Reduction of Fe(III)EDTA in a NOx scrubber liquor by a denitrifying bacterium and the effects of inorganic sulfur compounds on this process

Removal of nitric oxide in bioreactors: a review on the pathways, governing factors and mathematical modelling

The constant surge in nitric oxide in the atmosphere results in severe environmental degradation, negatively impacting human health and ecosystems, and is presently a global concern. Widely used physicochemical technologies for nitric oxide (NO) removal comes with high installation and operational costs and the production of secondary pollutants. Thus, biological treatment has been emphasized over the last two decades, but the poor solubility of NO in water makes it a challenging issue. The present article reviews the various technical aspects of biological treatment of nitric oxide, including the removal pathways and reactor configurations involved in the process. The most widely used technologies in this regard are chemical adsorption processes followed by biological reactors like biofilters, biotrickling filters and membrane bioreactors that enhance NO solubility and offer the flexibility and scope of further improvement in process design. The effect of various experimental and operational parameters on NO removal, including pH, carbon source, gas flow rate, gas residence time and presence of inhibitory components in the flue gas, is also discussed along with the developed mathematical models for predicting NO removal in a biological treatment system. There is an extensive scope of investigation regarding the development of an economical system to remove NO, and an exhaustive model that would optimize the process considering maximum practical parameters encountered during such operation. A detailed discussion made in this article gives a proper insight into all these areas.

A review: Biological technologies for nitrogen monoxide abatement

Nitrogen oxides (NOx), including nitrogen monoxide (NO) and nitrogen dioxide (NO2), are among the most important global atmospheric pollutants because they have a negative impact on human respiratory health, animals, and the environment through the greenhouse effect and ozone layer destruction. NOx compounds are predominantly generated by anthropogenic activities, which involve combustion processes such as energy production, transportation, and industrial activities. The most widely used alternatives for NOx abatement on an industrial scale are selective catalytic and non-catalytic reductions; however, these alternatives have high costs when treating large air flows with low pollutant concentrations, and most of these methods generate residues that require further treatment. Therefore, biotechnologies that are normally used for wastewater treatment (based on nitrification, denitrification, anammox, microalgae, and combinations of these) are being investigated for flue gas treatment. Most of such investigations have focused on chemical absorption and biological reduction (CABR) systems using different equipment configurations, such as biofilters, rotating reactors, or membrane reactors. This review summarizes the current state of these biotechnologies available for NOx treatment, discusses and compares the use of different microorganisms, and analyzes the experimental performance of bioreactors used for NOx emission control, both at the laboratory scale and in industrial settings, to provide an overview of proven technical solutions and biotechnologies for NOx treatment. Additionally, a comparative assessment of the advantages and disadvantages is performed, and special challenges for biological technologies for NO abatement are presented.

Study on NO Removal Characteristics of the Fe(II)EDTA and Fe(II)PBTCA Composite System

Fe²⁺ complexation wet denitrification technology has become a research hotspot. It is very important to achieve efficient regeneration of the absorbent and increase NO absorption in the Fe²⁺ complexation system. They are the key to the industrial application of the Fe²⁺ complexation absorption process. In this paper, 2-phosphonate-butane-1,2,4-tricarboxylic acid and ethylenediamine tetraacetic acid were used as ligands to prepare a composite system for the first time. The characteristics of NO removal were investigated under different temperatures, pHs, Fe²⁺ concentrations, O₂ contents, NO concentrations, CO₂ contents, and SO₂ concentrations. Compared with the single ligand, the results show that the denitrification performance of the solution with a complex ligand is significantly improved. In this system, pH 9, 40 °C temperature, and 20 mmol/L Fe²⁺ concentration are the economic ideal conditions for NO removal. The system can realize simultaneous removal of NO and SO₂, but SO₂ in flue gas has a dual effect on the NO removal reaction.

A new approach for the effective removal of NOx from flue gas by using an integrated system of oxidation-absorption-biological reduction

A new process of NO_x removal from flue gas, using an integrated system of oxidation-absorption-biological reduction (OABR), is introduced. The experimental results show that increasing the NO_x oxidation ratio in flue gas can effectively improve the NO_x removal efficiency of the OABR system. The NO_x removal efficiency could reach 98.8% with 0.02 M NaHCO₃ as the chemical absorbent and under the condition of the optimal NO_x oxidation ratio of 50%. During stable operation, the OABR system could maintain a high NO_x removal efficiency (above 94%) under the following conditions: 1-8 vol% (10⁴-8 × 10⁴ ppmv) O₂, 200-800 ppmv NO_x, 0.5-1.5 L/min gas flow rate and 100-800 ppmv SO₂. The nitrogen equilibrium results showed that about 59% of the nitrogen in the inlet NO_x were transformed to N₂ through microbial denitrification, 37% of the nitrogen were converted to biological nitrogen for microbial growth, and only 1.1% of the nitrogen remained in the liquid phase. This new approach has an excellent NO_x removal performance and great potential for industrial application.

Simultaneous cobalt(III)-histidine reduction and aerobic denitrification by Paracoccus versutus LYM

Cobalt(II)-histidine [Co(II)His] is potentially a better alternative to ferrous complexes in the chemical absorption-biological reduction (CABR) flue gas denitrification process in view of its higher oxygenation reversibility. Though with excellent O₂-resistant ability, Co(II)His was still gradually oxidized into Co(III)His, losing NO binding capacity. Thus, Co(III)His biological reduction is an indispensable step in CABR process. Co(III)His reduction by Paracoccus versutus LYM under aerobic condition in the presence of nitrate or nitrite was investigated. Results indicated that simultaneous Co(III)His reduction and aerobic denitrification were achieved by strain LYM. Co(III)His reduction was significantly promoted by denitrification process, but dramatically inhibited by 5-15 mM sulfite. Co(II)His absorbent regeneration could be facilitated by adjusting O₂ supply properly or adding nitrogen and carbon source regularly. These findings provide a basis for the application of Co(II)His as the absorbent in the CABR process and qualify P. versutus LYM as an applicable and competitive strain for this process.

Removal of NO with the hexamminecobalt solution catalyzed by the carbon treated with oxalic acid

NO can be removed at the same time with SO₂ by aqueous Co(NH₃)₆²⁺ solution. The reduction of Co(NH₃)₆³⁺ to Co(NH₃)₆²⁺ is catalyzed by activated carbon to regain the NO absorption ability of the scrubbing solution. Oxalic acid solution is explored to change the carbon surface to ameliorate its catalytic capability. The experimental results suggest that the best catalyst is prepared by impregnating the carbon sample in 0.7 mol l^-1 oxalic acid solution for 24 h followed by being activated at 600 °C for 5 h under nitrogen atmosphere. After being treated with oxalic acid solution, the surface area and the acidity on the carbon surface increase. The experiments show that the carbon modified with oxalic acid can get a much higher NO removal efficiency than the original carbon.

Reactivity of nano-size zinc powder in the aqueous solution of [FeIII(edta)(H2O)]. ENVIRONMENTAL TECHNOLOGY 2017;38:103-107. [PMID: 27227652 DOI: 10.1080/09593330.2016.1186745]

Nitrogen mono-oxide and sulfur dioxide can be removed by simultaneous absorption into aqueous mixed solutions of sulfite and [Fe^II(edta)]H₂O)]^2-, ferrous ion coordinated to an anion of ethylene-diaminetetraacetic acid (EDTA or edta). In the industrial system with coexisting oxygen in the gas phase, [Fe^II(edta)](H₂O)]^2- complex is oxidized to [Fe^III(edta)](H₂O)]^- by molecular oxygen. Because the ferric complex has no capability for reaction with NO, the suppression of this undesired oxidation process is a very important technological problem to be overcome. In our preceding work, we discussed the reduction kinetics of ferric ion by metal powder on the basis of the kinetic data regarding the ferric ion reduction in aqueous solutions of [Fe^III(edta)](H₂O)]^- containing aluminum, tin or zinc powders. Zinc powder of normal size was recognized as an effective reducing agent. In the present work, augmentation of reducing capability of zinc powder was examined more. The rate of reduction of nano-size zinc powder was found to be about 11 times higher than that of normal-size zinc one.

Selenium catalyzed Fe(III)-EDTA reduction by Na2SO3: a reaction-controlled phase transfer catalysis

Fe(II)-EDTA, a typical chelated iron, is able to coordinate with nitric oxide (NO) which accelerates the rates and kinetics of the absorption of flue gas. However, Fe(II)-EDTA can be easily oxidized to Fe(III)-EDTA which is unable to absorb NO. Therefore, the regeneration of fresh Fe(II)-EDTA, which actually is the reduction of Fe(III)-EDTA to Fe(II)-EDTA, becomes a crucial step in the denitrification process. To enhance the reduction rate of Fe(III)-EDTA, selenium was introduced into the SO3 (2-)/Fe(III)-EDTA system as catalyst for the first time. By comparison, the reduction rate was enhanced by four times after adding selenium even at room temperature (25 °C). Encouragingly, elemental Se could precipitate out when SO3 (2-) was consumed up by oxidation to achieve self-separation. A catalysis mechanism was proposed with the aid of ultraviolet-visible (UV-Vis) spectroscopy, Tyndall scattering, horizontal attenuated total reflection Fourier transform infrared (HATR-FTIR) spectroscopy, and X-ray diffraction (XRD). In the catalysis process, the interconversion between SeSO3 (2-) and nascent Se formed a catalysis circle for Fe(III)-EDTA reduction in SO3 (2-) circumstance.

Kinetic analysis of Fe3+reduction coupled with nitrate removal by Klebsiella sp. FC61 under different conditions

Klebsiellasp. FC61, a newly found iron-reducing bacterium, has the ability of simultaneously reducing Fe³⁺and nitrate under different pH and temperature conditions.

Application of ethylene diamine tetra acetic acid degrading bacterium Burkholderia cepacia on biotreatment process

Ethylene diamine tetra acetic acid (EDTA), the effluent of secondary biotreatment units, can be properly biodegraded by Burkholderia cepacia. Through batch degradation of EDTA, the raw wastewater of EDTA was controlled at 50 mg/L, and then nutrients was added in diluted wastewater to cultivate activated sludge, which the ratio of composition is depicted as "COD:N:P:Fe = 100:5:1:0.5". After 27 days, the removal efficiency of Fe-EDTA and COD was 100% and 92.0%, correspondingly. At the continuous process, the raw wastewater of EDTA was dictated at 166 mg/L before adding nutrients to cultivate activated sludge, in which the ratio of composition did also follow with batch process. After 22 days, the removal efficiency of Fe-EDTA and COD for experimental group was 71.46% and 62.58%, correspondingly. The results showed that the batch process was more suited for EDTA biodegradation.

Current advances of integrated processes combining chemical absorption and biological reduction for NO x removal from flue gas

Anthropogenic nitrogen oxides (NO x ) emitted from the fossil-fuel-fired power plants cause adverse environmental issues such as acid rain, urban ozone smoke, and photochemical smog. A novel chemical absorption-biological reduction (CABR) integrated process under development is regarded as a promising alternative to the conventional selective catalytic reduction processes for NO x removal from the flue gas because it is economic and environmentally friendly. CABR process employs ferrous ethylenediaminetetraacetate [Fe(II)EDTA] as a solvent to absorb the NO x following microbial denitrification of NO x to harmless nitrogen gas. Meanwhile, the absorbent Fe(II)EDTA is biologically regenerated to sustain the adequate NO x removal. Compared with conventional denitrification process, CABR not only enhances the mass transfer of NO from gas to liquid phase but also minimize the impact of oxygen on the microorganisms. This review provides the current advances of the development of the CABR process for NO x removal from the flue gas.

NOx removal in chemical absorption-biological reduction integrated system: process rate and rate-limiting step

Biological reduction of Fe(III)EDTA is considered as the key step that limits the removal efficiency of the chemical absorption-biological reduction integrated system. In this study, the process rates of each reaction step under typical conditions (T=50°C, C FeII(EDTA)=1-5 mmol/L, CNO=0-500 ppm, CO2=1-10%, pH=7) were determined. Relevant kinetic constants including rate constants of absorption part and Michaelis-Menten kinetic constants of regeneration part were also obtained. On this basis, the theoretical process rates of each reaction step were predicted and compared in a steady state. The results confirmed that the removal rate of NO in this system is limited by the biological reduction of Fe(III)EDTA. Moreover, it indicated that increasing the concentration of total iron appropriately could enhance the bioreduction of Fe(III)EDTA.

Removal of nitric oxide from simulated flue gas via denitrification in a hollow-fiber membrane bioreactor

A hollow-fiber membrane bioreactor (HMBR) was studied for its ability to treat nitric oxide (NO) from simulated flue gas. The HMBR was operated for 9 months and showed a maximum elimination capacity of 702 mg NO/(m2.day) with a removal efficiency of 86% (gas residence time of 30 sec, inlet NO concentration of 2680 mg/m3, pH 8). Varying operation parameters were tested to determine the stability and response of the HMBR. Both the inlet NO concentration and gas residence time influenced the removal of NO in the HMBR. NO elimination capacity increased with an increase in inlet NO concentration or a shortening of gas residence time. Higher removal efficiency of NO was obtained at a longer gas residence time or a lower inlet NO concentration. Microbial communities of the HMBR were sensitive to the variation in pH value and alkalescence corresponding to an optimum pH value of 8. In addition, NO elimination capacity and removal efficiency were inversely proportional to the inlet oxygen concentration. Sulfur dioxide had no great influence on elimination capacity and removal efficiency of NO. Product analysis was performed to study N20 and N2 production and confirmed that the majority of the microorganisms were denitrifying bacteria in the HMBR. Compared to other bioreactors treating NO, this study showed that the denitrifying HMBR was a good option for the removal of NO.

Fe(II)EDTA-NO reduction coupled with Fe(II)EDTA oxidation by a nitrate- and Fe(III)-reducing bacterium

The nitrate- and Fe(III)-reducing bacterium Paracoccus versutus LYM was characterized in terms of its ability to perform Fe(II)EDTA-NO reduction coupled with Fe(II)EDTA oxidation (NO-dependent Fe(II)EDTA oxidation, NDFO). It experienced a single anaerobic FeEDTA redox cycling through NDFO and dissimilatory Fe(III)EDTA reduction in FeEDTA culture. The increase in the Fe(II)EDTA concentration contributed to the ascending Fe(II)EDTA-NO reduction rate. The amount of glucose controlled the rate and extent of Fe(II) oxidation during NDFO. Without glucose addition, Fe(II)EDTA-NO reduction rate was at a rather slow rate even in presence of relatively sufficient Fe(II)EDTA. Unlike aqueous Fe(2+) and solid-phase Fe(II), Fe(II)EDTA could prevent cells from encrustations. These findings suggested the occurrence of NDFO preferred being beneficial via a mixotrophic physiology in the presence of an organic cosubstrate to being out of consideration for metabolic strategy.

Reduction of Fe(III)EDTA by Klebsiella sp. strain FD-3 in NOx scrubber solutions

Biological reduction of Fe(III) to Fe(II) is a key step in nitrogen oxides (NOx) removal by the integrated chemical absorption-biological reduction method, which determines the concentration of Fe(II) in the scrubbing liquid. A new Fe(III)EDTA reduction strain, named as FD-3, was isolated from mixed cultures used in the integrated NOx removal process and identified as Klebsiella sp. by 16S rDNA sequence analysis. The reduction abilities of FD-3 and the influence of nitrogen-containing compounds (Fe(II)EDTA-NO, NO3(-) and NO2(-)) and sulfur-containing compounds (SO4(2-), SO3(2-)) on the Fe(III)EDTA reduction were investigated. The results indicated that strain FD-3 could reduce Fe(III)EDTA efficiently. NO3(-), NO2(-) and Fe(II)EDTA-NO inhibit the reduction of Fe(III)EDTA and could also serve as electron acceptor for strain FD-3. SO3(2-) inhibited Fe(III)EDTA reduction while SO4(2-) had no obviously effect on Fe(III)EDTA reduction. The relationship between cell growth and Fe(III)EDTA reduction could be described by the models based on Logistic equation.

Synthesis of Fe3O4 poly(styrene-glycidyl methacrylate) magnetic porous microspheres and application in the immobilization of Klebsiella sp. FD-3 to reduce Fe(III)EDTA in a NO(x) scrubbing solution

Magnetic poly(styrene-glycidyl methacrylate) porous microspheres (MPPM) with high magnetic contents were prepared by surfactant reverse micelles and emulsion polymerization of monomers, in which the well-dispersed Fe(3)O(4) nanoparticles were modified by polyethylene glycol (PEG) and oleic acid (OA) respectively. The characterizations showed that both of the OA-MPPM and the PEG-MPPM were ferromagnetic, however, the OA-MPPM was used to immobilize the bacteria for more advantages. Therefore, the effects of monomer ratio, surfactant, crosslinker and amount of Fe(3)O(4) on the structure, morphology and magnetic contents of the OA-MPPM were investigated. Then, the OA-MPPM was utilized to immobilize Klebsiella sp. FD-3, an iron-reducing bacterium for Fe(III)EDTA reduction applied in NO(x) removal. Compared with free bacteria, the immobilized FD-3 showed a better tolerance to the unbeneficial pH and temperature conditions.

Reduction of NOx in Fe-EDTA and Fe-NTA solutions by an enriched bacterial population

An enriched biomass was developed from municipal sewage sludge consisting of three dominant bacteria, representing the genera of Enterobacter, Citrobacter and Streptomyces. The biomass was used in a series of batch experiments in order to determine kinetic constants associated with biomass growth and NOx reduction in aqueous Ferrous EDTA/NTA solutions and Ferric EDTA/NTA solutions using ethanol as organic electron donor. The maximum specific reduction rates of NOx in Ferrous EDTA and Ferrous NTA solutions were 0.037 and 0.047mMolesL(-1)d(-1)mg(-1) biomass, respectively while in Ferric EDTA and Ferric NTA solutions were 0.022 and 0.024mMolesL(-1)d(-1)mg(-1) biomass, respectively. In case of Ferric EDTA/NTA solution, the kinetic constants associated with reduction of Ferric EDTA/NTA to Ferrous EDTA/NTA were also evaluated simultaneously. The maximum specific reduction rates of Ferric EDTA and Ferric NTA were 0.0021 and 0.0026mMolesL(-1)d(-1)mg(-1) biomass. The significance of these observations are presented and discussed in this paper.