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

Industrial scale-up of flue gas bio-mitigation with chemolithotrophs in packed bed reactors: Exploring metabolite synthesis, mass transfer, and techno-economic analysis

Elevated emissions of flue gases deteriorate the quality of air, impacting both terrestrial and aquatic ecosystems through their contribution to acid rain and eutrophication. This study examines the bio-mitigation process in a packed bed reactor and its capacity to concurrently decrease the environmental consequences of industrial flue gases (CO2, NO, and SO2) and wastewater by employing mixed bacterial consortia. The highest biomass productivity achieved during the growth phase was 0.002 g L-1 h-1 in the aqueous medium and 0.006 g L-1 h-1 in the PU foam. The highest level of CO2 removal efficiency was 86.60%, while for NO and SO2, it was 77.03% and 82%, respectively. The comprehensive nutrient balance analysis revealed that the flue gas was primarily utilized for biomass assimilation. The FT-IR and GC-MS analysis detected metabolites, including carboxylic acids, esters, and fatty alcohols, that were produced during the process. The NMR study examined alterations in the concentration of metabolites within the cell, indicating metabolic pathways such as the TCA cycle, alanine, pyruvate, butanoate metabolism, and glycolysis. The mass transfer coefficient estimated for the gas-liquid-solid phase was ∼2.0 m s-1 for the flue gases. The scale-up of the reactor based on the mass transfer coefficient up to 20,000 L gives a net present value of $2,66,116.13 with a benefit-to-cost ratio of 1.47. Therefore, this study suggests that employing bacteria is a viable and energy-efficient approach to mitigate the adverse effects of flue gas on air quality. Additionally, it aids industries in minimizing waste and repurposing it for advantageous purposes, thereby diminishing their environmental footprint.

Sustainable synergistic approach to chemolithotrophs-supported bioremediation of wastewater and flue gas

Flue gas emissions are the waste gases produced during the combustion of fuel in industrial processes, which are released into the atmosphere. These identical processes also produce a significant amount of wastewater that is released into the environment. The current investigation aims to assess the viability of simultaneously mitigating flue gas emissions and remediating wastewater in a bubble column bioreactor utilizing bacterial consortia. A comparative study was done on different growth media prepared using wastewater. The highest biomass yield of 3.66 g L-1 was achieved with the highest removal efficiencies of 89.80, 77.30, and 80.77% for CO2, SO2, and NO, respectively. The study investigated pH, salinity, dissolved oxygen, and biochemical and chemical oxygen demand to assess their influence on the process. The nutrient balance validated the ability of bacteria to utilize compounds in flue gas and wastewater for biomass production. The Fourier Transform-Infrared Spectrometry (FT-IR) and Gas Chromatography-Mass Spectrometry (GC-MS) analyses detected commercial-use long-chain hydrocarbons, fatty alcohols, carboxylic acids, and esters in the biomass samples. The nuclear magnetic resonance (NMR) metabolomics detected the potential mechanism pathways followed by the bacteria for mitigation. The techno-economic assessment determined a feasible total capital investment of 245.74$ to operate the reactor for 288 h. The bioreactor's practicability was determined by mass transfer and thermodynamics assessment. Therefore, this study introduces a novel approach that utilizes bacteria and a bioreactor to mitigate flue gas and remediate wastewater.

Development of a flow-cell bioreactor for immobilized sulfidogenic sludge characterization using electrochemical H2S microsensors

The sulfate-reduction process plays a crucial role in the biological valorization of SOx gases. However, a complete understanding of the sulfidogenic process in bioreactors is limited by the lack of technologies for characterizing the sulfate-reducing activity of immobilized biomass. In this work, we propose a flow-cell bioreactor (FCB) for characterizing sulfate-reducing biomass using H2S microsensors to monitor H2S production in real-time within a biofilm. To replace natural immobilization through extracellular polymeric substance production, sulfidogenic sludge was artificially immobilized using polymers. Physical and sulfate-reducing activity studies were performed to select a polymer-biomass matrix that maintained sulfate-reducing activity of biomass while providing strong microbial retention and mechanical strength. Several operational conditions of the sulfidogenic reactor allowed to obtain a H2S profiles under different inlet sulfate loads and, additionally, 3D mapping was assessed in order to perform a hydraulic characterization. Besides, the effects of artificial immobilization on biodiversity were investigated through the characterization of microbial communities. This study demonstrated the appropriateness of immobilized-biomass for characterization of sulfidogenic biomass in FCB using H2S electrochemical microsensors, and beneficial microbiological communities shifts as well as enrichment of sulfate-reducing bacteria have been confirmed.

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.

Biochemical engineering for elemental sulfur from flue gases through multi-enzymatic based approaches - A review

Flue gases are the gases which are produced from industries related to chemical manufacturing, petrol refineries, power plants and ore processing plants. Along with other pollutants, sulfur present in the flue gas is detrimental to the environment. Therefore, environmentalists are concerned about its removal and recovery of resources from flue gases due to its activation ability in the atmosphere to transform into toxic substances. This review is aimed at a critical assessment of the techniques developed for resource recovery from flue gases. The manuscript discusses various bioreactors used in resource recovery such as hollow fibre membrane reactor, rotating biological contractor, sequential batch reactor, fluidized bed reactor, entrapped cell bioreactor and hybrid reactors. In conclusion, this manuscript provides a comprehensive analysis of the potential of thermotolerant and thermophilic microbes in sulfur removal. Additionally, it evaluates the efficacy of a multi-enzyme engineered bioreactor in this process. Furthermore, the study introduces a groundbreaking sustainable model for elemental sulfur recovery, offering promising prospects for environmentally-friendly and economically viable sulfur removal techniques in various industrial applications.

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.

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.

Technologies for deodorization of malodorous gases

There is an increasing number of citizens' complaints about odor nuisance due to production or service activity. High social awareness imposes pressure on entrepreneurs and service providers forcing them to undertake effective steps aimed at minimization of the effects of their activity, also with respect to emission of malodorous substances. The article presents information about various technologies used for gas deodorization. Known solutions can be included into two groups: technologies offering prevention of emissions, and methodological solutions that enable removal of malodorous substances from the stream of emitted gases. It is obvious that the selection of deodorization technologies is conditioned by many factors, and it should be preceded by an in-depth analysis of possibilities and limitations offered by various solutions. The aim of the article is presentation of the available gas deodorization technologies as to facilitate the potential investors with selection of the method of malodorous gases emission limitation, suitable for particular conditions.

Sulfur dioxide and o-xylene co-treatment in biofilter: Performance, bacterial populations and bioaerosols emissions

Sulfur dioxide (SO₂) and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO₂ and o-xylene in the present study. SO₂ and o-xylene could be removed simultaneously in a single biofilter. Their concentration ratio in the inlet stream influenced the removal efficiencies. It is worth noting that the removal of SO₂ could be enhanced when low concentrations of o-xylene were introduced into the biofilter. Pseudomonas sp., Paenibacillus sp., and Bacillus sp. were the main functional bacteria groups in the biofilter. Sulfur-oxidizing bacteria (SOB) and o-xylene-degrading bacteria (XB) thrived in the biofilter and their counts as well as their growth rate increased with the increase in amount of SO₂ and o-xylene supplied. The microbial populations differed in counts and species due to the properties and components of the compounds being treated in the biofilter. The presence of mixed substrates enhanced the diversity of the microbial population. During the treatment process, bioaerosols including potentially pathogenic bacteria, e.g., Acinetobacter lwoffii and Aeromonas sp., were emitted from the biofilter. Further investigation is needed to focus on the potential hazards caused by the bioaerosols emitted from waste gas treatment bioreactors.

Effect of calcium formate as an additive on desulfurization in power plants

SO₂ in flue gas needs to be eliminated to alleviate air pollution. As the quality of coal decreases and environmental standard requirements become more stringent, the high-efficiency desulfurization of flue gas faces more and more challenges. As an economical and environmentally friendly solution, the effect of calcium formate as an additive on desulfurization efficiency in the wet flue gas desulfurization (WFGD) process was studied for the first time. Improvement of the desulfurization efficiency was achieved with limited change in pH after calcium formate was added into the reactor, and it was found to work better than other additives tested. The positive effects were further verified in a power plant, which showed that adding calcium formate could promote the dissolution of calcium carbonate, accelerate the growth of gypsum crystals and improve the efficiency of desulfurization. Thus, calcium formate was proved to be an effective additive and can potentially be used to reduce the amount of limestone slurry required, as well as the energy consumption and operating costs in industrial desulfurization.

Effects of oxygen and water content on microbial distribution in the polyurethane foam cubes of a biofilter for SO2 removal

The performance of a biofilter for off-gas treatment relies on the activity of microorganisms and adequate O₂ and H₂O. In present study, a microelectrode was applied to analyze O₂ in polyurethane foam cubes (PUFCs) packed in a biofilter for SO₂ removal. The O₂ distribution varied with the density and water-containing rate (WCR) of PUFCs. The O₂ concentration dropped sharply from 10.2 to 0.8mg/L from the surface to the center of a PUFC with 97.20% of WCR. The PUFCs with high WCR presented aerobic-anoxic-aerobic areas. Three-dimensional simulated images demonstrated that the structure of PUFCs with high WCR consisted of an aerobic "shell" and an anoxic "core", with high-density PUFCs featuring a larger anoxic area than low-density PUFCs. Moreover, the H₂O distribution in the PUFC was uneven and affected the O₂ concentration. Whereas aerobic bacteria were observed in the PUFC surface, facultative anaerobic microorganisms were found at the PUFC core, where the O₂ concentration was relatively low. O₂ and H₂O distributions differed in the PUFCs, and the distribution of microorganisms varied accordingly.

Operational aspects of SO2 removal and microbial population in an integrated-bioreactor with two bioreaction zones

An integrated-bioreactor, which consisted of a suspended zone and an immobilized zone, was applied to treat gases containing SO₂. The removal of SO₂ in suspended zone differed slightly from that in immobilized zone. The influences of operational aspects such as SO₂ load, temperature, and pH on integrated-bioreactor performance and bacterial community composition were investigated. The synergistic action of the two zones led to effective reduction of SO₂, and the total removal efficiencies with the inlet concentration of 91-117 mg/m³, were over 85 % in steady state. Paenibacillus sp. and Lysinibacillus sp. dominated both zones as desulfurization bacteria. Results of polymerase chain reaction-denaturing gradient gel electrophoresis followed by clone library analysis indicated that temporal shifts in bacterial community composition in both zones developed differently. Differences in the concentration of introduced SO₂ and supported mode of microorganisms for survival, confirmed that bacterial community composition and abundance significantly differed among individual zones.