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PubMed2006

Experimental study on denitrification using coated electrode of immobilized denitrifying bacteria.

OBJECTIVE: To develop a coated electrode of immobilized denitrificants and to evaluate the performance of a bioelectrochemical reactor to enhance and control denitrification. METHODS: Denitrifying bacteria were developed by batch incubation and immobilized with polyvinyl alcohol (PVA) on the surface of activated carbon fiber (ACF) to make a coated electrode. Then the coated electrode (cathode) and graphite electrode (anode) were transferred to the reactor to reduce nitrate. RESULTS: After acclimated to the mixtrophic and autotrophic denitrification stages, the denitrifying bacteria could use hydrogen as an electron donor to reduce nitrate. When the initial nitrate concentration was 30.2 mg NO3- -N / L, the denitrification efficiency was 57.3% at an applied electric current of 15 mA and a hydraulic retention time (HRT) of 12 hours. Correspondingly, the current density was 0.083 mA/cm2. The nitrate removal rate of the reactor was 34.4 g NO3- -N/m3 x d, and the surface area loading was 1.34 g NO3- -N / m2 x d. CONCLUSION: The coated electrode may keep high quantity of biomass, thus achieving a high denitrification rate. Denitrification efficiencies are related to HRT, current density, oxidation reduction potential (ORP), dissolved oxygen (DO), pH value, and temperature.

Adsorption↗

PubMed1991

Marker exchange of the structural genes for nitric oxide reductase blocks the denitrification pathway of Pseudomonas stutzeri at nitric oxide.

Bacterial denitrification reverses nitrogen fixation in the global N-cycle by transforming nitrate or nitrite to dinitrogen. Both nitrite and nitric oxide (NO) are considered as the chemical species within the denitrification pathway, that precede nitrous oxide (N2O), the first recognized intermediate with N,N-bonds antecedent to N2. Molecular cloning of the structural genes for NO reductase from Pseudomonas stutzeri has allowed us to generate the first mutants defective in NO utilization (Nor- phenotype) by marker exchange of the norCB genes with a gene cassette for gentamicin resistance. Nitric oxide reductase was found to be an indispensable component for denitrification; its loss constituted a conditionally lethal mutation. NO as the sole product accumulated from nitrite by mutant cells induced for nitrite respiration (denitrification). The Nor- mutant lost the capability to reduce NO and did not grow anymore anaerobically on nitrate. A Nir-Nor- double mutation, that inactivated also the respiratory nitrite reductase cytochrome cd1 rendered the bacterium again viable under anaerobiosis. Our observations provide evidence for a denitrification pathway in vivo of NO2(-)----NO----N2O, and N,N-bond formation catalyzed by NO reductase and not by cytochrome cd1.

Amino Acid Sequence↗

PubMed1983

Denitrification of high concentrations of nitrites and nitrates in synthetic medium with different sources of organic carbon. II. Ethanol.

The course of denitrification of nitrites and nitrates (1000 mg N/l) in medium containing ethanol as a source of organic carbon was studied. Continuous cultures of a mixed population of autochtonous microflora isolated from the bottom sludge of a nitrogenous wastewater reservoir were set up in two types of culture units: chemostat-type column and anaerobic packed bed reactor. In medium with nitrites denitrification was found to be strongly inhibited by alkalization of the medium (efficiency of denitrification 17.7 mg N/l/h). When pH was adjusted the efficiency of nitrite denitrification was identical as for nitrates (166.3 mg N/l/h). The denitrification of 1 g of nitrate or nitrite nitrogen was found to require 2.00 and 1.28 g ethanol, respectively.

Bacteria↗

PubMedDate not supplied

Mechanism of charged pollutants removal in an ion exchange membrane bioreactor: drinking water denitrification.

The mechanism of anionic pollutant removal in an ion exchange membrane bioreactor (IEMB) was studied for drinking water denitrification. This hybrid process combines continuous ion exchange transport (Donnan dialysis) of nitrate and its simultaneous bioreduction to gaseous nitrogen. A nonporous mono-anion permselective membrane precludes direct contact between the polluted water and the denitrifying culture and prevents secondary pollution of the treated water with dissolved nutrients and metabolic products. Complete denitrification may be achieved without accumulation of NO3(-) and NO2(-) ions in the biocompartment. Focus was given to the effect of the concentration of co-ions, counterions, and ethanol on the IEMB performance. The nitrate overall mass transfer coefficient in this hybrid process was found to be 2.8 times higher compared to that in a pure Donnan dialysis process without denitrification. Furthermore, by adjusting the ratio of co-ions between the biocompartment and the polluted water compartment, the magnitude and direction of each individual anion flux can be easily regulated, allowing for flexible process operation and control. Synthetic groundwater containing 135-350 mg NO3(-) L(-1) was treated in the IEMB system. A surface denitrification rate of 33 g NO3(-) per square meter of membrane per day was obtained at a nitrate loading rate of 360 g NO3(-) m(-3)d(-1), resulting in a nitrate removal efficiency of 85%.

Bioreactors↗

PubMed1990

Combined heterotrophic nitrification and aerobic denitrification in Thiosphaera pantotropha and other bacteria.

Reports of the simultaneous use of oxygen and denitrification by different species of bacteria have become more common over the past few years. Research with some strains (e.g. Thiosphaera pantotropha) has indicated that there might be a link between this 'aerobic denitrification' and a form of nitrification which requires rather than generates energy and is therefore known as heterotrophic nitrification. This paper reviews recent research into heterotrophic nitrification and aerobic denitrification, and presents a preliminary model which, if verified, will provide at least a partial explanation for the simultaneous occurrence of nitrification and denitrification in some bacteria.

Aerobiosis↗

PubMed1992

Heterotrophic nitrification and aerobic denitrification in Alcaligenes faecalis strain TUD.

Heterotrophic nitrification and aerobic and anaerobic denitrification by Alcaligenes faecalis strain TUD were studied in continuous cultures under various environmental conditions. Both nitrification and denitrification activities increased with the dilution rate. At dissolved oxygen concentrations above 46% air saturation, hydroxylamine, nitrite and nitrate accumulated, indicating that both the nitrification and denitrification were less efficient. The overall nitrification activity was, however, essentially unaffected by the oxygen concentration. The nitrification rate increased with increasing ammonia concentration, but was lower in the presence of nitrate or nitrite. When present, hydroxylamine, was nitrified preferentially. Relatively low concentrations of acetate caused substrate inhibition (KI = 109 microM acetate). Denitrifying or assimilatory nitrate reductase were not detected, and the copper nitrite reductase, rather than cytochrome cd, was present. Thiosulphate (a potential inhibitor of heterotrophic nitrification) was oxidized by A. faecalis strain TUD, with a maximum oxygen uptake rate of 140-170 nmol O2.min-1.mg prot-1. Comparison of the behaviour of A. faecalis TUD with that of other bacteria capable of heterotrophic nitrification and aerobic denitrification established that the response of these organisms to environmental parameters is not uniform. Similarities were found in their responses to dissolved oxygen concentrations, growth rate and ammonia concentration. However, they differed in their responses to externally supplied nitrite and nitrate.

Aerobiosis↗

PubMed2003

Bacterial diversity in a marine methanol-fed denitrification reactor at the montreal biodome, Canada.

The bacterial biota of a methanol-fed denitrification reactor used to treat seawater at the Montreal Biodome were investigated using culture-dependent and molecular biology methods. The microbiota extracted from the reactor carriers were cultivated on three media. Three isolate types were recovered and their 16S ribosomal DNA (rDNA) genes were determined. The analysis showed that the isolate types were related to alpha-Proteobacteria. They are members of the Hyphomicrobium and Paracoccus genera and the Phyllobacteriaceae family. Uncultured bacteria were identified through a 16S rDNA library generated from total DNA extracted from the microbiota. Clones were screened for different restriction profiles and for different DGGE (denaturing gradient gel electrophoresis) migration profiles. More than 70% of clones have the same restriction profile, and the sequence of representative clones showed a relation with the Methylophaga members of the Piscirickettsia family (gamma-Proteobacteria). Sequences from other profiles were related to bacterial species involved in denitrification. The number of species in the denitrification reactor was estimated at 15. Bacterial colonization on newly added carriers in the denitrification reactor was monitored by PCR-DGGE. The DGGE migration profiles evolved during the first 5 weeks and then remained essentially unchanged. PCR-DGGE was also used to monitor the microbial profiles in various aquarium locations. As expected, bacterial populations differed from one location to another, except for the sand and trickling filters which presented similar DGGE migration profiles.

Alphaproteobacteria↗

PubMed2003

Stimulation of soil nitrification and denitrification by grazing in grasslands: do changes in plant species composition matter?

Stimulation of nitrification and denitrification by long term (from years to decades) grazing has commonly been reported in different grassland ecosystems. However, grazing generally induces important changes in plant species composition, and whether changes in nitrification and denitrification are primarily due to changes in vegetation composition has never been tested. We compared soil nitrification- and denitrification-enzyme activities (NEA and DEA, respectively) between semi-natural grassland sites experiencing intensive (IG) and light (LG) grazing/mowing regimes for 13 years. Mean NEA and DEA (i.e. observed from random soil sampling) were higher in IG than LG sites. The NEA/DEA ratio was higher in IG than LG sites, indicating a higher stimulation of nitrification. Marked changes in plant species composition were observed in response to the grazing/mowing regime. In particular, the specific phytomass volume of Elymus repens was lower in IG than LG sites, whereas the specific volume of Lolium perenne was higher in IG than LG sites. In contrast, the specific volume of Holcus lanatus, Poa trivialis and Arrhenatherum elatius were not significantly different between treatments. Soils sampled beneath grass tussocks of the last three species exhibited higher DEA, NEA and NEA/DEA ratio in IG than LG sites. For a given grazing regime, plant species did not affect significantly soil DEA, NEA and NEA/DEA ratio. The modification of plant species composition is thus not the primary factor driving changes in nitrification and denitrification in semi-natural grassland ecosystems experiencing long term intensive grazing. Factors such as trampling, N returned in animal excreta, and/or modification of N uptake and C exudation by frequently defoliated plants could be responsible for the enhanced microbial activities.

Animals↗

PubMed1988

A review of denitrification in on-site wastewater treatment systems.

The literature on denitrification and its relationship to on-site wastewater systems was reviewed. Denitrification is an important nitrogen removal mechanism in some alternative on-site wastewater systems. Nitrogen removal rates for conventional septic tank systems may vary from 0% to 35% but should be increased by pressure dosing. Denitrification rates for conventional on-site wastewater systems will depend upon loading rate, soil types and the height of the water table below the soil adsorption bed. Some alternative on-site wastewater systems may remove 70% to 80% of the nitrogen if a supplemental carbon source is used. Methanol and household wastes have been used as carbon sources. Crust formation in a soil adsorption bed may improve denitrification.

Journal Article↗

PubMed2006

Direct measurement of denitrification activity in a Gulf coast freshwater marsh receiving diverted Mississippi River water.

Wetland loss along the Louisiana Gulf coast and excessive nitrate loading into the Gulf of Mexico are interrelated environmental problems. Nitrate removal by soil denitrification activity was studied in a ponded freshwater marsh receiving diverted Mississippi River water for the purpose of reversing or slowing wetland loss. Labeled (15)N-nitrate was applied at 3.8 g N m(-2) into four replicate study plots after removing above ground vegetation. Nitrogen gas (N(2)) and nitrous oxide (N(2)O) emissions from the plots were determined by isotope ratio mass spectrometry (IRMS). Nitrous oxide emissions were also compared with the results determined by gas chromatograph (GC). Results showed that it took 2 weeks to remove the added nitrate with N(2)O emission occurring over a period of 4d. The apparent denitrification dynamics were assumed to follow the Michaelis-Menten equation. The maximum denitrification rate and K(m) value were determined as 12.6 mg N m(-2)h(-1), and 6.5 mg Nl(-1), respectively. Therefore the maximum capacity for nitrate removal by the marsh soil would be equivalent to 110 g N m(-2)yr(-1), with more than 30% of nitrogen gas evolved as N(2)O. For typical nitrate concentrations in Mississippi River water of about 1 mg N l(-1), nitrate would be removed at a rate of 14.7 g N m(-2)yr(-1) with N(2)O emission about 1.5%. A denitrification dynamic model showed that the efficiency of nitrate removal would largely depend on the water discharge rate into the ponded wetland. Higher discharge rate will result in less retention time for the water in the marsh where nitrate is denitrified.

Fresh Water↗

PubMed2006

Solid phase microextraction-gas chromatographic-mass spectrometric determination of nitrous oxide evolution to measure denitrification in estuarine soils and sediments.

A SPME-GC-MS method was developed to quantify nitrous oxide (N(2)O) to evaluate denitrification rates. There is a need for this sensitive and definitive N(2)O detection method to accurately measure the soil and sediment ability to convert anthropogenic mineral nitrogen loads to N(2) through denitrification hence decreasing estuarine waterway pollution loading. This method is applied to measure denitrification, which is a major pathway for inorganic nitrogen removal, by incorporating the acetylene (C(2)H(2)) block method on anaerobic assays. Currently, denitrification is largely measured using GCs fitted with TCD or ECD detectors. With a mean R(2) value of 0.996, the calibration curve spanned over three orders of magnitude (4.1-2030 nM) with a limit of detection (LOD) of 4.1 nM N(2)O (18 ppb) and a limit of quantification (LOQ) of 16 nM N(2)O (72 ppb). This detection method was valid with less than 15% relative standard deviation (RSD) and error for middle and high quality control (QC) points and less than 20% for low QC points on three experimental days. Measuring N(2)O using SPME-GC-MS technology allows for confidence in identification, high sensitivity, reproducibility, and short run times.

Chemical Fractionation↗

PubMed2005

Denitrification by the mix-culturing of fungi and bacteria with shell.

Denitrification by pure and mixed culture of Fusarium oxysporum and Pseudomonas stutzeri in different mineral medium and in synthetic wastewater were examined. The results obtained revealed that a rapid N2 evolution by F. oxysporum and P. stutzeri in mineral medium and synthetic wastewater was observed. In co-cultures of F. oxysporum and P. stutzeri, N2O produced by F. oxysporum was rapidly consumed by P. stutzeri. This indicated that mixed culture of F. oxysporum and P. stutzeri could be used for efficient nitrate and nitrite removal. Using synthetic wastewater, about 87% of nitrate was reduced by co-denitrification of F. oxysporum and P. stutzeri after incubation for 6 days. In the further denitrification tests, the interaction of shell and mixed culture of F. oxysporum and P. stutzeri was investigated. The dinitrogen was rapidly evolved (442.48 micromol N2 produced from 1.0 mmol of NO3(-) in 36 h). These results clearly showed that shell provide a suitable microenvironment for P. stutzeri, which is beneficial to the denitrification.

Biodegradation, Environmental↗

PubMed2004

Evidence of anoxic methane oxidation coupled to denitrification.

Denitrification using methane as sole electron donor under anoxic condition was investigated. Sludge produced by a denitrifying reactor using acetate as electron donor was put in contact with methane at partial pressures from 1.8 to 35.7kPa. Nitrate depletion and gaseous nitrogen production were measured. The denitrification rate was independent of the methane partial pressure when superior or equal to 8.8kPa. The nitrate depletion was asymptotic. A denitrification rate of 0.25g NO(3)(-)-Ng(-1) VSSd(-1) was observed at the onset of culturing, followed by a slower and lineal denitrification rate of 4.9x10(-3)g NO(3)(-)-Ng(-1) VSSd(-1). Abiotic nitrate removal or the availability of another carbon source were discarded from control experiments made in the absence of methane or using sterilized inoculum.

Atmospheric Pressure↗

PubMed2004

Biodegradation and effect of formaldehyde and phenol on the denitrification process.

Formaldehyde and phenol biodegradation during the denitrification process was studied at lab-scale, first in anoxic batch assays and then in a continuous anoxic reactor. The biodegradation of formaldehyde (260 mgl(-1)) as single carbon source and at phenol concentrations ranging from 30 to 580 mgl(-1) was investigated in batch assays, obtaining an initial biodegradation rate around 0.5g CH(2)OgVSS(-1)d(-1). With regard to phenol, its complete biodegradation was only observed at initial concentrations of 30 and 180 mgl(-1). The denitrification process was inhibited at phenol concentrations higher than 360 mgl(-1). Studies were also done using a continuous anoxic upflow sludge blanket reactor in which formaldehyde removal efficiencies above 99.5% were obtained at all the applied formaldehyde loading rates, between 0.89 and 0.14g COD (CH(2)O)l(-1)d(-1). The phenol loading rate was increased from 0.03 to 1.3g COD (C(6)H(6)O)l(-1)d(-1). Phenol removal efficiencies above 90.6% were obtained at phenol concentrations in the influent between 27 and 755 mgl(-1). However, when the phenol concentration was increased to 1010 mgl(-1), its removal efficiency decreased. Denitrification percentages around 98.4% were obtained with phenol concentrations in the influent up to 755 mgl(-1). After increasing phenol concentration to 1010 mgl(-1), the denitrification percentage decreased because of the inhibition caused by phenol.

Biodegradation, Environmental↗

PubMed2007

Hydrogen-dependent denitrification of water in an anaerobic submerged membrane bioreactor coupled with a novel hydrogen delivery system.

Hydrogen-dependent denitrification has gained significant attention due to its potential economic advantage over heterotrophic denitrification. However, effective hydrogen delivery and biomass retention under anaerobic conditions are significant challenges to implementation of this process. An innovative hydrogenotrophic denitrification system, that addresses these challenges, consisting of an anaerobic submerged membrane bioreactor (MBR) and a novel hydrogen delivery unit, was evaluated for removal of nitrate from a synthetic groundwater feed. The hydrogen delivery unit was designed to release hydrogen-supersaturated water to the reactor and was efficient in hydrogen delivery, providing complete mass transfer. The anaerobic submerged MBR was successful in both reducing nitrate from 25 mg NO(3)-Nl(-1) to below detection and separating biomass from treated water to produce effluent free of suspended solids. Nitrogen gas produced during denitrification was internally recycled to effectively achieve membrane scouring and reactor mixing. The total organic carbon was similar to that of the incoming feed water, averaging approximately 6 mgl(-1).

Anaerobiosis↗

PubMed2001

Simultaneous methanogenesis and denitrification of pretreated effluents from a fish canning industry.

A lab-scale hybrid upflow sludge bed-filter (USBF) reactor was employed to carry out methanogenesis and denitrification of the effluent from an anaerobic industrial reactor (EAIR) in a fish canning industry. The reactor was initially inoculated with methanogenic sludge and there were two different operational steps. During the first step (Step I: days 1-61), the methanogenic process was carried out at organic loading rates (OLR) of 1.0-1.25 g COD l-1 d-1 reaching COD removal percentages of 80%. During the second step (Step II: days 62-109) nitrate was added as KNO3 to the industrial effluent and the OLR was varied between 1.0 and 1.25 g COD l-1 d-1. Two different nitrogen loads of 0.10 and 0.22 g NO3(-)-N l-1 d-1 were applied and these led to nitrogen removal percentages of around 100% in both cases and COD removal percentages of around 80%. Carbon to nitrogen ratio (C:N) in the influent was maintained at 2.0 and eventually it was increased to 3.0, by means of glucose addition, to control the denitrification process. From these results it is possible to establish that wastewater produced in a fish canning industry can be used as a carbon source for denitrification and that denitrifying microorganisms were present in the initially methanogenic sludge. Biomass productions of 0.23 and 0.61 g VSS:g TOC fed for Steps I and II, respectively, were calculated from carbon global balances, showing an increase in biomass growth due to denitrification.

Animals↗

PubMed2001

Denitrification of groundwater with methane as sole hydrogen donor.

It was examined, whether methane can be used as hydrogen donor for an in situ denitrification of groundwater. It is demonstrated, that groundwater can serve as liquid medium and that the denitrification can occur at 10 degrees C. Efforts to enrich methanotrophic bacteria under anoxic conditions have not been successful. No methane oxidation occurred in the absence of oxygen. For this reason, the denitrification with methane must be performed in a two-stage process with aerobic methanotrophic bacteria producing metabolites, that are used as hydrogen donor by non-methanotrophic bacteria in anoxic areas. This kind of indirect denitrification was proved by quantifying nitrogen and nitrous oxide in enrichment cultures that were not stirred or shaken. Large numbers of non-methanotrophic bacteria being able to denitrify with methanol, acetate or proteins as sole hydrogen donor were enriched besides the methanotrophic bacteria under these conditions.

Aerobiosis↗

PubMed2003

Denitrification at low temperatures using a suspended carrier biofilm process.

The denitrification process was studied in a stirred lab-scale suspended carrier biofilm reactor at low temperatures (3-20 degrees C). The reactor was filled to 50% with Kaldnes K1 carriers. The denitrification rate showed only a rather weak dependence on the temperature, the rate at 3 degrees C being approximately 55% of that at 15 degrees C. The maximum denitrification rate obtained at 15 degrees C was 2.7 g NO(x)(-)-Nm(-2)carrier d (-1). The maximum denitrification rate at 3 degrees C during an 8-day period was found to be constant. During the 8 days, the hydraulic retention time was approximately 1.5h and the inlet NO(3)(-)-N concentration was 30 mg x l(-1).

Biofilms↗