Anammox activity improved significantly by the cross-fed NO from ammonia-oxidizing bacteria and denitrifying bacteria to anammox bacteria

Impaired denitrification of aerobic granules in response to micro/nanoplastic stress: Insights from interspecies interactions and electron transfer processes

The accumulation of micro/nanoplastics in wastewater significantly hinders denitrification in biological wastewater treatment systems, yet the intrinsic mechanisms are not fully understood. Herein, we combined signal molecule monitoring, electrochemical characterization and multi-omics analysis to investigate how quorum sensing (QS)-mediated microbial interactions influence denitrification in aerobic granular sludge systems. Results showed that after 90-day exposure to micro/nanoplastics, cross-talk between multiple signal molecules significantly declined, thereby disrupting the QS system to opportunely sense changes in the external environment. As a consequence of impaired QS, only 5 species exhibited up-regulation of the genes encoding amino acids and cofactors to sustain cross-feeding, while others, acting as "cheaters", relied on metabolites offered by cross-feeding but without reciprocating. This imbalance resulted in insufficient availability of metabolites, including redox-active metabolites such as riboflavin, and subsequently deteriorated the denitrification electron transfer process. Compared to the control group, the extracellular electron transfer capacity and denitrification electron transfer chain activity decreased to, respectively, 88.08 % and 63.33 % (microplastics-exposure) and 79.64 % and 63.75 % (nanoplastics-exposure), which directly contributed to the decline in nitrogen removal. Overall, this study provided deeper insights into the denitrification in complex microbial communities under the stress of micro/nanoplastics from the perspective of QS-mediated microbial social behavior.

Insights into the influence of organic and salinity on the two-stage partial nitritation/anammox process in treating food waste digestate

ABSTRACTFood waste digestate (FWD), which contains significant levels of ammonium, organic matter, and salinity, can interfere with treatment performance of the anammox process. In this study, a two-stage partial nitritation/anammox (PN/A) process was established to investigate nitrogen removal and microbial response in treating FWD at a nitrogen loading rate (NLR) of 0.27 ± 0.02 gN/L/d. High concentrations of free ammonia (58 mg/L) and free nitrous acid (0.3 mg/L) facilitated the initiation of the partial nitritation (PN) process, achieving an average NO2-/NH4+ ratio of 1.28 ± 0.08. For the anammox process, a nitrogen removal rate (NRR) of 0.72 ± 0.13 gN/L/d was achieved. Free ammonia (NH3) stripping, Anammox pathway, and denitrification pathway contributed 4.1 ± 0.3%, 5.1 ± 0.2%, and 84.0 ± 1.5% of the total nitrogen removal, respectively. Nitrosomonas, a salt-tolerant ammonia-oxidizing bacteria (AOB), was enriched to 1.0%, while Nitrospira, a nitrite-oxidizing bacteria (NOB), was effectively suppressed to 0.003%. The salt-tolerant anammox genera unclassified_f__Brocadiaceae (13.9%) and Candidatus_Kuenenia (4.8%) dominated the nitrogen removal pathway. The high enrichment of unclassified_f__Brocadiaceae ensured stable operation of the anammox process at 0.62 ± 0.11% salinity, even with a high initial FA inhibition concentration of 40 mg/L. Additionally, norank_f_A4b (1.34%) and norank_f_norank_o_SBR1031 (52.1%) facilitated the hydrolysis of refractory organic matter. Denitrifying bacteria, including Hyphomicrobium, Truepera, and unclassified_c__Alphaproteobacteria, played significant roles in nitrate removal, with a CODconsumed/NO3-removed ratio of 2.7 ± 0.2. This study highlights the application of a two-stage PN/A process for rapid startup and effective nitrogen removal from FWD.

Accelerated sludge granulation of novel complete ammonium and nitrate removal via denitratation anammox over nitrite process at elevated loading rates

The Complete Ammonium and Nitrate Removal via Denitratation Anammox Over Nitrite (CANDAN) process was evaluated for rapid sludge granulation in a lab-scale sequencing batch reactor. Over 119 days under increasing nitrogen loading rates (NLRs), the system finally achieved average 89.2 % total nitrogen removal at 1.93 kg N/m3/d NLR, with sludge particle sizes increasing from 215.6 μm to 924.5 μm. Higher NLRs significantly increased extracellular polymeric substances, especially hydrophobic proteins, enhancing sludge hydrophobicity and aggregation. Metagenomic analysis identified Candidatus Brocadia and Thauera as predominant and key microbial genera for nitrogen removal. Furthermore, the upregulation of carbon metabolism under heightened NLRs facilitated the synthesis of hydrophobic amino acids, promoting sludge granulation. These findings demonstrate NLR-driven granulation mechanisms, highlight optimizing NLR as key for accelerating granulation, providing insights to improve start-up and operational efficiency of CANDAN systems.

Enhancement of Partial Nitrification-Anaerobic Ammonia Oxidation in SBR Reactors via Surface-Modified Polyurethane Sponge Biofilm Carrier

The partial nitrification-anammox process offers a cost-effective, energy-efficient, and environmentally sustainable approach for nitrogen removal in wastewater treatment. However, its application under low ammonia nitrogen conditions faces operational challenges including prolonged start-up periods and excessive nitrite oxidation. This study employed a strategy combining polyurethane surface positive charge enhancement and zeolite loading to develop a carrier capable of microbial enrichment and inhibition of nitrate generation, aiming to initiate the partial nitrification-anammox process in a sequencing batch reactor. Operational results demonstrate that the modified carrier enabled the reactor to achieve a total nitrogen removal efficiency of 78%, with the effluent nitrate nitrogen reduced to 6.03 mg-N/L, successfully initiating the partial nitrification-anammox process. The modified carrier also exhibited accelerated biofilm proliferation (both suspended and attached biomass increased). Additionally, 16S rRNA revealed a higher relative abundance of typical anammox bacteria Candidatus Brocadia in the biofilm of the modified carrier compared to the original carrier, alongside a decline in nitrifying genera, such as Nitrolancea. These microbial shifts effectively suppressed excessive nitrite oxidation, limited nitrate accumulation, and sustained efficient nitrogen removal throughout the reactor's operation.

Microalgal-based urea wastewater treatment with p-Hydroxybenzoic acid enhances resource recovery and mitigates biological risks from Bisphenol A

Efficient nutrient recovery from source-separated urine is vital for wastewater treatment, with microalgae as a promising solution. However, bisphenol A (BPA) in urine can hinder microalgal resource recovery and pose water quality risks. The role of plant hormones in enhancing microalgal growth and pollutant removal is known, but their impact on BPA-laden urine treatment is not well-studied. Here, we explored para-hydroxybenzoic acid (p-HBA) in Chlorella for treating diluted urine with BPA. p-HBA boosted photosynthesis and glycolysis, increasing pyruvate and ATP production and enhancing microalgal growth by 45.7 %. It also optimized nitrogen metabolism, raising urea and nitrogen consumption by 35 % and 65 %, respectively, and protein content by 23.1 %. Enhanced oxidase and transferase expression improves BPA degradation by 40 %. Additionally, ARGs and plasmid abundance decreased by 24.3 % and 37.5 %, respectively, reducing the risk of ARG dissemination. This study shows that p-HBA significantly improves the efficiency and safety of urine resource recovery, offering a promising strategy for sustainable wastewater treatment.

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.

Roles of nitrite in facilitating nitrogen and sulfur conversion in the hybrid bioreactor of Sulfate-reduced ammonium oxidation and anaerobic ammonium oxidation

The hybrid bioreactor combining sulfate-reducing ammonium oxidation (Sulfammox) and Anammox offered potential for simultaneous nitrogen and sulfur removal, but the removal efficiency and microbial mechanism remain unclear. This study demonstrated that in the hybrid bioreactor, the ammonium utilization rate (AUR) of Sulfammox increased by 5.42 times. The promotion of NO2- on nitrogen and sulfur conversion in Sulfammox could be attributed to: 1) Increasing extracellular polymers substance (EPS) accelerated the stratification of granule sludge; 2) Increasing the relative abundance of Candidatus Brocadia by 29.55 times and Candidatus Anammoxoglobus by 3.17 times; 3) Upregulating the expression of nitrification (amo, hao and nxr) and sulfur metabolism (sat, aprAB dsr and sox) genes, associated with the pathways NH4+→NH2OH → NO2-→NO3- and SO42-→S2-→SO42-. Moreover, Candida Brocadia sapporoensis emerged as a potential specie of Sulfammox, mediating nitrification by hao and nxr, and sulfate reduction by sat and aprAB, thereby enabling electron transfer between nitrogen and sulfur.

Facilitating multiple nitrite for anammox process directly treating municipal wastewater: Optimized organics utilization and microbial composition

While direct anammox implementation is attractive when treating wastewater, nitrite (NO2--N) availability and excess organic matter significantly limit its practical application. This study proposed partial nitrification and endogenous partial denitrification/anammox (PN/A-EPD/A) for the treatment of real municipal wastewater (COD/N ratio: 2.8) within a single-stage reactor under anaerobic/aerobic/anoxic mode. Interestingly, with reducing dissolved oxygen concentration (5.0 ± 1.0 → 1.0 ± 0.5 mg-O2/L) during aerobic phase, Comammox Nitrospira clade A became dominated and introduced vast nitrate (NO3--N) into the subsequent anoxic stage. Both in-situ and ex-situ tests confirmed that sufficient NO3--N as electron acceptors were in favor of the EPD/A occurrence with endogenous organics utilization, which was obtained by anaerobic endogenous transformation. Metagenomic results confirmed the role of Thauera in facilitating NO3--N→NO2--N process, and further supporting AnAOB. As a result, Ca. Brocadia gradually enriched on granules (from 0.08% to 3.51%) and contributed up to 51.5 % to total inorganic nitrogen removal through the PN/A-EPD/A process. Optimized carbon utilization pathway promoted the re-cooperative balance of microorganisms and this process achieved efficient nitrogen removal (93.5%) and desirable quality of effluent (3.2 mg-N/L) when treating real municipal wastewater.

Hydrazine promoted nitrite reduction in partial-denitrification by enhancing organic-substrate uptake and electron transport

Partial denitrification coupled with anammox is a promising approach for sustainable nitrogen removal from wastewater. However, this coupling can be influenced by hydrazine (N2H4) released by anammox bacteria. This study aimed to reveal how N2H4 regulates partial denitrification. Short-term batch experiments showed that 0.5 to 10 mg N/L of N2H4 promoted nitrite (NO2-) accumulation, likely by inhibiting the electron transfer from cyt c to nitrite reductase. However, long-term exposure to N2H4 (0.5 and 1 mg N/L) shifted the microbial community and increased NO2- reduction. This exposure enriched the genera OLB8, Thauera, and f_Rhodocyclaceae, and increased the abundance of genes involved in EPS formation, substrate transport and electron transport. The long-term outcome was more NO2- reduction to N2 and more substrate (COD) oxidation. While N2H4 benefits NO2- accumulation in short-term, the mechanism is not sustainable, highlighting the importance of minimizing N2H4 release for successful in such coupled nitrogen removal systems.

Multi-faceted effects and mechanisms of granular activated carbon to enhance anaerobic ammonium oxidation (anammox) for nitrogen removal from wastewater

Nitrogen removal via anammox is efficient but challenged by their slow growth. Adding granular activated carbon (GAC) increased the total nitrogen removal rate to 66.99 g-N/m3/day, compared to 50.00 g-N/m3/day in non-GAC reactor. Both reactors dominated by Candidatus Brocadia (non-GAC: 36.25 %, GAC: 35.5 %) but GAC improved specific anammox activity. Functional metabolic profiling from metagenomic analysis unveiled that GAC enhanced pathways associated with electron shuttle production, potentially promoting intra/extracellular electron transfer. In nitrogen metabolism, GAC is indicated to facilitate anammox N2H4 synthesis process, and inhibit nitrification and full denitrification processes, functioned by Nitrosomonas and Castellaniella which are more abundant in the non-GAC reactor. GAC also enhanced dissimilatory nitrate reduction to ammonium and partial denitrification processes, providing anammox with NH4+/NO, which was conducted by Anaerolineae members (29.7 % in GAC-reactor and 7.8 % in non-GAC reactor sludge). This research illuminated the intricate microbial nitrogen cycling networks affected by GAC in anammox systems.

Alteration of nitrogen sink and emission by vegetation distribution in a wetland with significant change in water level

In wetlands, hydrological conditions drive plant community distribution, forming vegetation zones with plant species and material cycling. This mediates nitrogen migration and N2O emissions within wetlands. Five vegetation zones in a large wetland were studied during flooding and drought periods. Zones including mud flat, nymphoides, phalaris, carex, and reeds, distributed sequentially with increasing water level change rate. Carbon and nitrogen densities were higher during drought period. When sediments alternated between source and sink roles annually, N2O emissions varied significantly with zones and water levels. Emission flux decreased with higher C:N ratio in sediments, approximating a threshold at 0.23 μg m-2 h-1 when C:N ratio exceeded 25. Denitrifying nirS and nirK genes and anammox hzsB gene varied significantly with water level, most prominently in mud flat and nymphoides zones. Plant distribution under hydrological conditions alters soil stoichiometric ratio, influencing N2O emissions and microbial communities across vegetation zones. Therefore, in freshwater wetlands, hydraulic regulation and reduction in prolonged flooding would be an effective strategy for mitigation of greenhouse gas emissions.

Deciphering key microbes and their interactions within anaerobic ammonia oxidation systems

The stability of anaerobic ammonium oxidation (anammox) performance is inseparably linked to the dynamic equilibrium of microbial interactions. However, understanding of the key microbes within anammox systems remains limited. Through the analysis of 186 16S rRNA datasets combined with various ecological analysis methods, this study identified key microbes in the anammox process. Interactions between Candidatus_Kuenenia and other key microbes are the most significant with greater tolerance to differing water quality, while Candidatus_Jettenia have higher habitat specificity. Under adverse conditions, anammox bacteria can reduce the impact of unfavorable environments by enhancing interactions with certain microbes. This study comprehensively reviews the main functions of key microbes in the anammox system and their interactions, and summarizes several common interaction mechanisms, providing new insights for understanding the startup and stable operation of the anammox process.

Novel insights into self-defense function of anammox sludge under magnesium ions (Mg2+) stress based on Mg2+ transport system

Magnesium ion (Mg2+) plays an important role in the accumulation and stability of anaerobic ammonium-oxidizing bacteria (AnAOB). In this study, the response of anammox sludge to Mg2+ was comprehensively investigated by performance evaluation and metagenomics analysis. Appropriate Mg2+ (0.8 mmol/L) could improve the nitrogen removal performance, AnAOB activity, and the synthesis potential of some hydrophobic substances, while high Mg2+ (>1.6 mmol/L) has a negative effect. Meanwhile, Mg2+ transmembrane transport theory was introduced to reveal the response principle of AnAOB to Mg2+ from a novel insight. AnAOB may have a self-defense function based on the PhoQ/PhoP-MgtAB system. Low extracellular Mg2+ will activate this function to enhance Mg2+ influx, thereby improving the intracellular metabolism of AnAOB. Excessive Mg2+, however, dormant this function and induces Mg2+ efflux, which may decrease the intracellular Mg2+ and thus affect AnAOB metabolism. These findings provide valuable references for the Mg2+ regulation of anammox-based process.

Optimizing nitrogen removal in PD/A reactors: Effects of influent composition and temperature on system stability and microbial dynamics

This study investigates the performance and microbial community dynamics in two partial denitrification/anammox (PD/A) reactors with different influent wastewater compositions (differ in the presence/absence of NO2-) subjected to a controlled temperature gradient reduction from mesophilic (30 °C) to room temperature (20.92 °C) over 76 days. Two lab-scale PD/A reactors (R1 and R2), both operated with a total inorganic nitrogen (TIN) concentrations of 70 mg N/L. R1 maintained a NH4+/NO2-/NO3- ratio of 3:3:1 and a COD/NO3- ratio of 2.0, while R2 had an NH4+/NO3- ratio of 3:4, and COD/NO3- ratios of 2.0 and 2.5. Our findings reveal distinct responses to the temperature transitions: the optimization of the NH4+/NO2-/NO3- ratio at 3:3:1 facilitated more stable nitrogen removal as temperatures decreased. This stability can be attributed to the enhanced synchronization between anammox bacteria and denitrifiers, promoting a balanced bioconversion process that is less susceptible to temperature-induced disruptions. Notably, the specific anammox activity (SAA) in both reactors declined linearly with the decrease in temperature, but the relative abundance of anammox bacteria (Ca. Brocadia) in R1 increased from 2.1 % to 9.7 %. Furthermore, the percentage of anammox-related key genes was higher in R1 than in R2, suggesting a microbial mechanism underlying the stable performance of R1. These results underscore the significant impact of influent nitrogen composition on PD/A performance amid temperature gradients and highlight the critical role of optimizing influent ratios for maintaining efficient nitrogen removal. This study offers valuable insights into enhancing the stability of PD/A systems under varying thermal conditions.

Metabolic evolution and bottleneck insights into simultaneous autotroph-heterotroph anammox system for real municipal wastewater nitrogen removal

When biological nitrogen removal (BNR) systems shifted from treating simulated wastewater to real wastewater, a microbial succession occurred, often resulting in a decline in efficacy. Notably, despite their high nitrogen removal efficiency for real wastewater, anammox coupled systems operating without or with minimal carbon sources also exhibited a certain degree of performance reduction. The underlying reasons and metabolic shifts within these systems remained elusive. In this study, the simultaneous autotrophic/heterotrophic anammox system demonstrated remarkable metabolic resilience upon exposure to real municipal wastewater, achieving a nitrogen removal efficiency (NRE) of 82.83 ± 2.29 %. This resilience was attributed to the successful microbial succession and the complementary metabolic functions of heterotrophic microorganisms, which fostered a resilient microbial community. The system's ability to harness multiple electron sources, including NADH oxidation, the TCA cycle, and organics metabolism, allowed it to establish a stable and efficient electron transfer chain, ensuring effective nitrogen removal. Despite the denitrification channel's nitrite supply capability, the analysis of the interspecies correlation network revealed that the synergistic metabolism between AOB and AnAOB was not fully restored, resulting in selective functional bacterial and genetic interactions and the system's PN/A performance declined. Additionally, the enhanced electron affinity of PD increased interconversion of NO3--N and NO2--N, limiting the efficient utilization of electrons and thereby constraining nitrogen removal performance. This study elucidated the metabolic mechanism of nitrogen removal limitations in anammox-based systems treating real municipal wastewater, enhancing our understanding of the metabolic functions and electron transfer within the symbiotic bacterial community.

A comprehensive catalog encompassing 1376 species-level genomes reveals the core community and functional diversity of anammox microbiota

Research on the microbial community and function of the anammox process for environmentally friendly wastewater treatment has achieved certain success, which may mean more universal insights are needed. However, the comprehensive understanding of the anammox process is constrained by the limited taxonomic assignment and functional characterization of anammox microbiota, primarily due to the scarcity of high-quality genomes for most organisms. This study reported a global genome catalog of anammox microbiotas based on numerous metagenomes obtained from both lab- and full-scale systems. A total of 1376 candidate species from 7474 metagenome-assembled genomes were used to construct the genome catalog, providing extensive microbial coverage (averaged of 92.40 %) of anammox microbiota. Moreover, a total of 64 core genera and 44 core species were identified, accounting for approximately 64.25 % and 43.97 %, respectively, of anammox microbiota. The strict core genera encompassed not only functional bacteria (e.g., Brocadia, Desulfobacillus, Zeimonas, and Nitrosomonas) but also two candidate genera (UBA12294 and OLB14) affiliated with the order Anaerolineales. In particular, core denitrifying bacteria with observably taxonomic diversity exhibited diverse functional profiles; for instance, the potential of carbohydrate metabolism in Desulfobacillus and Zeimonas likely improves the mixotrophic lifestyle of anammox microbiota. Besides, a noteworthy association was detected between anammox microbiota and system type. Microbiota in coupling system exhibited complex diversity and interspecies interactions by limiting numerous core denitrifying bacteria. In summary, the constructed catalog substantially expands our understanding of the core community and their functions of anammox microbiota, providing a valuable resource for future studies on anammox systems.

The green footprint of anammox processes under simulated actual operating conditions: Focusing on the nitrous oxide and methane production

The anammox process has attracted increasing attention due to its advantages of low-carbon and energy-saving, nevertheless, greenhouse gas was still generated during its engineering applications process. Hence, it is vital to comprehensively understand the production characteristics and mechanisms of N2O and CH4 in anammox processes by responding to practical conditions including dissolved oxygen, temperature, and salinity. Results showed that N2O production increased by 192 %-358 %, while nitrogen removal efficiency (NRE) increased by 64.2 %-86.8 % with increasing temperature. The increased salinity inhibits 40.60 %-65.33 % N2O production with a decrease NRE of 7.85 %-18.2 %. CH4 production was the highest at 18-27 °C, reaching 3.07 ± 0.11-4.06 ± 0.16 mg·L-1, which were 1.59-2 and 1.29-1.38 times higher than that at 8-17 °C and 28-37 °C, respectively. Denitratisoma, Thauera, and Nitrosomonas were the main functional microbes for greenhouse gas production in anammox consortia. Notably, H2O2-induced intracellular Fenton reaction may be critical for the CH4 production in anammox consortia. This work provides valuable insights into achieving efficient nitrogen removal and minimizing carbon footprint in anammox systems and provides a theoretical basis for implementing the net-zero emission idea in wastewater treatment plants.

Enhancing the nitrogen removal of anammox sludge by setting up novel redox mediators-mediated anammox process

Anaerobic ammonium oxidizing (anammox) bacteria have been proven weak-electroactive. However, the impact of exogenous anthraquinone-2,6-disulfonate (AQDS) on the anammox activity, although it usually plays essential roles in the life activities of many other electroactive microorganisms, is still unknown. Therefore, this study further explored the influences of AQDS on the anammox activity and the interaction mechanism with anammox bacteria, as well as the behaviors of NH4+, NO2-, and NO3-. The results showed that exogenous AQDS increased the ammonium and total nitrogen removal rates by 12.8% and 10.7%, respectively. Interestingly, the conversion from NO2- to NO3- was significantly reduced after adding AQDS, resulting in a 40.1% reduction in NO3- production of anammox process. In this study, we found for the first time that anammox bacteria could not only carry out the conventional anammox process but also perform a weak redox mediator-mediated anammox process, which could achieve the 1:1 consumption of NH4+ and NO2-. The redox mediator-mediated anammox process was related to an endogenous redox mediator (ERM) synthesized and secreted by anammox bacteria, whose redox midpoint potential was around -0.26 V (vs. Ag/AgCl). After adding AQDS, not only the ERM-mediated anammox process was enhanced, but also two novel redox mediator-mediated anammox processes were introduced, including the AQDS-mediated anammox process and ERM-AQDS-mediated anammox process. These three redox mediator-mediated anammox processes significantly improved the nitrogen removal performance of anammox bacteria and reduced energy consumption. These findings will help reduce the dependence of anammox technology on NO2-, reduce the cost of subsequent treatment of NO3-, and provide new visions for optimizing and applying anammox technology.

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.

Metagenomic insights into microbial metabolic mechanisms of a combined solid-phase denitrification and anammox process for nitrogen removal in mainstream wastewater treatment

To overcome the significant challenges associated with nitrite supply and nitrate residues in mainstream anaerobic ammonium oxidation (anammox)-based processes, this study developed a combined solid-phase denitrification (SPD) and anammox process for low-strength nitrogen removal without the addition of nitrite. The SPD step was performed in a packed-bed reactor containing poly-3-hydroxybutyrate-co-3-hyroxyvelate (PHBV) prior to employing the anammox granular sludge reactor in the continuous-flow mode. The removal efficiency of total inorganic nitrogen reached 95.7 ± 1.2% under a nitrogen loading rate of 0.18 ± 0.01 kg N·m3·d-1, and it required 1.02 mol of nitrate to remove 1 mol of ammonium nitrogen. The PHBV particles not only served as biofilm carriers for the symbiosis of hydrolytic bacteria (HB) and denitrifying bacteria (DB), but also carbon sources that facilitated the coupling of partial denitrification and anammox in the granules. Metagenomic sequencing analysis indicated that Burkholderiales was the most abundant HB genus in SPD. The metabolic correlations between DB (Betaproteobacteria, Rhodocyclaceae, and Anaerolineae) and anammox bacteria (Candidatus Brocadiac and Kuenenia) in the granules were confirmed through microbial co-occurrence networks analysis and functional gene annotations. Additionally, the genes encoding nitrate reductase (Nap) and nitrite reductase (Nir) in DB primarily facilitated nitrate reduction, thereby supplying nitric oxide to anammox bacteria for subsequent nitrogen removal with hydrazine synthase (Hzs) and hydrazine dehydrogenase (Hdh). The findings provide insights into microbial metabolism within combined SPD and anammox processes, thus advancing the development of mainstream anammox-based processes in engineering applications.

Rapid start-up and operational characteristics of partial denitrification coupled with anammox driven by innovative strategies

The Partial Denitrification-Anammox (PD/A) process established a low-consumption, efficient and sustainable pathway for complete nitrogen removal, which is of great interest to the industry. Rapid initiation and stable operation of the PD/A systems were the main issues limiting its engineering application in wastewater nitrogen removal. A PD/A system was initiated in a continuous stirred-tank reactors (CSTRs) in the presence of low concentration of organic matter, and the effects of organic matter types and COD/NO3--N ratios on the performance of the PD/A system, and microbial community characteristics were explored. The results showed that low concentrations of organic matter could promote the rapid initiation of the Anammox process and then the strategy of gradually replacing NO2--N with NO3--N could successfully initiate the PD/A system at 70 days. The type of organic matter had a significant effect on the initiation of the Anammox and the establishment of the PD/A system. Compared to glucose, sodium acetate was more favorable for rapid start-up and the synergy among microorganisms, and organic matter was lower, with an optimal COD/NO3--N ratio of 3.0. Microorganisms differed in their sensitivity to environmental factors. The relative abundance of Planctomycetota and Proteobacteria in R2 was 51 %, with the presence of three typical anammox bacteria, Candidatus_Brocadia, Candidatus_Kuenenia, and Candidatus_Jettenia in the system. This study provides a new strategy for the rapid initiation and stable operation of the PD/A process.

Microbial Ecology of Granular Biofilm Technologies for Wastewater Treatment: A Review

Nowadays, the discharge of wastewater is a global concern due to the damage caused to human and environmental health. Wastewater treatment has progressed to provide environmentally and economically sustainable technologies. The biological treatment of wastewater is one of the fundamental bases of this field, and the employment of new technologies based on granular biofilm systems is demonstrating success in tackling the environmental issues derived from the discharge of wastewater. The granular-conforming microorganisms must be evaluated as functional entities because their activities and functions for removing pollutants are interconnected with the surrounding microbiota. The deep knowledge of microbial communities allows for the improvement in system operation, as the proliferation of microorganisms in charge of metabolic roles could be modified by adjustments to operational conditions. This is why engineering must consider the intrinsic microbiological aspects of biological wastewater treatment systems to obtain the most effective performance. This review provides an extensive view of the microbial ecology of biological wastewater treatment technologies based on granular biofilms for mitigating water pollution.