Role Of Denitrification Research Articles

Effect of organic carbon on the production of biofuel nitrous oxide during the denitrification process

The carbon source plays an important role in denitrification for nitrogen removal from wastewater. In this study, the denitrification performance and nitrous oxide (N2O) generation in four sequencing batch reactors (SBRs) fed with methanol, ethanol, sodium acetate and glucose were investigated. The maximum N2O generation was achieved when glucose was used as the carbon source, with a N2O conversion ratio of 56%. The high conversion ratio was contributed from the organic carbon of glucose and the glucose-acclimated denitrifiers. The nitrite accumulation and N2O generation during denitrification with glucose as the carbon source increased with increasing chemical oxygen demand to nitrogen ratios in the range of 2–8. The microbial community and their relative abundances varied greatly in the four reactors, and a low abundance of Thauera was found in the glucose-fed SBR, which might contribute to the greater N2O production. Practical strategies for N2O generation from the denitrification process using glucose as the carbon source were proposed so as to achieve energy recovery from nitrogen in wastewater.

The Role of Denitrification in Stormwater Detention Basin Treatment of Nitrogen.

The nitrogen (N) cycling dynamics of four stormwater basins, two often saturated sites ("Wet Basins") and two quick draining sites ("Dry Basins"), were monitored over a ∼ 1-year period. This study paired stormwater and greenhouse gas monitoring with microbial analyses to elucidate the mechanisms controlling N treatment. Annual dissolved inorganic N (DIN) mass reductions (inflow minus outflow) were greater in the Dry Basin than in the Wet Basin, 2.16 vs 0.75 g N m-2 yr-1, respectively. The Dry Basin infiltrated a much larger volume of water and thus had greater DIN mass reductions, even though incoming and outgoing DIN concentrations were statistically the same for both sites. Wet Basins had higher proportions of denitrification genes and potential denitrification rates. The Wet Basin was capable of denitrifying 58% of incoming DIN, whereas the Dry Basin only denitrified 1%. These results emphasize the need for more mechanistic attention to basin design because the reductions calculated by comparing inflow and outflow loads may not be relevant at watershed scales. Denitrification is the only way to fully remove DIN from the terrestrial environment and receiving waterbodies. Consequently, at the watershed scale the Wet Basin may have better overall DIN treatment.

A nitrogen removal system to limit water exchange for recirculating freshwater aquarium using DHS–USB reactor

ABSTRACTThis study proposes a biological nitrogen removal system for freshwater aquaria consisting of a down-flow hanging sponge (DHS) and an up-flow sludge blanket (USB). DHS–USB systems can perform nitrification and denitrification simultaneously, reducing ammonia (NH3) and nitrate (NO3−) toxicity in the water. The performance of the system was evaluated using on-site fresh water aquaria at ambient temperature (23–34°C) over 192 days. NH3 and nitrite (NO2−) were maintained at a detection limit of 0.01 mg N L−1 and NO3− was maintained below 10 mg N L−1, despite limited water exchange. The 16S rRNA gene of microorganisms from the sludge retained in the bioreactors was sequenced to identify the microbial communities present. Microbial community analysis revealed that ammonia oxidizing archaea (AOA), Ca. Nitrososphaera and Nitrosopumilus, played an important role in nitrification in the DHS reactor, while denitrifying bacteria Thauera played an important role in denitrification in the USB reactor. The proposed DHS–USB system is a promising technological advancement in the development of lower maintenance aquaria.

Revealing the bacterial profile of an anoxic-aerobic moving-bed biofilm reactor system treating a chemical industry wastewater

This study aimed at the characterization of the microbial community diversity of a moving bed-biofilm reactor (MBBR) system by pyrosequencing the 16S rRNA gene. The MBBR process comprised two stages (anoxic and aerobic) for organic matter and nitrogen removal from a pesticide-producing industry wastewater. Over 15,000 sequence reads from each reactor were analysed after 400 days of operation. Despite similar values of bacterial richness, the aerobic reactor exhibited a more equitable distribution of the bacterial groups, leading to higher values of diversity. Proteobacteria was observed to be the most dominant classified phylum in both reactors, accounting for more than 80% of the reads, while Alphaproteobacteria was preponderant at the class level. As observed for both phylum and class levels, the genus diversity was less pronounced in the anoxic reactor, which was highly dominated by very few genera. Among them, Hyphomicrobium (21%) was the most frequent one. These organisms possibly played an important role in denitrification, as COD abatement in the non-aerated reactor was mainly coupled to nitrite/nitrate reduction. The aerobic tank was dominated by the genus Methylobacillus (13%). Thiobacillus corresponded to the second most relevant genus in both reactors. As expected, no nitrifying bacteria were detected in the anoxic biofilm. In the aerated tank, however, ammonium oxidizers were represented by the Nitrosomonas genus, accounting for 2.5% of the entire bacterial population. Nitrospira- and Nitrobacter-like nitrite oxidizers coexisted in the aerobic reactor. The former was almost 10 times more frequent than the latter, despite the occurrence of salt shock loading events.

The effects of oxygen and metal oxide catalysts on the reduction reaction of NO with lignite char during combustion flue gas cleaning

The development of lignite-char-supported metal oxide catalyst for reduction of nitric oxide (NO) is investigated in this paper. The characteristics of NO reduction by copper and iron oxide catalysts supported on activated lignite chars (ALC) was studied using a fixed-bed reactor at 300°C. The results showed that the impregnation of Cu on ALC resulted in higher catalytic reactivity during NO reduction compared with that of Fe. Chemisorption of O2 and NO on Cu/ALC catalyst was found to play an important role in denitrification. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses showed that chemically adsorbed oxygen facilitates the formation of C(O) complex and oxidation of Cu0 to Cu+ for Cu/ALC catalyst. The C(O) intermediates and C* production formed due to the fact that C/O2 reaction promoted the reduction of NO. It is suggested that the catalytic reaction of NO in this case comprised of C/O2 reaction, C(O)/NO reaction and formation of N2 and CO2. Cu seemed to have significantly promoted the C(O) formation and CO oxidation compared with Fe. The catalytic reactivity of Cu species for C(O) formation and CO oxidation followed the order of Cu0>Cu+>Cu2+. Fe3O4 was believed to be the active phase in Fe catalyst. The oxygen and char-supported metal catalysts significantly promoted C/NO reaction, and therefore may lead to a lower operation temperature of NOx removal.

Toxicity of TiO₂ nanoparticle to denitrifying strain CFY1 and the impact on microbial community structures in activated sludge.

The antibacterial activity of titanium dioxide nanoparticles (TiO2 NPs) is well described, but little is known of their impact on specific microbial functions such as denitrification, nor on microbial community structure. In this study, a denitrifier (named as Pseudomonas stutzeri CFY1), which was isolated from the activated sludge and could remove up to 111.68 mg/L of NO3(-)-N under aerobic conditions, was utilized to evaluate the influences of TiO2 NPs on its nitrogen removal ability and associated gene expression under aerobic conditions. The variations of the bacterial diversity of activated sludge were also observed. The results showed that antibacterial activity increased with increasing concentrations of TiO2 NPs. Increased production of reactive oxygen species was responsible for TiO2 NPs toxicity. An up-regulation of denitrification genes was observed with increasing concentrations of TiO2 NPs under aerobic conditions. Accordingly, denitrification by P. stutzeri was accelerated when the concentration of TiO2 NPs was increased to 50 mg/L. However, the denitrification of CFY1 was inhibited at low concentrations of TiO2 NPs (5-25 mg/L), indicating that assimilatory and dissimilatory denitrification were synchronized in P. stutzeri CFY1; the latter process plays a major role in denitrification. Further study of the community using 454 pyrosequencing showed that after 7 days of exposure to 50 mg/L TiO2 NPs, the microbial composition of the activated sludge was significantly different and had a lower diversity compared to the controls.

Partial Nitrification and Denitrifying Phosphorus Removal in a Pilot-Scale ABR/MBR Combined Process

A pilot-scale combined process consisting of an anaerobic baffled reactor (ABR) and an aerobic membrane bioreactor (MBR) for the purpose of achieving easy management, low energy demands, and high efficiencies on nutrient removal from municipal wastewater was investigated. The process operated at room temperature with hydraulic retention time (HRT) of 7.5 h, recycle ratio 1 of 200%, recycle ratio 2 of 100%, and dissolved oxygen (DO) of 1 mg/L and achieved good effluent quality with chemical oxygen demand (COD) of 25 mg/L, NH4 (+)-N of 4 mg/L, total nitrogen (TN) of 11 mg/L, and total phosphorus (TP) of 0.7 mg/L. The MBR achieved partial nitrification, and NO2 (-)-N has been accumulated (4 mg/L). Efficient short-cut denitrification was occurred in the ABR with a TN removal efficiency of 51%, while the role of denitrification and phosphorus removal removed partial TN (14%). Furthermore, nitrogen was further removed (11%) by simultaneous nitrification and denitrification in the MBR. In addition, phosphorus accumulating organisms in the MBR sufficiently uptake phosphorus; thus, effluent TP further reduced with a TP removal efficiency of 84%. Analysis of fluorescence in situ hybridization (FISH) showed that ammonia oxidizing bacteria (AOB) and phosphorus accumulating organisms (PAOs) were enriched in the process. In addition, the accumulation of NO2 (-)-N was contributed to the inhibition on the activities of the NOB rather than its elimination.

Denitrification accelerates granular sludge formation in sequencing batch reactors

In this study, the role of denitrification on aerobic granular sludge formation in sequencing batch reactors (SBRs) was investigated. Formation of aerobic granular sludge was faster in SBRs fed with varying concentrations of nitrate or nitrite as compared to control, which received no nitrate or nitrite in the feed. The majority of the fed nitrate or nitrite was denitrified in the anoxic static fill phase, prior to aerobic reaction phase. Sludge characterization showed accumulation of calcium and chemical signature of calcium carbonate in the nitrate-fed SBRs. Feeding of sodium nitroprusside, a known nitric oxide (NO) donor, enhanced aggregation, production of extracellular polymeric substances and formation of aerobic granular sludge. The results support the hypothesis that denitrification facilitates cell aggregation and accelerates aerobic sludge granulation through NO signaling and CaCO3 formation. Nitrate or other intermediates of heterotrophic denitrification, therefore, have a positive effect on aerobic granulation in SBRs.

Contrasting Nutrient Mitigation and Denitrification Potential of Agricultural Drainage Environments with Different Emergent Aquatic Macrophytes.

Remediation of excess nitrogen (N) in agricultural runoff can be enhanced by establishing wetland vegetation, but the role of denitrification in N removal is not well understood in drainage ditches. We quantified differences in N retention during experimental runoff events followed by stagnant periods in mesocosms planted in three different vegetation treatments: unvegetated, cutgrass [ (L.) Sw.], and common cattail ( L.). We also quantified denitrification rates using membrane inlet mass spectrometry from intact cores extracted from each mesocosm treatment. All treatments retained 60% or more of NO-N loads during the 6-h experimental runoff event, but mesocosms planted with cutgrass had significantly higher (68%) retention than the cattail (60%) or unvegetated (61%) treatments. After the runoff event, mesocosms planted in cattail reduced NO-N concentrations by >95% within 24 h and cutgrass achieved similar reductions within 48 h, whereas reductions in the unvegetated mesocosms were significantly less (65%). Cores from cutgrass mesocosms had significantly higher average denitrification rates (5.93 mg m h), accounting for as much as 56% of the immobilized NO-N within 48 h, whereas denitrification rates were minimal in cores from the unvegetated (-0.19 mg m h) and cattail (0.2 mg m h) mesocosms. Our findings have implications for mitigating excess NO-N in agricultural runoff. While vegetated treatments removed excess NO-N from the water column at similar and significantly higher rates than unvegetated treatments, the high denitrification rates observed for cutgrass highlight the potential for permanent removal of excess N from agricultural runoff in vegetated ditches and wetlands.

Nitrate removal from high strength nitrate-bearing wastes in granular sludge sequencing batch reactors

A 6-L sequencing batch reactor (SBR) was operated for development of granular sludge capable of denitrification of high strength nitrates. Complete and stable denitrification of up to 5420mgL(-1) nitrate-N (2710mgL(-1) nitrate-N in reactor) was achieved by feeding simulated nitrate waste at a C/N ratio of 3. Compact and dense denitrifying granular sludge with relatively stable microbial community was developed during reactor operation. Accumulation of large amounts of nitrite due to incomplete denitrification occurred when the SBR was fed with 5420mgL(-1) NO3-N at a C/N ratio of 2. Complete denitrification could not be achieved at this C/N ratio, even after one week of reactor operation as the nitrite levels continued to accumulate. In order to improve denitrification performance, the reactor was fed with nitrate concentrations of 1354mgL(-1), while keeping C/N ratio at 2. Subsequently, nitrate concentration in the feed was increased in a step-wise manner to establish complete denitrification of 5420mgL(-1) NO3-N at a C/N ratio of 2. The results show that substrate concentration plays an important role in denitrification of high strength nitrate by influencing nitrite accumulation. Complete denitrification of high strength nitrates can be achieved at lower substrate concentrations, by an appropriate acclimatization strategy.

NirN Protein from Pseudomonas aeruginosa is a Novel Electron-bifurcating Dehydrogenase Catalyzing the Last Step of Heme d1 Biosynthesis

Heme d1 plays an important role in denitrification as the essential cofactor of the cytochrome cd1 nitrite reductase NirS. At present, the biosynthesis of heme d1 is only partially understood. The last step of heme d1 biosynthesis requires a so far unknown enzyme that catalyzes the introduction of a double bond into one of the propionate side chains of the tetrapyrrole yielding the corresponding acrylate side chain. In this study, we show that a Pseudomonas aeruginosa PAO1 strain lacking the NirN protein does not produce heme d1. Instead, the NirS purified from this strain contains the heme d1 precursor dihydro-heme d1 lacking the acrylic double bond, as indicated by UV-visible absorption spectroscopy and resonance Raman spectroscopy. Furthermore, the dihydro-heme d1 was extracted from purified NirS and characterized by UV-visible absorption spectroscopy and finally identified by high-resolution electrospray ionization mass spectrometry. Moreover, we show that purified NirN from P. aeruginosa binds the dihydro-heme d1 and catalyzes the introduction of the acrylic double bond in vitro. Strikingly, NirN uses an electron bifurcation mechanism for the two-electron oxidation reaction, during which one electron ends up on its heme c cofactor and the second electron reduces the substrate/product from the ferric to the ferrous state. On the basis of our results, we propose novel roles for the proteins NirN and NirF during the biosynthesis of heme d1.

Vertical Flow Constructed Wetland Spherical Light Ceramsite Substrate Nitrogen Factor Research

Haydite as filler, selecting canna as wetland plant denitrification effect of vertical flow constructed wetland research. In terms of the mechanism of denitrification, in view of the ceramsite adsorption, microbiological nitrification and denitrification reaction, plants absorb test in three aspects and to study the effect of various factors. Adsorption experiment, ceramsite to NH4+_N adsorption reached the maximum at 4 h, adsorption intensity is 0.0045 mg/g, device of NH4+_N in the running 92 days maximum theory is 1296 g. Microbial average intensity of nitration was 0.750 mg.h-1.kg-1. The denitrifying intensity of 1.090 mg.h-1.kg-1. Canna root, stem and leaf nitrogen content were increased by 7.73%, 7.73% and 9.92% per plant cannas average of 1.189 g, nitrogen absorption during the running period of 10 plants absorb about 11.89 g. Vertical flow constructed wetland, the choice of spherical light ceramsite substrate adsorption strength, suitable for packing of wetland. Canna better effect on the absorption of nitrogen, of the three microbes plays a main role for denitrification.

流域における窒素除去過程としての脱窒の役割

流域における窒素除去過程としての脱窒の役割

Acceleration of Denitrification in Turbid Rivers Due to Denitrification Occurring on Suspended Sediment in Oxic Waters

High suspended sediment (SPS) concentration exists in many rivers of the world. In the present study, the effects of SPS concentration on denitrification were investigated in airtight chambers with sediment samples collected from the Yellow River which is the largest turbid river in the world. Results from the nitrogen stable ((15)N) isotopic tracer experiments showed that denitrification could occur on SPS in oxic waters and the denitrification rate increased with SPS concentration; this was probably caused by the presence of low-oxygen microsites in SPS. For the water systems with both bed-sediment and SPS, the denitrification kinetics fit well to Logistic model, and the denitrification rate constant increased linearly with SPS concentration (p < 0.01). The denitrification caused by the presence of SPS accounted for 22%, 38%, 53%, and 67% of the total denitrification in systems with 2.5, 8, 15, and 20 g L(-1) SPS, respectively. The activity of denitrifying bacteria in SPS was approximately twice that in bed-sediment, and the denitrifying bacteria population showed an increasing trend with SPS concentration in both SPS and bed-sediment, leading to the increase of denitrification rate with SPS concentration. Furthermore, the denitrification in bed-sediment was accelerated by increased diffusion of nitrate from overlying water to bed-sediment under agitation conditions, which accompanied with the presence of SPS. When with 8 g L(-1) SPS, approximately 66% of the increased denitrification compared to that without SPS was attributed to denitrification on SPS and 34% to agitation conditions. This is the first report of the occurrence of denitrification on SPS in oxic waters. The results suggest that SPS plays an important role in denitrification in turbid rivers; its effect on nitrogen cycle should be considered in future study.

Diversity and Characterization of Culturable Fungi from Marine Sediment Collected from St. Helena Bay, South Africa

Marine fungi are known to originate from a wide variety of habitats within the marine environment. Marine sediment represents one environmental niche, with most fungi occurring in these sediments being facultative marine fungi with terrestrial origins. It has not been proven whether these fungi merely survive the harsh environmental conditions presented by the ocean sediment, as opposed to playing an active role in this ecological niche. During this study, marine sediment was collected from St. Helena Bay, on the west coast of the Western Cape, South Africa. Using dilution, enrichment, and repetitive culturing techniques, 59 fungal isolates were obtained from marine sediments and identified to at least genus level using morphological and molecular methods. Moreover, a series of tests were performed to characterize the physical and physicochemical attributes of the isolates. Results showed that the isolates not only survived but also had the potential to grow in the natural conditions present in this environment. Extracellular cellulase was produced by the filamentous fungal isolates indicating their probable role in detrital decay processes and therefore the carbon cycle on the ocean bed. Also, denitrification patterns were observed when isolates were grown in liquid media amended with NaNO(2), NaNO(3), and (NH(4))SO(4), implicating that these fungi have the potential to play an active role in denitrification, co-denitrification, and ammonification phases of nitrogen cycles occurring in the marine sediments.

Nitrogen Flow in a Recirculating Operation of Litopenaeus vannamei Maturation in Ecuador

The nitrogen flow together with dissolved nutrients and other parameters are described in a large shrimp maturation operation in Ecuador. In summary, only 8.9% of the nitrogen input ended in animal tissue. Nitrate-N and dissolved organic nitrogen (DON) accounted for more than 95% of the nitrogen pool. The nitrogen dynamics in the system is driven by a nitrification based trickling filter attached population and a free living heterotrophic carbon limited in the sump. The average nitrification rate of TAN (total ammonia nitrogen) averaged 44.81 gd -1. The trickling filters worked as a nitrifier body and also reducing the organic load. There is also some evidence that the trickling filters might have also play some role in denitrification. Nitrate never reached high concentrations (<3.7 mg L -1 nitrate-N), hence did not present a danger to the productivity of the system. In general either inorganic or organic phosphorous did not undergo any major change during the study. BOD values in the sump were low averaging 1.1 mg L -1 d -1 more likely as a result of the carbon limitation of the system. A combination of low C:N ratio and high load of organic nitrogen in the trickling filter could be part of the key factors running this system. The semi closed recirculating system presented in this study has been used since 2004 providing a steady yield of nauplii without the seasonal effects typical of open system and without the accumulation of deleterious amount of waste nitrogen or the presence of pathogens. The present study demonstrates the feasibility of using a simple and inexpensive semi closed recirculating systems in a large commercial scale.

東京港野鳥公園干潟における窒素循環の脱窒・アナモックスと付着藻類の役割

東京港野鳥公園干潟における窒素循環の脱窒・アナモックスと付着藻類の役割

Nitrate Removal Efficiency and Bacterial Community Dynamics in Denitrification Processes Using Poly (&lt;sc&gt;L&lt;/sc&gt;-lactic acid) as the Solid Substrate

Laboratory-scale solid-phase denitrification (SPD) reactors for nitrate removal were constructed by acclimating activated sludge with poly (L-lactic acid) (PLLA) having weight-average molecular weights (M(w)) of 9,900, 12,000, and 45,100 g mol(-1). A good nitrate removal rate (3.5-5.3 mg NO(3)(-)-N g [dry wt](-1) h(-1)) was found in the reactor containing PLLA of 9,900 g mol(-1), whereas the other two reactors with the higher M(w) PLLA showed low nitrate removal efficiency. Microbial community dynamics in the low M(w) PLLA-acclimated reactor were studied by 16S rRNA gene-targeted PCR-denaturing gradient gel electrophoresis and quinone profiling. Nonmetric multidimensional scaling analyses of these data sets revealed a marked population shift during acclimation of the SPD reactor with low M(w) PLLA. The 16S rRNA gene clone library and culture-dependent analyses showed that bacteria belonging to the family Comamonadaceae predominated and played the primary role in denitrification in the PLLA-using reactor; however, none of the bacterial isolates from the reactor degraded PLLA. These results suggest that the nitrate removal property of the PLLA-using SPD reactor is attained through the bioavailability of hydrolysates released abiotically from the solid substrate.

Contributions of biofilm and suspended sludge to nitrogen transformation and nitrous oxide emission in hybrid sequencing batch system

Hybrid system combines the nature of suspended growth and attached growth has been widely applied to wastewater treatment. In this research, the contributions to N transformation and N 2O emission by biofilm and suspended sludge in the hybrid sequencing-batch reactor for a simultaneous nitrification, denitrification and phosphorus removal process were investigated. For the hybrid system, nitrification occurred mostly in the suspended sludge, while the biofilm played the major role in denitrification. The interaction of the biofilm and the suspended sludge in the same reactor resulted in a better overall nitrogen removal performance with simultaneous nitrification and denitrification. However, N 2O emission was the main end product of nitrogen removal for the hybrid system; while it was N 2 for the biofilm. The relative low N 2O emissions from the pure biofilm and the pure suspended sludge corresponded to the relatively high nitrate at the end of the aeration period compared with the hybrid system.

CALIPSO polar stratospheric cloud observations: second-generation detection algorithm and composition discrimination

Abstract. This paper focuses on polar stratospheric cloud (PSC) measurements by the CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) lidar system onboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) spacecraft, which has been operating since June 2006. We describe a second-generation PSC detection algorithm that utilizes both the CALIOP 532-nm scattering ratio (ratio of total-to-molecular backscatter coefficients) and 532-nm perpendicular backscatter coefficient measurements for cloud detection. The inclusion of the perpendicular backscatter measurements enhances the detection of tenuous PSC mixtures containing low number densities of solid (likely nitric acid trihydrate, NAT) particles and leads to about a 15% increase in PSC areal coverage compared with our original algorithm. Although these low number density NAT mixtures would have a minimal impact on chlorine activation due to their relatively small particle surface area, these particles may play a significant role in denitrification and therefore are an important component of our PSC detection. In addition, the new algorithm allows discrimination of PSCs by composition in terms of their ensemble backscatter and depolarization in a manner analogous to that used in previous ground-based and airborne lidar PSC studies. Based on theoretical optical calculations, we define four CALIPSO-based composition classes which we call supercooled ternary solution (STS), ice, and Mix1 and Mix2, denoting mixtures of STS with NAT particles in lower or higher number densities/volumes, respectively. We examine the evolution of PSCs for three Antarctic and two Arctic seasons and illustrate the unique attributes of the CALIPSO PSC database. These analyses show substantial interannual variability in PSC areal coverage and also the well-known contrast between the Antarctic and Arctic. The CALIPSO data also reveal seasonal and altitudinal variations in Antarctic PSC composition, which are related to changes in HNO3 and H2O observed by the Microwave Limb Sounder on the Aura satellite.