Oxygen minimum zones (OMZs), such as those found in the eastern South Pacific (ESP), are the most important N.sub.2 O sources in the global ocean relative to their volume. N.sub.2 O production is ...related to low O.sub.2 concentrations and high primary productivity. However, when O.sub.2 is sufficiently low, canonical denitrification takes place and N.sub.2 O consumption can be expected. N.sub.2 O distribution in the ESP was analyzed over a wide latitudinal and longitudinal range (from 5° to 30° S and from 71-76° to ~ 84° W) based on ~ 890 N.sub.2 O measurements. Intense N.sub.2 O consumption, driving undersaturations as low as 40%, was always associated with secondary NO.sub.2 .sup.-- accumulation (SNM), a good indicator of suboxic/anoxic O.sub.2 levels. First, we explore relationships between ÎN.sub.2 O and O.sub.2 based on existing data of denitrifying bacteria cultures and field observations. Given the uncertainties in the O.sub.2 measurements, a second relationship between ÎN.sub.2 O and NO.sub.2 .sup.-- (> 0.75 μM) was established for suboxic waters (O.sub.2 < 8 μM). We reproduced the apparent N.sub.2 O production (ΔN.sub.2 O) along the OMZ in ESP with high reliability (r.sup.2 = 0.73 p = 0.01). Our results will contribute to the quantification of the N.sub.2 O that is recycled in O.sub.2 deficient waters, and improve the prediction of N.sub.2 O behavior under future scenarios of OMZ expansion and intensification.
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•An efficient HSND-MBBR was established successfully by inoculating HNAD bacteria.•The HNAD via shortcut process dominated in HSND-MBBR and enhanced at low C/N.•HNADs (S. ...maltophilia), DPAOs and GAOs were the main function genus.•HSND-MBBR could regulate nitrogen metabolic pathways to adapt various C/N ratios.
Traditional simultaneous nitrification and denitrification process was restricted by the stringent operation conditions and the inhibition of heterotrophic bacteria to ammonia oxidizing bacteria. To address these problems, a long-term simultaneous nitrification and denitrification-moving bed biofilm reactor (SND-MBBR) was successfully started by inoculating heterotrophic nitrification and aerobic denitrification (HNAD) bacterium Stenotrophomonas maltophilia DQ01 and investigated at different C/N ratios. Remarkable SND efficiency (94.21%) and total nitrogen removal (94.43%) were achieved at C/N of 7.5, and declined with C/N decreasing due to the reduction of electron donation and consumption. The combined stoichiometry and kinetics analyses confirmed that the HNAD via short-cut process dominated in feast phase and spiraled upwards with decreasing C/N, as evidenced by extremely low NXR activity and Nitrospira abundance (below 0.1%), suggesting that the inadequate electron donation was favorable for partial nitrification and denitrification. Furthermore, endogenous nitrification and denitrification occurred without COD consumption in famine stage, and decelerated at lower C/N due to the less stored internal carbon. High throughput sequencing revealed that HNADs (represented by Stenotrophomonas maltophilia), denitrifying phosphorus accumulating organisms and denitrification glycogen accumulating organisms dominated during the community succession and nitrogen removal process. Moreover, Candidatus Competibacter and Dechloromonas were negatively correlated with nitrite, leading to the accumulation of nitrite in famine phase. COG analysis showed the accumulated nitrite might affect the defense system and signal transduction. This study provided a new strategy for nitrogen removal and gave a new insight into the SND mechanism under different C/N conditions.
Fe0-mediated autotrophic denitrification (ADN) can be suppressed by iron oxide coverage resulting from Fe0 corrosion. The mixotrophic denitrification (MDN) coupling Fe0-mediated ADN with ...heterotrophic denitrification (HDN) can circumvent the weakening of Fe0-mediated ADN over operation time. But the interaction between HDN and Fe0-mediated ADN for nitrogen removal of secondary effluent with deficient bioavailable organics remains unclear. When the influent COD/NO3−-N ratio increased from 0.0 to 1.8–2.1, the TN removal efficiency was promoted significantly. The increased carbon source did not inhibit ADN, but promoted ADN and HDN synchronously. The formation of extracellular polymeric substances (EPS) was also facilitated concomitantly. Protein (PN) and humic acid (HA) in EPS increased significantly, which capable of accelerating electron transfer of denitrification. Due to that the electron transfer of HDN occurs intracellularly, the EPS with the capacity of accelerating electron transfer had a negligible influence on HDN. But for Fe0-mediated ADN, the increased EPS as well as corresponding PN and HA facilitated TN and NO3−-N removal significantly, while accelerated the electron release originating from Fe0 corrosion. The bioorganic-Fe complexes were generated on Fe0 surface after used, meaning that the soluble EPS and soluble microbial products (SMP) participated in the electron transfer of Fe0-mediated ADN. The coexistence of HDN and ADN denitrifiers demonstrated the synchronous enhancement of HDN and ADN by the external carbon source. From the perspective of EPS and related SMP, the insight of enhancing Fe0-mediated ADN by external carbon source is beneficial to implement high-efficiency MDN for organics-deficient secondary wastewater.
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•Organic carbon source promoted HDN and Fe0-mediated ADN with their denitrifiers in MDN simultaneously.•MDN coupling HDN with Fe0-mediated ADN tackled the weakening of Fe0-mediated ADN caused by Fe0 corrosion suppression.•Organic carbon source triggered the formation and increase of EPS and related SMP.•HA and PN in EPS and SMP facilitated the extracellular electron transfer of ADN.
Nitrate (NO3−) pollution in water and wastewater has become a serious global issue. Biological denitrification, which reduces NO3− to N2 (nitrogen gas) by denitrifying microorganisms, is an efficient ...and economical process for the removal of NO3− from water and wastewater. During the denitrification process, electron donor is required to provide electrons for reduction of NO3−. A variety of electron donors, including organic and inorganic compounds, can be used for denitrification. This paper reviews the state of the art of various electron donors used for biological denitrification. Depending on the types of electron donors, denitrification can be classified into heterotrophic and autotrophic denitrification. Heterotrophic denitrification utilizes organic compounds as electron donors, including low-molecular-weight organics (e.g. acetate, methanol, glucose, benzene, methane, etc.) and high-molecular-weight organics (e.g. cellulose, polylactic acid, polycaprolactone, etc.); while autotrophic denitrification utilizes inorganic compounds as electron donors, including hydrogen (H2), reduced sulfur compounds (e.g. sulfide, element sulfur and thiosulfate), ferrous iron (Fe2+), iron sulfides (e.g. FeS, Fe1−xS and FeS2), arsenite (As(Ш)) and manganese (Mn(II)). The biological denitrification processes and the representative denitrifying microorganisms are summarized based on different electron donors, and their denitrification performance, operating costs and environmental impacts are compared and discussed. The pilot- or full-scale applications were summarized. The concluding remarks and future prospects were provided. The biodegradable polymers mediated heterotrophic denitrification, as well as H2 and sulfur mediated autotrophic denitrification are promising denitrification processes for NO3− removal from various types of water and wastewater.
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•Various electron donors for biological denitrification were analyzed and summarized.•Representative denitrifying microorganism for nitrate removal were introduced.•Merits and demerits of different electron donors for denitrification were compared.•Recent advances in pilot-scale application of various electron donors were provided.
Solid and liquid organic substances as carbon sources for denitrification process were deeply explored. In this study, the effect of three carbon sources, referred to as poly ...(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly (lactic acid) (PHBV/PLA) polymer, glucose and CH3COONa, on denitrification performance, microbial community and functional genes were investigated. It was found that maximum denitrification rates of 0.37, 0.46 and 0.39gN/(L·d) were achieved in PHBV/PLA, glucose and CH3COONa supported denitrification systems, respectively. Meanwhile, Illumina MiSeq sequencing revealed that three carbon sources led to different microbial community structures. It can be seen that Brevinema/Thauera/Dechloromonas, Tolumonas/Thauera/Dechloromonas, Thauera dominated in the PHBV/PLA, glucose and CH3COONa supported denitrification systems, respectively. Transcriptome-based analysis further indicated that the glucose supported denitrification system showed the highest FPKM values (the fragments per kilobase per million mapped reads) of the genes participating in the dissimilatory nitrate reduction process, corresponding to the greatest effluent NH4+-N concentration. A better knowledge of effect of different carbon sources on denitrification process will be significant for nitrate removal in practice.
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•The maximum denitrification rate was lowest in PHBV/PLA supported system.•The relative abundance of denitrification bacteria was highest in CH3COONa system.•PHBV/PLA and glucose systems showed abundant hydrolysis and fermenting bacteria.•The FPKM value of functional genes for DNRA process was highest in glucose system.
•Mixotrophic denitrification (C/N = 3) was achieved in the pyrite-based VFCW.•The highest TN and TP removal rate were achieved with the pyrite addition (100%).•The mixed addition of pyrite was better ...for N and P removal.•The autotrophic and heterotrophic bacteria were significantly promoted by pyrite.
Deep nitrogen removal from low-carbon wastewater is a pressing water treatment challenge as of yet. Eight sets of vertical-flow constructed wetland (VFCW) intensified by pyrite were designed and applied to treat with low C/N ratio wastewater in this research. The results showed that the addition of pyrite (100% added) significantly promoted TN removal with an efficiency higher than 27.05% under low C/N ratio conditions, indicating that mixotrophic denitrification was achieved in VFCW. Microbial analysis showed that the community structure and diversity of microorganisms were changed significantly, and the growth of autotrophic (Thiobacillus) and heterotrophic bacteria (Thauera) concomitantly enhanced. It is recommended that the addition amount of pyrite is 75% of the wetland volume, meantime, mixing evenly with 25% high porosity substrate (such as activated carbon, volcanic stone, etc.), which could enhance the effective adhesion of microorganisms and their contact area with pyrite, ultimately improve the denitrification capacity of the VFCW.
This study was to enhance the nitrogen removal efficiency in the sequencing batch reactor (SBR) process by adding sulfur-based carriers. The nitrogen removal efficiency of the control group was ...compared with that of the experimental group through a two-series operation of SBR1 without carrier and SBR2 with the carrier under the condition of no external carbon source. A total nitrogen (T-N) removal efficiency of 6.6%, 72.6%, and 79.9% was observed in SBR1, SBR2 (5%), and (10%), respectively. The T-N removal efficiency was improved in the system with carriers, which showed an increase in the removal efficiency of approximately 91.7%. The results suggest that the inclusion of the carrier led to an elevation in the sulfur ratio, implying an augmented surface area for sulfur-based denitrifying microorganisms. Additionally, CaCO3 contributed essential alkalinity for sulfur denitrification, thereby preventing a decline in pH. Regardless of the carrier, the efficiency of organic matter removal surpassed 89%, indicating that the sulfur-based carrier did not adversely affect the biological reaction associated with organic matter. Therefore, autotrophic denitrification was successfully performed using a sulfur carrier in the SBR process without an external carbon source, improving the nitrogen removal efficiency.
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•This study aims to improve the removal efficiency of nitrate nitrogen.•The removal efficiency of T-N was improved by up to about 91.7%.•Thiobacillus and Sulfurimonas were dominant in SBR with sulfur carrier.•The sulfur denitrification reaction has occurred with remarkable accuracy.•CaCO3 played a role in providing the alkalinity required for the sulfur denitrification.
Removal of nitrogen from wastewater with low carbon/nitrogen ratio was treated by using a denitrification packed bed reactor. Composite fillers with both autotrophic and heterotrophic denitrification ...capacity were prepared by mixing melted polycaprolactone and elemental sulfur at various alkalinity ratios (heterotrophic to autotrophic ratios of 1:2, 1:1, 3:2, and 2:1). Optimum denitrification was achieved at a ratio of 2:1. The diversity of the microbial community in the biofilm on the surface of the composite fillers showed that the increase of the elemental sulfur in the composite fillers has led to the increase of the microbial abundance. Furthermore, biofilm composition developed from a single dominant species to multiple species, and genes related to sulfur metabolism increased while those related to denitrification decreased slightly.
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•New composite fillers with mixotrophic denitrification capacity were synthesized.•The pH of the system was well balanced with the filler prepared 2:1 alkalinity ratio.•No accumulation of NO2−-N was observed with NO3− of 30 mg/L in the influent.•Genes related to sulfur metabolism is increased in the mixotrophic system.
Anaerobic ammonium oxidation (anammox), a promising technology for bio-nitrogen removal, has been a research hotspot in the field of leachate treatment. However, the inhibitory effect of organic ...matter and high-strength nitrogen on anammox bacteria and the limitation of the theoretical total nitrogen removal efficiency of anammox (<90%) are obstacles to its wider application. The mechanisms of the inhibitory effects of organic matter, ammonium, and nitrite on anammox bacteria, and the corresponding control strategies are summaries. The anammox-based processes developed for advanced nitrogen removal (ANR) in recent years, including anammox-based heterotrophic denitrification, anammox-based partial denitrification, and anammox-based constructed wetlands are systematically discussed. An integrated anaerobic system of simultaneous denitrification and methanogenesis (anaerobic membrane bioreactor) + anammox-based processes was proposed for the ANR and optimal energy recovery from leachate. This process showed a 16% increase in biogas yield, a 64% decrease in aeration energy consumption, and the decrease in the external carbon source is expected to be 100% compared to conventional leachate treatment processes such as anoxic/oxic-membrane bioreactors. Finally, a few research perspectives on leachate treatment using anammox-based processes are reviewed. The conclusions drawn from the studies presented herein provide guidance for further research and engineering applications in the field of leachate treatment.
Highlights
AnMBR pretreatment is proposed for energy recovery and elimination of inhibition of anammox bacteria by organics.
Anammox-based heterotrophic denitrification, partial denitrification, and anammox-based constructed wetlands are discussed for ANR.
SDM is proposed for ANR from leachate via anammox effluent recirculation.
An SDM(AnMBR)+anammox based process is proposed for energy saving and recovery.
Elemental sulfur-driven autotrophic denitrification (SADN) is a cost-effective approach for treating secondary effluent from wastewater treatment plants (WWTPs). Additional organics are generally ...supplemented to promote total nitrogen (TN) removal, reduce nitrite accumulation and sulfate production, and balance the pH decrease induced by SADN. However, understanding of the impacts of organic supplementation on microbial communities, nitrogen metabolism, denitrifier activity, and SADN rates in sulfur-based denitrification reactors is still limited. Here, a sulfur-based denitrification reactor was continuously operated for 272 days during which six different C/N ratios were tested successively (2.7, 1.5, 0.7, 0.5, 0.25, and 0). Organic supplementation improved TN removal and decreased NO2− accumulation, but reduced the relative abundance of denitrifiers and the contribution of autotrophic nitrate-reducing bacteria (aNRB) to TN removal during the long-term operation of reactor. Predictive functional profiling showed that nitrogen metabolism potential increased with decreasing C/N ratios. SADN was the predominant removal process when the C/N ratio was ≤0.7 (achieving 60% contribution when C/N = 0.7). Although organic supplementation weakened the dominant role of aNRB in denitrification, batch tests for the first time demonstrated that it could accelerate the SADN rate, attributed to the improvement of sulfur bioavailability, likely via the formation of polysulfide. A possible nitrogen removal pathway with multiple electron donors (i.e., sulfur, organics, sulfide, and polysulfide) in a sulfur-based denitrification reactor with organic supplementation was therefore proposed. However, supplementation with a high level of organics could increase the operational cost and effluent concentrations of sulfide and organics as well as enrich heterotrophic denitrifiers. Moreover, microbial community had substantial changes at C/N ratios of >0.5. Accordingly, an optimal C/N ratio of 0.25–0.5 was suggested, which could simultaneously minimize the additional operating cost associated with organic supplementation and maximize TN removal and SADN rates.
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•Overlooked N removal pathways induced by organic supplementation were unraveled.•Organic supplementation accelerated SADN rates likely via the formation of polysulfide.•AD dominated nitrogen removal in a sulfur-based denitrification reactor with a C/N ratio ≤0.7•Organic supplementation with a C/N ratio >0.5 significantly shape the microbial communities.•A C/N ratio range of 0.25–0.5 was recommended to optimize system's performance.
