Taxonomical and functional microbial community dynamics in an Anammox-ASBR system under different Fe (III) supplementation

Unravelling the influence of microplastics with/without additives on radish (Raphanus sativus) and microbiota in two agricultural soils differing in pH

Here we investigated the effects of three types of microplastics (MPs), i.e., PS (P), ABS (B), PVC (V), and each with additive (MPAs) (PA, BA, and VA), on soil health, microbial community, and plant growth in two acidic and slightly alkaline soils. Incubation experiment revealed that although MPs and MPAs consistently stimulated soil nutrients and heavy metals (e.g., Mn, Cu) in weakly alkaline soils, only BA and VA led to increase in soil nutrients and heavy metals in acidic soils. This suggests distinct response patterns in the two soils depending on their initial pH. Concerning microorganisms, MPs and MPAs reduced the assembly degree of bacteria in acidic soils, with a reduction of Chloroflexi and Acidobacteriota but an increase of WPS-2 in VA. Culture experiment showed consistent positive or negative responses in radish seed germination, roots, and antioxidant activity across MPs and MPAs types in both soils, while the responses of seed heavy metals (e.g., Cr, Cd) were consistent in acidic soils but dependent on MPs and MPAs types in alkaline soils. Therefore, our study strongly suggests that the effects of MPs on soil-microbial-plant systems were highly dependent on initial soil characteristics and the types of MPs with plastic additives.

Insights into carbon-neutral treatment of rural wastewater by constructed wetlands: A review of current development and future direction

In recent years, with the global rise in awareness regarding carbon neutrality, the treatment of wastewater in rural areas is increasingly oriented towards energy conservation, emission reduction, low-carbon output, and resource utilization. This paper provides an analysis of the advantages and disadvantages of the current low-carbon treatment process of low-carbon treatment for rural wastewater. Constructed wetlands (CWs) are increasingly being considered as a viable option for treating wastewater in rural regions. In pursuit of carbon neutrality, advanced carbon-neutral bioprocesses are regarded as the prospective trajectory for achieving carbon-neutral treatment of rural wastewater. The incorporation of CWs with emerging biotechnologies such as sulfur-based autotrophic denitrification (SAD), pyrite-based autotrophic denitrification (PAD), and anaerobic ammonia oxidation (anammox) enables efficient removal of nitrogen and phosphorus from rural wastewater. The advancement of CWs towards improved removal of organic and inorganic pollutants, sustainability, minimal energy consumption, and low carbon emissions is widely recognized as a viable low-carbon approach for achieving carbon-neutral treatment of rural wastewater. This study offers novel perspectives on the sustainable development of wastewater treatment in rural areas within the framework of achieving carbon neutrality in the future.

The role of the combined nitrogen-sulfur-carbon cycles for efficient performance of anammox-based systems

The combined anammox/mixotrophic denitrification process was conducted in two granular sequencing batch reactors (SBRs) during a 200-day operation. Both reactors were fed with synthetic medium, but SBR2 was enriched with additional sulfate (SO42-) which influenced sulfate reduction ammonium oxidation (SRAO) and heterotrophic reduction of SO42- by sulfate reducing bacteria. It was hypothesized that the addition of SO42- could positively impact the removal rates of N-S-C compounds. A low C/N ratio (0.4-1.6) was maintained to prevent inhibition of anaerobic ammonium oxidizing bacteria (AnAOB), and alternating chemical oxygen demand (COD) on/off conditions were used to regenerate AnAOB during COD-off phases and heterotrophic denitrifiers during COD-on phases. Stoichiometric analysis showed that introducing SO42- in SBR2 enhanced the ammonium utilization rate, which was approximately 10 % higher compared to SBR1 in the final stage of the experiment (25.8 vs. 22.8 mg N/(g VSS·h)). The total nitrogen removal efficiencies ranged from 62 % to 99 % in both reactors, with SBR2 consistently exhibiting approximately 4 % higher efficiency than SBR1. In SBR2, the maximum overall SO42- utilization efficiency reached 27 % under COD-off conditions, while overall COD utilization was almost complete under COD-on conditions. A strong correlation (R2 = 0.98) was observed between SO42- production and COD utilization. The key players responsible for N and S transformations in response to SO42- addition were Candidatus Brocadia and Chloroflexi - Anaerolineae. This study highlights the potential to enhance the overall efficiency of N-S-C removal by implementing an integrated anammox/mixotrophic denitrification process. The combination of cycles emerges as a sustainable approach for treating wastewater rich in N-S-C compounds.

Metagenomic insights into the mechanism for the rapid enrichment and high stability of Candidatus Brocadia facilitated by Fe(Ⅲ)

The rapid enrichment of anammox bacteria and its fragile resistance to adverse environment are the critical problems facing of anammox processes. As an abundant component in anammox bacteria, iron has been proved to promote the activity and growth of anammox bacteria in the mature anammox systems, but the functional and metabolic profiles in Fe(III) enhanced emerging anammox systems have not been evaluated. Results indicated that the relative abundance of functional genes involved in oxidative phosphorylation, nitrogen metabolism, cofactors synthesis, and extracellular polymers synthesis pathways was significantly promoted in the system added with 5 mg/L Fe(III) (R5). These enhanced pathways were crucial to energy generation, nitrogen removal, cell activity and proliferation, and microbial self-defense, thereby accelerating the enrichment of anammox bacteria Ca. Brocadia and facilitating their resistance to adverse environments. Microbial community analysis showed that the proportion of Ca. Brocadia in R5 also increased to 64.42 %. Hence, R5 could adapt rapidly to the increased nitrogen loading rate and increase the nitrogen removal rate by 108 % compared to the system without Fe(III) addition. However, the addition of 10 and 20 mg/L Fe(III) showed inhibitory effects on the growth and activity of anammox bacteria, which exhibited the lower relative abundance of Ca. Brocadia and unstable or even collapsed nitrogen removal performance. This study not only clarified the concentration range of Fe(III) that promoted and inhibited the enrichment of anammox bacteria, but also deepened our understanding of the functional and metabolic mechanisms underlying enhanced enrichment of anammox bacteria by Fe(III), providing a potential strategy to hasten the start-up of anammox from conventional activated sludge.

Functions and mechanisms of sponge iron-mediated multiple metabolic processes in anaerobic ammonium oxidation

Sponge iron (SI) is a promising material for nitrogen removal from wastewater. This study reveals the potential functions and mechanisms of SI-mediated multiple metabolic processes in the nitrogen removal of Anammox. The results showed that although the SI application prolonged the start-up time of the reactor, achieved efficient and stable nitrogen removal after a successful start-up. The total nitrogen removal efficiency of the SI-Anammox system (92.62%) was 13.30% higher than that of R0 without SI (79.32%). The increase in nitrogen removal performance was accompanied by an increase in SAA and EPS content. Further microbial analysis showed significant enrichment of functional microorganisms, such as Candidatus_Brocadia, Nitrosomonas, Ellin6067, and Nitrospira. Multi-omics evidence suggests that efficient nitrogen removal is ultimately attributable to the enhancement of the specific key Fe- and N-functional genes in Anammox.

Manganese-mediated ammonium removal by a bacterial consortium from wastewater: Experimental proof and biochemical mechanisms

Manganese-redox-mediated nitrogen transformation is promising for ammonium wastewater treatment. However, due to the limited contact between insoluble Mn and the microbe, extracellular electron transfer (EET) inefficiencies become a technical bottleneck in the technical practical application. To overcome this obstacle, humic acid (HA) was introduced to synthesize manganese-humic acid complex (Mn-HA) to increase Mn solubility. The TIN (Total Inorganic Nitrogen) removal rate constant k was 3.18, 1.08, 3.56, 1.13 and 1.05 times higher than CK (Control group) at 10, 15, 20, 40 and 60 mg/L influent nitrate in the MH group, respectively. Mn-HA was inferred to stimulated the nitrogen removal by providing more reaction active sites, bridging Mn-O bonds to transfer electrons and playing a redox role in the respiratory chain. A Mnammox-NDMO (manganese oxide reduction-coupled ammonium oxidation - nitrate/nitrite- dependent manganese oxidation) bacteria consortium was enriched in MH group, containing Mnammox bacteria Geothrix, Geobacter and NDMO bacteria Pseudomonas and Bacillus.

Enhancement and mechanisms of iron-assisted anammox process

Anaerobic ammonium oxidation (anammox) is a sustainable biological nitrogen removal technology that has limited large-scale applications owing to the low cell yield and high sensitivity of anammox bacteria (AnAOB). Fortunately, iron-assisted anammox, being a highly practical method could be an effective solution. This review focused on the iron-assisted anammox process, especially on its performance and mechanisms. In this review, the effects of iron in three different forms (ionic iron, zero-valent iron and iron-containing minerals) on the performance of the anammox process were systematically reviewed and summarized, and the strengthening effects of Fe (II) seem to be more prominent. Moreover, the detailed mechanisms of iron-assisted anammox in previous researches were discussed from macro to micro perspectives. Additionally, applicable iron-assisted methods and unified strengthening mechanisms for improving the stability of nitrogen removal and shortening the start-up time of the system in anammox processes were suggested to explore in future studies. This review was intended to provide helpful information for scientific research and engineering applications of iron-assisted anammox.

Extensive data analysis and kinetic modelling of dosage and temperature dependent role of graphene oxides on anammox

Anaerobic ammonium oxidation (anammox) is carbon friendly biological nitrogen removal process, and recently more focus is given to improving the anammox activity. Because of its high adsorption and modifiability, graphene and its derivative in wastewater treatment have received much attention. However, the specific effects and mechanisms of graphene oxide (GO) and reduced graphene oxide (RGO) on anammox are still controversial. Extensive data analysis was performed to explore the effects of GO and RGO on anammox. Statistical analysis revealed that 100 mg/L GO significantly promoted the anammox process, while 200 mg/L of GO inhibited the anammox process. The promotion of anammox performance under the influence of RGO was dependent on the temperature. The Logistic model was utilized for depicting the variation of nitrogen removal efficiency under promoting dosage of graphene oxides. A neural network model-based analysis was performed to reach anammox's potential mechanisms under the influence of two graphene oxides. Spearman correlation analysis showed that GO and RGO had significant positive correlations with nitrogen removal efficiency and specific anammox activity (p < 0.01), especially for RGO. In addition, the abundance of Planctomycetes and Nitrospirae was positively correlated with the addition of graphene oxides. This work comprehensively unraveled the role of graphene oxide materials on the anammox process and provided practical directions for the enhancement of anammox.

A critical review of exogenous additives for improving the anammox process

Anammox achieves chemoautotrophic nitrogen removal under anaerobic and anoxic conditions and is a low-carbon wastewater biological nitrogen removal process with broad application potential. However, the physiological limitations of AnAOB often cause problems in engineering applications, such as a long start-up time, unstable operation, easily inhibited reactions, and difficulty in long-term strain preservation. Exogenous additives have been considered an alternative strategy to address these issues by retaining microbes, shortening the doubling time of AnAOB and improving functional enzyme activity. This paper reviews the role of carriers, biochar, intermediates, metal ions, reaction substrates, redox buffers, cryoprotectants and organics in optimizing anammox. The pathways and mechanisms of exogenous additives, which are explored to solve problems, are systematically summarized and analyzed in this article according to operational performance, functional enzyme activity, and microbial abundance to provide helpful information for the engineering application of anammox.

Intracellular and extracellular protective mechanisms of the anammox consortia against exogenous sulfadimidine

Antibiotics and antibiotic resistance genes (ARGs) have been recognized as emerging high-risk pollutants for human and animal health. This study systematically investigated the comprehensive effects of a typical antibiotic (sulfadimidine, SDM) in livestock and poultry breeding wastewater on the anammox process, with the aim of elucidating the intracellular and extracellular protective mechanisms of the anammox consortia to the antibiotic stress. Results revealed that the high-concentration SDM significantly reduced the specific anammox activity (SAA) by 37.8%. Changes in the abundance of Candidatus Kuenenia showed a similar trend with that of SAA, while other nitrogen-related microorganisms (e.g., Nitrosomonas and Nitrospira) contributed to the nitrogen removal especially during the inhibitory period. Resistance of the anammox consortia to SDM mainly depended on the protection of ARGs and EPS. Network analysis revealed the host range of eARGs was relatively larger than that of iARGs, and intI1 was closely associated with representative denitrifiers. In addition, metaproteomic analysis and molecular docking results indicated that abundant proteins in EPS could detain SDM in the extracellular matrix through forming complex via hydrogen bond. These findings provide a guidance for the stable operation of anammox process and ARGs transfer controlling.

Function of Fe(III)-minerals in the enhancement of anammox performance exploiting integrated network and metagenomics analyses

Iron is a recognized physiological requirement for microorganisms but, for anaerobic ammonium oxidation (anammox) bacteria, its role extends well beyond that of a nutritional necessity. In this study, the function of two typical Fe(III)-minerals (ferrihydrite and magnetite) in anammox processes was evaluated in the absence/presence of Fe(II) by integrated network and metagenomics analyses. Results showed that Fe-(III) minerals addition increased the activity of cellular processes and pathways associated with granule formation, enabling the peak values of particle size to increase by 144% and 115%, respectively. Notably, ferrihydrite (5 mM) enhanced nitrogen removal by 4.8% and 4.1%, respectively, in the short-term and long-term absence of Fe(II). Ferrihydrite also promoted the retention of anammox bacteria affiliated with phylum Planctomycetes in the reactor, contributing to an 11% higher abundance with ferrihydrite amendment when compared with the control (without iron additions) in the short-term absence of Fe(II). Network-based analyses revealed that ferrihydrite facilitated the microbial community to form densely clustered and complex topologies to improve resistance to environmental disturbance (i.e., Fe(II) deficiency), and effectively increased the underlying cooperation and facilitation in the community. Metagenomic analysis revealed that there was limited promotion of anammox central metabolism by the extra addition of Fe(III)-minerals in the presence of Fe(II), highlighting the poor utilization of Fe(III)-minerals by anammox bacteria under Fe(II) sufficiency. This study deepens our understanding of the function of Fe(III)-minerals in anammox systems at the community and functional level, and provides a fundamental basis for developing Fe-based anammox enhancement technologies.

Anammox Bacteria Are Potentially Involved in Anaerobic Ammonium Oxidation Coupled to Iron(III) Reduction in the Wastewater Treatment System

Anaerobic ammonium oxidation coupled to nitrite reduction (termed as Anammox) was demonstrated as an efficient pathway to remove nitrogen from a wastewater treatment system. Recently, anaerobic ammonium oxidation was also identified to be linked to iron(III) reduction (termed Feammox) with dinitrogen, nitrite, or nitrate as end-product, reporting to enhance nitrogen removal from the wastewater treatment system. However, little is known about the role of Anammox bacteria in the Feammox process. Here, slurry from wastewater reactor amended with ferrihydrite was employed to investigate activity of Anammox bacteria in the Feammox process using the ¹⁵N isotopic tracing technique combined with 16S rRNA gene amplicon sequencing. A significantly positive relationship between rates of ¹⁵N₂ production and iron(III) reduction indicated the occurrence of Feammox during incubation. Relative abundances of Anammox bacteria including Brocadia, Kuenenia, Jettenia, and unclassified Brocadiaceae were detected with low relative abundances, whereas Geobacteraceae dominated in the treatment throughout the incubation. ¹⁵N₂ production rates significantly positively correlated with relative abundances of Geobacter, unclassified Geobacteraceae, and Anammox bacteria, revealing their contribution to nitrogen generation via Feammox. Overall, these findings suggested Anammox bacteria or cooperation between Anammox bacteria and iron(III) reducers serves a potential role in Feammox process.

Responses of anammox process to elevated Fe(III) stress: Reactor performance, microbial community and functional genes

The aim of present study was to re-evaluate the impacts of elevated Fe(III) stress on anaerobic ammonium oxidation (anammox) process. The results indicated that long-term low concentration Fe(III) (5 and 10 mg/L) exposure significantly improved the nitrogen removal efficiency of anammox process, while high concentration Fe(III) (50 and 100 mg/L) significantly deteriorated the reactor performance. Batch assays showed that the specific anammox activity, heme c content and hydrazine dehydrogenase activity were significantly increased and decreased under low and high concentration Fe(III) exposure, respectively, indicating an enhancement and inhibition of anammox activity. Moreover, the presence of high concentration Fe(III) significantly shifted the anammox community structure. Ca. Brocadia was the predominant anammox genus, whose abundance decreased from 14.26% to 8.13% as Fe(III) concentration increased from 0 to 100 mg/L. In comparison, the abundance of denitrifiers progressively increased from 3.70% to 6.68% with increasing Fe(III) concentration. These suggested that different functional bacteria differed in their responses to Fe(III) stress. Furthermore, long-term Fe(III) exposure significantly up-regulated the abundances of genes associated with nitrogen metabolism and Fe(III) reduction. Overall, the obtained findings are expected to advances our understanding of the responses of anammox process to elevated Fe(III) stress.

Insights into microbial community variability and functional genes of various Candidatus Scalindua-based anammox processes treating nitrogen-rich saline wastewater

Marine anammox bacteria (MAB) has been enriched in four sequencing batch reactors to treat nitrogen-rich saline wastewater. The community variability and cell activity of MAB were studied under different operating conditions. Besides, a novel hydrazine oxidoreductase (Hzo) primer set was designed and used for fast detection of MAB. The results indicated that, independent of operating conditions, Candidatus Scalindua wagneri was the dominant species in nitrogen-rich saline wastewater treatment. Low inoculation pretreatment temperature was a useful operational method to enhance the MAB abundance. Both the enzyme synthesis and cell penetrativity were promoted by Fe(III) addition, which benefited to improve the nitrogen removal performance. High influent NH₄⁺-N and NO₂^--N could decrease the synthesis of enzyme and protein which related with nitrogen removal from saline wastewater through MAB. The Hzo gene was an effective functional gene for specific and fast detection of MAB in engineered systems.

Community Composition and Spatial Distribution of N-Removing Microorganisms Optimized by Fe-Modified Biochar in a Constructed Wetland

Microbial nitrogen (N) removal capability can be significantly enhanced in a horizontal subsurface flow constructed wetland (HSCW) amended by Fe-modified biochar (FeB). To further explore the microbiological mechanism of FeB enhancing N removal, nirS- and nirK-denitrifier community diversities, as well as spatial distributions of denitrifiers and anaerobic ammonium oxidation (anammox) bacteria, were investigated in HSCWs (C-HSCW: without biochar and FeB; B-HSCW: amended by biochar; FeB-HSCW: amended by FeB) treating tailwater from a wastewater treatment plant, with C-HSCW without biochar and FeB and B-HSCW amended by biochar as control. The community structures of nirS- and nirK-denitrifiers in FeB-HSCW were significantly optimized for improved N removal compared with the two other HSCWs, although no significant differences in their richness and diversity were detected among the HSCWs. The spatial distributions of the relative abundance of genes involved in denitrification and anammox were more heterogeneous and complex in FeB-HSCW than those in other HSCWs. More and larger high-value patches were observed in FeB-HSCW. These revealed that FeB provides more appropriate habitats for N-removing microorganisms, which can prompt the bacteria to use the habitats more differentially, without competitive exclusion. Overall, the Fe-modified biochar enhancement of the microbial N-removal capability of HSCWs was a result of optimized microbial community structures, higher functional gene abundance, and improved spatial distribution of N-removing microorganisms.

Optimizing anammox capacity for weak wastewater in an AnSBBR using aerobic activated sludge as inoculation

Process optimization is essential for improving the efficiency of anaerobic ammonium oxidation (anammox) process in a practical application. In this study, an anaerobic sequence biofilm batch reactor (AnSBBR) inoculated with aerobic activated sludge was chosen as an efficient mainstream anammox reactor for treating low-nitrogen wastewater. To optimize the AnSBBR-anammox process, eight different operation stages lasting for a total of 215 days were conducted by regulating key process parameters. Principal components analysis revealed significant effects of the substrate ratio (SR) and volumetric exchange ratio (VER) on anammox performance, while other parameters (cycle time, hydraulic retention time and nitrogen loading rate) played minor roles. The highest removal efficiencies for ammonia and total nitrogen, respectively, reached 99.8% and 95.3% under optimal conditions. High-throughput sequencing found the anammox species Candidatus Brocadia and Candidatus Kuenenia made up as much as 8.5% and 3.5%, respectively, of the microbial community. Redundancy analysis indicated that these taxa were also greatly influenced by operating parameters, particularly SR and VER. This research helps to decode the correlations among nitrogen removal capacity, process parameters and the microbial community to enhance anammox in an AnSBBR system.

Effects of Fe3+ on microbial communities shifts, functional genes expression and nitrogen transformation during the start-up of Anammox process

In this study, the effect of Fe³⁺ on the start-up of Anammox process was investigated. Four EGSB reactors were operated with the addition of 0 (R1), 0.04 (R2), 0.08 (R3) and 0.14 (R4) mmol/L Fe³⁺, respectively. The results showed that Fe³⁺ remarkably improved the nitrogen loading rate (NLR) and operation efficiency of the reactor. After 180 days, the influent NH₄⁺-N concentration in the four reactors was 201.4, 301.8, 343.2, 380.2 mg N/L, and the NLR was 589.3, 877.6, 993.0, 1105.8 mg N/(L·d), respectively. And the nitrogen removal rate (NRR) in R2, R3 and R4 was respectively 1.54, 1.73 and 1.94 times of that in R1. High throughput sequencing revealed that Fe³⁺ could promote the enrichment of Anammox bacteria Candidatus Brocadia. Moreover, the analysis by qPCR indicated that the abundance of Anammox 16S rRNA gene and the functional gene hzsB increased, which showed a positive correlation with the concentration of Fe³⁺.

Construction of autotrophic nitrogen removal system based on zero-valent iron (ZVI): performance and mechanism

In this study, the performance and mechanism of nitrogen removal in sequencing batch reactors (SBRs) with and without zero-valent iron (ZVI) was investigated. The results showed that ZVI had a capacity to promote NH₄⁺-N conversion, NO₂^--N accumulation and total inorganic nitrogen (TIN) removal, with the TIN removal rate being increased by 29.45%. The ZVI also had a significant impact on microbial community structure by means of high-throughput pyrosequencing, increasing the enrichment of Anammox (anaerobic ammonium oxidation) bacteria Candidatus Brocadia and Feammox (anaerobic ferric ammonium oxidation) bacteria Ignavibacterium. With ZVI addition, the main pathway of nitrogen removal was changed from nitrification-heterotrophic denitrification to Anammox and Feammox.

Bioaugmentation of marine anammox bacteria (MAB)-based anaerobic ammonia oxidation by adding Fe(III) in saline wastewater treatment under low temperature

This work investigated a new method of using Fe(III) to enhance the reactor performance enriched with marine anammox bacteria (MAB). The experiments were conducted in a sequencing batch reactor at low temperature (15 °C), high salinity (35 g/L) and varying Fe(III) concentrations (0-250 mg/l). The results of this study showed that at low Fe(III) (6 mg Fe/L), the rate of ammonium removal, nitrite removal and specific anammox activity remarkably increased to 0.42 kg/(m³·d), 0.53 kg/(m³·d), 0.56 kg/(kg·d), respectively. However, Fe(III) at above 120 mg Fe/L, the reaction time was significantly shortened from 5 to 2 h. MAB-based nitrite removal could be predicated based on the change of pH (ΔpH) and oxidation-reduction potential (ΔORP). Kinetics analysis demonstrated, the "Remodified Logistic Model" could simulate the Fe(III) enhanced anammox process. Overall, this research shed the light of designing a new high-rate anaerobic nitrogen removal technology for carbon insufficient, nitrogen-laden saline wastewater.

Impacts of salt shocking and the selection of a suitable reversal agent on anammox

In this study, an anaerobic ammonium oxidation (anammox) reactor, which was inhibited by a salinity of 50 g NaCl L^-1 during a long-term experiment, was rapidly restarted by decreasing the salinity to 20 g NaCl L^-1 and adding biomass. The effects of exposure time and shock concentrations on the anammox reactor indicate that anammox granular sludge has a high tolerance to salinity and strong ability for self-recovery. The nitrogen removal efficiency was higher than 50% after exposure to 50 g NaCl L^-1 for 66 h. To shorten the time taken for effluent nitrogen concentrations to attain national standards (GB18918-2002) after the anammox reactor was shocked with NaCl, reactor performance (i.e., recovery) after the addition of K⁺, glycine betaine, Fe²⁺, and hydroxylamine were compared after the reactor was inhibited by 80 g NaCl L^-1. The results indicate that hydroxylamine was the best reversal agent. The recovery time of the anammox reactor could be shortened by 50% following the addition of hydroxylamine. The most favorable NH₂OH-N/NO₂^--N concentration ratio for improving nitrogen removal of anammox was 1:11. The abundances of Planctomycetes and its genera Candidatus Kuenenia and Brocadiaceae_g_unclassified increased after repeated salinity shock-recovery phases, indicating that Candidatus Kuenenia and Brocadiaceae_g_unclassified are able to adapt to NaCl shocking and recovery.

Effect of ferric hydroxide on membrane fouling in membrane bioreactor treating pharmaceutical wastewater

Membrane fouling is considered as a main drawback for MBR technology especially treating industrial wastewater. Therefore, this study aimed to investigate the effect of fouling in membrane bioreactor (MBR) treating pharmaceutical wastewater with the addition of ferric hydroxide. Two identical lab-scale MBRs, namely, a control MBR (Co-MBR) and an enhanced MBR dosed with ferric hydroxide (Fe-MBR), were operated in parallel. The results demonstrate membrane fouling was retarded by 35% with the addition of iron. Further exploration of membrane fouling mechanisms showed iron addition resulted in increase in biomass floc size, enhancement of bacteria activity and reduction of dissolved organic concentration, especially carbohydrate, biopolymer and low molecular weight compounds concentrations in mixed liquor. There was also lower abundance of bacterial associated with biofilm formation in the Fe-MBR compared with the Co-MBR. These findings collectively contributed to the positive impacts on membrane fouling mitigation.

The Phylogeny, Biodiversity, and Ecology of the Chloroflexi in Activated Sludge

It is now clear that several of the filamentous bacteria in activated sludge wastewater treatment plants globally, are members of the phylum Chloroflexi. They appear to be more commonly found in treatment plants designed to remove nitrogen (N) and phosphorus (P), most of which operate at long sludge ages and expose the biomass to anaerobic conditions. The Chloroflexi seem to play an important beneficial role in providing the filamentous scaffolding around which flocs are formed, to feed on the debris from lysed bacterial cells, to ferment carbohydrates and to degrade other complex polymeric organic compounds to low molecular weight substrates to support their growth and that of other bacterial populations. A few commonly extend beyond the floc surface, while others can align in bundles, which may facilitate interfloc bridging and hence generate a bulking sludge. Although several recent papers have examined the phylogeny and in situ physiology of Chloroflexi in activated sludge plants in Denmark, this review takes a wider look at what we now know about these filaments, especially their global distribution in activated sludge plants, and what their functional roles there might be. It also attempts to outline why such information might provide us with clues as to how their population levels may be manipulated, and the main research questions that need addressing to achieve these outcomes.

Enhanced nitrogen removal through marine anammox bacteria (MAB) treating nitrogen-rich saline wastewater with Fe(III) addition: Nitrogen shock loading and community structure

Marine anammox bacteria (MAB) were used to treat nitrogen-rich saline wastewater with Fe(III) addition under nitrogen shock loading. Ammonia loading rate (ALR) and nitrite loading rate (NLR) gradually increased from 0.033 and 0.039 to 0.68 and 0.89 kg/(m³·d), respectively. With 5 mg/L Fe(III) addition, ammonia removal rate (ARR) and nitrite removal rate (NRR) reached maximal values of 0.56 and 0.60 kg/(m³·d), respectively. The value of ΔNO₂^--N/ΔNH₄⁺-N was lower than theoretical ratio due to existing marine Feammox process. The growth rate of MAB was accelerated by Fe(III) and it dominated the reactor (27.70%). Besides, MAB were synergized with Marinicella and Caldithrix to achieve higher total nitrogen removal. Haldane model was proper to analyze and predict the effect resulting from nitrite on the activity of MAB under nitrogen shock loading. Overall, this study provides novel insights into the effect of Fe(III) on MAB treating nitrogen-rich wastewater.

Roles of MnO2 on performance, sludge characteristics and microbial community in anammox system

The long-term impacts of MnO₂ on performance, sludge characteristics and microbial community of biogranule-based anaerobic ammonium oxidation (anammox) process were evaluated in an up-flow anaerobic sludge blanket reactor. It was found that the total nitrogen removal efficiency of reactor was fluctuated between 90%-93% at 1-200mgL^-1 MnO₂. Notably, the specific anammox activity was increased to maximum value of 657.3±10.6mgTNg^-1VSSd^-1 at 50mgL^-1 MnO₂ and then slightly decreased, but still higher than that achieved at 0-15mgL^-1 MnO₂, which had similar variation trends to the content of heme c and extracellular polymeric substances in anammox granules. High throughput sequencing indicated that MnO₂ could improve the microbial richness and diversity of anammox granules and Candidatus Kuenenia was always the dominant species, and its abundance continued to increase to 21.3% at the end of operational experiment. Therefore, MnO₂ could be applied to enhance the anammox process and the optimal influent MnO₂ concentration was lower than 50mgL^-1 in view of the reactor performance and cost issues.

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

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

Bacterial community evolutions driven by organic matter and powder activated carbon in simultaneous anammox and denitrification (SAD) process

A distinct shift of bacterial community driven by organic matter (OM) and powder activated carbon (PAC) was discovered in the simultaneous anammox and denitrification (SAD) process which was operated in an anti-fouling submerged anaerobic membrane bio-reactor. Based on anammox performance, optimal OM dose (50 mg/L) was advised to start up SAD process successfully. The results of qPCR and high throughput sequencing analysis indicated that OM played a key role in microbial community evolutions, impelling denitrifiers to challenge anammox's dominance. The addition of PAC not only mitigated the membrane fouling, but also stimulated the enrichment of denitrifiers, accounting for the predominant phylum changing from Planctomycetes to Proteobacteria in SAD process. Functional genes forecasts based on KEGG database and COG database showed that the expressions of full denitrification functional genes were highly promoted in R_C, which demonstrated the enhanced full denitrification pathway driven by OM and PAC under low COD/N value (0.11).