Anammox Process Research Articles

Exposure to zinc and dialkyldimethyl ammonium compound alters bacterial community structure and resistance gene levels in partial sulfur autotrophic denitrification coupled with the Anammox process

Dialkyldimethyl ammonium compound (DADMAC) is widely used in daily life as a typical disinfectant and often co-exists with the heavy metal zinc in sewage environments. This study investigated the effects of co-exposure to zinc (1 mg/L) and DADMAC (0.2–5 mg/L) on the performance, bacterial community, and resistance genes (RGs) in a partial sulfur autotrophic denitrification coupled with anaerobic ammonium oxidation (PSAD-Anammox) system in a sequencing batch moving bed biofilm reactor for 150 days. Co-exposure to zinc and low concentration (0.2 mg/L) DADMAC did not affect the nitrogen removal ability of the PASD-Anammox system, but increased the abundance and transmission risk of free RGs in water. Co-exposure to zinc and medium-to-high (2–5 mg/L) DADMAC led to fluctuations in and inhibition of nitrogen removal, which might be related to the enrichment of heterotrophic denitrifying bacteria dominated by Denitratisoma. Co-exposure to zinc and high concentration DADMAC (5 mg/L) stimulated the secretion of extracellular polymeric substances and increased the proliferation risk of intracellular RGs in sludge. This study provided insights into the application of PSAD-Anammox system and the ecological risks of wastewater containing zinc and DADMAC.

Inhibition, Recovery and Stabilization of MBR-Anammox Process: Enhancing Nitrogen Removal by Biochar-supported Nano Zero-valent Iron Adoption

Anaerobic ammonium oxidation (Anammox) is recognized as a promising option to energy-neutral wastewater treatment, yet difficulties encountered in practice due to its poor stability. This work investigated the effects of biochar-supported nano zero-valent iron (nZVI-BC) on nitrogen removal performance of anammox process. Three membrane bioreactors (MBRs) suitable for slowly growing anammox bacteria was operated for 100 days, undergoing startup, dissolved oxygen (DO) inhibition, performance recovery and stabilization periods. The results showed that nZVI-BC adoption could improve the nitrogen removal efficiency (NRE) by 5.5–27.3 % and 3.1–20.7 % and nitrogen removal rate (NRR) by 5.4–28.6 % and 3.2–22.9 %, compared with control group and biochar adoption, respectively. Throughout the experimental periods, nZVI-BC was conducive to enrich anammox bacteria and increased the functional gene copies associated with anammox metabolism. Meanwhile, co-occurrence network analysis promulgated that nZVI-BC boosted the robustness and interaction of microbial community. Furthermore, the electrochemical analysis of the extracellular polymeric substance (EPS) revealed that nZVI-BC adoption augmented the extracellular electron transport (EET) process of anammox biomass. Metagenomic sequencing revealed that nZVI-BC reinforced the complete dissimilatory nitrate reduction to ammonium (DNRA) pathway in Candidatus Brocadia, the dominant anammox bacteria, potentially reducing nitrate production and enhancing nitrogen removal. The study manifested the possibility of nZVI-BC to improve the anammox robustness and nitrogen removal performance, and provided operational guidance for its engineering application.

Full-Scale Demonstration of Nitrogen Removal from Mature Landfill Leachate Using a Two-Stage Partial Nitritation and Anammox Process

The excessive discharge of nitrogen leads to water eutrophication. The partial nitritation and anammox (PN/A) process is a promising technology for biological nitrogen removal in wastewater treatment. However, applying it to mature landfill leachate (MLL) faces challenges, as the toxic substances (e.g., heavy metal) within MLL inhibit the activity of anammox bacteria. Therefore, most previous studies focused on diluted, pretreated, or chemically adjusted MLL. This study demonstrated at full scale that the two-stage PN/A process can treat raw MLL. Initially, the operational issue of sludge floatation resulted in rapid biomass loss with overflow discharging, which selectively suppresses nitrite-oxidizing bacteria (NOB), promoting the achievement of nitrite accumulation. After that, the NOB suppression was self-sustained by the high in situ free ammonia concentration, i.e., 26.2 ± 15.9 mg N/L. In the subsequent anammox tank, nitrogen removal primarily occurred via the anammox process, complemented by denitrification, achieving total nitrogen removal efficiency exceeding 72%. In addition, the nitrogen removal capacity of this system was significantly influenced by temperature with the nitrogen-loading rate above 0.4 kg N/m3/d at 38 °C and approximately 0.1 kg N/m3/d at 21 °C. The optimization of system operation, such as gradually increasing MLL content, remains necessary to enhance nitrogen removal capacity further.

Enhanced anammox performance under lower nitrite accumulation in modified partial nitritation-anammox (PN/A) process

Higher nitrite accumulation, which is challenging to achieve reliably, is always sought to obtain better nitrogen removal performance in traditional partial nitritation-anammox (PN/A) process. This study developed a modified PN/A process by introducing nitrite-oxidizing bacteria and endogenous metabolism. Advanced nitrogen removal performance of 95.5 % was achieved at a low C/N ratio of 2.7 under nitrite accumulation ratio (NAR) fluctuations. Higher nitrate accumulation at lower NAR (70 ∼ 40 %) resulted in superior anammox contribution (60 ∼ 75 %) and nitrogen removal performance (93 ∼ 98 %). This was attributed to the higher nitrogen removal efficiency of the post-anoxic endogenous partial denitrification coupling anammox process, although the PN/A process occurring first possessed a faster anammox rate of 2.0 mg NH4+-N /(g VSS⋅h). The introduction of nitrate allowed more nitrite flow to anammox, promoting a high enrichment of anammox bacteria (Ca. Brocadia, 0.3 % to 2.8 %). This study provides new insights into the practical application of the PN/A process.

Organic acids released by submerged macrophytes with damaged leaves alter the denitrification microbial community in rhizosphere

Submerged macrophytes have important impacts on the denitrification and anaerobic ammonia-oxidizing (anammox) processes. Leaf damage in these plants probably changes the rhizosphere environment, affecting organic acid release and denitrifying bacteria. However, there is a lack of comprehensive understanding of the specific changes. This study investigated these changes in the rhizosphere of Potamogeton crispus with four degrees of leaf excision. When 0 %, 30 %, 50 % and 70 % of leaves were excised, the concentrations of total organic acid were 31.45, 32.67, 38.26, and 35.16 mg/L, respectively. The abundances of nirS-type denitrifying bacteria were 2.10 × 1010, 1.59 × 1010, 2.54 × 1010, and 4.67 × 1010 copies/g dry sediment, respectively. The abundances of anammox bacteria were 7.58 × 109, 4.59 × 109, 3.81 × 109, and 3.90 × 109 copies/g dry sediment, respectively. The concentration of total organic acids and the abundance of two denitrification microorganisms in the rhizosphere zone were higher than those in the root zone and non-rhizosphere zone. With increasing leaf damage, the number of OTUs in the Pseudomonas genus of nirS-type denitrifying bacteria first increased and then decreased, while that of the Thauera genus was relatively stable. The overall increase in the OTU number of anammox bacteria indicated that leaf damage promotes root exudates release, thereby leading to an increase in their diversity. The co-occurrence network revealed that the two denitrification microorganisms had about 60.52 % positive connections in rhizosphere while 64.73 % negative connections in non-rhizosphere. The abundance and community composition of both denitrification microorganisms were positively correlated with the concentrations of various substances such as oxalic acid, succinic acid, total organic acids and NO2--N. These findings demonstrate that submerged plant damage has significantly impacts on the structure of denitrification microbial community in the rhizosphere, which may alter the nitrogen cycling process in the deposit sediment. SynopsisThis study reveals leaf damage of macrophyte changed the rhizosphere denitrification microbial community, which is helpful to further understand the process of nitrogen cycle in water.

Quorum sensing mediated response mechanism of anammox consortia to anionic surfactant: Molecular simulation and molecular evidence

The widespread use of surfactants raise challenges to biological wastewater treatment. Anaerobic ammonium oxidation (anammox) process has the potential to treat wastewater containing anionic surfactants, but the response of anammox consortia at the molecular level under long-term exposure is unclear. Using high-throughput sequencing and gene quantification, combined with molecular docking, the effect of sodium dodecyl sulfonate (SDS) on anammox consortia were investigated. Levels of reactive oxygen species (ROS) might be lower than the threshold of oxidative damage, while the increase of lactate dehydrogenase (LDH) represented the cell membrane damage. Decreased abundance of functional genes (hdh, hzsA and nirS) indicated the decrease of the anammox bacterial abundance. Trace amounts of N-acyl homoserine lactone (AHL, C6-HSL, C8-HSL and C12-HSL) contained in influent could induce endogenous quorum sensing (QS), which could regulate the correlation between functional bacteria to optimize the microbial community and strengthen the resistance of anammox consortia to SDS. In addition, the proliferation of disinfectant resistance genes might increase the environmental pathogenicity of sewage discharge. This work highlights the potential response mechanism of anammox consortium to surfactants and provides a universal microbial-friendly bioenhancement strategy based on QS.

Mechanisms of anammox granular sludge reactor effluent as biostimulant: Shaping microenvironment for anammox metabolism

Effluent from anammox granular sludge (AnGS) bioreactor contains microbes and microbial products. This study explored mechanisms of utilizing AnGS-effluent as biostimulant for anammox process enhancement. Compared with no AnGS-effluent supplemented control reactor, 5.0 and 1.3 times higher ammonium nitrogen and total inorganic nitrogen removal rates, respectively were obtained with continuous AnGS-effluent supplementation after 98 days’ operation. Anammox bacteria from Candidatus Brocadia accounted for 0.1 % (DNA level) and 1.3 %–1.5 % (RNA level) in control reactor, and 2.9 % (DNA level) and 54.5 %–55.4 % (RNA level) in the AnGS-effluent-fed reactor. Influent microbial immigration evaluation showed that bacterial immigration via AnGS-effluent supplementation was not the main contributor to active anammox community development. Amino acids biosynthesis, B-vitamins and coenzymes metabolism related pathways were facilitated by AnGS-effluent supplementation. AnGS-effluent supplementation aided anammox metabolic activity by shaping microenvironment and microbial interactions. This study provides insights into enhancing anammox bacterial metabolism with AnGS-effluent microbial products as biostimulant.

Mechanism of nano-scale zero-valent iron modified biochar for enhancing low-nitrogen anammox process resistance to low temperatures

Two anaerobic ammonia oxidation (anammox) systems, one with adding nano-scale zero-valent iron modified biochar (nZVI@BC) and the other with adding biochar, were constructed to explore the feasibility of nZVI@BC for enhancing the resistance of low-nitrogen anammox processes to low temperatures. The results showed that the average nitrogen removal efficiency with nZVI@BC addition at low temperatures was maintained at about 80%, while that with biochar addition gradually decreased to 69.49%. The heme-c content of biomass with nZVI@BC was significantly higher by 36.60%-91.45%. Additional, nZVI@BC addition resulted in more extracellular polymeric substances, better biomass granulation, and a higher abundance of anammox bacteria. In particularly, anammox genes hzsA/B/C, hzo and hdh played a pivotal role in maintaining nitrogen removal performance at 15°C. These findings suggest that nZVI@BC has the potential to enhance the resistance of low-nitrogen anammox processes to low temperatures, making it a valuable approach for practical applications in low-nitrogen and low-temperature wastewater treatment.

Analysis of the signal molecular regulation mechanism of anammox biofilm/particles in low salinity environment from the point of view of sludge structure cohesion

The application of anaerobic ammonium oxidizing (anammox) in the treatment of municipal wastewater with low matrix has always been challenging. At the same time, the substitution of seawater and the extensive use of deicing salt in winter increase the salinity of municipal wastewater with low matrix, which increases the difficulty of treatment. This study focused on the performance of anammox biofilm (AM) and granular sludge (AG) in salinity environment from the point of view of signal molecular regulation and sludge structure cohesion. AM could adapt and form a stable biofilm after acclimation at 0.6 % salinity, while AG collapsed due to the decrease of particle size and the sharp decrease of the abundance of anammox bacteria. AM protected anammox-related genus such as Candidatus Kuenenia and Ignavibacterium by releasing more endogenous C8-HSL and C12-HSL to ensure stable nitrogen removal. Endogenous C8-HSL and C12-HSL stabilize the anammox process by enhancing EPS to increase water output and increasing COD consumption by some heterotrophic bacteria, respectively. The modularization of the microbial community network of AM was 0.937. the rich microbial diversity improves the salinity impact performance of AM. The microorganisms responsible for nitrogen metabolism, sulfur metabolism, and protein export in AM were significantly higher than AG when the salinity reached 0.6 %. In conclusion, this research illustrated that the AM could maintain good nitrogen removal performance in the mainstream municipal low-salt wastewater, clarified the mechanism of signal molecules regulating and promoting the anammox process, and provided theoretical support for the application of anammox in mainstream engineering.

Granular sludge characterization and microbial response in a hydroxyapatite (HAP)- anammox coupled process at different nitrogen loading rates

To enhance the treatment capacity and operational stability of the anammox process for nutrient-rich wastewater disposal, a hydroxyapatite (HAP)-anammox coupled process was developed in a granular sludge-based upflow bioreactor. The impact of nitrogen loading rate (NLR) on process performance was investigated by gradually increasing the NLR from 1 to 1.5, 3, and 5 kgN/m3/d for 264 days continuous operation. TN and TP removal rates of 82.51 ± 3.58 % and 60.49 ± 2.82 % were achieved at the NLR of 5 kgN/m3/d. The precipitation of Ca and phosphorus resulted in HAP crystals formation evidenced by sludge morphology and component analysis, which enhanced sludge settling properties and facilitated biomass enrichment. The HAP-anammox granular sludge was characterized by the outer layer HAP crystals formed on inner anammox granules, while highly mineralized granular sludge with higher density distributed at the bottom of the reactor is conducive to HAP-based phosphorus recovery. After a long-term accumulation, the abundance of Planctomycetota phylum gradually increased (from 7.7 % to 14.1 %), consisting of three species of anammox bacteria, namely Candidatus_Brocadia_sapporoensis, Candidatus_Brocadia_sinica and Candidatus_Kuenenia_stuttgartiensis. Nitrogen metabolic pathway analysis illustrated that denitrification was also present except the anammox reaction, synergistically contributing to superior nitrogen removal in the HAP-anammox process.

Nitrogen Removal Performance and Microbial Community Structure of IMTA Ponds (Apostistius japonicus-Penaeus japonicus-Ulva)

Denitrification and anaerobic ammonium oxidation (anammox) are key processes for nitrogen removal in aquaculture, reducing the accumulated nitrogen nutrients to nitrogen gas or nitrous oxide gas. Complete removal of nitrogen from aquaculture systems is an important measure to solve environmental pollution. In order to evaluate the nitrogen removal potential of marine aquaculture ponds, this study investigated the denitrification and anammox rates, the flux of nitrous oxide (N2O) at the water–air interface, the sediment microbial community structure, and the gene expression associated with the nitrogen removal process in integrated multi-trophic aquaculture (IMTA) ponds (Apostistius japonicus-Penaeus japonicus-Ulva) with different culture periods. The results showed that the denitrification and anammox rates in sediments increased with the increase of cultivation periods and depth, and there was no significant difference in nitrous oxide gas flux at the water–air interface between different cultivation periods (p > 0.05). At the genus and phylum levels, the abundance of microorganisms related to nitrogen removal reactions in sediments changed significantly with the increase of cultivation period and depth, and was most significantly affected by the concentration of particulate organic nitrogen (PON) in sediments. The expression of denitrification gene (narG, nirS, nosZ) in surface sediments was significantly higher than that in deep sediments (p < 0.05), and was negatively correlated with denitrification rate. All samples had a certain anammox capacity, but no known anammox bacteria were found in the microbial diversity detection, and the expression of gene (hzsB) related to the anammox process was extremely low, which may indicate the existence of an unknown anammox bacterium. The data of this study showed that the IMTA culture pond had a certain potential for nitrogen removal, and whether it could make a contribution to reducing the pollution of culture wastewater still needed additional practice and evaluation, and also provided a theoretical basis for the nitrogen removal research of coastal mariculture ponds.Graphical

Synergistic Integration of Anammox and Endogenous Denitrification Processes for the Simultaneous Carbon, Nitrogen, and Phosphorus Removal.

The feasibility of a synergistic endogenous partial denitrification-phosphorus removal coupled anammox (SEPD-PR/A) system was investigated in a modified anaerobic baffled reactor (mABR) for synchronous carbon, nitrogen, and phosphorus removal. The mABR comprising four identical compartments (i.e., C1-C4) was inoculated with precultured denitrifying glycogen-accumulating organisms (DGAOs), denitrifying polyphosphate-accumulating organisms, and anammox bacteria. After 136 days of operation, the chemical oxygen demand (COD), total nitrogen, and phosphorus removal efficiencies reached 88.6 ± 1.0, 97.2 ± 1.5, and 89.1 ± 4.2%, respectively. Network-based analysis revealed that the biofilmed community demonstrated stable nutrient removal performance under oligotrophic conditions in C4. The metagenome-assembled genomes (MAGs) such as MAG106, MAG127, MAG52, and MAG37 annotated as denitrifying phosphorus-accumulating organisms (DPAOs) and MAG146 as a DGAO were dominated in C1 and C2 and contributed to 89.2% of COD consumption. MAG54 and MAG16 annotated as Candidatus_Brocadia (total relative abundance of 16.5% in C3 and 4.3% in C4) were responsible for 74.4% of the total nitrogen removal through the anammox-mediated pathway. Functional gene analysis based on metagenomic sequencing confirmed that different compartments of the mABR were capable of performing distinct functions with specific advantageous microbial groups, facilitating targeted nutrient removal. Additionally, under oligotrophic conditions, the activity of the anammox bacteria-related genes of hzs was higher compared to that of hdh. Thus, an innovative method for the treatment of low-strength municipal and nitrate-containing wastewaters without aeration was presented, mediated by an anammox process with less land area and excellent quality effluent.

Bibliometric analysis of wastewater treatment processes based on anaerobic ammonia oxidation process

In the realm of water treatment, the anaerobic ammonia oxidation (anammox) process stands out as one of the most innovative breakthroughs. Bibliometrics is an effective method for the evaluation of scientific results and the development of research trends in a particular field of study. Employing VOSviewer and CiteSpace, this study comprehensively analyzed scholarly articles and research trends related to anammox water treatment from 2014 to 2023. The findings revealed a total of 1225 articles in this domain, exhibiting an increasing trend every year in the world, while China emerges as the foremost contributor with close collaborations with the United States, Australia, and other nations. The examination of keyword co-occurrence and cluster network showcases coupled anammox-based reactor startup and opefrational strategies, nitrogen removal studies, nitrous oxide investigations and microbial community analyses are long-term academic endeavors. Furthermore, keyword burst and temporal network analysis,the operational control conditions, driving processes and analysis of microbial macrogenes for mainstream anammox in wastewater treatment plants need more research in the future to improve the feasibility of this technology in engineering applications. Additionally, a meticulous scrutiny of the top 20 landmark and highly cited research articles over the past decade underscores a few persistent intriguing themes, such as “mainstream anammox,” “biological nitrogen removal,” and “16 S rRNA genes,” In summary, this study contributes a nuanced understanding of the contemporary landscape and development trends within the field of anammox water treatment, which will shed light on the future research efforts.

Ferroheme/Ferriheme Directly Involved in the Synthesis and Decomposition of Hydrazine as an Electron Carrier during Anammox.

Anammox bacteria performed the reaction of NH4+ and NO with hydrazine synthase to produce N2H4, followed by the decomposition of N2H4 with hydrazine dehydrogenase to generate N2. Ferroheme/ferriheme, which serves as the active center of both hydrazine synthase and hydrazine dehydrogenase, is thought to play a crucial role in the synthesis and decomposition of N2H4 during Anammox due to its high redox activity. However, this has yet to be proven and the exact mechanisms by which ferroheme/ferriheme is involved in the Anammox process remain unclear. In this study, abiotic and biological assays confirmed that ferroheme participated in NH4+ and NO reactions to generate N2H4 and ferriheme, and the produced N2H4 reacted with ferriheme to generate N2 and ferroheme. In other words, the ferroheme/ferriheme cycle drove the continuous reaction between NH4+ and NO. Raman, ultraviolet-visible spectroscopy, and X-ray absorption fine structure spectroscopy confirmed that ferroheme/ferriheme is involved in the synthesis and decomposition of N2H4 via the core FeII/FeIII cycle. The mechanism of ferroheme/ferriheme participation in the synthesis and decomposition of N2H4 was proposed by density functional theory calculations. These findings revealed for the first time the heme electron transfer mechanisms, which are of great significance for deepening the understanding of Anammox.

Partial denitrification in rope-type biofilm reactors: Performance, kinetics, and microflora using internal vs. external carbon sources

Stable nitrite accumulation through partial denitrification (PDN) represents an efficient pathway to support the anammox process, but limited studies explored the internal wastewater carbon sources and biofilm processes. This study assessed the viability of the PDN process, biofilm community evolution, and functional enzyme formation in rope-type biofilm media reactors using primary effluent (PE) and anaerobically pretreated wastewater carbon sources for the first time. Comparison was made with external carbon (acetate) under varied pH and biofilm thicknesses, maintaining a favourable sCOD: NO3-N ratio of 3. The wastewater’s internal carbon resulted in thinner biofilms; nevertheless, modest nitrite accumulation (0.24 g/m2/d) occurred only at elevated pH. The highest nitrite accumulation (0.79 g/m2/d) was exhibited in the biofilm thickness-controlled acetate-fed reactor, featuring porous biofilms dominated by denitrifier Thauera (10.24 %) and imbalance between Nar, Nap, and Nir reductases. Using internal wastewater carbon sources offers a sustainable avenue for adopting the PDN process in full-scale application.

Rapid reactivation of long-term frozen preservation anammox granular sludge by biochar: Performance, mechanism and artificial neural network optimization

Anaerobic ammonia oxidation (Anammox) is an efficient nitrogen removal technology for wastewater, and has been successfully applied in practical wastewater treatment. The preservation and rapid reactivation of anammox bacteria (AnAOB) play an important role in the anammox application. Biochar has been widely used in the water treatment industry due to its stable structure, economic and environmental protection characteristics. Hence, this study used biochar to accelerate anammox granular sludge (AnGS) performance recovery after 60 d preservation under low-temperature frozen (−20 °C). The time of AnGS recovery in the group with biochar addition was shortened by 15 d than the natural recovery group. Meanwhile, biochar addition improved the shock loading resistance of the anammox system. EPS secretion, and the types and quantities of functional groups in EPS increased under biochar stimulation, especially tighter PN. The functional groups in biochar can act as electron shuttles during anammox process, accelerating the electron transfer rate. Biochar addition enhanced the relative abundance of AnAOB, especially Candidatus Brocadia. PICRUSt analysis indicated that biochar promoted key gene related to anammox process and accelerated the recovery of frozen sludge. In addition, the changes in effluent nitrogen removal efficiency were successfully predicted by artificial neural network modeling with R = 0.9895 and MSE = 0.0048. This result may provide a new technological idea for the rapid recovery of AnGS under long time frozen conditions.

Exploring the maximum nitrite production rate through the granular sludge-type reactor to match the needs of anammox process realizing efficient nitrogen removal

The reliable and efficient nitrite production rate (NPR) through nitritation process is the prerequisite for the efficient running of subsequent processes, like the anammox process and the nitrite shunt. However, there has been scant research on stable and productive nitritation process in recent years. In this study, at a stable hydraulic retention time of 12.0 h and with precise and strict DO control, the upper limit of the NPR was initially investigated using a continuous-flow granular sludge reactor. The NPR of 1.69 kg/m3/d with a nitrite production efficiency of 81.97% was finally achieved, which set a record until now in similar research. The median sludge particle size of 270.0 μm confirmed the development of clearly defined granular sludge. The genus Nitrosomonas was the major ammonium oxidizing bacteria. In conclusion, this study provides valuable insights for the practical application of the effective nitritation process driving subsequent nitrogen removal processes.

Novel insights into intrinsic mechanisms of magnetic field on long-term performance of anaerobic ammonium oxidation process

The performance of an anaerobic ammonium oxidation (anammox) reactor with the magnetic field of 40 mT was systematically investigated. The total nitrogen removal rate was enhanced by 16% compared with that of the control group. The enhancing mechanism was elucidated from the improved mass transfer efficiency, the complicated symbiotic interspecific relationship and the improved levels of functional genes. The magnetic field promoted formation of the loose anammox granular sludge and the homogeneous and well-connected porous structure to enhance the mass transfer. Consequently, Candidatus Brocadia predominated in the sludge with an increase in abundance of 13%. Network analysis showed that the positive interactions between Candidatus Brocadia and heterotrophic bacteria were strengthened, which established a more complicated stable microbial community. Moreover, the magnetic field increased the levels of hdh by 26% and hzs by 35% to promote the nitrogen metabolic process. These results provided novel insights into the magnetic field-enhanced anammox process.

Response of anammox consortia to inhibition from high ferroferric oxide nanoparticles concentration and potential recovery mechanism

The substantial discharge of ferroferric oxide nanoparticles (Fe3O4 NPs) into sewage threatens the survival of functional microorganisms in wastewater treatment. This study elucidated responses of anaerobic ammonium oxidation (anammox) consortia to inhibition from high Fe3O4 NPs concentration and recovery mechanisms. The nitrogen removal efficiency decreased by 20.3 % and recovered after 55 days under 1000 mg/L Fe3O4 NPs concentration. Toxicity was attributed to reactive oxygen species (ROS) production. The excessive ROS damaged membrane integrity, nitrogen metabolism, and DNA synthesis, resulting in the inhibition of anammox bacteria activity. However, recovery mechanisms of anammox consortia activity were activated in response to 1000 mg/L Fe3O4 NPs. The increase of heme oxygenase-1, thioredoxin, and nicotinamide adenine dinucleotide-quinone oxidoreductase genes alleviated oxidative stress. Furthermore, the activation of metabolic processes associated with membrane and DNA repair promoted recovery of anammox bacteria activity. This study provided new insights into NPs contamination and control strategies during anammox process.

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.