Application Of Anammox Research Articles

Community assembly and succession of the functional membrane biofilm in the anammox dynamic membrane bioreactor: Deterministic assembly of anammox bacteria.

The anammox dynamic membrane bioreactor (DMBR) exhibits potential for efficient nitrogen removal via anammox processes. The functional membrane biofilm in the anammox DMBR significantly enhances nitrogen removal, ensuring robust operation. Nevertheless, ecological mechanisms underpinning the nitrogen removal function of the membrane biofilm remain unclear. We investigated the community succession and assembly of the membrane biofilm communities in two anammox DMBRs utilizing distinct inoculated anammox sludges. Anammox bacteria displayed niche differentiation in both DMBRs. Anammox bacteria Candidatus Kuenenia was selectively enriched to 8.5% abundance in the membrane biofilm communities, contributing to 5.2-7.2% of the nitrogen removal load. Membrane biofilm communities were primarily assembled through deterministic processes. Specifically, the selective enrichment of Candidatus Kuenenia on the membrane biofilms was primarily governed by homogenous selection process, explaining 9.67-9.82% of the variance. The deterministic assemblies of anammox bacteria were mainly influenced by the high substrate affinity of Candidatus Kuenenia and the limited availability of substrates (NH4+ and NO2-) in the membrane biofilms. Furthermore, the relatively weak permeate drag force during the DMBR filtration facilitated the preferential colonization of microbes from the anammox sludge to the membrane biofilm, resulting in the deterministic formation of the membrane biofilm communities with nitrogen removal function. Our findings offer insights into the ecological mechanisms driving the deterministic assembly of the functional membrane biofilm communities in the anammox DMBRs, informing the precise regulation of membrane biofilms for improved nitrogen removal in anammox applications of wastewater treatment.

Rapid Start-Up of Anammox Process with a Stepwise Strategy: System Performance, Microbial Community Succession and Mechanism Exploration

Anammox has emerged as a primary alternative to conventional biological nitrogen removal because of its excellent nitrogen removal performance and minimal energy utilization. However, the slow growth and reproduction of anammox bacteria (AnAOB) leads to an overlong start-up period, which severely restricts the full-scale promotion and application of anammox in wastewater treatment plants. Therefore, in this study, a sequencing batch biofilm reactor (SBBR) equipped with combined packing was used to investigate the rapid start-up of the anammox process. The result showed that the anammox reactor started successfully in only 75 days using a stepwise strategy, and the total nitrogen removal rate (TNRR) increased from 0.02 kg N m−3 d−1 on day 1 to 0.23 kg N m−3 d−1 on day 75. The primary AnAOB was Candidatus Kuenenia with a relative abundance of 37.20% at the end of the start-up of the anammox reactor. Denitrifying bacteria, nitrifying bacteria, and hydrolytic bacteria were also detected in the reactor. The synergistic interactions between AnAOB and these bacteria facilitated the efficient removal of pollutants. This study can offer a potential approach for the start-up of anammox in domestic wastewater treatment plants, which is conducive to achieving widespread application of anammox.

Making waves: Harnessing anammox bacteria coupled with dissimilatory nitrate reduction to ammonium for sustainable wastewater management.

Anaerobic ammonia oxidation (anammox) which converts nitrite and ammonium to dinitrogen gas is an energy-efficient nitrogen removal process. One of the bottlenecks for anammox application in wastewater treatment is the stable supply of nitrite for anammox bacteria. Dissimilatory nitrate reduction to ammonium (DNRA) is a process that converts nitrate to nitrite and then to ammonium. Significantly, it has been reported that some anammox bacteria can perform DNRA by reducing nitrate to nitrite and ammonium nitrogen with little low-molecular-weight organic acids such as volatile fatty acids. Here, we propose an innovative nitrogen removal process, i.e., nitrification and anammox coupled with partial DNRA (i.e., NPDA), and make a theoretical comparison with previously accepted partial nitrification and anammox (PNA) and partial denitrification and anammox (PdNA) for nitrogen removal. Under similar conditions of oxygen consumption, removal efficiency, external carbon source addition, and greenhouse gas emission, the novel NPDA process can better facilitate resource-effective and environment-friendly wastewater treatment. Thermodynamic analysis indicates that partial DNRA-anammox appears to be preferred, oxidizing per mole of NH4 +produces higher energy gain than that of conventional anammox alone. The carbon source limitation rather than nitrate limitation is the key to the realization of NPDA process. This perspective highlights the positive role of DNRA for sustainable wastewater management.

Temperature effects on nitrogen removal and N2O emissions in anammox reactors.

Mainstream anammox faces challenges in adapting to non-optimal temperatures and managing greenhouse gas emissions. This study investigates nitrogen removal and N2O emissions in attached-growth anammox reactors subjected to rapid temperature shifts (15 - 55 °C). Temperature reductions to 15 - 25 °C had minimal impact on the anammox bacterial populations, with nitrogen removal rates of 0.37 ± 0.11 gN/(L•d) and 0.88 ± 0.10 gN/(L•d) at 15 °C and 25 °C, respectively. In contrast, increasing temperatures to 45 - 55 °C significantly diminished both anammox biomass and bioactivity. The reactor at 35 °C exhibited the lowest N2O emissions (< 1.0 mgN/(L•d)), while emissions rose to approximately 5.0 mgN/(L•d) at 15 °C and 3.4 mgN/(L•d) at 55 °C (during 295-395 d), primarily due to denitrification performed by coexisting ammonia-oxidizing bacteria and denitrifying microbes. This study provides insights into temperature adaptability and N2O emission risks, supporting mainstream anammox applications.

Feasibility of double nitrite supply through partial nitrification and partial denitrification driven by sludge fermentation

Challenges in obtaining stable nitrite have impeded the use of anammox in municipal wastewater treatment. This study explored the feasibility of using sludge fermentation products as carbon source and selective nitrification inhibitor to supply nitrite via partial nitrification (PN) and partial denitrification (PD). PD was initiated within 15 days, achieving nitrite transformation rate of over 90 % with a carbon/nitrogen ratio of 3 and a reaction time of 0.75 h. The dominant genus, Romboutsia, increased in relative abundance from 4.1 to 35 %. Organic acids in sludge fermentation products, like acetate (200 mg/L) and propionate (400 mg/L), selectively suppressed nitrite-oxidizing bacteria (NOB) more than ammonia-oxidizing bacteria (AOB), leading to PN. Combining anaerobic exposure with sludge fermentation products addition achieved PN with over 80.0 % nitrite accumulation. AOB increased tenfold in the long term, significantly outpacing NOB growth. This strategy simplifies difficulty of anammox application and shows broad application potential in municipal wastewater treatment.

Achieving advanced nitrogen removal with anammox and endogenous partial denitrification driven by efficient hydrolytic fermentation of slowly-biodegradable organic matter

Anammox-based processes are pivotal for elevating nitrogen removal efficiency in municipal wastewater treatment. This study established a novel HF-EPDA system combined in-situ hydrolytic fermentation (HF) with endogenous partial denitrification (EPD) and anammox. Slowly-biodegradable organic matter (SBOM) was degraded and transformed into endogenous polymers for driving production of sufficient nitrite by EPD, further promoted the nitrogen removal via anammox process. Processes above formed positive feedback, guaranteeing the robustness and recoverability of system. After a 92-day suspension during operation, advanced nitrogen removal was still achieved with excellent nitrogen removal efficiency of 95.84 ± 1.73 %, treating with actual domestic wastewater and synthetic nitrate wastewater. Candidatus Brocadia and Candidatus Competibacter were dominant bacteria on biofilms responsible for the anammox and EPD process respectively, while the main hydrolytic fermentation organisms norank_o SBR1031 was enriched in floc sludge. This study highlights the reliable potential for expanding anammox application with simultaneous improvement of SBOM utilization.

Novel Anoxic-Anaerobic-Oxic process successfully enriched anammox bacteria under actual municipal wastewater

Anaerobic ammonia oxidation (Anammox) exhibits promise for wastewater treatment,but the enrichment of anammox bacteria (AnAOB) in municipal wastewater treatment plants is a significant challenge. This study constructed a novel Anoxic-Anaerobic-Oxic (AAnO) process with a pure biofilm anoxic zone fed with actual fluctuating municipal wastewater and operated for six months to enrich AnAOB at ambient temperature. High-throughput sequencing (HTS), qPCR, and fluorescence in situ hybridization showed that AnAOB were successfully enriched in the anoxic biofilms, reaching 1.56 % relative abundance on day 75 detected by HTS. During the period from day 130 to day 186, the anammox process contributed to 55.8 ± 19.2 % of the nitrogen removal in the anoxic zone. Phylogenetic analysis revealed this AnAOB species was closely related to Candidatus Brocadia fulgida. This study provides technical support for the application of anammox in mainstream wastewater.

Synergy between Nitrogen Removal and Fermentation Bacteria Ensured Efficient Nitrogen Removal of a Mainstream Anammox System at Low Temperatures.

Simultaneous partial nitrification, anammox, denitrification, and fermentation (SNADF) is a novel process achieving simultaneous advanced sludge reduction and nitrogen removal. The influence of low temperatures on the SNADF reactor was explored to facilitate the application of mainstream anammox. When temperature decreased from 32 to 16 °C, efficient nitrogen removal was achieved, with a nitrogen removal efficiency of 81.9-94.9%. Microbial community structure analysis indicated that the abundance of Candidatus Brocadia (dominant anaerobic ammonia oxidizing bacteria (AnAOB) in the system) increased from 0.03% to 0.18%. The abundances of Nitrospira and Nitrosomonas increased from 1.6% and 0.16% to 2.5% and 1.63%, respectively, resulting in an increase in the ammonia-oxidizing bacteria (AOB) to nitrite-oxidizing bacteria (NOB) abundance ratio from 0.1 to 0.64. This ensured sufficient nitrite for AnAOB, promoting nitrogen removal. In addition, Candidatus Competibacter, which plays a role in partial denitrification, was the dominant denitrification bacteria (DNB) and provided more nitrite for AnAOB, facilitating AnAOB enrichment. Based on the findings from microbial correlation network analysis, Nitrosomonas (AOB), Thauera, and Haliangium (DNB), and A4b and Saprospiraceae (fermentation bacteria), were center nodes in the networks and therefore essential for the stability of the SNADF system. Moreover, fermentation bacteria, DNB, and AOB had close connections in substrate cooperation and resistance to adverse environments; therefore, they also played important roles in maintaining stable nitrogen removal at low temperatures. This study provided new suggestions for mainstream anammox application.

Feasibility of simultaneous optimization of Anammox start-up and nitrogen removal performance by intermittent dosing of nanoscale zero-valent iron

The long acclimation period and sensitivity to environmental conditions of Anammox are the bottlenecks for its promotion and application. An innovative strategy was adopted to accelerate functional microbial enhancement and improve nitrogen removal performance by inoculating cryopreserved Anammox sludge and activated sludge with intermittent dosing of nanoscale zero-valent iron (nZVI). The acclimation time was shortened by 76 days with nitrogen removal efficiency (NRE) reaching up to 91.07 %. Anammox, NDFO (nitrate/nitrite-dependent Fe(II) oxidation), Feammox (Fe(III) reduction coupled with anaerobic ammonium oxidation) and abiotic reactions were coupled in the system with nZVI, contributing to 69.79 %, 15.14 %, 9.84 % and 0.25 % of nitrogen removal, respectively. Further microbial analysis demonstrated significant enrichment of functional microorganisms, such as Candidatus Jettenia, Acidovorax and Comamonas. High-efficient nitrogen removal was attribute to the increase of functional genes involved in Anammox, electronic transfer, heme C synthesis and iron metabolism. This work provides an inspiring idea for the mainstream Anammox application.

Deciphering the anammox microbial community succession with humic acid exposure to optimize large anammox granules for robust nitrogen removal

The robustness of the anaerobic ammonia oxidation (anammox) process in treating wastewater with high concentrations of humic acids (HAs), including landfill leachate and sludge anaerobic digestion liquid, has been paid great attention. This study revealed that the anammox sludge granule size of 1.0–2.0 mm could be robust under the HA exposure with high concentrations. The total nitrogen removal efficiency (NRE) was 96.2% at the HA concentration of 20–100 mg/L, while the NRE was 88.5% at the HA concentration of 500 mg/L, with reduced by 7.7%. The increased extracellular polymeric substances (EPS) content which was stimulated by the HA exposure favored the formation of large granules (1.0–2.0 mm) by enveloping medium and micro granules (0.2–1.0 mm). The abundance of anammox bacteria Candidatus Brocadia was found to be higher (14.2%) in large anammox granules sized 1.0–2.0 mm, suggesting a potentially high anammox activity. However, the abundance of denitrifiers Denitratisoma increased by 4.3% in ultra-large anammox granules sized >2.0 mm, which could be attributed to the high EPS content for heterotrophic denitrifiers metabolism as organic matter. The feedback mechanism of the anammox community for maintaining the ecological function under the HA exposure resulted in a closely related microbial community, with positive and negative correlations in the ecological network increased by 64.3%. This study revealed that the HA exposure of the anammox system resulted in the anammox granules of 1.0–2.0 mm size being the dominant granules with robust nitrogen removal, providing significant guidance for the optimization of anammox granules for an efficient treatment of HA-containing wastewater in anammox applications.

Deciphering the adaptation mechanism of anammox consortia under sulfamethoxazole stress: A model coupling resistance accumulation and interspecies-cooperation

Sulfamethoxazole (SMX) is frequently detected in wastewater where anammox applications are promising. While it has been demonstrated that anammox consortia can adapt to SMX stress, the underlying community adaptation strategy has not yet been fully addressed. Therefore, in this study, we initially ascertained anammox consortia’s ability to co-metabolize SMX in batch tests. Then, a 200-day domestication process of anammox consortia under SMX stress was carried out with community variations and transcriptional activities monitored by metagenomic and metatranscriptomic sequencing techniques. Despite the initial drop to 41.88 %, the nitrogen removal efficiency of the anammox consortia rebounded to 84.64 % post-domestication under 5 mg/L SMX. Meanwhile, a 4.85-fold accumulation of antibiotic resistance genes (ARGs) under SMX stress was observed as compared to the control group. Interestingly, the anammox consortia may unlock the SMX-inhibited folate synthesis pathway through a novel interspecies cooperation triangle among Nitrospira (NAA), Desulfobacillus denitrificans (DSS1), and the core anammox population Candidatus Brocadia sinica (AMX1), in which the modified dihydropteroate synthase (encoded by sul1) of NAA reconnected the symbiotic cooperation between AMX1 and DSS1. Overall, this study provides a new model for the adaptation strategies of anammox consortia to SMX stress.

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.

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.

Advanced nitrogen removal from municipal wastewater by autotrophy-heterotrophy coupled anammox system in a novel simultaneous microaerobic/limited-oxygen SBR: Interspecific correlation network

Nowadays, autotrophic nitrogen removal of mainstream municipal wastewater by anammox is highly promising. However, due to the lack of a long-term stable nitrite-oxidizing bacteria (NOB) inhibition strategy, the accumulation of NO3−-N byproducts severely affects the nitrogen removal efficiency (NRE). In this study, a simultaneous autotrophy-heterotrophy coupled anammox system was developed in a microaerobic/oxygen-limited SBR through the co-induction of the regulation of aeration intensity and limited organics to achieve the optimization of the mainstream Partial nitrification-anammox (PN/A) processes. The nitrogen removal system constructed by anammox and denitrification achieved the high NRE of 90.77 ± 1.82 %. Under the autotrophic-heterotrophic multiple induction of nitrite supply (PN, partial denitrification and endogenous partial denitrification), the contribution of the nitrogen removal by anammox increased to 57.93 %. The high-throughput sequencing analysis showed that the relative abundance of AnAOB increased from 0.40 % to 0.67 %. In-situ tests assay further demonstrated that the realization of multi-channel nitrite supply facilitated the enrichment of anammox bacteria (AnAOB). The endogenous denitrifying bacterial genus Candidatus (Ca.) Competibacter was significantly enriched in the system (7.98 %, P ≤ 0.001), which enhanced the deep removal of NOX−-N and organics. Correlation network analysis indicated that closer and more balanced interspecies interactions were the key to the high efficiency and stability of the autotrophy-heterotrophy coupled anammox system. Based on the nitrite recirculation and denitrification performance, the simultaneous autotrophy-heterotrophy coupled anammox system established by the novel SBR provides a potential strategy for mainstream anammox applications.

Self-cultivating anammox granules for enhancing wastewater nitrogen removal in nitrification–denitrification flocculent sludge system

The feasibility of self-cultivating anammox granules for enhancing wastewater nitrogen removal was investigated in a nitrification–denitrification flocculent sludge system. Desirable nitrogen removal efficiency of 84 ± 4 % was obtained for the influent carbon to nitrogen ratio of 1–1.3 (NH4+-N: 150–200 mg N/L) via alternate anaerobic/oxic/anoxic mode. Meanwhile, some red granular sludge was formed in the system. The abundance and activity of anaerobic ammonia oxidation bacteria (AnAOB) increased from ‘not detected’ in seed sludge to 0.57 % and 29.4 ± 0.7 mg N/(g mixed liquor volatile suspended solids·h) in granules, respectively, suggesting successful cultivation of anammox granules. Furthermore, some denitrifying bacteria with capability of partial denitrification were enriched, such as Candidatus Competibacter (2.45 %) and Thauera (5.75 %), which could cooperate with AnAOB, facilitating AnAOB enrichment. Anammox was dominant in nitrogen removal with the contribution to nitrogen removed above 68.8 ± 0.3 %. The strategy of self-cultivating anammox granules could promote the application of anammox.

Achieving transformation from denitrifying biofilter to partial denitrification/anammox biofilter through self-enrichment of anammox bacteria

The application of anammox in denitrifying biofilter (DNBF) has been proven to be stable and feasible, but self-enrichment of anammox bacteria (AnAOB) in DNBF is difficult and rarely reported. During a 111-day operation in a single-stage DNBF, average NH4+-N removal remained at only 0.55 mg/L, showing limited partial denitrification/anammox performance. Subsequently, in another two-stage DNBF system, an average NH4+-N removal of 6.45 mg/L was achieved in 164 days, better than single-stage DNBF. Batch tests revealed partial denitrification activity of the primary biofilter and anammox activity of the secondary biofilter. Metagenomic analysis demonstrated that the secondary biofilter enriched Candidatus Brocadia from 0 to 23.81 %, 11.16 % and 14.09 % in the top, middle and bottom sections, respectively. Key enzymes of AnAOB including hdh and hzs, were distributed along the secondary biofilter, confirming the main role of anammox in nitrogen removal. Overall, this study demonstrated the potential for transformation from conventional denitrifying biofilter to partial denitrification/ anammox biofilter through self-enrichment of AnAOB in two-stage DNBF system compared to the single-stage DNBF.

Achieving rapid endogenous partial denitrification by regulating competition and cooperation between glycogen accumulating organisms and phosphorus accumulating organisms from conventional activated sludge

In anaerobic/aerobic/anoxic (A/O/A) process, endogenous denitrification (ED) is critically important, and achieving steady endogenous partial denitrification (EdPD) is crucial to carbon saving and anammox application. In this study, EdPD was rapidly realized from conventional activated sludge by expelling phosphorus accumulating organisms (PAOs) in anaerobic/anoxic (A/A) mode during 40 days, with nitrite transformation rate (NTR) surging to 82.8 % from 29.4 %. Competibacter was the prime EdPD-fulfilling bacterium, soaring to 28.9 % from 0.5 % in phase II. Afterwards, balance of high NTR and phosphorus removal efficiency (PRE) were attained by well regulating competition and cooperation between PAOs and glycogen accumulating organisms (GAOs) in A/O/A mode, when the Competibacter (21.7 %) and Accumulibacter (7.3 %, mainly Acc_IIC and Acc_IIF) were in dominant position with balance. The PRE recovered to 88.6 % and NTR remained 67.7 %. Great balance of GAOs and PAOs contributed to advanced nitrogen removal by anammox.

Rapid enrichment of anammox bacteria for low-strength wastewater treatment: Role of influent nitrite and nitrate ratios in sequencing batch reactors (SBRs)

Anaerobic ammonium oxidation (Anammox) bacteria (AnAOB) have a long doubling time, which represents one of the key challenges for starting up anammox-based reactors. This study investigated the effect of varied nitrite/nitrate ratios on the anammox reactor startup process using five lab-scale anammox sequencing batch reactors (SBRs) (R1-R5). Nitrate addition significantly accelerated AnAOB enrichment startup, particularly during nitrite accumulation phase. The total start-up time was shortened by 55–71 days, compared to the reactor without nitrate. In R1 (nitrite/nitrate=10:0), anammox contributed the highest nitrogen removal percentage (91%), while R2 (nitrite/nitrate=7:3), with nitrate added, exhibited the highest anammox activity (53.84 mg NH4+-N/g VSS/day) in the steady-state phase. As nitrate proportions increased (R3-R5), anammox activity gradually declined due to limited available COD required for the conversion of NO3- to NO2-. Furthermore, it was found that nitrate-added improved the sludge settleability, with lower SVI30. 16S rRNA gene revealed that Ca. Brocadia was the predominant AnAOB in R1, R2 and R3, where nitrite was the primary NOx--N species (≥50%) in the influent. While in the reactor with low concentration of nitrite (R4: nitrite/nitrate=3:7), Ca. Kuenenia was the dominant AnAOB. This study successfully established a complex and balanced ecosystem with multi-species coexistence, where AnAOB served as the primary functional group on nitrogen removal, supported by denitrification bacteria and dissimilatory nitrate reduction to ammonium (DNRA) bacteria. This study proposes a rapid start-up strategy for the anammox process, which overcomes the bottleneck of long start-up time and helps to promote the application of anammox in wastewater treatment.

Evaluation of the economic and environmental benefits of partial nitritation anammox and partial denitrification anammox coupling preliminary treatment in mainstream wastewater treatment

Anaerobic ammonium oxidation (anammox) technology is considered the best alternative for current wastewater treatment to improve resource recovery and energy efficiency. Evaluation of the economic and environmental benefits of partial denitrification anammox (PDA) and partial nitritation anammox (PNA) from a plant-wide perspective, which are the two most common mainstream anammox processes, is crucial for guiding the development direction of anammox, but research is still lacking. In this study, two plant-wide processes with chemically enhanced primary treatment-PDA (CEPT-PDA) and high rate activated sludge-PNA (HRAS-PNA) as the core units respectively, were firstly proposed and analysed, and life cycle assessment (LCA) was conducted to assess environmental impacts (EIs). The results of energy and economic analysis showed that the net energy consumption of CEPT-PDA and HRAS-PNA was 0.11 kwh/m3 and 0.16 kwh/m3 respectively; however, the operating cost of CEPT-PDA was 16.54% higher than that of HRAS-PNA due to the requirement for more chemicals. Compared with CEPT-PDA, the total EIs of HRAS-PNA decreased by 14.80%. The EI categories related to human toxicity and ecotoxicity contributed greatly to total EIs, accounting for 95.81% in CEPT-PDA and 96.75% in HRAS-PNA. Major environmental impacts were attributed to coagulant and energy consumption in two processes. In addition, improving the iron recycling efficiency was more beneficial for CEPT-PDA and further narrowed the gap between CEPT-PDA and HRAS-PNA on EIs. This study identifies that CEPT-PDA is competitive in the engineering application of mainstream anammox but reducing iron addition is a prerequisite.

Enhancing mainstream anammox process by adding Fe3O4 nanoparticles

In order to further promote the application of mainstream anammox, magnetic field enhancing technology was applied to improve the anammox start-up and operation performance under the conditions of low temperature and substrates concentrations. Two UASBs were adopted as anammox reactors and run in parallel. The controlling group and the magnetic field enhancing group (with 2.4 g/L Fe3O4 NPs) were recorded as UASBC and UASBM. The results showed that UASBC and UASBM successfully took 37 days and 33 days to start mainstream anammox with TNRE of 90.03% and 85.05%, respectively. The maximum TNLR of UASBC and UASBM reached 0.54 mg N(m3·d)−1 and 0.82 mg N(m3·d)−1 with the maximum TNRE of 86.41% and 85.50% during 121 days operation. The results showed that magnetic filed could change morphological characteristics of AnAOB and strengthen sludge granulation by adjusting the composition of EPS. Microbial high-throughput sequencing analysis results showed the phylum of Planctomycetes dominated in UASBC and UASBM with the relative abundance of 26.41% and 32.68% on 121 d. Candidatus Kuenenia was cultured as the dominant bacteria, and it was speculated that magnetic filed had the ability to promoting the enrichment of Candidatus Kuenenia. These findings were interesting and meaningful, and could provide new ideas for long-term application of mainstream anammox.