High Denitrification Efficiency Research Articles

Research Progress in Flue Gas Denitrification Technology Based on Oxidation Theory

Because of its mild reaction condition, relatively high denitrification efficiency and ability of combined removal of various pollutants, the flue gas denitrification technology based on oxidation theory has become a new and feasible method for flue gas denitrification. The technology has been applied extensively and studied in depth. This paper reviews the influencing factors, reaction mechanism, reaction products and subsequent absorption reaction of the oxidation of NO in flue gas with gas phase and liquid phase oxidants at high and low temperatures. On this basis, the shortcoming of the technology and the key research directions for the future are analyzed and discussed, laying the basis for industrial applications of the denitrification technology based on oxidation theory.

다양한 Ball Mill Method에 의해 제조된 V/TiO2 촉매의 NH3-SCR 활성 증진연구

본 연구에서는, <TEX>$150{\sim}400^{\circ}C$</TEX> 영역에서 <TEX>$NO_x$</TEX>를 제어하기 위한 ball mill 기법을 사용한 선택적 환원촉매(SCR)의 연구를 수행하였다. 제조된 촉매들의 구조적 특성 및 산화가 특성을 확인하기 위하여 XRD, BET, XPS 분석을 수행하였다. 다양한 ball mill 기법에 의해 제조된 촉매는 <TEX>$250^{\circ}C$</TEX> 이하의 온도구간에서의 활성의 차이를 보였다. 이중 가장 우수한 탈질효율을 갖는 촉매를 기준으로, ball mill 시간이 3시간일 때 가장 높은 활성을 나타내었다. XPS 분석 결과, vanadium의 비 화학양론종의 존재 및 원자 수 증가가 활성증진에 유리하게 작용한 것으로 나타났다. 또한 <TEX>$O_2$</TEX> on-off 실험을 통해 격자산소량의 양과 탈질 효율과의 상관관계를 나타내었고, 이는 서로 비례관계에 있음을 확인하였다. In this study, the selective catalytic reduction (SCR) for NOx removal was investigated in the temperature range of <TEX>$150{\sim}400^{\circ}C$</TEX>. XRD, BET and XPS analyses to determine the structural properties and valence state characteristics of the catalyst were performed. Various ball mill method were shown to a difference in activity at a low temperature below <TEX>$250^{\circ}C$</TEX>. Based on the catalyst with the highest denitrification efficiency, the ball mill time was the best result at 3 h. As a result of XPS analysis, the presence of the non-stoichiometric vanadium species and the increase of the number of atoms were attributed to a positive effect in the SCR reaction. it was confirmed that the correlation between the amount of lattice oxygen and the denitrification efficiency through the <TEX>$O_2$</TEX> on-off experiment, and it was in a proportional relationship to each other.

Performance and microbial communities of completely autotrophic denitrification in a bioelectrochemically-assisted constructed wetland system for nitrate removal

A bioelectrochemically-assisted constructed wetland (BECW) system was used to treat nitrate-contaminated wastewater without organic carbon source. The denitrification performance and microbial community composition of a BECW in closed-circuit mode (BECW-C) was compared to a BECW in open-circuit mode (BECW-O). The highest denitrification efficiency (78.92±3.12%) was obtained in the BECW-C with an applied current of 15mA. No nitrite accumulation was observed during the autotrophic denitrification process in the BECW-C. The significantly higher denitrification efficiency of the BECW-C compared to the BECW-O suggested enhanced denitrification due to in situ generation of hydrogen. The bacterial communities in the anode, cathode and rhizosphere regions collected from the BECW-C (with 10 or 15mA) and the BECW-O were characterized using 16S rRNA pyrosequencing technology, which revealed different microbial community structures among the treatments. The results also indicated that Thiohalophilus and Clostridium sensu stricto might be responsible for autotrophic denitrification in the BECW-C.

Catalytic reduction of NO using iron oxide impregnated biomass and lignite char for flue gas treatment

In this paper, iron oxide catalysts supported on corncob and lignite chars are used for catalytic reduction of NO in flue gas. Denitrification experiments were carried out in a fixed-bed reactor at temperatures of 100, 150, 200 and 300°C by using simulated flue gas containing NO. Catalyst samples before and after denitrification were analyzed using Brunauer–Emmett–Teller (BET) analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope with an energy dispersive X-ray auxiliary (SEM–EDX). Results show that biomass–lignite chars impregnated with iron oxide had a high reactivity during catalytic reduction of NO. The denitrification efficiency of biomass–lignite chars impregnated with iron oxide catalyst was higher than that of un-impregnated char. The highest catalytic performance was achieved at corncob to lignite ratio of 5:5. Synergetic effects between lignite and biomass during co-gasification were attributed to the potassium migration from biomass to lignite char which improved the efficiency of NO removal. The catalysts had the highest denitrification efficiency at 300°C and the reactions mechanism has been discussed.

Direct contribution of clams (Ruditapes philippinarum) to benthic fluxes, nitrification, denitrification and nitrous oxide emission in a farmed sediment

The influence of the manila clam (Ruditapes philippinarum) on N-cycle processes, and oxygen and nutrient fluxes in a farmed sediment was investigated using a multiple core incubation approach and parallel incubations of individual clams. Clam population/biomass density varied ∼8-fold between cores and all sediment-water column solute (O2. N2, N2O, NH4+, NOX and DIN) fluxes and benthic process (N-regeneration, nitrification and denitrification) rates were strongly and significantly correlated with clam density/biomass. Isolated clams exhibited high rates of respiration, N-excretion, nitrification and denitrification of 2050 ± 70, 395 ± 49, 201 ± 42 and 235 ± 40 nmol individual−1 h−1, respectively.The direct contribution of the clams and their associated microbiota to benthic processes was estimated by multiplying the per individual rates by the number of clams in each incubated core. The clams on average directly accounted for 64–133% of total rates of sediment oxygen demand, N-regeneration, nitrification and denitrification, indicating that they regulated processes primarily through their own metabolic activity and that of bacteria that colonise them.Clams and the farmed sediments were significant sources of the greenhouse gas N2O, but this was primarily due to their high nitrification and denitrification rates, rather than high specific N2O yields, as N2O emissions represented <1% of total N2O + N2 production. The clam-farmed sediments had a high denitrification efficiency of 67 ± 10%, but this ecosystem service came at the environmental cost of increased N-regeneration and N2O emission rates. The measured N2O emissions indicate that bivalve aquaculture may be a significant source of N2O. It is therefore recommended that N2O emissions should be included in the impact assessments of current and future bivalve-farming projects.

Evaluation of denitrification–nitrification biofilter systems in treating wastewater with low carbon: nitrogen ratios

A two-stage biological aerated/anoxic filter (BAF) system for denitrification–nitrification was developed to increase nitrogen removal in the treatment of municipal wastewater with low carbon:nitrogen (C/N) ratio . This system exhibited a high denitrification efficiency (67%), despite the low C/N ratio, and the ratio of reduced nitrate to consumed organic compounds was greater than the theoretical value due to the minimization of the conversion of organic carbon to biomass growth, the maintenance of low levels of dissolved oxygen in recycled water, and the maximization of use of organic carbon biosorbed inside biomass in the denitrification BAF. The maximum rate of nitrogen removal was achieved at a recycle ratio of 170%, and the headloss in two BAFs was maintained after a 24-h backwash. Biological nitrogen removal in a two-stage BAF system was possible in a short hydraulic retention time (1.2 h) because the maximum reaction rates of nitrifiers and denitrifiers in each column were achieved.

An Ecological Network Analysis of nitrogen cycling in the Laurentian Great Lakes

As water moves through the Laurentian Great Lakes system, it experiences a steep gradient in physical and chemical conditions between oligotrophic Lake Superior and eutrophic Lake Erie, likely affecting stocks and flows of nitrogen (N) across these lakes. We used published rates, supplemented by measurements conducted during a series of research cruises from 2010 to 2012, to construct three coupled 4-compartment N models for Lakes Superior, Huron, and Erie. Linear Inverse Modeling was used to identify plausible solutions to this model, and subsequent analysis focused on the most parsimonious model solution. For the most parsimonious model solution, we used Ecological Network Analysis (ENA) to analyze N flow and cycling in this steady-state model, and to examine the ultimate source of the N removed via denitrification within each lake. We also calculated denitrification efficiencies for each lake (the fraction of N removed through denitrification relative to all N exported) for 10,000 possible solutions to the underdetermined model. The average path length of N atoms in Lake Superior was 47.4, compared to 25.7 in Lake Huron and 15.2 in Lake Erie. Lake Superior's long (191 years) hydrologic residence time and relatively high N cycling rates allow for N atoms to have multiple opportunities to enter the sediment N pool and ultimately be removed through denitrification. Despite having a low areal denitrification rate, Lake Superior had a higher denitrification efficiency (86±1%; mean±95% CI) compared to Lake Huron (64±12%), and Lake Erie (48±7%). This long residence time also makes Lake Superior highly sensitive to changes in loading rates and internal processes, probably contributing to the steady nitrate rise over the past century.

Starch/polyvinyl alcohol blended materials used as solid carbon source for tertiary denitrification of secondary effluent

Starch/polyvinyl alcohol (PVA) blended materials for using as a solid carbon source (SCS) were prepared by blending PVA and gelatinized starch in an aqueous solution system, in which PVA served as framework material and starch as carbon source. The optimization of starch content and temperature effects were investigated. It was indicated that higher denitrification efficiency could be achieved with more starch in the materials. The average specific denitrification rates were 0.93, 0.66, 0.37 and 0.36 mg/(g·day) corresponding to starch content of 70%, 60%, 40% and 30% respectively at 37°C. The denitrification rates increased when operating temperature was raised from 23°C to 30°C and then 37°C. The mechanism of carbon release was analyzed incorporating the experimental results of abiotic release in deionized water. The organic carbon was mainly hydrolyzed by microbes, and the biological release efficiencies were at the range of 89.2% to 96.0%. A long-term experiment with a continuous flow reactor with SCS material containing 70% starch was conducted to gain some experience for practical application. When the influent nitrate concentration was in the range of 35.2 to 39.1 mg/L, hydraulic retention time of 4 hr, and operating temperature of 30°C, a nitrogen removal efficiency up to 94.6% and denitrification rate of 0.217 kg/(m3·day) was achieved. The starch-based materials developed in this study can be used as a solid carbon source for tertiary nitrogen removal from secondary effluent.

Complete autotrophic denitrification in a single reactor using nitritation and anammox gel carriers

A novel aerobic denitrification reactor, aerobic denitrification using nitrifying and anoxic ammonium-oxidizing (anammox) bacteria immobilized on gel carriers in a single stage (AIGES), was developed. Two types of gel carriers, a nitritation gel carrier and an anammox gel carrier, were installed in single reactor, and the denitrification performance of simultaneous nitritation and anammox was evaluated. The denitrification performance increased gradually with increased aeration rate, reaching a denitrification rate of 1.4 kg N m(-3) d(-1) 2 weeks after the nitritation and anammox gel carriers were mixed. A high average denitrification efficiency of 82% was confirmed. Stable aerobic denitrification performance was observed for more than half a year. In the startup period of AIGES operation, ammonia-oxidizing bacteria were shown by fluorescence in situ hybridization analysis to grow on the surface layer of anammox gel cubes. These results indicated that anammox gel carriers promptly adapted to an aerobic environment by altering the microbial ecosystem.

Effect of [formula omitted] ratio and seed sludge on simultaneous methanogenesis and denitrification in intermittent organic solid waste treatment

The effect of the COD/NO3−–N ratio and seed sludges on methanogenesis and denitrification in intermittent organic waste treatment was investigated in a batch experiment. To evaluate the effects of denitrification sludge, two different experimental conditions were used: methanogenic sludge only conditions (M conditions) and methanogenic sludge plus denitrification sludge conditions (MD conditions). The experimental results showed that simultaneous methanogenesis and denitrification occurred at COD/NO3−–N ratio of 17.2 in the M conditions and 17.2 and 5.74 in the MD conditions. A relatively high denitrification efficiency (high nitrate removal rate and low N2O emission) and high methane production were achieved in the MD conditions, compared with the M conditions. The inoculation of denitrification sludge with methanogenic sludge appeared to enhance denitrification activity, resulting in the recovery of the methanogenesis activity. The performance of simultaneous methanogenesis and denitrification was affected by the COD/NO3−–N ratio in the batch reactor, rather than the COD/NO3−–N ratio of the substrate itself. The solubilization rate should also be considered when conducting simultaneous methanogenesis and denitrification in organic solid waste treatment.

Sulfide-Oxidizing Autotrophic Denitrification: an Evaluation for Nitrogen Removal from Anaerobically Pretreated Domestic Sewage

Nitrogen removal from effluents of anaerobic reactors using conventional nitrification/denitrification processes depends on the availability of electron donors for denitrification. As sulfide is normally present in such effluents, autotrophic denitrification using sulfide can be an alternative to avoid or reduce the requirements of exogenous organic carbon sources. This study evaluated the application of sulfide-oxidizing autotrophic denitrification to anaerobically pretreated domestic sewage. A denitrifying reactor was fed with a mixture, at different proportions, of anaerobically pretreated (containing sulfides and residual organic matter) and nitrified (containing nitrates) effluents produced by reactors treating synthetic domestic sewage. Autotrophic denitrification was responsible for most of the nitrogen removal and coexisted with heterotrophic activity, resulting in high denitrification efficiencies. Efficient denitrification could be attained at a molar NO3 (-)/S(2-) ratio of 2.1, higher than values reported before, and this represents an important parameter for the strategic application of the process. Under the experimental conditions studied, autotrophic denitrification showed to be an efficient and feasible alternative to conventional denitrification using exogenous electron donors.

Comparing feed-forward versus neural gas as estimators: application to coke wastewater treatment

Numerous papers related to the estimation of wastewater parameters have used artificial neural networks. Although successful results have been reported, different problems have arisen such as overtraining, local minima and model instability. In this paper, two types of neural networks, feed-forward and neural gas, are trained to obtain a model that estimates the values of nitrates in the effluent stream of a three-step activated sludge system (two oxic and one anoxic). Placing the denitrification (anoxic) step at the head of the process can force denitrifying bacteria to use internal organic carbon. However, methanol has to be added to achieve high denitrification efficiencies in some industrial wastewaters. The aim of this paper is to compare the two networks in addition to suggesting a methodology to validate the models. The influence of the neighbourhood radius is important in the neural gas approach and must be selected correctly. Neural gas performs well due to its cooperation–competition procedure, with no problems of stability or overfitting arising in the experimental results. The neural gas model is also interesting for use as a direct plant model because of its robustness and deterministic behaviour.

Simultaneous Nitrification and Denitrification in an SBR with a Modified Cycle During Reject Water Treatment

Abstract In this study, the dependence between volumetric exchange rate (n) in an SBR (Sequencing Batch Reactor) with a modified cycle and simultaneous nitrification and denitrification (SND) efficiency during the treatment of anaerobic sludge digester supernatant was determined. In the SBR cycle alternating three aeration phases (with limited dissolved oxygen (DO) concentration up to 0.7 mg O2/L) and two mixing phases were applied. The lengths of each aeration and mixing phases were 4 and 5.5 h, respectively. Independently of n, a total removal of ammonium was achieved. However, at n = 0.1 d-1 and n = 0.3 d-1 nitrates were the main product of nitrification, while at n = 0.5 d-1, both nitrates and nitrites occurred in the effluent. Under these operational conditions, despite low COD/N (ca. 4) ratio in the influent, denitrification in activated sludge was observed. A higher denitrification efficiency at n = 0.5 d-1 (51.3%) than at n = 0.1 d-1 (7.8%) indicated that n was a crucial factor influencing SND via nitrite and nitrate in the SBR with a low oxygen concentration in aeration phases.

Isolation of an Aerobic Denitrifying Bacterial Strain from a Biofilter for Removal of Nitrogen Oxide

A strain of bacteria CP1 with high nitrogen removal efficiency was newly isolated from the biofilm of a biofilter for removal of NOx from flue gas. The isolate was identified as Pseudomonas aeruginosa based on its physiological and biochemical characteristics and the results of 16S rRNA gene homology analysis. The new isolate had a high denitrifying ability, removing 98.49% of the nitrate in a 24-h period under aerobic conditions, with no nitrite accumulation. With regard to the nitrogen balance, the percentage of nitrogen lost in the flask culture was estimated to be 32.3%, which was presumed to be converted to nitrogen gas. An analysis of its denitrification activity showed that the optimal C/N and temperature were 12 and 30°C-40°C, respectively. By using glucose, sodium citrate and succinate, CP1 removed nitrate with high denitrification efficiency. The change in DO did not influence the effects of denitrification when it varied from 0 to 7.2 mg/L. The results show that CP1 could be a good candidate for the process of aerobic denitrification.

Denitrification of drinking water using a hybrid heterotrophic/autotrophic/BAC bioreactor

Abstract The performance of a hybrid heterotrophic/autotrophic/BAC bioreactor (HHABB) for denitrification of drinking water was studied in continuous mode for several months to determine the optimal conditions. The HHABB was consisted of three compartments: ethanol heterotrophic part (EH-part), sulfur autotrophic part (SA-part) and BAC-part (including anoxic and aerobic sections). The experiments were conducted at six runs with NO3 − loading rates ranged from 0.36 to 1.45 kgN m−3 d−1, C:N ratios 0.53 and 0.70 and approximately constant NO3 − concentration of 30 mgN l−1. At lower NO3 − loading rates (0.36 and 0.72 kgN m−3 d–1), the C:N ratio 0.53 provided high denitrification efficiencies (96–99%) with very low effluent DOC and trihalomethane formation potential (THMFP) concentrations of 0.33–0.50 mgC l−1 and 26–41 μg l−1, respectively. In contrast, at No3 − loading rate 1.07 kgN m−3 d−1, an increase in C:N ratio to 0.70 was required to achieve suitable results. The aerobic BAC-part showed suitable efficie...

Behavior of autotrophic denitrification and heterotrophic denitrification in an intensified biofilm-electrode reactor for nitrate-contaminated drinking water treatment

An intensified biofilm-electrode reactor (IBER) was developed to treat nitrate-contaminated drinking water. Different running conditions were conducted to investigate the behavior of autotrophic denitrification (AD) and heterotrophic denitrification (HD) in the IBER. In AD process, the nitrate nitrogen coulomb-reduction rate was used to evaluate the performance of the reactor. The maximum NO3--N removal efficiency was 6.8% at the current of 60mA, while nitrate nitrogen coulomb-reduction rate was 0.024mgC−1. The optimum conditions for HD process were C/N=0.8 and HRT=8h, under which complete NO3--N removal and no NO2--N accumulation were observed. With the cooperative effect of AD and HD in the heterotrophic and autotrophic denitrification (HAD) process, large treatment capacity, high denitrification efficiency, and low nitrite and ammonia accumulation were achieved. The results proved that HAD process was superior to single AD and HD for nitrate removal in the IBER.

Experimental investigations of ammonia adsorption and nitric oxide reduction on activated coke

In this work the enhancement of ammonia adsorption on activated coke has been investigated to increase the efficiency of the denitrification in the dry flue gas cleaning system located at Infraserv GmbH & Co. Hoechst KG in Frankfurt am Main, Germany. The influence of loading temperatures and sulfur components content of the activated coke on the ammonia adsorption were studied. Additionally, urea was tested as an alternative loading substance. Increasing ammonia adsorption was observed by raising loading temperatures. The highest ammonia loading was possible at the highest temperature tested at 469 °C. The activated coke loaded at these conditions, as well as the one loaded with urea, was found to have higher denitrification efficiency than that loaded at present conditions of about 114 °C. The results of this study allowed the recommendation of possible measures to be applied in the plant to increase its denitrification efficiency.

DENITRIFYING POTENTIAL OF AN ACTIVATED SLUDGE DERIVED CONSORTIUM

The aim of this work was the evaluation of the denitrification potential of a consortium of activated sludge adapted to anoxic conditions. As the carbon source is the main parameter influencing the denitrification process, in the first stage three carbon sources (acetate, citrate and glucose) were assayed in batch activity tests. The highest denitrification efficiency was attained with acetate, being nitrate and nitrite completely reduced. The adapted sludge was then used as a potential denitrifying consortium on an anoxic rotating biological contactor (RBC) with acetate as carbon source. Two C/N ratios were assayed (2 and 3) as well as two nitrate loads (220 and 300 mg/L). At the highest nitrate concentration, the best denitrification efficiency (nitrate removal higher than 99% without nitrite or acetate accumulation) was attained at C/N=3. From the results it can be concluded that the activated sludge possesses high denitrifying capacity and can easily be adapted to anoxic conditions. Moreover, the RBC revealed to be a good alternative solution to the conventional processes.

Novel 3-dimensional bioelectrode for mediatorless bioelectrochemical denitrification

A novel bioelectrochemical method for denitrification was developed using electricity as the electron donor. The novel electrode contained both Ochrobactrum anthropi SY509, which was permeabilized as a biocatalyst, and copper powder as a conducting material. Using this electrode, a high denitrification efficiency of 1 mmol N-NO(3)(-)/g dry cell x h was achieved via direct electron transfer without using mediator.

Nitrate removal without carbon source feeding by permeabilized Ochrobactrum anthropi SY509 using an electrochemical bioreactor

Biological denitrification is very attractive due to its economical and environmental advantages. However, an external carbon source is required to maintain biological activity in biological denitrification. Permeabilized cells have been used to achieve denitrification that does not require an external carbon source. In this study, permeabilized Ochrobactrum anthropi SY509, which contains the denitrifying enzymes, nitrate reductase, nitrite reductase, nitric oxide reductase and nitrous oxide reductase, was used. NADH participates in denitrifying enzyme reaction as an electron donor. However, in the bioelectrochemical method, a redox molecule was used for electron transfer to the enzyme, and the denitrification was performed bioelectrochemically. This redox molecule functions as an artificial electron transferring agent, and is thus called a mediator. Mediated bioelectrocatalysis is a useful system for many redox biocatalyst reactions as the aforementioned mediator mediates the biocatalytic reaction between electrode and biocatalyst. In this study, neutral red was selected as a mediator. For application to a real wastewater treatment system, immobilization of biocatalyst and mediator on the electrode is essential. Carbon nanopowder was used as a support material to immobilize neutral red. When both the permeabilized cells and the carbon nanopowder with the mediator were immobilized on a graphite felt electrode, mediator leakage was completely prevented and high denitrification efficiency was obtained.