Simultaneous removal of SO2 and NO in a rotating drum biofilter coupled with complexing absorption by FeII(EDTA)

Performance and kinetics of rotating drum biofilter aerobic simultaneous purifying SO2 and NOx

The rotating drum biofilter (RDB) was investigated as a biological process for purifying SO2 and NOx. After 25 days of film hanging, the inlet concentration was less than 2800 mg·m-3, and the NOx inlet concentration was less than 800 mg·m-3, with greater than 90% desulphurisation and denitration efficiency. Bacteroidetes and Chloroflexi were the dominant bacteria in desulphurisation, while Proteobacteria were the dominant bacteria in denitrification. The sulphur and nitrogen in RDB were balanced when the SO2 inlet concentration was 1200 mg·m-3 and the NOx inlet concentration was 1000 mg·m-3. The best results were obtained SO2-S removal load was 28.12 mg·L-1·h-1 and NOx-N removal load was 9.78 mg·L-1·h-1. when SO2 concentration was 1200 mg·m-3, NOx concentration was 800 mg·m-3, and empty bed retention time (EBRT) was 75.36 s. The liquid phase dominated the SO2 purification process, and the experimental data fit better with the liquid phase mass transfer model. NOx purification was governed by the biological and liquid phases, with the modified biological-liquid phase mass transfer model fitting the experimental data better.

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.

Biological treatments of mercury and nitrogen oxides in flue gas: biochemical foundations, technological potentials, and recent advances

Nitrogen oxides (NO_x) and mercury (Hg) are commonly found coexistent pollutants in combustion flue gas. Ever-increasing emission of atmospheric Hg and NO_x has caused considerable environmental risks. Traditional flue gas demercuration and denitration techniques have many socioeconomic, technological and environmental drawbacks. Biotechnologies can be a promising and prospective alternative strategy. This article discusses theoretical foundation (biochemistry and genomic basis) and technical potentials (Hg⁰ bio-oxidation coupled to denitrification) of bioremoval of Hg and NO_x in flue gas and summarized recent experimental and technological advances. Finally, several specific technical perspectives have been put forward to better guide future researches.

Simultaneous removal of sulphur dioxide and nitric oxide at different oxygen concentrations in a thermophilic biotrickling filter (BTF): Evaluation of removal efficiency, intermediates interaction and characterisation of microbial communities

Simultaneous flue gas desulphurisation and denitrification in biotrickling filter was investigated under different O₂ concentrations (0%, 3%, 5%, 8% and 10%) at 45 °C. NO and SO₂ removal efficiency, intermediates (NO₃^-, NO₂^-, NO₂, SO₄^2- and S^2-) interaction and accumulation, S⁰ recovery and microbial community structure were investigated. Results indicated the highest NO removal efficiency was 96.5% at 5% O₂. Maximum SO₂ removal efficiency was 95.6% at 3% O₂. Moreover, N intermediates accumulation increased when O₂ concentration increased from 0% to 10%. The lowest S^2- concentration of 61 mg/L and the maximum S⁰ recovery of 76.9% were achieved at 5% O₂. The bioreactor at 10% O₂ contained less bacterial OTUs richness and evenness compared with other conditions. Illumina analysis indicated Proteobacteria, Firmicutes and Bacteroidetes were the dominant members. Overall, microbial community structure differs significantly under different O₂ concentrations.

Reduction of FeII(EDTA)-NO by Mn powder in wet flue gas denitrification technology: stoichiometry, kinetics, and thermodynamics

Conversion of Fe^II(EDTA)-NO or Fe^III(EDTA) into Fe^II(EDTA) is a key process in a wet flue gas denitrification technology with Fe^II(EDTA) solution. In this work, the stoichiometry, kinetics, and thermodynamics of Fe^II(EDTA)-NO reduction by Mn powder were investigated. We first studied the Fe^II(EDTA)-NO reduction and product distribution to speculate a possible stoichiometry of Fe^II(EDTA)-NO reduction by Mn powder. Then, the effects of major influencing factors, such as pH value, temperature, and Mn concentration, were studied. The pseudo-second-order model was established to describe the Fe^II(EDTA)-NO reduction. Simultaneously, according to Arrhenius and Eyring-Polanyi equations, the reaction activation energy (E_a), enthalpy of activation (∆H^‡), and entropy of activation (∆S^‡) were calculated as 23.68 kJ/mol, 21.148 kJ/mol, and - 149.728 J/(k mol), respectively. Additionally, simultaneous reduction of Fe^III(EDTA) and Fe^II(EDTA)-NO was investigated to better study the mechanism of Fe^II(EDTA) regeneration, suggesting that there was a competition between the two reduction processes. Finally, a simple schematic mechanism of NO absorption by Fe^II(EDTA) combined with regeneration of manganese ion and ammonium was proposed. These fundamental researches could offer a valuable guidance for wet flue gas denitrification technology with Fe^II(EDTA) solution.

Bio-oxidation of Elemental Mercury into Mercury Sulfide and Humic Acid-Bound Mercury by Sulfate Reduction for Hg0 Removal in Flue Gas

Bioconversion of elemental mercury (Hg⁰) into immobile, nontoxic, and less bioavailable species is of vital environmental significance. Here, we investigated bioconversion of Hg⁰ in a sulfate-reducing membrane biofilm reactor (MBfR). The MBfR achieved effective Hg⁰ removal by sulfate bioreduction. 16 S rDNA sequencing and metagenomic sequencing revealed that diverse groups of mercury-oxidizing/sulfate-reducing bacteria (Desulfobulbus, Desulfuromonas, Desulfomicrobium, etc.) utilized Hg⁰ as the initial electron donor and sulfate as the terminal electron acceptor to form the overall redox. These microorganisms coupled Hg⁰ bio-oxidation to sulfate bioreduction. Analysis on mercury speciation in biofilm by sequential extraction processes (SEPs) and inductively coupled mass spectrometry (ICP-MS) and by mercury temperature programmed desorption (Hg-TPD) showed that mercury sulfide (HgS) and humic acid-bound mercury (HA-Hg) were two major products of Hg⁰ bio-oxidation. With HgS and HA-Hg comprehensively characterized by X-ray diffraction (XRD), excitation-emission matrix spectra (EEM), scanning electron microscopy-energy disperse spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), it was proposed that biologically oxidized mercury (Hg²⁺) further reacted with biogenic sulfides to form cubically crystallized metacinnabar (β-HgS) extracellular particles. Hg²⁺ was also complexed with functional groups -SH, -OH, -NH^-, and -COO^- in humic acids from extracellular polymeric substances (EPS) to form HA-Hg. HA-Hg may further react with biogenic sulfides to form HgS. Bioconversion of Hg⁰ into HgS was therefore achieved and can be a feasible biotechnique for flue gas demercuration.

Simultaneous removal of SO2 and NO by FeII(EDTA) solution: promotion of Mn powder and mechanism of reduction

The effect of Mn powder addition on the simultaneous removal of SO₂ and NO coupled with Fe^II(EDTA) absorption was investigated in this work. In the NO absorption system with Fe^II(EDTA), SO₂ reduced Fe^II(EDTA)-NO to Fe^II(EDTA) with a reduction efficiency reaching 88.5% under the conditions of 4000 mg/m³ SO₂, pH 8.0, 44 °C, and the flow rate of 1.2 L/min within 60 min. Introducing 0.1 M Mn powder with SO₂ increased the Fe^II(EDTA)-NO reduction efficiency to 96.8% within 5 min. SO₂ was also removed by reducing Fe^II(EDTA)-NO and converted into SO₄^2- at a removal efficiency of 100%. After adding Mn powder, NO was removed through the following reaction: [Formula: see text]. Mn powder functioned as a reductant to regenerate the absorption of solution, and the coordinated NO in Fe^II(EDTA)-NO was reduced to NH₄⁺. The resource utilization rate of N reached approximately 77.2%. The integrated technology is a potential solution for flue gas treatment in industrial sectors with coal-fired power plants and industrial boiler. Graphical abstract.

Simultaneous removal of nitric oxide and sulfur dioxide in a biofilter under micro-oxygen thermophilic conditions: Removal performance, competitive relationship and bacterial community structure

The efficiency of a biofilter to simultaneously remove nitric oxide (NO) and sulfur dioxide (SO₂) was investigated under thermophilic (48 ± 2 °C) micro-oxygen (3 vol%) conditions. After the start-up stage (Days 0-14), the stable operation period was divided into three stages. SO₂ inlet concentration remained 500 mg/m³, NO inlet concentrations were 300 mg/m³ (Days 15-40), 500 mg/m³ (Days 41-70) and 700 mg/m³ (Days 71-100). In each stable stage, the removal efficiency of NO and SO₂ exceeded 90%, the maximum removal rates of NO and SO₂ were 98.08% and 99.61%, respectively. The final products of SO₂ were mostly sulphur. Nitrate-reducing bacteria inhibited sulphate-reducing bacteria. Illumina high-throughput sequencing confirmed that the relative abundance of nitrate-reducing bacteria was positively correlated with NO removal efficiency, the relative abundance of sulphate-reducing bacteria was related to the conversion rate of sulphur.

Simultaneous Biological and Chemical Removal of Sulfate and Fe(II)EDTA-NO in Anaerobic Conditions and Regulation of Sulfate Reduction Products

In the simultaneous flue gas desulfurization and denitrification by biological combined with chelating absorption technology, SO2 and NO are converted into sulfate and Fe(II)EDTA-NO which need to be reduced in biological reactor. Increasing the removal loads of sulfate and Fe(II)EDTA-NO and converting sulfate to elemental sulfur will benefit the application of this process. A moving-bed biofilm reactor was adopted for sulfate and Fe(II)EDTA-NO biological reduction. The removal efficiencies of the sulfate and Fe(II)EDTA-NO were 96% and 92% with the influent loads of 2.88 kg SO42−·m−3·d−1 and 0.48 kg NO·m−3·d−1. The sulfide produced by sulfate reduction could be reduced by increasing the concentrations of Fe(II)EDTA-NO and Fe(III)EDTA. The main reduction products of sulfate and Fe(II)EDTA-NO were elemental sulfur and N2. It was found that the dominant strain of sulfate reducing bacteria in the system was Desulfomicrobium. Pseudomonas, Sulfurovum and Arcobacter were involved in the reduction of Fe(II)EDTA-NO.

Control of H2S generation in simultaneous removal of NO and SO2 by rotating drum biofilter coupled with FeII(EDTA)

Simultaneous removal of SO₂ and NO from flue gas can be biologically achieved by the rotating drum biofilter with Fe^II(EDTA) as a solvent. One issue related with this process is the generation of H₂S. To control its generation, the pathways of H₂S formation were investigated, and the parametric tests were conducted. The addition of Fe^II(EDTA) (10 mM) increased the removal efficiency of NO and SO₂, while the S^2- concentration decreased from 81 to 3.5 mM. The parametric tests showed that the high NO concentration favored the SO₂ removal and significantly inhibited the H₂S generation. High-throughput sequencing showed that the dominant denitrifying bacteria were Pseudomonas (9.09%), and the main sulfate-reducing bacteria were Desulfovibrio (5.84%). The long-term operation confirmed that the system could effectively simultaneous perform biological denitrification and desulfurization, and the H₂S could be controlled.

Nitric oxide removal from flue gas with ammonium using AnammoxDeNOx process and its application in municipal sewage treatment

A novel AnammoxDeNOx process was designed to simultaneously remove NOx in flue gas and ammonium wastewater, with the aim of exploring the possibility of using NO as a long-term and stable electron acceptor for anammox bacteria. The performance of the AnammoxDeNOx process indicated a NOx removal efficiency from simulated flue gas (including CO₂, SO₂, O₂ and NO₂) of 87-96% using simulated ammonium wastewater. With municipal wastewater, the removal efficiencies for NOx were 70-90%, total nitrogen 40-70%, and COD 80-90% (NO concentration: 100-500 ppm). The anammox genus underwent considerable changes from the dominant Candidatus Kuenenia in the stage of domestication to the predominant Candidatus Brocadia, which then became the dominant species in the simulated flue gas and actual municipal wastewater stages.

Simultaneous removal of NO and SO2 using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS)

Simultaneous removal process of SO₂ and NO from flue gas using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS) in a VUV spraying reactor was proposed. The key influencing factors, active species, reaction products and mechanism of SO₂ and NO simultaneous removal were investigated. The results show that vacuum ultraviolet light (185 nm) achieves the highest NO removal efficiency and yield of and under the same test conditions. NO removal is enhanced at higher PMS concentration, light intensity and oxygen concentration, and is inhibited at higher NO concentration, SO₂ concentration and solution pH. Solution temperature has a double impact on NO removal. CO₂ concentration has no obvious effect on NO removal. and produced from VUV-activation of PMS play a leading role in NO removal. O₃ and ·O produced from VUV-activation of O₂ also play an important role in NO removal. SO₂ achieves complete removal under all experimental conditions due to its very high solubility in water and good reactivity. The highest simultaneous removal efficiency of SO₂ and NO reaches 100% and 91.3%, respectively.