Lead removal in flue gas from sludge incineration by denitrification: Insights from metagenomics and metaproteomics.

Flue gas lead emission during sludge incineration damages to human health and ecological environment seriously. Therefore, a denitrifying bio-trickling filter (DNBTF) for lead removal in flue gas from sludge incineration was investigated. Lead removal efficiency was up to 90.7% in 60 days' operation. Lead speciation in biofilms of DNBTF consists of 84.27% residue lead, 15.18% organic bound lead, and less than 1% exchangeable and reducible lead. Lead resistant bacteria and lead resistant-denitrifying bacteria accounted for 85.04% and 58.25%, respectively. Lead resistant microorganisms(Pseudomonas, Azoarcus, Stappia, Pararhodobacter, Paracoccus, Azospirillum, Hyphomonas, Rhodobacter, Polymorphum, Brevunimonas, Stenotrophomonas) could resist the toxicity of Pb2+ in flue gas by transport protein and binding protein, and detoxify Pb2+ in flue gas by extracellular polymeric substances (EPS) adsorption, protein binding and precipitation under the action of resistance genes, such as pbrAB, golT, troABCD, znuABC, czcABCD, pcoB, copA, as shown by integrated metagenomic and metaproteomic analyses. The biofilm was characterized by FTIR, XRD, 3D-EEM, and SEM-EDS. XRD and SEM-EDS spectra indicated the formation of pyromorphite from bioconversion of lead in flue gas. Lead-containing flue gas was bio-stabilized in the form of pyromorphite and HA-Pb via complexation of humic acids in extracellular polymeric substances (EPS), biosorption and biodeposition. This provides a new way of sludge incineration flue gas lead removal using a denitrifying biotricking filter.

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

Nitrogen oxides (NOx) and mercury (Hg) are commonly found coexistent pollutants in combustion flue gas. Ever-increasing emission of atmospheric Hg and NOx 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 NOx in flue gas and summarized recent experimental and technological advances. Finally, several specific technical perspectives have been put forward to better guide future researches.

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 (ß-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 elemental mercury and NO by mercury induced thermophilic community in membrane biofilm reactor.

Thermophilic membrane biofilm reactor (TMBR) for elemental mercury (Hg0) and NO removal in simulated flue gas was investigated at oxygen content of 6% and 60 °C. The performance, the microbial community structures, gene function and the mechanism for Hg0 and NO removal in the TMBR were evaluated. TMBR achieved effective simultaneous Hg0 and NO removal in 210 days of operation, Hg0 and NO removal efficiency were up to 88.9% and 85.3%, respectively. Mercury induced thermophilic community had been formed significantly. Comamonas, Pseudomonas, Desulfomicrobium, Burkholderia and Halomonas were thermophilic mercury resistant bacteria. Brucella, Paracoccus, Tepidiphilus, Proteobacteria, Pseudomonas and Symbiobacterium were nitrifying/denitrifying genera, and had functional genes of mercury and nitrogen metabolism, as shown by16S rDNA and metagenomic sequencing. The biofilm in TMBR was characterized by XPS, HPLC. XPS and HPLC spectra indicate the formation of a mercuric species (Hg2+) from mercury oxidation. TMBR used oxygen as electron acceptor, NO and Hg0 as electron donor in nitrification; O2, NO and NO3- could be used as electron acceptor and Hg0 as electron donor in denitrification.

Sulfide-carbonate-mineralized functional bacterial consortium for cadmium removal in flue gas.

Sulfide-carbonate-mineralized functional bacterial consortium was constructed for flue gas cadmium biomineralization. A membrane biofilm reactor (MBfR) using the bacterial consortium containing sulfate reducing bacteria (SRB) and denitrifying bacteria (DNB) was investigated for flue gas cadmium (Cd) removal. Cadmium removal efficiency achieved 90%. The bacterial consortium containing Citrobacter, Desulfocurvus and Stappia were dominated for cadmium resistance-nitrate-sulfate reduction. Under flue gas cadmium stress, ten cadmium resistance genes (czcA, czcB, czcC, czcD, cadA, cadB, cadC, cueR, copZ, zntA), and seven genes related to sulfate reduction, increased in abundance; whereas others, nine genes related to denitrification, decreased, indicating that cadmium stress was advantageous to sulfate reduction in the competition with denitrification. A bacterial consortium could capable of simultaneously cadmium resistance, sulfate reduction and denitrification. Microbial induced carbonate precipitation (MICP) and biological adsorption process would gradually yield to sulfide-mineralized process. Flue gas cadmium could transform to Cd-EPS, cadmium carbonate (CdCO3) and cadmium sulfide (CdS) bioprecipitate. The functional bacterial consortium was an efficient and eco-friendly bifunctional bacterial consortium for sulfide-carbonate-mineralized of cadmium. This provides a green and low-carbon advanced treatment technology using sulfide-carbonate-mineralized functional bacterial consortium for the removal of cadmium or other hazardous heavy metal contaminants in flue gas.

Mechanistic insights into tris(2-chloroisopropyl) phosphate biomineralization coupled with lead (II) biostabilization driven by denitrifying bacteria.

The ubiquity and persistence of organophosphate esters (OPEs) and heavy metal (HMs) pose global environmental risks. This study explored tris(2-chloroisopropyl)phosphate (TCPP) biomineralization coupled to lead (Pb2+) biostabilization driven by denitrifying bacteria (DNB). The domesticated DNB achieved synergistic bioremoval of TCPP and Pb2+ in the batch bioreactor (efficiency: 98 %).TCPP mineralized into PO43- and Cl-, and Pb2+ precipitated with PO43-. The TCPP-degrading/Pb2+-resistant DNB: Achromobacter, Pseudomonas, Citrobacter, and Stenotrophomonas, dominated the bacterial community, and synergized TCPP biomineralization and Pb2+ biostabilization. Metagenomics and metaproteomics revealed TCPP underwent dechlorination, hydrolysis, the TCA cycle-based dissimilation, and assimilation; Pb2+ was detoxified via bioprecipitation, bacterial membrane biosorption, EPS biocomplexation, and efflux out of cells. TCPP, as an initial donor, along with NO3-, as the terminal acceptor, formed a respiratory redox as the primary energy metabolism. Both TCPP and Pb2+ can stimulate phosphatase expression, which established the mutual enhancements between their bioconversions by catalyzing TCPP dephosphorylation and facilitating Pb2+ bioprecipitation. TCPP may alleviate the Pb2+-induced oxidative stress by aiding protein phosphorylation. 80 % of Pb2+ converted into crystalized pyromorphite. These results provide the mechanistic foundations and help develop greener strategies for synergistic bioremediation of OPEs and HMs.

Pb0 flue gas biosorption in denitrifying MBfR: Characteristics and binding ability of extracellular polymeric substances.

Pb0 in flue gas which is ubiquitous in the environment, poses a certain threat to human and ecology, but the study on EPS-dependent stabilization of lead to remove Pb0 from flue gas remains insufficient. In this investigation, the characteristics and heavy metals-binding ability of four EPS fractions were evaluated. The EPS were extracted from denitrifying membrane biofilm reactor (MBfR) and divided into slime EPS (S-EPS), loosely-bound EPS (LB-EPS), tightly-bound EPS (TB-EPS) and EPS in circulating flow (Y-EPS). The S, LB, TB-EPS related to Pb stabilization on biofilm need more attention. Compared to Pb-S-EPS (0.013 mg g-1) and Pb-LB-EPS (0.13 mg g-1), the Pb-TB-EPS (0.26 mg g-1) was mainly stable form of vapor Pb0, since TB-EPS's higher content (30.67-82.44 mg g-1 VSS), proteins (13.47-36.32 mg g-1 VSS) and polysaccharides (9.37-32.48 mg g-1 VSS) concentration. Particularly, proteins related ligands were more effective in S, LB, TB-EPS dependent adsorption of Pb, complexing with hydrophobic acid ligands further strengthened in TB-EPS adsorption. The Pb-EPS complex formed via binding with functional groups (such as O-H, N-H, C-H and CC) on EPS, also facilitated by loose structure of proteins. This study enlightens the researchers on the bio-treatment and EPS-dependent biosorption of Pb0 in flue gas in denitrifying MBfR.

Arsenic removal in flue gas through anaerobic denitrification and sulfate reduction cocoupled arsenic oxidation.

Arsenic in flue gas from municipal solid waste incineration can damage to human health and ecological environment. A sulfate-nitrate-reducing bioreactor (SNRBR) for flue gas arsenic removal was investigated. Arsenic removal efficiency attained 89.4%. An integrated metagenomic and metaproteomic investigation showed that three nitrate reductases (NapA, NapB and NarG), three sulfate reductases (Sat, AprAB and DsrAB), and arsenite oxidase (ArxA) regulated nitrate reduction, sulfate reduction and bacterial As(III)-oxidation, respectively. Citrobacter and Desulfobulbus could synthetically regulate the expression of arsenite-oxidizing gene, nitrate reductases and sulfate reducatases, which involved in As(III) oxidation, nitrate and sulfate reduction. A bacterial consortium containing Citrobacter, UG_Enterobacteriaceas, Desulfobulbus and Desulfovibrio could capable of simultaneously arsenic oxidation, sulfate reduction and denitrification. Anaerobic denitrification and sulfate reduction were cocoupled to arsenic oxidation. The biofilm was characterized by FTIR, XPS, XRD, EEM, and SEM. XRD and XPS spectra verified the formation of aarsenic species (As(V)) from flue gas As(III) conversion. Arsenic speciation in biofilms of SNRBR consisted of 77% residual arsenic, 15.9% organic matter-bound arsenic, and 4.3% strongly absorbed arsenic. Flue gas arsenic was bio-stabilized in the form of Fe-As-S and As-EPS through biodeposition, biosorption and biocomplexation. This provides a new way of flue gas arsenic removal using the sulfate-nitrate-reducing bioreactor.

Coupled catalytic-biodegradation of toluene over manganese oxide-coated catalytic membranes.

Volatile organic compounds (VOCs) harm human health and the ecological environment. This work demonstrated manganese oxide catalytic membrane coupled to biodegradation of toluene in a catalytic membrane biofilm rector (CMBfR). Toluene removal efficiency in CMBfR was up to 91% in a 200-day operation. Manganese oxide combined to membrane biofilm reactor could promote degradation of toluene. Manganese oxide catalysts were characterized by XRD, Raman, XPS, and FT-IR. Raman and XPS spectra verified the existence of Mn defects, adsorbed oxygen species, and the oxygen vacancy, which was catalytic of toluene on the Mn oxides coated membranes significantly. Pseudomonas, Hydrogenophaga, Flavobacterium, Bacillus, Clostridium and Prosthecobacter were the dominant bacteria of toluene degradation. Mn oxides catalysis could degrade toluene into intermediate products; these products were entered into the biological phase eventually metabolized to CO2 and H2O. These results show that the catalytic membrane biofilm reactor is achievable and opens new possibilities for applying the catalytic membrane biofilm reactor to VOCs treatment.

Simultaneous desulfurization and denitrification by microwave reactor with ammonium bicarbonate and zeolite.

Microwave reactor with ammonium bicarbonate (NH(4)HCO(3)) and zeolite was set up to study the simultaneous removal of sulfur dioxide (SO(2)) and nitrogen oxides (NO(x)) from flue gas. The results showed that the microwave reactor filled with NH(4)HCO(3) and zeolite could reduce SO(2) to sulfur with the best desulfurization efficiency of 99.1% and reduce NO(x) to nitrogen with the best NO(x) purifying efficiency of 86.5%. Microwave desulfurization and denitrification effect of the experiment using ammonium bicarbonate and zeolite together is much higher than that using ammonium bicarbonate or zeolite only. NO(x) concentration has little effect on denitrification but has no influence on desulfurization, SO(2) concentration has no effect on denitrification. The optimal microwave power and empty bed residence time (EBRT) on simultaneous desulfurization and dentrification are 211-280 W and 0.315 s, respectively. The mechanism for microwave reduced desulfurization and denitrification can be described as the microwave-induced catalytic reduction reaction between SO(2), NO(x) and ammonium bicarbonate with zeolite being the catalyst and microwave absorbent.

Nitrification/denitrification shaped the mercury-oxidizing microbial community for simultaneous Hg0 and NO removal.

A denitrifying/nitrifying membrane biofilm reactor for simultaneous removal of Hg0 and NO was investigated. Hg0 and NO removal efficiency attained 94.5% and 86%, respectively. The mercury-oxidizing microbial community was significantly shaped by nitrification/denitrification after the supply of gaseous Hg0and NO continuously. Dominant genera Rhodanobacter and Nitrosomonas participated in Hg0 oxidation, nitrification and denitrification simultaneously. Hg0 oxidizing bacteria (Gallionella, Rhodanobacter, Ottowia, Nitrosomonas and etc.), nitrifying bacteria (Nitrosomonas, Rhodanobacter, Diaphorobacte and etc.) and denitrifying bacteria (Nitrosomonas, Rhodanobacter, Castellaniella and etc.) co-existed in the MBfR, as shown by metagenomic sequencing. X-ray photoelectron spectroscopy (XPS) and high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) confirmed the formation of a mercuric species (Hg2+) from mercury bio-oxidation. Mechanism of mercury oxidation can be described as the bacterial oxidation of Hg0 in which Hg0 serves as electron donor, NO serves as electron donor in nitrification and electron acceptor in denitrification, oxygen serves as electron acceptor.

[Nitric Oxide Removal with a Fe-TiO2/PSF Hybrid Catalytic Membrane Bioreactor].

The Fe-doped titanium dioxide (Fe-TiO2) was prepared by the sol-gel method and was loaded on polysulfone (PSF) hollow fiber membrane. A novel Fe-TiO2/PSF hybrid catalytic membrane biofilm reactor (HCMBfR) was investigated for nitric oxide removal, to further improve the elimination capacity. HCMBfR exhibited a good stability in the 180-day operation period, the NO removal efficiency was up to 93.2% and the maximum elimination capacity reached 167.1 g · (m³ · h)⁻1. The additional use of the biofilm to wet Fe-TiO2/PSF membrane catalysis reactor led to the enhancement of NO removal efficiency from 59. 5% to 66% . The NO removal efficiency in the intimate coupling of Fe-TiO2/PSF hybrid catalytic membrane and biofilm reactor ( HCMBfR) increased from 1.4% to 13% as compared to that of the membrane biofilm reactor (MBfR) only. The optimal illumination intensity, gas residence time, pH and nC/nN were 670 lx, 9 a, 6.8-7.2 and 3.7, respectively.

[Gaseous phenol removal in a bio-trickling filter].

The performance of a bio-trickling filter (BTF) for treatment of phenol, a model pollutant, was presented. Influences of factors on phenol removal efficiency were studied. The BTF exhibited a high removal efficiency for phenol. The experimental results showed that the phenol efficiency reached 99.5% and kept 98% in the long-term run. The optimal residence time, pH value and spray density were 20.6 s, 7.0 and 1.67 m(3) x (m(2) x h)(-1), respectively. The microbial community structures in the bio-trickling filter for phenol removal were assessed by PCR-DGGE. Based on the 16S rDNA sequence data,results showed that the predominant bacteria for degradation of phenol were Polaromonas sp., Acinetobacter sp., Acidovorax sp., Veillonella parvula and Corynebacterium sp., GC-MS was used to detect component of BTF's outlet gases and pyruvic acid (CH3COCOOH) was found as one kind of intermediates of phenol degradation. Then one possible biodegradation pathway of phenol was inferred.

[Hydrogen sulfide removal by the combination of non-thermal plasma and biological process].

A bench scale system integrating a non-thermal plasma (NTP) unit with a biotricking filtration (BTF) unit for the treatment of gases containing hydrogen sulfide (H2S) was investigated. The additional use of the biotrickling filter to NTP reactor not only leads to the enhancement of hydrogen sulfide removal efficiency up from 83.4% to 90.1%, but also eliminates gas-phase intermediate products from NTP degradation of H2S to produce sulfate and H2O. The dynamic changes of microbial community in BTF influenced by ozone from NTP were assessed by PCR-DGGE. Results show that the microbial community was affected by ozone. After the integration, a part of microorganisms disappeared, and meanwhile some new microorganisms appeared. The microbial community structure in BTF changed from eight bands to nine bands; three bands which have the functions of desulfurization disappeared and four bands which have the functions of desulfurization appeared; five bands which have the functions of desulfurization and sulfate reduction were unchanged. The bacterial groups in the BTF unit of NTP-BTF system include Uncultured Thiobacillus sp., Acidithiobacillus thiooxidans strain dfI, Uncultured Thiobacillus sp., Uncultured Acidiphilium sp., Uncultured Xanthomonadaceae bacterium clone SBLE6C12, Uncultured 8-Proteobacterium and Paracraurococcus sp. 1PNM-27.

[Mechanism and performance of styrene oxidation by O3/H2O2].

It can produce a large number of free radicals in O3/H2O2, system, ozone and free radical coupling oxidation can improve the styrene removal efficiency. Styrene oxidation by O3/H2O2 was investigated. Ozone dosage, residence time, H2o2 volume fraction, spray density and molar ratio of O3/C8H8 on styrene removal were evaluated. The experimental results showed that styrene removal efficiency achieved 85.7%. The optimal residence time, H2O2, volume fraction, spray density and O3/C8H8 molar ratio were 20. 6 s, 10% , 1.72 m3.(m2.h)-1 and 0.46, respectively. The gas-phase degradation intermediate products were benzaldehyde(C6H5CHO) and benzoic acid (C6H5 COOH) , which were identified by means of gas chromatography-mass spectrometry(GC-MS). The degradation mechanism of styrene is presented.

[Mechanism and performance of a membrane bioreactor for treatment of toluene vapors].

The performance of a membrane bioreactor for treatment of toluene as a model pollutant is presented. Effects of toluene inlet concentration, residence time, spray density and pH of liquid phase on the toluene removal rate were evaluated. The experimental results showed that the toluene removal efficiency reached 99%. The optimal pH, residence time and spray density were 7.2, 6.4 s and 2.5 m3 x (m2 x h)(-1), respectively. The gas-phase biodegradation intermediate products were acetaldehyde acid (C2H2O3) and vinyl formic acid (C3H4O2), which were identified by means of gas chromatography/mass spectrometry (GC/MS). The mechanism of toluene degradation using a membrane bioreactor can be described as the combination of mass transfer from hollow fiber membrane to biofilm and biological degradation. Toluene (C6H5CH3) and oxygen diffused from the gas phase to the wet layer of the biofilm and were then consumed by the microbial communities. Toluene was oxidized to the intermediate organic products such as acetaldehyde acid (C2H2O3) and vinyl formic acid (C3H4O2), and the intermediate products were then converted to CO2 and H2O through continuous biological oxidation reactions.

Removal of gaseous toluene by the combination of photocatalytic oxidation under complex light irradiation of UV and visible light and biological process.

Photocatalysis is a promising technology for treatment of gaseous waste; its disadvantages, however, include causing secondary pollution. Biofiltration has been known as an efficient technology for treatment volatile organic compounds (VOCs) at low cost of maintenance, and produces harmless by-products; its disadvantages, include large volume of bioreactor and slow adaptation to fluctuating concentrations in waste gas. A bench scale system integrated with a photocatalytic oxidation and a biofilter unit for the treatment of gases containing toluene was investigated. The integrated system can effectively oxidize toluene with high removal efficiency. The photocatalytic activity of N-TiO(2)/zeolite was evaluated by the decomposition of toluene in air under UV and visible light (VL) illumination. The N-TiO(2)/zeolite has more photocatalytic activity under complex light irradiation of UV and visible light for toluene removal than that of pure TiO(2)/zeolite under UV or visible light irradiation. N-TiO(2)/zeolite was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectrum analysis (XPS), Fourier transform infrared spectroscopy (FT-IR), and as-obtained products were identified by means of gas chromatography/mass spectrometry (GC/MS). Results revealed that the photocatalyst was porous and was high photoactive for mineralizing toluene. The high activity can be attributed to the results of the synergetic effects of strong UV and visible light absorption, surface hydroxyl groups. The photocatalytic degradation reaction of toluene with the N-TiO(2)/zeolite follows Langmuir-Hinshelwood kinetics. Toluene biodegradation rate matches enzymatic oxidation kinetics model.

Biopurification of industrial waste gas from rubber regeneration.

By using the biopurifying technology, the organic waste gas in low concentrations emitted from the rubber-regeneration process was purified in this research. The result of the 100-day continuous running test of the industrial test device indicated that the purification efficiency of toluene in the rubber-regeneration waste gas could be maintained at about 90% for a long period of time and the treated waste gas could meet the China National Emission Standard. The cost of waste gas biotreatment was about 0.12-0.14% of rubber-regeneration production value of the factory. The biopurifying technology of waste gas displayed its excellent technical advancement and economic rationale. The following industrialized device was run continuously and passed the examination and acceptance by the local EPA.