Fixed nitrogen removal mechanisms associated with sulfur cycling in tropical wetlands

Response of microbial communities to exogenous nitrate nitrogen input in black and odorous sediment

Since nitrate nitrogen (NO3--N) input has proved an effective approach for the treatment of black and odorous river waterbody, it was controversial whether the total nitrogen concentration standard should be raised when the effluent from the sewage treatment plant is discharged into the polluted river. To reveal the effect of exogenous nitrate (NO3--N) on black odorous waterbody, sediments with different features from contaminated rivers were collected, and the changes of physical and chemical characteristics and microbial community structure in sediments before and after the addition of exogenous NO3--N were investigated. The results showed that after the input of NO3--N, reducing substances such as acid volatile sulfide (AVS) in the sediment decreased by 80 % on average, ferrous (Fe2+) decreased by 50 %, yet the changing trend of ammonia nitrogen (NH4+-N) in some sediment samples increased while others decreased. High-throughput sequencing results showed that the abundance of Thiobacillus at most sites increased significantly, becoming the dominant genus in the sediment, and the abundance of functional genes in the metabolome increased, such as soxA, soxX, soxY, soxZ. Network analysis showed that sediment microorganisms evolved from a single sulfur oxidation ecological function to diverse ecological functions, such as nitrogen cycle nirB, nirD, nirK, nosZ, and aerobic decomposition. In summary, inputting an appropriate amount of exogenous NO3--N is beneficial for restoring and maintaining the oxidation states of river sediment ecosystems.

A mixed blessing of influent leachate microbes in downstream biotreatment systems of a full-scale landfill leachate treatment plant

In landfill leachate treatment plants (LLTPs), the microbiome plays a pivotal role in the decomposition of organic compounds, reduction in nutrient levels, and elimination of toxins. However, the effects of microbes in landfill leachate influents on downstream treatment systems remain poorly understood. To address this knowledge gap, we collected 23 metagenomic and 12 metatranscriptomic samples from landfill leachate and activated sludge from various treatment units in a full-scale LLTP. We successfully recovered 1,152 non-redundant metagenome-assembled genomes (MAGs), encompassing a wide taxonomic range, including 48 phyla, 95 classes, 166 orders, 247 families, 238 genera, and 1,152 species. More diverse microbes were observed in the influent leachate than in the downstream biotreatment systems, among which, an unprecedented ∼30 % of microbes with transcriptional expression migrated from the influent to the biological treatment units. Network analysis revealed that 399 shared MAGs across the four units exhibited high node centrality and degree, thus supporting enhanced interactions and increased stability of microbial communities. Functional reconstruction and genome characterization of MAGs indicated that these shared MAGs possessed greater capabilities for carbon, nitrogen, sulfur, and arsenic metabolism compared to non-shared MAGs. We further identified a novel species of Zixibacteria in the leachate influent with discrete lineages from those in other environments that accounted for up to 17 % of the abundance of the shared microbial community and exhibited notable metabolic versatility. Meanwhile, we presented groundbreaking evidence of the involvement of Zixibacteria-encoded genes in the production of harmful gas emissions, such as N2O and H2S, at the transcriptional level, thus suggesting that influent microbes may pose safety risks to downstream treatment systems. In summary, this study revealed the complex impact of the influent microbiome on LLTP and emphasizes the need to consider these microbial characteristics when designing treatment technologies and strategies for landfill leachate management.

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.

Impact of current anthropogenic activities on Blesbokspruit wetland microbiome and functions

Till present, natural wetlands have been continuously subjected to intensive pollution stress in recent years, mainly because of the rapidly growing industrialization and urbanization that are associated with a myriad of anthropogenic activities and land use practices. These man-made sources of pollution change the chemical properties of the natural wetlands, which in turn alter their microbial ecological biodiversity and functions. For the first time, the impact of the current anthropogenic activities and land use practices on the Blesbokspruit wetland chemical status and their consequential effect on the microbial structure and functions were investigated. Sites of high pollution intensity were identified using geographic information systems mapping (GISMapping) and the wetland microbiome and functional profile were studied through the use of high throughput shotgun metagenomics sequencing analysis. The predominant phyla that stemmed along the Blesbokspruit wetland were found to be Proteobacteria which was more dominant in water (93 %) than in the sediments (89 %), followed by firmicutes which was more abundant in sediments (9 %) than in water (6 %), and Bacteroidetes were relatively low in abundance within both the sediments (2 %) and the overlying water (1 %). The genera Klebsiella (70.4 %-28.2 %), Citrobacter (52.0 %-30.6 %), Escherichia (51.0 %-8.4 %), and Lynsinibacillus (9.3 %-1.5 %) were observed in most water and sediment samples. Within the six polluted sites, Site 2 was found to be the most highly polluted site in the Blesbokspruit wetland with very high COD (900 mg/L), TOC (11.60 mg/L), NO3- (39.74 mg/L), NO2- (12.64 mg/L), PO43 (4.14 mg/L), Fl- (143.88 mg/L), Cl- (145.95 mg/L) concentrations recorded in the water and high levels of TOC (0.37 mg/L), TC (6.92 %), TN (1.82 %), TS (0.53 %) in sediments. The microbial community structure and functions were found to be strongly influenced by the high organic content from the intense agricultural activities and sewage spillages and heavy metals from the mining activities nearby.

A predictive model for determining the nitrite concentration in the effluent of an anammox reactor using ensemble regression tree algorithm

Anaerobic ammonium oxidation (anammox) is a cost-effective biological nitrogen removal method for treating wastewater. Nitrite has strong negative effect on microbial activity of anammox bacteria, while the conventional equitment available for determining nitrite on-line is challenging due to high price. By knowing the concentration of nitrite in the effluent, its concentration in the reactor can be controlled accordingly. To investigate this, an ensemble regression tree algorithm was used to establish the predictive model proposed in the current work. Moreover, the Bayesian algorithm was adopted to systematically optimize various parameters of machine learning algorithms. The predicted concentrations of nitrite were in good agreement with the observed values, and the coefficient of determination (R2) and root mean squared error (RMSE) values reached 0.91 and 4.81, respectively. Furthermore, the model established by the ensemble regression tree algorithm was compared with models established by commonly used machine learning algorithms. Finally, the established models were applied to another anammox reactor, and the predicted results of ensemble regression tree model were found to be in good agreement with the experimental values with R2 and RMSE values of 0.84 and 6.34, respectively.

Vertically stratified methane, nitrogen and sulphur cycling and coupling mechanisms in mangrove sediment microbiomes

BACKGROUND

Mangrove ecosystems are considered as hot spots of biogeochemical cycling, yet the diversity, function and coupling mechanism of microbially driven biogeochemical cycling along the sediment depth of mangrove wetlands remain elusive. Here we investigated the vertical profile of methane (CH₄), nitrogen (N) and sulphur (S) cycling genes/pathways and their potential coupling mechanisms using metagenome sequencing approaches.

RESULTS

Our results showed that the metabolic pathways involved in CH₄, N and S cycling were mainly shaped by pH and acid volatile sulphide (AVS) along a sediment depth, and AVS was a critical electron donor impacting mangrove sediment S oxidation and denitrification. Gene families involved in S oxidation and denitrification significantly (P < 0.05) decreased along the sediment depth and could be coupled by S-driven denitrifiers, such as Burkholderiaceae and Sulfurifustis in the surface sediment (0-15 cm). Interestingly, all S-driven denitrifier metagenome-assembled genomes (MAGs) appeared to be incomplete denitrifiers with nitrate/nitrite/nitric oxide reductases (Nar/Nir/Nor) but without nitrous oxide reductase (Nos), suggesting such sulphide-utilizing groups might be an important contributor to N₂O production in the surface mangrove sediment. Gene families involved in methanogenesis and S reduction significantly (P < 0.05) increased along the sediment depth. Based on both network and MAG analyses, sulphate-reducing bacteria (SRB) might develop syntrophic relationships with anaerobic CH₄ oxidizers (ANMEs) by direct electron transfer or zero-valent sulphur, which would pull forward the co-existence of methanogens and SRB in the middle and deep layer sediments.

CONCLUSIONS

In addition to offering a perspective on the vertical distribution of microbially driven CH₄, N and S cycling genes/pathways, this study emphasizes the important role of S-driven denitrifiers on N₂O emissions and various possible coupling mechanisms of ANMEs and SRB along the mangrove sediment depth. The exploration of potential coupling mechanisms provides novel insights into future synthetic microbial community construction and analysis. This study also has important implications for predicting ecosystem functions within the context of environmental and global change. Video Abstract.

Highly Enriched Anammox Bacteria with a Novel Granulation Model Regulated by Epistylis spp. in Domestic Wastewater Treatment

Anammox granulation is an efficient solution proffered to enrich slow-growing anammox bacteria (AnAOB), but the lack of effective granulation strategies for low-strength domestic wastewater impedes its application. In this study, a novel granulation model regulated by Epistylis spp. for highly enriched AnAOB was revealed for the first time. Notably, anammox granulation was achieved within 65 d of domestic wastewater treatment. The stalks of Epistylis spp. were found to act as the skeleton of granules and provide attachment points for bacterial colonization, and the expanded biomass layer in turn provided more area for the unstalked free-swimming zooids. Additionally, Epistylis spp. exerted much less predation stress on AnAOB than on nitrifying bacteria, and AnAOB tended to grow in aggregates in the interior of granules, thus favoring the growth and retention of AnAOB. Ultimately, the relative abundance of AnAOB reached up to a maximum of 8.2% in granules (doubling time of 9.9 d) compared to 1.1% in flocs (doubling time of 23.1 d), representing the most substantial disparity between granules and flocs. Overall, our findings advance the current understanding of interactions involved in granulation between protozoa and microbial communities and offer new insight into the specific enrichment of AnAOB under the novel granulation model.

Associations of soil bacterial diversity and function with plant diversity in Carex tussock wetland

Some species of Carex can form tussocks, which are usually distributed in valleys and flood plains. The soil microbial community diversity and function of micro–habitats formed by tussocks are associated with plant diversity, and research on these associations can guide Carex tussock wetland restoration. In this study, we selected tussock wetlands dominated by Carex appendiculata, including natural wetlands (NW), artificially restored wetlands (ARW), and naturally restored wetlands (NRW), and investigated plant diversity. Soil samples were collected from the quadrats of each sample plot with the maximum (ma), median (me), and minimum (mi) plant Shannon index values, and high-throughput sequencing was used to analyze the bacterial community composition, diversity, and functions. The plant diversity indexes of neither ARW nor NRW significantly differed from that of NW, but the companion species in NRW were hygrophytes and mesophytes, in contrast to only hygrophytes serving as companion species in NW and ARW. The soil bacterial communities at the operational taxonomic unit level of the nine quadrats with different plant Shannon index values significantly (p &lt; 0.01) differed. The relative abundances of the dominant phyla (Proteobacteria, Chloroflexi, and Bacteroidetes) and the dominant genera (Geobacter, Sideroxydans, and Clostridium except for unassigned genera) significantly (p &lt; 0.05) differed under the different levels of plant diversity. The plant Shannon index, soil moisture content, total organic carbon, N, and P were significantly (p &lt; 0.05 or p &lt; 0.01) correlated with the bacterial Shannon index. The phylogenetic diversity of the bacterial community in NW was significantly (p &lt; 0.0001) different from those in ARW and NRW, and that in ARW was also significantly (p &lt; 0.05) different from that in NRW. The functional groups of bacterial communities associated with plant diversity. In the NWme, ARWme, and NRWme bacterial communities, the relative proportions of functional groups related to soil N cycle were higher, but those related to soil S and C cycles were lower. Considering the rehabilitation of both plant and microbial communities, the methods used for establishing the ARW are recommended for Carex tussock wetland restoration.

Riddles of Lost City: Chemotrophic Prokaryotes Drives Carbon, Sulfur, and Nitrogen Cycling at an Extinct Cold Seep, South China Sea

Deep-sea cold seeps are one of the most productive ecosystems that sustained by hydrocarbons carried by the fluid. Once the seep fluid ceases, the thriving autotrophic communities die out, terming as the extinct seep. But heterotrophic fauna can still survive even for thousands of years. The critical role of prokaryotes in active seeps are well defined, but their functions in extinct seeps are poorly understood to date. Here, we clarified the diversity, taxonomic specificity, interspecies correlation, and metabolic profiles of sediment prokaryotes at an extinct seep site of Haima cold seep, South China Sea. Alpha diversity of archaea significantly increased, while that of bacteria remained unchanged in extinct seep compared to active seep. However, archaea composition did not differ significantly at extinct seep from active or nonseep sites based on weighted-unifrac dissimilarity, while bacteria composition exhibited significant difference. Distribution of archaea and bacteria showed clear specificity to extinct seeps, indicating the unique life strategies here. Prokaryotes might live chemolithoautotrophically on cycling of inorganic carbon, sulfur, and nitrogen, or chemoorganotrophically on recycling of hydrocarbons. Notably, many of the extinct seep specific species and networked keystone lineages are classified as Proteobacteria. Regarding the functional diversity and metabolic flexibility of this clade, Proteobacteria is supposed to integrate the geochemical cycles and play a critical role in energy and resource supplement for microbiome in extinct seep. Collectively, our findings shed lights on the microbial ecology and functional diversity in extinct seeps, providing new understanding of biogeochemical cycling after fluid cessation. IMPORTANCE This research paper uncovered the potential mechanisms for microbiota mediated geochemical cycling in extinct cold seep, advancing our understanding in deep sea microbiology ecology.

A review: Manganese-driven bioprocess for simultaneous removal of nitrogen and organic contaminants from polluted waters

Water pollutants, such as nitrate and organics have received much attention for their harms to ecological environment and human health. The redox transformation between Mn(Ⅱ) and Mn(Ⅳ) for nitrogen and organics removal have been recognized for a long time. Mn(Ⅱ) can act as inorganic electron donor to drive autotrophic denitrification so as to realize simultaneous removal of Mn(Ⅱ), nitrate and organic pollutants. Mn oxides (MnOx) also play an important role in the adsorption and degradation of some organic contaminants and they can change or create new oxidation pathways in the nitrogen cycle. Herein, this paper provides a comprehensive review of nitrogen and organic contaminants removal pathways through applying Mn(Ⅱ) or MnOx as forerunners. The main current knowledge, developments and applications, pollutants removal efficiency, as well as microbiology and biochemistry mechanisms are summarized. Also reviewed the effects of factors such as the carbon source, the environmental factors and operation conditions have on the process. Research gaps and application potential are further proposed and discussed. Overall, Mn-based biotechnology towards advanced wastewater treatment has a promising prospect, which can achieve simultaneous removal of nitrogen and organic contaminants, and minimize sludge production.

Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 ± 1 °C (A_med) and 15 ± 3 °C (A_low). Results showed that anammox was successful after 138 d for A_low, only 7 d longer than A_med. Stable operation to 194 d in A_low, the nitrogen loading rate (NLR) increased to 1.01 kg m^-3·d^-1, giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of A_med (90%). More extracellular polymeric substance (EPS) was produced by the microbes of A_low compared to A_med, which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in A_med with relative abundance 7.4%, while the "cold-tolerant" Candidatus Kuenenia with 4% was the dominant anammox bacteria in A_low. The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Nutrient dynamics and microbial community response in macrophyte-dominated lakes: Implications for improved restoration strategies

Although lakes dominated by macrophytes are conducive to ecological balance, this balance is easily disrupted by excessive nutrients flowing into the lake. However, knowledge of whether excessive nutrients lead to different microbial environmental vulnerabilities in the lake sediment between macrophyte-dominated areas and macrophyte-free areas is a prerequisite for the implementation of targeted protection measures. In this study, we investigated bacterial communities in sediments using high-throughput sequencing of 16S rRNA genes. Our results showed that the sources of total nitrogen (TN) and organic matter (OM) were related to the macrophytes. The structure, drivers, and interspecific associations of bacterial community, which were more susceptible to increased changes in TN and OM, differed significantly between macrophyte-dominated areas and macrophyte-free areas. More precisely, the lake edge, where was occupied by macrophytes, had a higher proportion of deterministic phylogenetic turnover (88.89%) than other sites, as well as a wider ecological niche and a tighter network structure. Further, as the difference in TN increased, the main assembly processes in surface sediments changed from stochastic to deterministic. However, the majority of phyla from the lake edge showed a greater correlation with excessive nutrients, and the selection of the community by excessive nutrients was more obvious at the edge of the lake. In addition, our results demonstrated that the stability of the bacterial community in macrophyte-free areas is greater than in macrophyte-dominated areas, while an excessively high deterministic process ratio and nutrient (TN and OM) concentration significantly reduced bacterial community stability at macrophyte-dominated areas. Taken together, these results provide a better understanding of the effects of excessive nutrients derived from macrophytes on bacterial community patterns, and highlight the importance of avoiding the accumulation of TN and OM in macrophyte-dominated areas to enhance the sustainability of the ecosystem after restoration of lakes with macrophytes.

A review of anammox-based nitrogen removal technology: From microbial diversity to engineering applications

The anaerobic ammonium oxidation (anammox) process has the advantages of high efficiency and low energy consumption, so it has broad application prospects in biological denitrification of wastewater. However, the application of anammox technology to existing wastewater treatment is still challenging. The main problems are the insufficient supply of nitrite and the susceptibility of anammox bacteria to environmental factors. In this paper, from the perspective of the diversity of anammox bacteria, the habitats and characteristics of anammox bacteria of different genera were compared. At the same time, laboratory research and engineering applications of anammox technology in treating wastewater from different sources were reviewed, and the progress of and obstacles to the practical application of anammox technology were clarified. Finally, a focus for future research was proposed to intensively study the water quality barrier factors of anammox and its regulation strategies. Meanwhile, a combined process was developed and optimized on this basis.

Niche differentiation and symbiotic association among ammonia/nitrite oxidizers in a full-scale rotating biological contactor

Although the distribution of ammonia/nitrite oxidizers had been profiled in different habitats, current understanding is still limited regarding their niche differentiation in the integrated biofilm reactors, the symbiotic associations of ammonia/nitrite oxidizers, as well as the parasitic interaction between viruses and those functional organisms involved in the nitrogen cycle. Here, the integrated metagenomics and metatranscriptomics are applied to profile the ammonia/nitrite oxidizers communities and transcriptional activities changes along the flowpath of a concatenated full-scale rotating biological contactor (RBC) (frontend Stage-A and backend Stage-B). 19 metagenome-assembled genomes (MAGs) of ammonia/nitrite oxidizers were recovered by using a hybrid assembly approach, including four ammonia-oxidizing bacteria (AOB), two ammonia-oxidizing archaea (AOA), two complete ammonia oxidation bacteria (comammox), eight nitrite-oxidizing bacteria (NOB), and three anaerobic ammonium oxidation bacteria (anammox). Diverse AOB and anammox dominated Stage-A and collectively contributed to nitrogen conversion. With the decline of ammonia concentration along the flowpath, comammox and AOA appeared and increased in relative abundance in Stage-B, accounting for 8.8% of the entire community at the end of this reactor, and their dominating role in nitrogen turnover was indicated by the high transcription activity of their corresponding function genes. Moreover, the variation in the abundance of viruses infecting ammonia and nitrite oxidizers suggests that viruses likely act as a biotic factor mediating ammonia/nitrite oxidizer populations. This study demonstrates that complex factors shaped niche differentiation and symbiotic associations of ammonia/nitrite oxidizers in the RBC and highlights the importance of RBCs as model systems for the investigation of biotic and abiotic factors affecting the composition of microbiomes.

Resilience of organohalide-detoxifying microbial community to oxygen stress in sewage sludge

Organohalide pollutants are prevalent in the environment, causing harms to wildlife and human. Organohalide-respiring bacteria (OHRB) could detoxify these pollutants in anaerobic environments, but the most competent OHRB (i.e., Dehalococcoides) is susceptible to oxygen. This study reports exceptional resistance and resilience of sewage sludge microbial communities to oxygen stress for attenuation of structurally distinct organohalide pollutants, including tetrachloroethene, tetrabromobisphenol A, and polybrominated diphenyl ethers. The dehalogenation rate constant of these organohalide pollutants in oxygen-exposed sludge microcosms was maintained as 74-120% as that in the control without oxygen exposure. Subsequent top-down experiments clarified that sludge flocs and non-OHRB contributed to alleviating oxygen stress on OHRB. In the dehalogenating microcosms, multiple OHRB (Dehahlococcoides, Dehalogenimonas, and Sulfurospirillum) harboring distinct reductive dehalogenase genes (pceA, pteA, tceA, vcrA, and bdeA) collaborated to detoxify organohalide pollutants but responded differentially to oxygen stress. Comprehensive microbial community analyses (taxonomy, diversity, and structure) demonstrated certain resilience of the sludge-derived dehalogenating microbial communities to oxygen stress. Additionally, microbial co-occurrence networks were intensified by oxygen stress in most microcosms, as a possible stress mitigation strategy. Altogether the mechanistic and ecological findings in this study contribute to remediation of organohalide-contaminated sites encountering oxygen disturbance.

Feammox in alluvial-lacustrine aquifer system: Nitrogen/iron isotopic and biogeochemical evidences

Groundwater nitrogen contamination is becoming increasingly serious worldwide, and natural nitrogen attenuation processes such as anaerobic ammonium oxidation coupled to iron reduction ("Feammox") play an important role in mitigating contamination. Although there has been intensive study of Feammox in soils and sediments, still lacks research on this process in groundwater. This study makes effort to demonstrate the occurrence of Feammox in groundwater by combining information from Fe/N isotope composition, the quantitative polymerase chain reaction (qPCR) assay, and 16S rRNA gene sequencing. Poyang Lake Plain of Yangtze River in central China was selected as the case study area. The critical evidences that indicate Feammox in groundwater include favorable hydrogeochemical conditions of the alluvia-lacustrine aquifer systems, the simultaneous enrichment of ¹⁵N in ammonium and ⁵⁶Fe, the relative high abundance of Acidimicrobiaceae bacterium A6, and the joint elevation of the abundance of the Feammox bacteria and the concentration of Fe(III). Redundancy analysis (RDA) indicated that Geothrix and Rhodobacter may participate directly or cooperatively in the Feammox process. Ammonium-oxidizing archaea (AOA) involved in ammonium-oxidizing or Feammox process may be stimulated by Fe(III) under a low oxygen concentration and weakly acidic condition. Anammox may be indirectly enhanced by products of the nitrogen transformation processes involving Feammox bacteria and AOA. Fe(III) concentration is an important environmental factor affecting the abundance of functional microorganisms related to nitrogen cycling and the composition of ammonium-oxidizing and iron-reducing microbes. Specific geological background (such as the widespread red soils) and anthropogenic input of ammonium, iron, and acidic substances may jointly promote Feammox in groundwater.

Effects of Mn2+ and humic acid on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes in wastewater treatment

Considering the wide occurrence of Mn²⁺ and humic acid (HA) in environmental media, the effects of Mn²⁺ (5-16 mg/L) and HA (10 mg/L) on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes (HMRGs) were investigated in wastewater treatment using sequencing batch bioreactors (SBRs). The treatment efficiencies of influent chemical oxygen demands (COD), NH₄⁺-N, and PO₄^3--P were unaffected during the entire operational processes irrespective of whether Mn²⁺ and HA were supplied. Although the functional prediction of genetic information via sequencing analysis showed that the microbial activity was not influenced by Mn²⁺ and HA from different SBRs, the abundance of dominant phyla (Proteobacteria, Actinobacteriota, Firmicutes, and Bacteroidota), classes (Saccharimonadia, Gammaproteobacteria, and Bacilli), and genera (unidentified_Chloroplast, TM7a, Micropruina, Candidatus_Competibacter, Lactobacillus, OLB12, and Pediococcus) was different. Compared to the SBR without Mn²⁺ and HA supplementation, the abundance of functional genes for nitrogen and phosphorus removal (narG, nirS, nosZ, ppk, and phoD) and HMRGs (corA and mntA) significantly increased under Mn²⁺ stress, but significantly decreased with the addition of HA except for genes nirS and ppk. The abundance of genes corA and mntA was related to the partially dominant microbes and functional genes, and might be reduced by supplying HA. This study provides insight into the effects of Mn²⁺ and HA on functional genes for nitrogen and phosphorus removal and HMRGs in wastewater treatment.

Bio-augmentation with dissimilatory nitrate reduction to ammonium (DNRA) driven sulfide-oxidizing bacteria enhances the durability of nitrate-mediated souring control

Biological souring (producing sulfide) is a global challenge facing anaerobic water bodies, especially the oil reservoir fluids. Nitrate injection has demonstrated great potential in souring control, and dissimilatory nitrate reduction to ammonium (DNRA) bacteria was proposed to play crucial roles in the process. How to durably control souring with nitrate amendment, however, remains undiscovered. Herein, Gordonia sp. TD-4, a DNRA-driven sulfide-oxidizing bacterium, was used to elucidate the effects of bio-augmentation with DNRA bacteria on the durability of nitrate-mediated souring control. The results revealed that nitrate amendment combined with bio-augmentation with TD-4 after souring could effectively control souring and enhance the durability of nitrate-mediated souring control, while nitrate amendment before souring failed to persistently control souring. Nitrate amendment before and after souring resulted in different evolution dynamics of nitrate-reducing bacteria. Denitrifying bacteria were enriched in reactors amended with nitrate before souring or in dissolved sulfide exhausted reactors amended with nitrate after souring. The heterotrophic denitrifying activity of denitrifying bacteria, however, decreased the durability of nitrate-mediated souring control. Comparative and functional genomics analysis identified potential niche adaptation mechanisms (autotrophic and heterotrophic nitrate/nitrite reduction, including DNRA and denitrification) of predominant SRB in nitrate-amended environments, which were responsible for the rapid resumption of sulfide accumulation after the depletion of nitrate and nitrite. Pulsed injection of nitrate combined with bio-augmentation with DNRA-driven sulfide-oxidizing bacteria was proposed as a potential method to enhance the durability of nitrate-mediated souring control. The findings were innovatively applied to simultaneous bio-demulsification and souring control of emulsified and sour produced water from the petroleum industry.

Determination of the Hydrodynamic Characteristics of a Typical Inland Saline-Alkali Wetland in Northeast China

Hydrological connectivity in wetland ecosystems comprises a combination of hydrodynamic, hydrochemical, and biological characteristics. Hydrodynamic characteristics are important for the transmission of energy, matter, and information between surface water bodies and are critical for maintaining the health of wetland ecosystems. The hydrodynamic characteristics of wetlands are the temporal and spatial changes in the water level, flow direction, quantity, recharge, and discharge conditions of surface water and groundwater. Identifying wetland hydrodynamic characteristics is of great significance in revealing the hydrological patterns and biogeochemical phenomena of wetland ecosystems. The Momoge National Nature Reserve (MNNR) is a wetland located in the semi-arid region of northeast China, where the hydrodynamic characteristics are still unclear. In this study, water level monitoring of surface water and groundwater in MNNR was carried out, and wetland recharge and discharge were calculated according to a water balance analysis. The submerged wetland area was simulated based on an improved distributed hydrological model, SWAT-DSF, and compared with remote sensing data. The results showed that the dynamic characteristics of wetland surface water and groundwater are mostly affected by topography and recharge water sources. The water resources in the reserve are in a positive state of equilibrium in the wet season (September), with an equilibrium difference of 276.41 × 104 m3/day. However, it displays a negative equilibrium state in dry (November) and other (June) seasons, with an equilibrium difference of −12.84 × 104 m3/day and −9.11 × 104 m3/d, respectively. The difference between the submerged areas of the MNNR wetland during the wet and dry seasons was 250 km2.

Simultaneous partial nitrification, anammox, and denitrification in an upflow microaerobic membrane bioreactor treating middle concentration of ammonia nitrogen wastewater with low COD/TN ratio

The rapid start-up and operating characteristics of simultaneous partial nitrification, anammox, and denitrification (SNAD) process was investigated using synthetic wastewater with a low C/N ratio (COD: NH₄⁺-N = 200 mg/L: 200 mg/L) in a novel upflow microaerobic membrane bioreactor (UMMBR). The average removal efficiencies of COD, NH₄⁺-N, and TN in the stable phase were 89%, 96%, and 86%, respectively. Carmine granule, which coexisted with sludge floc, appeared on day 83. The high sludge concentration (12.9-17.2 g/L) and the upflow mode of the UMMBR could establish some anaerobicregions for anammox process. The anammox bacteria and short-cut denitrification (NO₂^-→N₂) bacteria with activities of 4.46 mg NH₄⁺-N/gVSS·h and 2.57 mg NO₂^--N/gVSS·h contributed TN removal of 39% and 61% on day 129, respectively. High-throughput sequencing analysis revealed that the ammonia-oxidizing archaea (AOA, 49.45% in granule and 17.05% in sludge floc) and ammonia-oxidizing bacterial (AOB, 1.30% in sludge floc) dominated the nitrifying microbial community. Candidatus Jettenia (47.14%) and Denitratisoma (10.92%) mainly existed in granule with positive correlations. Some heterotrophic bacteria (OLB13, SJA-15, 1-20, SBR1031, and SJA-28) in sludge floc benefited system stability and sludge activity and protected Candidatus Jettenia from adverse environments.

The influences of soil sulfate content on the transformations of nitrate and sulfate during the reductive soil disinfestation (RSD) process

The transformations and products of sulfate (SO₄^2-) and nitrate (NO₃^-), especially the influences of SO₄^2- content on the transformations during RSD process, are unclear. In this study, a series of soil SO₄^2- contents (from 333 to 3000 mg S kg^-1) were prepared before RSD treatment. The results indicated that nearly all the cumulative NO₃^- (>98.6%) was removed and not affected by the soil SO₄^2- content. The ¹⁵N recovery results showed that 0.57-1.24% and 2.94-4.59% of NO₃^- translated into ammonium (NH₄⁺) and organic N, respectively, and high SO₄^2- contents stimulated the processes of NO₃^- dissimilatory reduction and NO₃^- immobilization. The soluble SO₄^2- contents decreased by 397-922 mg S kg^-1, but the contents of total sulfur, sulfide, and sulfate precipitation varied slightly after RSD, indicating that the decreased SO₄^2- was mainly immobilized into organic sulfur in all soils. In addition, a fraction of decreased SO₄^2- was adsorbed to the soil with a relatively high SO₄^2- content. The leaching of SO₄^2- was high (42.9-602 mg S kg^-1) during the RSD process, and the leaching amounts increased with increasing soil SO₄^2- content. In terms of the gases emitted from the transformations of NO₃^- and SO₄^2-, the cumulative emissions of nitrous oxide (N₂O) and six sulfurous gases (hydrogen sulfide, carbonyl sulfide, carbon disulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide) were in the ranges of 17.1-21.2 mg N kg^-1 and 7.78-23.5 μg S kg^-1, respectively, during the whole RSD process. The emissions of sulfurous gases were inhibited by high soil SO₄^2- content, but the N₂O emissions were unaffected. In conclusion, the soil SO₄^2- content influenced the transformations of NO₃^- and SO₄^2- during RSD process, and the SO₄^2- leaching and N₂O emissions might threaten the environment which should be concerned.

Relationship between nitrifying microorganisms and other microorganisms residing in the maize rhizosphere

The microbial network of rhizosphere is unique as a result of root exudate. Insights into the relationship that exists with the energy metabolic functional groups will help in biofertilizer production. We hypothesize that there exists a relationship between nitrifying microorganisms and other energy metabolic functional microbial groups in the maize rhizosphere across different growth stages. Nucleospin soil DNA extraction kit was used to extract DNA from soil samples collected from maize rhizosphere. The 16S metagenomics sequencing was carried out on Illumina Miseq. The sequence obtained was analyzed on MG-RAST. Nitrospira genera were the most abundant in the nitrifying community. Nitrifying microorganisms were more than each of the studied functional groups except for nitrogen-fixing bacteria. Also, majority of the microorganisms were noticed at the fruiting stage and there was variation in the microbial structure across different growth stages. The result showed that there exists a substantial amount of both negative and positive correlation within the nitrifying microorganisms, and between them and other energy metabolic functional groups. The knowledge obtained from this study will help improve the growth and development of maize through modification of the rhizosphere microbial community structure.

Investigation of dissimilatory nitrate reduction to ammonium (DNRA) in urban river network along the Huangpu River, China: rates, abundances, and microbial communities

Dissimilatory nitrate reduction to ammonium (DNRA) is an essential intermediate step in the nitrogen cycle, and different sediment physicochemical properties can affect the DNRA process. But the detailed research on the environmental nitrogen cycling in urban river networks based on DNRA communities and the functional gene nrfA is lacking. In this study, the flow line of the Huangpu River in Shanghai was analyzed using isotope tracer, quantitative real-time PCR, and high-throughput sequencing techniques to evaluate the role of DNRA on the stability of the river network and marine. The significant positive correlation between the rate of DNRA and sediment organic carbon was identified. At the genus level, Anaeromyxobacter is the most dominant. Notably, both heterotrophic and autotrophic DNRA species were discovered. This study added diversity to the scope of urban freshwater river network ecosystem studies by investigating the distribution of DNRA bacteria along the Huangpu River. It provided new insights into the biological nitrogen cycle of typical urban inland rivers in eastern China.

Biochar-mediated DNRA pathway of anammox bacteria under varying COD/N ratios

Coupling dissimilatory nitrate reduction to ammonium (DNRA) pathway with anammox process has a prominent advantage in enhancement of nitrogen removal. However, the anammox bacteria driven-DNRA is difficult to proceed at normal autotrophic circumstance. Herein, for the first time, biochar (prepared by bamboo) was used as a mediator to stimulate the DNRA pathway of anammox bacteria under varying chemical oxygen demand (COD) to nitrogen (COD/N) ratios (0.1-0.7), and the underlying stimulation mechanism was elucidated by metagenomics sequencing analysis. Results showed that biochar addition (10 g/L) stimulated DNRA pathway of anammox bacteria at low COD/N ratios (0.1-0.5), thus enhancing the nitrogen removal efficiency (NRE) of the anammox system by 7.2%-16.4% and 0.9%-3.0%, respectively, compared to that of tests without sodium acetate and biochar (p<0.05). This enhancement was attributed to the improved extracellular electron accepting capacity of anammox biomass by biochar. The easily obtained electrons (from sodium acetate) further increased the relative abundances of anammox-related (hzs) and complete DNRA-related (napAB and nrfAH) genes (p<0.05), which catalyze electron-consuming reactions. The stimulated anammox pathway and DNRA pathway further increased the specific anammox activity and the relative abundance of anammox bacteria (especially Ca. Jettenia) by 15.5%-23.0% and 11.3%-82.6% compared with that without biochar, respectively. Metagenomics sequencing also revealed that anammox bacteria, Ca. Jettenia caeni, was the main bacteria for DNRA metabolism in this system. Our findings reveal that biochar could selectively stimulate DNRA pathway of anammox bacteria affiliated by a low amount of carbon, which provides a novel strategy to improve the nitrogen removal of anammox-based processes.

Heterotrophic ammonium assimilation: An important driving force for aerobic denitrification of Rhodococcus erythropolis strain Y10

Studies on microbial ammonium removal have focused on the heterotrophic nitrification of microorganisms and have rarely studied the role of ammonium assimilation. In this study, Rhodococcus erythropolis strain Y10 with the capacity of aerobic denitrification was screened from the surface flow constructed wetlands that treat high-strength ammonium swine wastewater. Instead of through nitrification, this strain removed ammonium through heterotrophic ammonium assimilation, with the removal rate of 9.69 mg/L/h. The KEGG nitrogen metabolism pathway analysis combined with nitrogen balance calculation manifested that the removal of nitrate and nitrite by R. erythropolis Y10 was achieved through two pathways: 1) assimilation reduction to biomass nitrogen and 2) aerobic denitrification reduction to gaseous nitrogen. Ammonium addition improved the aerobic denitrification rate of nitrate and nitrite. The maximal reduction rates of nitrate and nitrite increased from 7.82 and 7.23 mg/L/h to 9.09 and 8.09 mg/L/h respectively, when 100 mg/L ammonium was separately added to 150 mg/L nitrate and nitrite. Furthermore, the removal efficiency of total nitrogen increased from 69.80% and 77.65% to 89.19% and 91.88%, respectively. Heterotrophic ammonium assimilation promoted the aerobic denitrification efficiency of Rhodococcus erythropolis strain Y10.

Fate of Dissolved Nitrogen in a Horizontal Levee: Seasonal Fluctuations in Nitrate Removal Processes

Horizontal levees are a nature-based approach for removing nitrogen from municipal wastewater effluent while simultaneously providing additional benefits, such as flood control. To assess nitrogen removal mechanisms and the efficacy of a horizontal levee, we monitored an experimental system receiving nitrified municipal wastewater effluent for 2 years. Based on mass balances and microbial gene abundance data, we determined that much of the applied nitrogen was most likely removed by heterotrophic denitrifiers that consumed labile organic carbon from decaying plants and added wood chips. Fe(III) and sulfate reduction driven by decay of labile organic carbon also produced Fe(II) sulfide minerals. During winter months, when heterotrophic activity was lower, strong correlations between sulfate release and nitrogen removal suggested that autotrophic denitrifiers oxidized Fe(II) sulfides using nitrate as an electron acceptor. These trends were seasonal, with Fe(II) sulfide minerals formed during summer fueling denitrification during the subsequent winter. Overall, around 30% of gaseous nitrogen losses in the winter were attributable to autotrophic denitrifiers. To predict long-term nitrogen removal, we developed an electron-transfer model that accounted for the production and consumption of electron donors. The model indicated that the labile organic carbon released from wood chips may be capable of supporting nitrogen removal from wastewater effluent for several decades with sulfide minerals, decaying vegetation, and root exudates likely sustaining nitrogen removal over a longer timescale.

High efficient bio-denitrification of nitrate contaminated water with low ammonium and sulfate production by a sulfur/pyrite-based bioreactor

Sulfur-based autotrophic denitrification (SAD) and pyrite-based autotrophic denitrification (PAD) are important technologies that address nitrate pollution, but high sulfate production and low denitrification efficiency, respectively, limit their application in engineering. A bio-denitrification reactor with sulfur and pyrite as filler materials was studied to remove NO₃^--N from nitrate contaminated water. At an influent NO₃^--N concentration of 50 mg/L, NO₃^--N removal efficiency of the sulfur/pyrite-based bioreactor was 99.2%, producing less NH₄⁺-N and SO₄^2- than the sulfur-based bioreactor, even after long-term operation. Denitrification performance was significantly related to environmental variable, especially dissolved oxygen. Proteobacteria and Epsilonbacteraeota were the predominant phyla in the sulfur/pyrite-based bioreactor, and fewer dissimilatory nitrate reductions to ammonia process-related bacteria were enriched compared to those in the sulfur-based bioreactor. Sulfur-pyrite bio-denitrification provides an efficient alternative method for treatment of nitrate contaminated water.

Nitrogen cycling in a tropical coral reef ecosystem under severe anthropogenic disturbance in summer: Insights from isotopic compositions

Coral reefs, one of the most productive ecosystems, have been dramatically declining in recent decades. While studies contend a prominent correlation between coral reef degradation and increased anthropogenic nitrogen (N) loads, a quantitative description of the N sources and cycling processes in these ecologically important ecosystems is lacking. Through a comprehensive depiction of the δ¹⁵N compositions of seawaters and sediments, we systematically accessed the N cycling processes in the Weizhou coral reef ecosystem. The correlations between the nitrate (NO₃^-) concentrations and isotopic compositions (δ¹⁵N/δ¹⁸O-NO₃^-) indicated the pelagic NO₃^- loads were largely regulated by mixing between precipitation and sewage. Biological NO₃^- turnover processes appeared to be weak. In the sediments, N₂ fixation contributed about one-third of the sedimentary organic N, with the rest coming from the settlement of pelagic organic N. We also uncovered significant sedimentary mineralization-nitrification-denitrification processes in which the N loss was greater than the input. While pelagic N significantly contributed to the sedimentary N, the N export from the sediments to surface seawater was potentially short-circuited by the high N retention and recycling efficiencies of the organisms in the coral reef ecosystem. Overall, this study shows that the complex N cycling processes in the ecosystem are effectively reflected in the isotopic compositions of seawater and sediment, thus adding an important dimension to understanding the N cycling in coral reef ecosystems.

Activities and metabolic versatility of distinct anammox bacteria in a full-scale wastewater treatment system

Anaerobic ammonium oxidation (anammox) is a key N₂-producing process in the global nitrogen cycle. Major progress in understanding the core mechanism of anammox bacteria has been made, but our knowledge of the survival strategies of anammox bacteria in complex ecosystems, such as full-scale wastewater treatment plants (WWTPs), remains limited. Here, by combining metagenomics with in situ metatranscriptomics, complex anammox-driven nitrogen cycles in an anoxic tank and a granular activated carbon (GAC) biofilm module of a full-scale WWTP treating landfill leachate were constructed. Four distinct anammox metagenome-assembled genomes (MAGs), representing a new genus named Ca. Loosdrechtii, a new species in Ca. Kuenenia, a new species in Ca. Brocadia, and a new strain in "Ca. Kuenenia stuttgartiensis", were simultaneously retrieved from the GAC biofilm. Metabolic reconstruction revealed that all anammox organisms highly expressed the core metabolic enzymes and showed a high metabolic versatility. Pathways for dissimilatory nitrate reduction to ammonium (DNRA) coupled to volatile fatty acids (VFAs) oxidation likely assist anammox bacteria to survive unfavorable conditions and facilitate switches between lifestyles in oxygen fluctuating environments. The new Ca. Kuenenia species dominated the anammox community of the GAC biofilm, specifically may be enhanced by the uniquely encoded flexible ammonium and iron acquisition strategies. The new Ca. Brocadia species likely has an extensive niche distribution that is simultaneously established in the anoxic tank and the GAC biofilm, the two distinct niches. The highly diverse and impressive metabolic versatility of anammox bacteria revealed in this study advance our understanding of the survival and application of anammox bacteria in the full-scale wastewater treatment system.

Acceleration of polychlorinated biphenyls remediation in soil via sewage sludge amendment

Bioremediation of polychlorinated biphenyls (PCBs) is impeded by difficulties in massively cultivating bioinoculant. Meanwhile, sewage sludge is rich in pollutant-degrading microorganisms and nutrients, drawing our attention to investigate their potential to be used as a supplement for bioremediation of PCBs. Here we reported extensive microbial reductive dechlorination of PCBs by waste activated sludge (WAS) and digestion sludge (DS), which were identified to harbor multiple putative organohalide-respiring bacteria (i.e., Dehalococcoides, Dehalogenimonas, Dehalobacter, and uncultivated Dehalococcoidia) and PCB reductive dehalogenase genes (i.e., pcbA4 and pcbA5). Consequently, amendment of 1-20% (w/w) fresh WAS/DS enhanced the attenuation of PCBs by 126-544% in a soil microcosm compared with the control soil, with the fastest dechlorination of PCBs being achieved when spiked with 20% fresh WAS. Notably, dechlorination pathways of PCBs were also changed by sludge amendment. Microbial and physicochemical analyses revealed that the enhanced dechlorination of PCBs by sludge amendment was largely attributed to the synergistic effects of sludge-derived nutrients, PCB-dechlorinating bacteria, and stimulated growth of beneficial microorganisms (e.g., fermenters). Finally, risk assessment of heavy metals suggests low potential ecological risks of sludge amendment in soil. Collectively, our study demonstrates that sewage sludge amendment could be an efficient, cost-effective and environment-friendly approach for in situ bioremediation of PCBs.

Manganese oxides in Phragmites rhizosphere accelerates ammonia oxidation in constructed wetlands

Phragmites reeds are widely used in constructed wetlands (CWs) for treating wastewater. The enrichment of microorganisms and Fe/Mn plaque in Phragmites rhizospheres largely contributes to pollutant removal. However, their interactions and potential synergistic roles in water purification are poorly understood. To address the issue, we first compared the microbial community traits in the Phragmites rhizosphere and adjacent bulk soil in six long-term operated CWs. Results showed that enriched microbes and functional genes in the Phragmites rhizosphere were largely involved in Mn oxidation, resulting in a two to three times enrichment of Mn oxides in the rhizosphere. In turn, the enriched Mn oxides played significant roles in driving microbial community composition and function. To further understand the biological manganese oxidation in the rhizosphere, we identified Mn-oxidizing bacteria using genome-centric analysis and found that 92% of identified Mn-oxidizing bacteria potentially participated in nitrogen cycling. We then conducted relationships between Mn-oxidizing genes and different nitrogen cycling genes and found Mn-oxidizing gene abundance was significantly correlated with ammonia oxidation gene amoA (R = 0.65). Remarkably, complete ammonia oxidation (comammox) Nitrospira, accounting for 39.11% of ammonia oxidizers, also positively correlated with Mn-oxidizing microbes. Based on the above observations, we inferred that the use of Mn oxides as a substrate in CWs may enhance ammonia oxidation. To apply this to actual engineering, we explored treatment performance in a pilot-scale Mn-amending CW. As expected, ammonia removal capacity improved by 23.34%, on average, in the Mn-amending CW. In addition, the abundance of amoA genes increased significantly in the Mn-amending CW, indicating improved biological processes rather than chemical reactions.

Integration of CW-MFC and anaerobic granular sludge to explore the intensified ammonification-nitrification-denitrification processes for nitrogen removal

The integration of constructed wetland-microbial fuel cell (CW-MFC) and anaerobic granular sludge (AGS) is an important way to promote its ammonification efficiency and decrease the land use scale. This study explored the integration of CW-MFC and AGS for nitrogen removal via the intensified ammonification-nitrification-denitrification processes with initial NH₃-N, NO₃-N, Org-N and total nitrogen (TN) concentrations of 10.5, 13.8, 21.4, and 45.7 mg L^-1 in wastewater. Two reactors with AGS inoculated with a separated area (R1) and directly inoculated into gravel substrate (R2) were designed, respectively. Results showed that chemical oxygen demand (COD) removal efficiency could reach 85% in R1 and 81% in R2, and the conversion of Org-N to NH₃-N and NO₃-N to gaseous nitrogen were 80% and 90%, respectively. Although the conversion efficiency of NH₃-N to NO₂-N/NO₃-N via nitrification process was only 18%, it could reach 45%, 94%, and 98% with the aeration rates of 50-, 100-, and 200-mL min^-1. According to microstructural property and microbial community analyses, the separation gravel substrate and AGS areas in R1 availed for stable particle size of AGS, archaeal diversity, and metabolic activity even with a 1.5 times daily wastewater treatment capacity than that of R2. Overall, although the intensified ammonification-nitrification-denitrification processes for nitrogen removal could be achieved with supplementary aeration, further investigation is still needed to explore other substrate materials and high CW-MFC/AGS volume ratio for intensified nitrification process in CW-MFC associated with AGS.

Haloalkaliphilic denitrifiers-dependent sulfate-reducing bacteria thrive in nitrate-enriched environments

As bridge in global cycles of carbon, nitrogen, and sulfur, sulfate-reducing bacteria (SRB) play more and more important role under various environments, especially the saline-alkali environments with significant increase in area caused by human activities. Sulfate reduction can be inhibited by environmental nitrate. However, how SRB cope with environmental nitrate stress in these extreme environments still remain unclear. Here, after a long-term enrichment of sediment from saline-alkali Qinghai Lake of China using anaerobic filter reactors, nitrate was added to evaluate the response of SRB. With the increase in nitrate concentrations, the inhibition on sulfate reduction was gradually observed. Interestingly, extension of hydraulic retention time can relieve the inhibition caused by high nitrate concentration. Mass balance analysis showed that nitrate reduction is prior to sulfate reduction. Further metatranscriptomic analysis shows that, genes of nitrite reductase (periplasmic cytochrome c nitrite reductase gene) and energy metabolisms (lactate dehydrogenase, formate dehydrogenase, pyruvate:ferredoxin-oxidoreductase, and fumarate reductase genes) in SRB was down-regulated, challenging the long-held opinion that up-regulation of these genes can relieve the nitrate inhibition. Most importantly, the nitrate addition activated the denitrification pathway in denitrifying bacteria (DB) via significantly up-regulating the expression of the corresponding genes (nitrite reductase, nitric oxide reductase c subunit, nitric oxide reductase activation protein and nitrous oxide reductase genes), quickly reducing the environmental nitrate and relieving the nitrate inhibition on SRB. Our findings unravel that in response to environmental nitrate stress, haloalkaliphilic SRB show dependency on DB, and expand our knowledge of microbial relationship during sulfur and nitrogen cycles.

Application of constructed wetlands in treating rural sewage from source separation with high-influent nitrogen load: a review

Constructed wetlands (CWs) are characterized by low construction cost, convenient maintenance and management, and environmentally friendly features. They have emerged as promising technologies for decentralized sewage treatment across rural areas. Source separation of black water and gray water can facilitate sewage recycling and reuse of reclaimed water, reduce the size of treatment facilities, and lower infrastructure investment and operating cost. This is consistent with the concept of sustainable development. However, black water contains high concentrations of ammonia nitrogen, and the denitrification capacity of CWs is not excellent due to insufficient carbon source. Therefore, application of CWs for black water treatment faces challenges. This article provides a review on the progress in CWs for treatment of the sewage with high-influent nitrogen load, with emphasis on the commonly used strengthening means and the role of plants in nitrogen removal via CWs. The current issues of rural sewage treatment with high-influent nitrogen load by CWs are also assessed. Finally, the challenges and perspectives are discussed for the optimization of CWs-enhanced denitrification strategies.

Microorganisms that participate in biochemical cycles in wetlands

Several biochemical cycles are performed in natural wetlands (NWs) and constructed wetlands (CWs). The knowledge of the microorganisms could be used to monitor the restoration of wetlands or the performance of the wastewater treatment. Regarding bacteria, Proteobacteria phylum is the most abundant in NWs and CWs, which possesses a role in N, P, and S cycles, and in the degradation of organic matter. Other phyla are present in lower abundance. Archaea participate in methanogenesis, methane oxidation, and the methanogenic N2 fixation. Sulfur and phosphorus cycles are also performed by other microorganisms, such as Chloroflexi or Nitrospirae phyla. In general, there is more information about the N cycle, especially nitrification and denitrification. Processes where archaea participate (e.g. methane oxidation, methanogenic N2 fixation) are still unclear their metabolic role and several of these microorganisms have not been isolated so far. The study can use 16S rDNA genes or functional genes. The use of functional genes gives information to monitor specific microbial populations and 16S rDNA is more suitable to perform the taxonomic classification. Also, there are several Candidatus microorganisms, which have not been isolated so far. However, it has been described their metabolic role in the biochemical cycles in wetlands.

Rapid initiation and stable maintenance of municipal wastewater nitritation during the continuous flow anaerobic/oxic process with an ultra-low sludge retention time

Rapid achievement of nitritation of mainstream municipal wastewater in a continuous-flow process is attractive since it favors the involvement of the anammox process and reduces the operational costs. In this study, a feasible and economical strategy is proposed to rapidly achieve the nitritation of municipal wastewater. By aggressively discharging excess sludge during the seasonal warming period (temperature increasing from 18°C to 22°C), nitritation was established in 15 days with a nitrite accumulation ratio of 85.09% in a continuous-flow anaerobic/oxic (An/O) reactor. Meanwhile, qPCR results revealed that amoA abundance increased from (1.78±0.10) × 10⁸ copies/(g VSS) to (1.05±0.11) × 10¹⁰ copies/(g VSS) while the abundance of nitrite-oxidizing bacteria decreased from (1.1±0.02) × 10¹⁰ copies/(g VSS) to (5.01±0.02) × 10⁸ copies/(g VSS). The temperature gradually stabilized at 26°C during the following operational period and stable nitritation was maintained with a nitrite accumulation ratio above 90%, which was mainly attributed to a short sludge retention time (SRT) of 4.3 days and a low dissolved oxygen of 0.86 ± 0.5 mg/L. Falling temperature negatively impacted the stability of nitritation, but nitritation could be restarted by aggressively discharging excess sludge during another temperature increase period. Overall, this study provides a feasible strategy to start-up nitritation that has great potential applications for municipal wastewater treatment.