Simultaneous combined microbial removal of sulfur dioxide and nitric oxide from a gas stream

A comprehensive review of flue gas bio-mitigation: chemolithotrophic interactions with flue gas in bio-reactors as a sustainable possibility for technological advancements

Flue gas mitigation technologies aim to reduce the environmental impact of flue gas emissions, particularly from industrial processes and power plants. One approach to mitigate flue gas emissions involves bio-mitigation, which utilizes microorganisms to convert harmful gases into less harmful or inert substances. The review thus explores the bio-mitigation efficiency of chemolithotrophic interactions with flue gas and their potential application in bio-reactors. Chemolithotrophs are microorganisms that can derive energy from inorganic compounds, such as carbon dioxide (CO2), nitrogen oxides (NOx), and sulfur dioxide (SO2), present in the flue gas. These microorganisms utilize specialized enzymatic pathways to oxidize these compounds and produce energy. By harnessing the metabolic capabilities of chemolithotrophs, flue gas emissions can be transformed into value-added products. Bio-reactors provide controlled environments for the growth and activity of chemolithotrophic microorganisms. Depending on the specific application, these can be designed as suspended or immobilized reactor systems. The choice of bio-reactor configuration depends on process efficiency, scalability, and ease of operation. Factors influencing the bio-mitigation efficiency of chemolithotrophic interactions include the concentration and composition of the flue gas, operating conditions (such as temperature, pH, and nutrient availability), and reactor design. Chemolithotrophic interactions with flue gas in bio-reactors offer a potentially efficient approach to mitigating flue gas emissions. Continued research and development in this field are necessary to optimize reactor design, microbial consortia, and operating conditions. Advances in understanding the metabolism and physiology of chemolithotrophic microorganisms will contribute to developing robust and scalable bio-mitigation technologies for flue gas emissions.

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.

Optimization of SO2 and NOx sequential wet absorption in a two-stage bioscrubber for elemental sulphur valorisation

Flue gases contain SO₂ and NO_x that can be treated together for elemental sulphur recovery in bioscrubbers, a technology that couples physical-chemical and biological processes for gaseous emissions treatment in a more economic manner than classical absorption. Sequential wet absorption of SO₂ and NO_x from flue gas is thoroughly studied in this work in a two-stage bioscrubber towards elemental sulphur valorisation pursuing reuse of biological process effluents as absorbents. The optimal operating conditions required for SO₂ and NO_x absorption in two consecutive spray absorbers were defined using NaOH-based absorbents. Overall, removal efficiencies of 98.9% and 55.9% for SO₂ and NO_x abatement were obtained in two in-series scrubbers operated under a gas contact time of 1 and 100 s, and a liquid-to-gas ratio of 7.5 and 15 L m^-3, respectively. Higher NO_x removal efficiency to clean gas emission was obtained by oxidants dosing in the absorber for NO_x absorption. High NaHCO₃ concentration in a two-stage bioscrubber effluent was exploited as alkaline absorbent for flue gas treatment. The performance of scrubbers using an absorbent mimicking a reused effluent exhibited the same removal efficiencies than those observed using NaOH solutions. In addition, the reuse of bioprocess effluent reduced reagents' consumption by a 63.7%. Thus, the two-stage bioscrubber proposed herein offers an environmentally friendly and economic alternative for flue gas treatment.

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.

Continuous desulfurization and bacterial community structure of an integrated bioreactor developed to treat SO2 from a gas stream

Sulfide dioxide (SO2) is often released during the combustion processes of fossil fuels. An integrated bioreactor with two sections, namely, a suspended zone (SZ) and immobilized zone (IZ), was applied to treat SO2 for 6months. Sampling ports were set in both sections to investigate the performance and microbial characteristics of the integrated bioreactor. SO2 was effectively removed by the synergistic effect of the SZ and IZ, and more than 85% removal efficiency was achieved at steady state. The average elimination capacity of SO2 in the bioreactor was 2.80g/(m(3)·hr) for the SZ and 1.50g/(m(3)·hr) for the IZ. Most SO2 was eliminated in the SZ. The liquid level of the SZ and the water content ratio of the packing material in the IZ affected SO2 removal efficiency. The SZ served a key function not only in SO2 elimination, but also in moisture maintenance for the IZ. The desired water content in IZ could be feasibly maintained without any additional pre-humidification facilities. Clone libraries of 16S rDNA directly amplified from the DNA of each sample were constructed and sequenced to analyze the community composition and diversity in the individual zones. The desulfurization bacteria dominated both zones. Paenibacillus sp. was present in both zones, whereas Ralstonia sp. existed only in the SZ. The transfer of SO2 to the SZ involved dissolution in the nutrient solution and biodegradation by the sulfur-oxidizing bacteria. This work presents a potential biological treatment method for waste gases containing hydrophilic compounds.

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.

Sulfate removal by Desulfovibrio sp. CMX in chelate scrubbing solutions for NO removal

To study the effects of Fe chelate solution and nitrosyl-complex (Fe(II)EDTA-NO), which might be introduced in the simultaneous biodesulfurization and denitrification process, on the sulfate removal process, a sulfate reducing bacteria Desulfovibrio sp. CMX was investigated for its sulfate removal capacity in the presence of Fe chelate additives and Fe(II)EDTA-NO. Meanwhile, Fe(II)EDTA-NO reduction was also investigated. The addition of Fe(II)EDTA and Fe(III)EDTA could stimulate the sulfate reduction performance. Although Fe(II)EDTA-NO could inhibit the strain, CMX could survive by consuming lactate and recover its sulfate reducing activity after Fe(II)EDTA-NO removed. Sulfate reduction could be enhanced in higher Fe(II)EDTA-NO concentrations (2 and 4 mM) by lactate applied at the middle stage of the experiment, and 72.2% and 62.6% sulfate were removed in 182 h, respectively. In this study, above 90% Fe(II)EDTA-NO (0.25-4 mM) was removed less than 60 h, which was much faster than sulfate reduction.

Enhanced biological removal of NOχ from flue gas in a biofilter by Fe(II)Cit/Fe(II)EDTA absorption

A mixed absorbent had been proposed to enhance the chemical absorption-biological reduction process for NO(x) removal from flue gas. The mole ratio of the absorbent of Fe(II)Cit to Fe(II)EDTA was selected to be 3. After the biofilm was formed adequately, some influential factors, such as the concentration of NO, O(2), SO(2) and EBRT were investigated. During the long-term running, the system could keep on a steady NO removal efficiency (up to 90%) and had a flexibility in the sudden changes of operating conditions when the simulated flue gas contained 100-500 ppm NO, 100-800 ppm SO(2), 1-5% (v/v) O(2), and 15% (v/v) CO(2). However, high NO concentration (>800 ppm) and relative short EBRT (<100s) had significant negative effect on NO removal. The results indicate that the new system by using mixed-absorbent can reduce operating costs in comparison with the single Fe(II)EDTA system and possesses great potential for scale-up to industrial applications.

The control of mercury vapor using biotrickling filters

The feasibility of using biotrickling filters for the removal of mercury vapor from simulated flue gases was evaluated. The experiments were carried out in laboratory-scale biotrickling filters with various mixed cultures naturally attached on a polyurethane foam packing. Sulfur oxidizing bacteria, toluene degraders and denitrifiers were used and compared for their ability to remove Hg 0 vapor. In particular, the biotrickling filters with sulfur oxidizing bacteria were able to remove 100% of mercury vapor, with an inlet concentration of 300-650 microg m(-3), at a gas contact time as low as six seconds. 87-92% of the removed mercury was fixed in or onto the microbial cells while the remaining left the system with the trickling liquid. The removal of mercury vapors in a biotrickling filter with dead cells was almost equivalent to this in biotrickling filters with live cells, indicating that significant abiotic removal mechanisms existed. Sulfur oxidizing bacteria biotrickling filters were the most effective in controlling mercury vapors, suggesting that sulfur played a key role. Identification of the location of metal deposition and of the form of metal was conducted using TEM, energy dispersive X-ray analysis (EDAX) and mercury elution analyses. The results suggested that mercury removal was through a series of complex mechanisms, probably both biotic and abiotic, including sorption in and onto cellular material and possible biotransformations. Overall, the study demonstrates that biotrickling filters appear to be a promising alternative for mercury vapor removal from flue gases.

Effect of sulfur compounds on biological reduction of nitric oxide in aqueous Fe(II)EDTA2− solutions

Biological reduction of nitric oxide (NO) in aqueous solutions of EDTA chelated Fe(II) is one of the main steps in the BioDeNOx process, a novel bioprocess for the removal of nitrogen oxides (NOx) from polluted gas streams. Since NOx contaminated gases usually also contain sulfurous pollutants, the possible interferences of these sulfur compounds with the BioDeNOx process need to be identified. Therefore, the effect of the sulfur compounds Na2SO4, Na2SO3, and H2S on the biological NO reduction in aqueous solutions of Fe(II)EDTA2- (25 mM, pH 7.2, 55 degrees C) was studied in batch experiments. Sulfate and sulfite were found to not affect the reduction rate of Fe(II)EDTA2- complexed NO under the conditions tested. Sulfide, either dosed externally or formed during the batch incubation out of endogenous sulfur sources or the supplied sulfate or sulfite, influences the production and consumption of the intermediate nitrous oxide (N2O) during Fe(II)EDTA2- bound NO reduction. At low concentrations (0.2 g VSS/l) of denitrifying sludge, 0.2 mM free sulfide completely inhibited the nitrosyl-complex reduction. At higher biomass concentrations (1.3-2.3 g VSS/l), sulfide (from 15 microM to 0.8 mM) induced an incomplete NO denitrification with N2O accumulation. The reduction rates of NO to N2O were enhanced by anaerobic sludge, presumably because it kept FeEDTA in the reduced state.

Denitrification and nitric oxide reduction in an aerobic toluene-treating biofilter

The presence of significant denitrification activity in an aerobic toluene-treating biofilter was demonstrated under batch and flow-through conditions. N2O concentrations of 9.2 ppmv were produced by denitrifying bacteria in the presence of 15% acetylene, in a flow-through system with a bulk gas phase O2 concentration of >17%. The carbon source for denitrification was not toluene but a byproduct or metabolite of toluene catabolism. Denitrification conditions were successfully used for the reduction of 60 ppmv nitric oxide to 15 ppmv at a flow rate of 3 L min-1 (EBRT of 3 min) in a fully aerated, 17% v/v O2 (superficially aerobic) biofilter. Higher NO removal efficiency (97%) was obtained by increasing the toluene supply to the biofilter.