid intelligent algorithm

Anaerobic ammonium oxidation (ANAMMOX) has been regarded as an efficient process to treat nitrogen-containing wastewater. However, the treatment process is not fully understood in terms of reaction mechanisms, process simulation, and control. In this paper, a multi-objective control strategy mixed soft-sensing model (MCSSM) is developed to systematically design the operating variations for multi-objective control by integrating the developed model, a least square support vector machine optimized with principal component analysis (PCA-LSSVM) and non-dominated sorting genetic algorithm-II (NSGA-II). The results revealed that the PCA-LSSVM model is a feasible and efficient tool for predicting the effluent ammonia nitrogen concentration ([Formula: see text]) and the total nitrogen removal concentration (C_{TN, rem}) with determination coefficients (R²) were 0.997 for [Formula: see text] and 0.989 for C_{TN, rem}, and gives us the reasonable solutions in influent by using NSGA-II. To achieve a better removal effect, the influent pH should be kept between 7.50 and 7.52, the COD/TN ratio is suggested to maintain at 0.15 and the NH₄⁺-N/NO₂^--N ratio is suggested to maintain at 0.61. The developed MCSSM approach and its general modeling framework have a high potential of applicability and guidance to bioprocess in wastewater treatment, and numerical models can be structured for predicting and optimization and experiments can be conducted for data acquisition and model establishment.

Effect of Fe (II) in low-nitrogen sewage on the reactor performance and microbial community of an ANAMMOX biofilter

In this study, the effect of Fe (II) on Anaerobic Ammonium Oxidation (ANAMMOX) process was investigated by step-wise increasing the Fe (II) in influent from 1 to 50 mg L^-1. The nitrogen removal, biofilm property and the microbial community were analyzed in each phase. Results showed that, the anaerobic ammonia-oxidizing bacteria (AAOB) bioactivity and the nitrogen removal of ANAMMOX system were slightly improved to 0.58 from the initial 0.51 kg m^-3 d^-1 by Fe (II) in 1-5 mg L^-1. The nitrogen removal was suppressed and could recover to the initial level during the same period under 10-20 mg L^-1 Fe (II), while it did not recover to the initial level under 30 mg L^-1 Fe (II) and showed no recovery performance under 50 mg L^-1 Fe (II). The irreversible suppression threshold of Fe (II) was calculated as 50 mg L^-1. The iron content in ANAMMOX biofilm presented linear correlation with the influent Fe (II) in 1-20 mg L^-1, which then tended to be stable when Fe (II) was higher. Dehydrogenase activity (DHA) showed similar and faster response to Fe (II) than the microbial activity, and it was an effective pre-indicator for the nitrogen removal performance in the ANAMMOX system suffered Fe (II). The Fe (II) feeding firstly led to the relative abundance of AAOB decreased to 11.04% from the initial 35.46%, and finally picked up to 19.39% after the long-term acclimatization.

[Effects of Environmental Factors on the Synergy of Functional Bacteria in Completely Autotrophic Granular Sludge]

To obtain experimental evidences for optimizing a completely autotrophic nitrogen removal process based on granules, the effects of dissolved oxygen (DO) concentration, temperature (t), initial ammonium (NH₄⁺-N) concentration, and solution pH conditions on the synergy between the aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AMX) were investigated using a single factor batch experiment, while the analysis of the microbial community structure within them was conducted using MiSeq high-throughput pyrosequencing. Results revealed that AOB (genus Nitrosomonas) and AMX (genus Candidatus Kuenenia) dominated in the granules, representing relative abundances of 32.9% and 9.8%, respectively. For the granules, the highest specific nitrogen removal rate of q(TN)=(17.7±1.0) mg·(g·h)^-1 was obtained at a DO concentration of 2 mg·L^-1, while the initial NH₄⁺-N concentration was set at 100 mg·L^-1. And a lower DO level resulted in partial nitritation became the rate-limiting step of process, otherwise, it would be the ANAMMOX reaction instead. According to the free energy of the reactions, the activity of AMX was more sensitive to low temperature than that of AOB. When the reaction temperature was lower than 30℃, nitrite accumulation could be observed in bulk liquid, with the significant decrease of q(TN) for the granules. Under the same oxygen supply conditions, an initial NH₄⁺-N concentration lower than 100 mg·L^-1 could inhibit the activity of AMX partly. However, with an initial NH₄⁺-N concentration over 150 mg·L^-1, either oxygen-limiting or high free ammonia concentration could lead to the dramatic decrease of q(TN). In addition, the effective synergy of the two types of ammonium oxidizers in granules was always achieved at solution pH in the range of 7.0-8.5.

[Characteristics and Performance of Embedded ANAMMOX Bacteria in Treating Saline Wastewater]

In order to improve the mechanical stability of the material, the embedded raw material combination was studied in the experiment, and seawater was added to optimize the performance of the material. The results indicated that the optimal material ratio was polyvinyl alcohol (PVA 125 g·L^-1)-alginate sodium (SA 20 g·L^-1)-activated carbon (40 g·L^-1). The curing time was 18 h. After adding seawater, the beads were found to have larger pore sizes inside, and the pores were distributed unevenly because of the Hofmeister effect. At the same time, the mechanical stability and biological capacity were found to be significantly higher than those of the fresh water group. The Raman spectra analysis showed that the addition of seawater made the-OH on PVA have greater crosslinking reactions with the crosslinker. The activated sludge was used to treat wastewater containing sea water, and after an operation of 21 d, the removal rate of NH₄⁺-N was about 90%, and the stoichiometric ratio of △NH₄⁺-N:△NO₂^--N:△NO₃^--N was stable at 1:(1.04±0.1):(0.17±0.02). From the 21st day to the 46th day, the reactor was run in a steady state. When the nitrogen load rate doubled, the ammonia nitrogen removal rate and stoichiometry had little variations. The total nitrogen removal rate was about 85%, and the total nitrogen removal load rate was 0.2 kg·(m³·d)^-1.

[Start-Up and Regional Characteristics of a Pilot-scale Integrated PN-ANAMMOX Reactor]

The start-up and regional characteristics of a pilot scale integrated PN-ANAMMOX reactor was studied. The results show that inoculated nitrosation suspension filler in the anaerobic zone, ANAMMOX sludge, and common anaerobic sludge in the anaerobic zone can start the reactor quickly. The PN-ANAMMOX reactor was successfully started at 74 days. The removal rate of total nitrogen increased from 0.02 kg·(m³·d)^-1 to 0.48 kg·(m³·d)^-1. The analysis of the nitrogen conversion characteristics in two regions showed that the AOB had been in a dominant position in the aerobic zone, and the NOB was inhibited by DO and the matrix, NPR_a increased from 0.22 kg·(m³·d)^-1 to 0.58 kg·(m³·d)^-1, and NAP_a could reach 95% with the increase in anaerobic denitrification capacity. The anaerobic zone was a critical region of the integrated PN-ANAMMOX reactor, and NRR_ana increased from 0.02 kg·(m³·d)^-1 to 4.7 kg·(m³·d)^-1. During the start-up period (temperature decreased from 32℃ to 27℃), the changes first affected the anaerobic zone, NRR_ana decreased to 3.7 kg·(m³·d)^-1 (about 21%), with little effect on the aerobic zone. The two regions can achieve a large ANAMMOX bacteria enrichment, as, during this time, the aerobic zone also has a certain denitrification capacity, while the anaerobic zone featured enhanced denitrification.

[Analysis of CANON Process Start-up with Fiber Carrier]

A CANON reactor with fiber carrier was started up by seeding nitrification sludge and ANAMMOX sludge to study the operating characteristics of a fiber carrier. The results showed that total nitrogen removal load rose from 0.09 kg·(m³·d)^-1 to 0.9 kg·(m³·d)^-1 and remained steady in the 85th day. This indicated that fiber carrier is beneficial to the accumulation of sludge, and the reactor can maintain a higher biomass. The DO in the reactor reached 5 mg·L^-1 with the enrichment of microorganisms, biofilm thickening, and the improvement of the reactor's ability. The DO gradient of the biofilm from the outside to the inside was 0.32-0 mg·L^-1, which could be obtained by a microelectrode. It was shown that the permeability of oxygen to the biofilm decreased, and the amount of nitrifying microorganisms decreased with biofilm thickening. The quantitative PCR results showed that the abundance of ANAMMOX was an order of magnitude more than before. The abundance of AOB increased slightly, while the abundance of NOB stayed at a relatively low level.

[Lab-scale ANAMMOX Process in a Wastewater Treatment Plant]

A lab-scale, completely anaerobic ammonium oxidation (ANAMMOX) process was operated in a municipal wastewater treatment plant (WWTP). Sewage effluent treated by an A/O process and nitrification process was input as the substance to start up the up-flow ANAMMOX filter reactor. After the 109^th day, the ammonia removal rate and nitrite removal rate were greater than 90% for 15 successive days and the nitrogen removal rate was higher than 70%. The ANAMMOX filter reactor successfully started up. From days 245 to 333, the reactor was running during the winter. The weight of biomass reached 12.24 mg·g^-1, and the average nitrogen removal rate was 54.3%. Backwash was adopted at day 461, and the weight of biomass decreased to 8.01 mg·g^-1. From days 605 to 693, the reactor was running in the winter again. The weight of biomass was 10.41 mg·g^-1, and the average nitrogen removal rate was sustained at 69.7%. Compared with the previous winter, the weight of biomass was lighter but the total nitrogen removal loading was 23% greater. For the entire operation, the ANAMMOX rate at high temperature was stable but that at low temperature increased from 1.5 kg·(kg·d)^-1 to 3.6 kg·(kg·d)^-1. The results show:Long-term domestication at low temperature was in favor of improving treatment efficiency of ANAMMOX process in cold environment and realized ANAMMOX process operated efficiently in winter.

Composition characterization and transformation mechanism of refractory dissolved organic matter from an ANAMMOX reactor fed with mature landfill leachate

This study applied combined spectroscopy techniques to assess rDOM compositional characteristic and investigated its transformation mechanisms during the treatment of mature landfill leachate by ANAMMOX process. A novel rDOM metabolism mechanism was proposed in this study for the first time. A stable, high nitrogen removal rate of 5.95 kg N/m³/day and a rDOM conversion efficiency of 51% were achieved in ANAMMOX reactor (AR). In additionally, the initial rDOM removal was closely related to sludge adsorption, with the adsorption force mainly originating from electrostatic interaction and hydrophobicity. As the operating time increased, the removal mechanism of rDOM in the AR changed from adsorption to adsorption-biodegradation and finally stabilized. Furthermore, Anaerolineaceae, associated with the hydrophobic reaction, were the primary degraders for the rDOM and Candidatus Kuenenia dominated the nitrogen consumption. rDOM removal efficiency was suggested to be increased by a moderate enhancement of Anaerolineaceae content in the AR.

[Effect of Carbon Source on Lab-scale SAD Process in a Wastewater Treatment Plant]

Lab-scale anaerobic ammonia oxidation and denitrification (SAD) processes were operated simultaneously in a municipal waste water treatment plant (WWTP). Sewage treated by the A/O and nitrification process was used as the substance to start up an anaerobic ammonia oxidation filter reactor. Adding glucose and sodium propionate to influent was used as the substance to start up the SAD filter reactor after the successful start-up of the ANAMMOX reactor. The SAD process performed well with an average total nitrogen concentration in the effluent of 6.41 mg·L^-1 when 30 mg·L^-1 glucose was added to the effluent sewage at ambient temperature. Compared with the ANAMMOX process, the total nitrogen concentration in the effluent from the SAD process decreased 42%. The stability of the SAD process was destroyed and the SAD process turned into a denitrification process when 30 mg·L^-1 glucose was added in the influent sewage in a low temperature environment. In normal and low temperature environments, the SAD process functioned well, and the average total nitrogen concentration of the effluent was 6.54 mg·L^-1 when 30 mg·L^-1 sodium propionate was added in the influent sewage. Compared with glucose, sodium propionate had little influence on the SAD process.

[Start-up and Characteristics of the Microbial Community Structure of ANAMMOX]

An anaerobic ammonium oxidation (ANAMMOX) reactor was successfully started up in 17 days, with the up-flow anaerobic sludge blanket (UASB) reactor being seeded with mixed anaerobic sludge from laboratory cultures with an ANAMMOX function and aerobic activated sludge from a municipal sewage treatment plant in a volume ratio of 1:2. The processes could be divided into two phases of hydrolysis, enhanced and steady. Anaerobic ammonium oxidation bacteria (AAOB) were enriched by improving the reactor volume load gradually after the steady phase. When the volume load increased from 0.10 kg·(m³·d)^-1 to 0.44 kg·(m³·d)^-1, the removal of total nitrogen (TN) also increased from 0.09 kg·(m³·d)^-1 to 0.42 kg·(m³·d)^-1. The color of the sludge changed from a light red that deepened gradually in the UASB reactor. At that time, the proportion of the sludge particle size greater than 0.2 mm increased from 10.90% to 38.37%.The sludges from the inoculation phase and from the phase when the volume load was increasing were analyzed by high-throughput sequencing, indicating that Chloroflexi, Proteobacteria, WWE3, Actinobacteria, Planctomycetes, and so on were the dominant species. The proportion of Proteobacteriain the denitrification bacteria was gradually reduced from 21.60% to 14.20% with an increase in the degree of AAOB enrichment, while the Planctomycetes increased from 0.73% to 15.50%. Candidatus Brocadia, Candidatus Jettenia, and Candidatus Kuenenia were the main species of Planctomyceteswhen the volume load increased to 0.44 kg·(m³·d)^-1 in the reactor, and the Candidatus Brocadia was the main species of AAOB, which accounted for 13.40%.

Coupling autotrophic denitrification with partial nitritation-anammox (PNA) for efficient total inorganic nitrogen removal

The performance of and the microbial ecology in an integrated lab scale set up comprising of a PN/A bioreactor and an elemental sulfur-supported packed bed autotrophic denitrification (ESSAD) are reported. The PN/A reactor exhibited an average removal rate of 0.56±0.103kgNm^-3d^-1, whereas the ESSAD reactor removed an average of 0.0018kg NO₃^--Nm^-3d^-1. The combined average removal rate was 0.6kgNm^-3d^-1, yielding an overall total inorganic nitrogen efficiency of 97%. Based on 16S rRNA gene clone libraries from the ESSAD reactor, the extracted Operational Taxonomic Units (OTUs) formed a clade with Thiobacillus denitrificans sp. indicating a common ancestral relationship. High throughput amplicon sequencing targeting V3 region of 16S rRNA gene for the biofilm in the ESSAD also revealed an abundance of the Thiobacillus genus. Additionally, 16s rRNA amplicon sequencing of the genomic DNA from the PN/A reactor reflected a dominance of the Planctomycetes phylum.

A coupled system of half-nitritation and ANAMMOX for mature landfill leachate nitrogen removal

A coupled system of membrane bioreactor-nitritation (MBR-nitritation) and up-flow anaerobic sludge blanket-anaerobic ammonium oxidation (UASB-ANAMMOX) was employed to treat mature landfill leachate containing high ammonia nitrogen and low C/N. MBR-nitritation was successfully realized for undiluted mature landfill leachate with initial concentrations of 900-1500 mg/L [Formula: see text] and 2000-4000 mg/L chemical oxygen demand. The effluent [Formula: see text] concentration and the [Formula: see text] accumulation efficiency were 889 mg/L and 97% at 125 d, respectively. Half-nitritation was quickly realized by adjustment of hydraulic retention time and dissolved oxygen (DO), and a low DO control strategy could allow long-term stable operation. The UASB-ANAMMOX system showed high effective nitrogen removal at a low concentration of mature landfill leachate. The nitrogen removal efficiency was inhibited at excessive influent substrate concentration and the nitrogen removal efficiency of the system decreased as the concentration of mature landfill leachate increased. The MBR-nitritation and UASB-ANAMMOX processes were coupled for mature landfill leachate treatment and together resulted in high effective nitrogen removal. The effluent average total nitrogen concentration and removal efficiency values were 176 mg/L and 83%, respectively. However, the average nitrogen removal load decreased from 2.16 to 0.77 g/(L d) at higher concentrations of mature landfill leachate.

[Investigation of Initiation and Shock Process of ANAMMOX Based on Color Space]

Anaerobic ammonia oxidation (ANAMMOX) is an efficient and energy-saving denitrification technology, but it still lacks a simple and easy method to characterize its start-up process and stable state. Based on the analysis of water quality, color space was used to monitor the color change of sludge during the start-up of ANAMMOX, and the species and quantity of microbial flora were analyzed by high-throughput sequencing technology. The results were as follows. ① According to water quality characteristics, the whole start-up process can be divided into activity lag phase, activity enhancement period, load increase period, and stable operation period. At the same time, HSV and CIELAB color space indicators decreased first, then increased, and finally remained stable. The change of sludge color was consistent with the change of water quality and the change of dominant bacteria based on the molecular biology testing, which implies correlations among these three. Therefore, color space can be used to characterize the start-up process of ANAMMOX. ② When subjected to shocks caused by high load, H, S, a^*, b^*, C_ab^*, and TIN volume removal rate all decreased, while H_ab suddenly increased. The impact characteristic of the system was accurately expressed by all of the color indicators. This paper proposes a color space-based method for characterizing all phases of the start-up of ANAMMOX and a shock process index system that provides a theoretical basis for applying color space in ANAMMOX systems.

[Conversion Pathways of Substrates in Sulfate-Reducing Ammonia Oxidation System]

The phenomenon of simultaneous transformation of ammonium and sulfate under the conditions of inoculating ANAMMOX culture has gotten the attention of researchers. However, there are some problems and doubts reported in the related literature. In this study, the characteristics of ammonium and sulfate synchronous transformation were investigated in a CFSTR via inoculation with ANAMMOX culture. Under the condition of oxygen removal and non-filling, in the unfilled sealed fermentation tank, the average conversion of NH₄⁺-N was 50.8 mg·L^-1 while that of sulfate-sulfur was 4.5 mg·L^-1. Elemental analysis results showed that the observed yellow solid was not elemental sulfur but rather iron-containing compounds. However, no obvious change of ammonium was observed when using a filled sealed batch reactor. Only sulfate transformed significantly, and the transformation rate was affected by the inoculation biomass. Under these two conditions, the ORP in the reactor was completely different. This is an indication that the synchronous transformation of ammonium and sulfate observed in both our study and other related studies is probably not a process mediated by ANAMMOX organisms, in which sulfate acted as the electron acceptor to oxidize ammonium. Actually, ammonium and sulfate transformation were completely independent: ammonium oxidation is due to the micro oxygen environment created by the reactor operation form, whereas sulfate conversion is attributed to the sulfate heterotrophic reduction that results from the organic matter release via microbial decay. This transformation can clarify and explain the problems and doubts reported in the related research.

[Start-up of Granule CANON Process and the Strategy for Enhancing Total Nitrogen Removal Rate]

To shorten the start-up time of the CANON granular sludge process and improve the total nitrogen removal rate in the engineering, the start-up method of CANON granular sludge process and the strategy for enhancing the total nitrogen removal rate were studied in an SBR reactor. During the experiment, the temperature was controlled at 30℃±1℃ and the pH was 7-8, the aeration rate and settling time were operated according to the sludge properties and effect of nitrogen removal. The results showed that the transition of the sludge properties from combined floc-granule to granule was realized after 55 d. The total nitrogen removal rate reached 0.32 kg·(m³·d)^-1 and remained stable after 117 d, thus the reactor was started up successfully. With constant improvement of the aeration rate, the average NRR was maintained at 1.35 kg·(m³·d)^-1 after 77 d and improvement of the process load was achieved. The results showed that there was good correlation between the NRR and DO, therefore, the NRR can be determined by observing the DO and the process can be maintained stably.

[Removal of Nitrogen from Alcohol Wastewater by PN-ANAMMOX]

An integrated partial nitrification anaerobic ammonia oxidation reactor was used to explore the feasibility of nitrogen removal from recycled ethanol wastewater. The results show that the integrated partial nitrification-anaerobic ammonia oxidation (PN-ANAMMOX) reactor was started successfully after 40 d under the conditions of pH 7.8±0.5, temperature 30-35℃, and aerobic ORP value 120-150 mV. The total nitrogen removal rate of 0.125 kg·(m³·d)^-1 increased to 0.75 kg·(m³·d)^-1, Inoculation of mature nitrosated biofilms and anaerobic ammonium oxide granules can accelerate the start of the reactor. The effects of alcohol wastewater on the PN-ANAMMOX reactor were mainly caused by biodegradable TOC, The biodegradable TOC concentration of 100mg·L^-1 in alcohol wastewater can reduce the removal rate of total nitrogen from 0.75 kg·(m³·d)^-1 to 0.25 kg·(m³·d)^-1,this inhibition can be restored. Different concentrations of alcohol wastewater were dosed into the PN-ANAMMOX reactor to acclimate the bacteria. The total nitrogen removal rate first decreased and then increased, as the influent concentration gradient increased, which was beneficial for improving the efficiency of nitrogen removal by extending the HRT and increasing the dissolved oxygen in the PN stage. Finally, the nitrogen removal rate stabilized at 0.65 kg·(m³·d)^-1. These results show that PN-ANAMMOX can be used for the treatment of alcohol wastewater.