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.
Fungi play a key role in the nitrogen cycle. Diverse fungi are known to reduce nitrate or nitrite to gaseous nitrogen oxides such as nitric oxide, nitrous oxide (N2O), and dinitrogen via ...denitrification or co-denitrification (microbially mediated nitrosation), and to ammonium via ammonia fermentation (fungal dissimilatory nitrate reduction to ammonium). These processes could significantly contribute to the emission of N2O from soils and the removal of nitrogen from nitrate and nitrite-contaminated environments. However, fungal N2O production may not be necessarily related to their denitrification activity sensu stricto (i.e., reduction of nitrate or nitrite to gaseous N oxides for respiration): N2O can be produced by partially abiotic processes. Therefore, fungi that can reduce nitrate or nitrite to N2O should not be called denitrifying fungi instantaneously. Experiments should be carefully conducted to better discriminate fungal denitrification, co-denitrification, and chemo-denitrification. Various analytical tools have been developed and applied to clarify fungal denitrification and other nitrate/nitrite reduction processes, including the substrate-induced respiration-inhibition method, stable isotope analyses, and culture-dependent and -independent molecular and genomic approaches. In this mini-review, we overview fungal denitrification and other nitrate/nitrite reduction processes, discuss their environmental impacts, summarize recent advancements in the methods to study fungal denitrification, and provide insights on future research opportunities.
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•Fungal denitrification and nitrate/nitrite reduction processes are reviewed.•Fungi greatly contribute to the emission of N2O from soils.•N2O can be produced from non-denitrifying fungi by partially abiotic processes.•Various tools to study fungal denitrification are evaluated.•Future opportunities are discussed to advance the fungal denitrification research.
Antibiotics commonly exist in municipal, livestock and industrial wastewaters. However, the response of key microbiota performance in wastewater treatment plants to antibiotic exposure lacks ...systematic research. In this study, the short-term acute stress of four commonly used antibiotics (sulfamethoxazole, chlortetracycline, ciprofloxacin, and amoxicillin) on microbial denitrification performance was systematically investigated. All tested antibiotics exhibited the inhibitory effects in varying degrees by repeated addition for six cycles. The nitrate removal efficiencies (NrE) decreased to 7.98–26.80%, accompanied by the significant decrease of the expressed narG gene, by exposure to sulfamethoxazole, chlortetracycline or amoxicillin. Nitrite reduction was inhibited more severely than nitrate reduction, which was further verified by the low- or non-expressed nirS and nosZ genes. Furthermore, a higher antibiotic concentration made stronger inhibitory effect. Except for chlortetracycline, 2.09–6.80 times decrease of k value was commonly observed as concentration increased from 10 to 50 or 100 mg L−1. Even in a short period (24 h), antibiotics largely decreased the abundance of the dominant denitrifying bacterial genera (Thauera, Comamonas, etc.), while, some unclassified populations (Labrenzia, Longilinea, etc.) were enriched. This study provides theoretical researches on the microbial denitrification behaviors influenced by exposure to different antibiotics.
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•Selective stress of commonly used antibiotics on denitrification was observed.•Inhibitory on denitrification in varied degree by four antibiotics.•Repeated addition decreased the abundance of denitrifying community structure.•Low expressed narG, nirS and nosZ gene verified the inhibited denitrification.
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•Two biosafety strains were isolated from freshwater aquaculture ponds.•Significant nitrogen removal abilities were detected in the two strains.•The presence and function of the ...denitrification genes were demonstrated.•Immobilization culture assays showed potential application of the two strains.
Two biosafety strains, identified as Pseudomonas mendocina S16 and Enterobacter cloacae DS'5, were isolated from freshwater aquaculture ponds and showed significant heterotrophic nitrification-aerobic denitrification abilities. Within 48 h, the inorganic nitrogen removal efficiencies in the two strains were 66.59 %–97.97 % (S16) and 72.27 %–96.44 % (DS'5). The optimal conditions for organic nitrogen removal of the two strains were temperature 20–35 °C and carbon/nitrogen (C/N) ratio 10–20 while using sodium citrate as the carbon source. Sequence amplification demonstrated the presence of the denitrification genes in both the two strains, and quantitative real-time PCR results showed that the coupled expression of nap + nar would improve the nitrate removal rate in S16. The nitrogen removal efficiencies of the two strains in immobilization culture systems were 79.80 %–98.58 % (S16) and 60.80 %–98.40 % (DS'5). This study indicated the great potential application of the two strains in aquaculture tail water treatment.
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•Biogenic and chemical sulfur were compared for denitrification and membrane fouling.•Biogenic sulfur showed 20% higher denitrification rates than chemical sulfur in MBR.•Trans ...membrane pressures (TMPs) were higher in the MBR fed with biogenic sulfur.•Denitrifying Proteobacteria dominated the microbial communities of both MBRs.
Two sulfur-oxidizing membrane bioreactors (SMBRs) performing autotrophic denitrification at different HRTs (6–26 h), one supplemented with biogenic elemental sulfur (S0bio) and the other with chemically-synthesized elemental sulfur (S0chem), were compared in terms of nitrate reduction rates, impact on membrane filtration and microbial community composition. Complete denitrification with higher rates (up to 286 mg N-NO3−/L d) was observed in the SMBR supplemented with S0bio (SMBRbio), while nitrate was never completely reduced in the SMBR fed with S0chem (SMBRchem). Trans membrane pressure was higher for SMBRbio due to smaller particle size and colloidal properties of S0bio. Microbial communities in the two SMBRs were similar and dominated by Proteobacteria, with Pleomorphomonas and Thermomonas being the most abundant genera in both bioreactors. This study reveals that S0bio can be effectively used for nitrate removal in autotrophic denitrifying MBRs and results in higher nitrate reduction rates compared to S0chem.
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•Transforming heterotrophic to autotrophic denitrification was feasible.•NO2−-N accumulation gradually occurred in the transformation process.•The most complicated interspecific ...interaction was in heterotrophic process.•EC1.7.2.2 promoted the enzymes abundance of NO2−-N accumulation.
For investigating the microbial community, interspecific interaction and nitrogen metabolism during the transform process from heterotrophic to synergistic and autotrophic denitrification, a filter was built, and carbon source and sulfur concentration were changed to release the transformation process. The results demonstrated that the transformation process was feasible to keep nitrate nitrogen (NO3−-N) discharge concentration lower than 15 mg L−1, however, nitrite nitrogen (NO2−-N) accumulation and its rate reached 7.85% at initial stages. The dominant denitrification gunes were Methylophilaceae, Thiovulaceae and Hydrogenophilaceae for three processes, respectively, and the microbial interspecific interaction of heterotrophic denitrification was more complex than others. NO2−-N accumulation was confirmed by the low abundance of EC1.7.7.1 and EC1.7.2.1, and the dominance degree of dark oxidation of sulfur compounds and dark sulfide oxidation improved in synthesis and autotrophic denitrifications.
•Complete nitrate reduction in solid phase denitrification with 0–1 mg L−1 OTC.•Efficient nitrate reduction still achieved after domestication with 5 mg L−1 OTC.•OTC stress mainly promoted ...tetracycline resistance genes abundances.•125 types of denitrifying genera contained otrA favorable for resisting OTC stress.•Denitrification genes NAR, NIR and NOR significantly declined as OTC ≥ 0.25 mg L−1.
The coexistence of nitrate and antibiotics in wastewater is a common problem. The study aimed to explore the response of denitrifying community, denitrification genes and antibiotic resistance genes (ARGs) to oxytetracycline (OTC) stress in polycaprolactone (PCL) supported solid-phase denitrification (SPD) reactors. Complete nitrate reduction (greater than99%) was achieved in SPD system with OTC stress of 0, 0.05, 0.25 and 1 mg L−1 during three-month operation, while it significantly declined by about 5% at a further increased OTC level of 5 mg L−1. The efficient denitrification strongly related with a rich diversity of denitrifiers, while the abundances of which dramatically reduced as the OTC concentration reached ≥0.25 mg L−1, which caused significant decline of denitrification genes, especially for narH, narJ, narI nirD, nosZ, and norB. Tetracycline resistance genes were a major type of promoted ARGs by different OTC stress, mainly related with the increase of tet36, tetG, tetA, tetM and tetC.
Microorganisms play a crucial role in both the nitrogen cycle and greenhouse gas emissions. A recent discovery has unveiled a new denitrification pathway called oxygenic denitrification, entailing ...the enzymatic reduction of nitrite to nitric oxide (NO) by a putative nitric oxide dismutase (nod) enzyme. In this study, the presence of the nod gene was detected and subsequently enriched in anaerobic-activated sludge, farmland soil, and paddy soil samples. After 150 days, the enriched samples exhibited significant denitrification, and concomitant oxygen production. The removal efficiency of nitrite ranged from 64.6 % to 79.0 %, while the oxygen production rate was between 15.4 μL/min and 18.6 μL/min when exposed to a sole nitrogen source of 80 mg/L sodium nitrite. Additionally, batch experiments and kinetic analyses revealed the intricate pathways and underlying mechanisms governing the oxygenic denitrification reaction by using CARBOXY-PTIO, 18O-labelled water, and acetylene to unravel the intricacies of the reaction. The quantitative polymerase chain reaction (qPCR) results indicated a significant surge in the abundance of nod genes, escalating from 7.59 to 10.12-fold. Moreover, analysis of 16S ribosomal DNA (rDNA) amplicons revealed Proteobacteria as the dominant phylum and Thauera as the main genus, with the presumed affiliation. In this study, a new nitrogen conversion pathway, oxygenic denitrification, was discovered in environmental samples. This process provides the possibility for the control of nitrous oxide in the treatment of nitrogenous wastewater.
The carbon source is essential as an electron donor in the heterotrophic denitrification process. When there is a lack of organic carbon sources in the system, an external carbon source is needed to ...improve denitrification efficiency. This review compiles the effects of liquid, solid and gaseous carbon sources on denitrification. Sodium acetate has better denitrification efficiency and is usually the first choice for external carbon sources. Fermentation by-products have been demonstrated to have the same denitrification efficiency as sodium acetate. Compared with cellulose-rich materials, biodegradable polymers have better and more stable denitrification performance in solid-phase nitrification, but their price is higher than the former. Methane as a gaseous carbon source is studied mainly by aerobic methane oxidation coupled with denitrification, which is feasible using methane as a carbon source. Liquid carbon sources are better controlled and utilized than solid carbon sources and gaseous carbon sources. In addition, high carbon to nitrogen ratio and hydraulic retention time can promote denitrification, while high dissolved oxygen (DO>2.0 mg L−1) will inhibit the denitrification process. At the same time, high temperature is conducive to the decomposition of carbon sources by microorganisms. This review also considers the advantages and disadvantages of different carbon sources and cost analysis to provide a reference for looking for more economical and effective external carbon sources in the future.
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•Alternative carbon sources can replace traditional carbon sources to reduce nitrate.•Organic waste as a carbon source is more environmentally friendly and economical.•Mixed carbon sources can increase bioavailability and reduce costs.•The optimization of process parameters is the key to nitrogen removal.
The integrated sulfur- and Fe0-based autotrophic denitrification process in an anoxic fluidized-bed membrane bioreactor (AnFB-MBR) was developed for the nitrate-contaminated water treatment in order ...to control sulfate generation and avoid alkalinity supplement. The nitrate removal rate of the AnFB-MBR reached 1.22 g NO3−-N L−1d−1 with NO3−–N ranging 40–200 mg L−1 at hydraulic retention times of 1.0–5.0 h. The denitrification in the integrated system was simultaneously carried out by sulfur- and Fe0-oxidizing autotrophic denitrifiers. The effluent sulfate generation was decreased by 29.3–70.3% and 31.2–50.9% due to the functional role of Fe0-based denitrification in the integrated system. Alkalinity produced by Fe0-oxidizing autotrophic denitrification could compensate for the alkalinity consumption by sulfur-based autotrophic denitrification. The sulfur- and Fe0-oxidizing autotrophic denitrifying bacterial consortium was composed mainly of bacteria from Thiobacillus, Sulfurimonas, and Geothrix genera. The integrated modes leads to a harmonious co-existence of sulfur- and Fe0-oxidizing denitrifying microbes, which may make a difference to the functional performance of the bioreactor. Overall, the integrated sulfur- and Fe0-based autotrophic denitrification could overcome the shortcomings of excess sulfate generation and external alkalinity supplementation compared to the sole sulfur-based autotrophic denitrification, indicating further potential for the technology in practice.
•Sulfur- and Fe0-based autotrophic denitrification was integrated in AnFB-MBR.•The integrated Sulfur- and Fe0-based denitrification process reduced sulfate production.•The integrated sulfur- and Fe0-based denitrification eliminated alkalinity supplementation.•Thiobacillus, Sulfurimonas, and Geothrix genera dominated in the microbial community.•The communities had implications on the functional performance of the bioreactor.
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