Biodegradation of ethanethiol in aqueous medium by a new Lysinibacillus sphaericus strain RG-1 isolated from activated sludge

The critical roles of propanethiol oxidoreductase and sulfide-quinone oxidoreductase in the propanethiol catabolism pathway in Pseudomonas putida S-1

Propanethiol (PT) is a hazardous pollutant that poses risks to both the environment and human well-being. Pseudomonas putida S-1 has been identified as a microorganism capable of utilizing PT as its sole carbon source. However, the metabolic pathway responsible for PT degradation in P. putida S-1 has remained poorly understood, impeding its optimization and practical application. In this study, we investigated the catabolic network involved in PT desulfurization with P. putida S-1 and identified key gene modules crucial to this process. Notably, propanethiol oxidoreductase (PTO) catalyzes the initial degradation of PT, a pivotal step for P. putida S-1's survival on PT. PTO facilitates the oxidation of PT, resulting H2S, H2O2, and propionaldehyde (PA). Catalase-peroxidase catalyzes the conversion of H2O2 to oxygen and water, while PA undergoes gradual conversion to Succinyl-CoA, which is subsequently utilized in the tricarboxylic acid cycle. H2S is digested in a comprehensive desulfurization network where sulfide-quinone oxidoreductase (SQOR) predominantly converts it to sulfane sulfur. The transcriptome analysis suggests that sulfur can be finally converted to sulfite or sulfate and exported out of the cell. The PT degradation capacity of P. putida S-1 was enhanced by increasing the transcription level of PTO and SQOR genes in vivo.IMPORTANCEThis work investigated the PT catabolism pathway in Pseudomonas putida S-1, a microorganism capable of utilizing PT as the sole carbon source. Critical genes that control the initiation of PT degradation were identified and characterized, such as pto and sqor. By increasing the transcription level of pto and sqor genes in vivo, we have successfully enhanced the PT degradation efficiency and growth rate of P. putida S-1. This work does not only reveal a unique PT degradation pathway but also highlights the potential of enhancing the microbial desulfurization process in the bioremediation of thiol-contaminated environment.

Superior dimethyl disulfide degradation in a microbial fuel cell: Extracellular electron transfer and hybrid metabolism pathways

To enhance the biological degradation of volatile organic sulfur compounds, a microbial fuel cell (MFC) system with superior activity is developed for dimethyl disulfide (DMDS) degradation. The MFC achieves a removal efficiency near 100% within 6 h (initial concentration: 90 mg L^-1) and a maximum biodegradation rate constant of 0.743 mM h^-1. The DMDS removal load attains 2.684 mmol h^-1 L^-1, which is 6.18-2440 times the loads of conventional biodegradation processes reported. Meanwhile, the maximum power density output and corresponding current density output are 5.40 W m^-3 and 40.6 A m^-3, respectively. The main mechanism of extracellular electron transfer is classified as mediated electron transfer, supplemented by direct transfer. Furthermore, the mass balance analysis indicates that methanethiol, S⁰, S^2-, SO₄^2-, HCHO, and CO₂ are the main intermediate and end products involved in the hybrid metabolism pathway of DMDS. Overall, these findings may offer basic information for bioelectrochemical degradation of DMDS and facilitate the application of MFC in waste gas treatment. ENVIRONMENTAL IMPLICATION: Dimethyl disulfide (DMDS), which features poor solubility, odorous smell, and refractory property, is a typical pollutant emitted from the petrochemical industry. For the first time, we develop an MFC system for DMDS degradation. The superior DMDS removal load per unit reactor volume is 6.18-2440 times those of conventional biodegradation processes in literature. Both the electron transfer route and the hybrid metabolism pathway of DMDS are cleared in this work. Overall, these findings give an in-depth understanding of the bioelectrochemical DMDS degradation mechanism and provide an efficient alternative for DMDS removal.

Newly isolated Enterobacter cloacae sp. HN01 and Klebsiella pneumoniae sp. HN02 collaborate with self-secreted biosurfactant to improve solubility and bioavailability for the biodegradation of hydrophobic and toxic gaseous para-xylene

The gas-liquid mass transfer rate of hydrophobic volatile organic compounds (VOCs) is the limiting step in a biological treatment system. The present study aimed to utilize self-producing biosurfactants to enhance the bioavailability of hydrophobic gaseous VOCs. Two novel gram-negative rod-shaped bacteria, Enterobacter cloacae strain HN01 and Klebsiella pneumoniae strain HN02 were successfully isolated from sewage sludge by using blood agar and methylene blue agar plates. The two strains can use para-xylene (PX), a hydrophobic VOC model, as the only carbon source for biosurfactant production. Both strains can produce glycolipid biosurfactants, as confirmed by the emulsification index, Nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Results indicated that PX can be completely decomposed at an initial concentration of 15.50 mg L^-1, pH value of 7.0, and temperature of 30 °C within 36 h. The Yano model is suitable for the prediction of the growth kinetics of strains over the entire PX concentration range. Gas chromatography/mass spectrometry analysis indicated that PX was converted into four and four intermediates in the presence of the strains HN01 and HN02, respectively, and the possible mechanisms were proposed. The results can be used in purifying industrial hydrophobic gaseous VOCs and improving the bioavailability of VOCs with self-produced biosurfactants.

The role of Fe3O4@biochar as electron shuttle in enhancing the biodegradation of gaseous para-xylene by aerobic surfactant secreted strains

To study the role of electron shuttles in accelerating the biodegradation of volatile organic compounds (VOCs) and provide theoretical support for purification of waste gas containing PX, two self-producing biosurfactant strains were used to improve solubility, and the magnetic Fe₃O₄@biochar composites were prepared as electron shuttles to accelerate extracellular electron transfer during the process of para-xylene (PX) biodegradation. The composites were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The biodegradation time of PX by Enterobacter sp. HN01 and Klebsiella sp. HN02 decreased from 192 h to 12 h and 120 to 12 h, and approximately 93.75% and 90.00% of the removal times were saved after the addition of the composites. Furthermore, the effects of Fe₃O₄@biochar on the bacterial biosurfactant secretion, self-enzyme activity, and bacterial growth inhibition by PX were explored. The electron transport capacity of Fe₃O₄@biochar was 4.583 mmol·e^-/g detected by mediated electrochemical reduction and mediated electrochemical oxidation, and possible electron transport pathways were revealed. The possible products of PX biodegradation by HN01 and HN02 were determined through gas chromatography-mass spectrometry. The molecular structure of PX was deduced through density functional theory calculation to validate the key product. Results indicated that Fe₃O₄@biochar can be used as an electronic shuttle to accelerate extracellular electron transfer and significantly improve VOCs removal rate.

Microbial detoxification of dimethoate through mediated hydrolysis by Brucella sp. PS4: molecular profiling and plant growth-promoting traits

High toxicity of dimethoate requires efficient ways for detoxification and removal of its residues in contaminated environments. Microbial remediation is a process that utilizes the degradation potential of microbes to provide a cost-effective and reliable approach for pesticide abatement. For this purpose, a dimethoate-degrading bacterium Brucella sp. was isolated from a contaminated agricultural soil sample in Multan, Pakistan. This isolate was found to tolerate up to 100 ppm of dimethoate in minimal salt medium and was further evaluated for plant growth-promoting traits. The strain gave positive results for amylase, ammonia, and catalase production, while other traits such as indole acetic acid production and potassium solubilization were also confirmed. Thus, the strain could play an important role for plant nutrient transmission in the plant rhizosphere. Optimization of growth parameters (i.e., pH and temperature) depicted the potential of PS4 to be best tolerating dimethoate, with maximum cell density at λ 600 nm. Optimum pH and temperature for growth were found to be 6 and 35 °C, respectively. Based on optimization results as well as different attributes, the rhizospheric bacterial isolate PS4 was further subjected to a batch degradation experiment under different concentrations of dimethoate (25, 50, 75, and 100 ppm). This promising dimethoate-degrading isolate was found to degrade 83% of dimethoate (at 100 ppm) within a period of 7 days. In addition, it degraded 88% of dimethoate at 50 ppm, indicating that the bacterial isolate utilized dimethoate solely as a source of energy. The strain followed the first order reaction kinetics, depicting its dependence on dimethoate as energy and carbon source. Molecular profiling further supported its role in plant growth promotion and multi-stress tolerance. This research showed that Brucella sp. is capable of degrading dimethoate, and therefore, it would be useful in the investigation of novel bioremediation techniques at pesticide-polluted sites.

Co-Treatment with Single and Ternary Mixture Gas of Dimethyl Sulfide, Propanethiol, and Toluene by a Macrokinetic Analysis in a Biotrickling Filter Seeded with Alcaligenes sp. SY1 and Pseudomonas Putida S1

The biotrickling filter (BTF) treatment is an effective way of dealing with air pollution caused by volatile organic compounds (VOCs). However, this approach is typically used for single VOCs treatment but not for the mixtures of VOC and volatile organic sulfur compounds (VOSCs), even if they are often encountered in industrial applications. Therefore, we investigated the performance of BTF for single and ternary mixture gas of dimethyl sulfide (DMS), propanethiol, and toluene, respectively. Results showed that the co-treatment enhanced the removal efficiency of toluene, but not of dimethyl sulfide or propanethiol. Maximum removal rates (rmax) of DMS, propanethiol and toluene were calculated to be 256.41 g·m−3·h−1, 204.08 g·m−3·h−1 and 90.91 g·m−3·h−1, respectively. For a gas mixture of these three constituents, rmax was measured to be 114.94 g·m−3·h−1, 104.17 g·m−3·h−1 and 99.01 g·m−3·h−1, separately. Illumina MiSeq sequencing analysis further indicated that Proteobacteria and Bacteroidetes were the major bacterial groups in BTF packing materials. A shift of bacterial community structure was observed during the biodegradation process.

Biodegradation and metabolic pathway of fenvalerate by Citrobacter freundii CD-9

Fenvalerate is a pyrethroid insecticide with rapid action, strong targeting, broad spectrum, and high efficiency. However, continued use of fenvalerate has resulted in its widespread presence as a pollutant in surface streams and soils, causing serious environmental pollution. Pesticide residues in the soil are closely related to food safety, yet little is known regarding the kinetics and metabolic behaviors of fenvalerate. In this study, a fenvalerate-degrading microbial strain, CD-9, isolated from factory sludge, was identified as Citrobacter freundii based on morphological, physio-biochemical, and 16S rRNA sequence analysis. Response surface methodology analysis showed that the optimum conditions for fenvalerate degradation by CD-9 were pH 6.3, substrate concentration 77 mg/L, and inoculum amount 6% (v/v). Under these conditions, approximately 88% of fenvalerate present was degraded within 72 h of culture. Based on high-performance liquid chromatography and gas chromatography-mass spectrometry analysis, ten metabolites were confirmed after the degradation of fenvalerate by strain CD-9. Among them, o-phthalaldehyde is a new metabolite for fenvalerate degradation. Based on the identified metabolites, a possible degradation pathway of fenvalerate by C. freundii CD-9 was proposed. Furthermore, the enzyme localization method was used to study CD-9 bacteria and determine that its degrading enzyme is an intracellular enzyme. The degradation rate of fenvalerate by a crude enzyme solution for over 30 min was 73.87%. These results showed that strain CD-9 may be a suitable organism to eliminate environmental pollution by pyrethroid insecticides and provide a future reference for the preparation of microbial degradation agents and environmental remediation.

Experimental study on volatile sulfur compound inhibition using a single-chamber membrane-free microbial electrolysis cell

Odor emissions from sewer systems and wastewater treatment plants have attracted much attention due to the potential negative effects on human health. A single-chamber membrane-free microbial electrolysis cell was proposed for the removal of sulfides in a sewer system. The feasibility of the use of volatile sulfur compounds and their removal efficiency in liquid and headspace gas phases were investigated using synthetic wastewater with real sewer sediment and Ru/Ir-coated titanium electrodes. The results indicate that hydrogen sulfide and volatile organic sulfur compounds were effectively inhibited in the liquid phase upon electrochemical treatment at current densities of 1.55, 2.06, and 2.58 mA/cm², and their removal rates reached up to 86.2-100%, except for dimethyl trisulfide, the amount of which increased greatly at 1.55 mA/cm². In addition, the amount of volatile sulfur compounds in the headspace decreased greatly; however, the total theoretical odor concentration was still high, and methanethiol and ethanethiol greatly contributed to the total strength of the odor concentration due to their low odor threshold concentrations. The major pathway for sulfide removal in the single-chamber membrane-free microbial electrolysis cell is biotic oxidation, the removal rate of which was 0.4-0.5 mg/min, 4-5 times that of indirect electrochemical oxidation.

Whole Genome Sequencing and Comparative Genomic Analyses of Lysinibacillus pakistanensis LZH-9, a Halotolerant Strain with Excellent COD Removal Capability

Halotolerant microorganisms are promising in bio-treatment of hypersaline industrial wastewater. Four halotolerant bacteria strains were isolated from wastewater treatment plant, of which a strain LZH-9 could grow in the presence of up to 14% (w/v) NaCl, and it removed 81.9% chemical oxygen demand (COD) at 96 h after optimization. Whole genome sequencing of Lysinibacillus pakistanensis LZH-9 and comparative genomic analysis revealed metabolic versatility of different species of Lysinibacillus, and abundant genes involved in xenobiotics biodegradation, resistance to toxic compound, and salinity were found in all tested species of Lysinibacillus, in which Horizontal Gene Transfer (HGT) contributed to the acquisition of many important properties of Lysinibacillus spp. such as toxic compound resistance and osmotic stress resistance as revealed by phylogenetic analyses. Besides, genome wide positive selection analyses revealed seven genes that contained adaptive mutations in Lysinibacillus spp., most of which were multifunctional. Further expression assessment with Codon Adaption Index (CAI) also reflected the high metabolic rate of L. pakistanensis to digest potential carbon or nitrogen sources in organic contaminants, which was closely linked with efficient COD removal ability of strain LZH-9. The high COD removal efficiency and halotolerance as well as genomic evidences suggested that L. pakistanensis LZH-9 was promising in treating hypersaline industrial wastewater.

Ethanethiol gas removal in an anoxic bio-scrubber

The performance of ethanethiol removal in an anoxic lab-scale bio-scrubber was investigated under different operating parameters and conditions for 300 days. The removal efficiency (RE) of ethanethiol was examined as a function of inlet concentration, empty bed residence time (EBRT) and spray density of irrigation. The results showed the best operation conditions and operation characteristics of the bio-scrubber for this study were at an inlet concentration of 150 mg/m³, a spray density of 0.23 m³/m² h and an EBRT of 90 s. An average RE of 91% and elimination capacity (EC) of 24.74 g/m³ h was found for all inlet ethanethiol concentrations. Variations in spray density higher than 0.23 m³/m² h had no effect on ethanethiol RE at different ethanethiol concentrations. The average experimental yield values were closer to the Y_ET/NO3^- theoretical value of 0.74 when the main product was elemental sulphur (S^o). This indicates that S^o and other forms of sulphur were formed rather than sulphate (SO₄^2-) as the end product. Furthermore, growth kinetics for bio-degradation were evaluated in batch culture experiments using the Monod model, and bio-kinetic parameters of μ_max, K_s, Y_xs and q_max were obtained as 0.14 1/h, 1.17 mg/L, 0.52 g_x/g_s and 0.26 g_s/g_x h, respectively.

Seasonal and spatial variation in the sediment bacterial community and diversity of Lake Bosten, China

To explore the influence of seasonal and regional environmental factors on the bacterial community composition (BCC) and diversity in the sediments of Lake Bosten, the 16S rRNA gene of sediment bacteria in four samples from the lake center area and the macrophyte-dominated area were sequenced using 454 pyrosequencing. According to the operational taxonomic units (OTUs), diversity index, relative abundance, and redundancy analysis (RDA) of the bacteria, the results showed that (i) the bacterial diversity of the lake center area was lower than that of the macrophyte-dominated area, and it was higher in winter than that in summer as a whole; (ii) seasonal factors and geographical changes had obvious effects on the abundance of dominant bacteria, including Proteobacteria and Firmicutes; (iii) a large number of unclassified bacteria were detected in this study, and the dominant unclassified genera in both lake areas included unclassified Sva0485, unclassified Anaerolineaceae, and unclassified Nitrospiraceae; and (iv) TN and TOC were the main environmental factors influencing the sediment bacterial community in Lake Bosten, as determined by RDA analysis. The study provides a reference for the in-depth understanding the impact with the change of time and space on sediment microbes in Lake Bosten.

Elimination of ethanethiol released from municipal wastes by absorption sequencing electrochemical oxidation

As a typical municipal waste landfill gas, ethanethiol can become an air pollutant because of its low odor threshold concentration and toxicity to human beings. A hybrid process of absorption combined with electrochemical oxidation to degrade ethanethiol was investigated. The ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) was employed as an absorbent to capture ethanethiol from the air stream. Electrochemical oxidation demonstrated that ethanethiol could be oxidized on a β-PbO₂ anode modified with fluoride, while [BMIM]BF₄ was used as an electrolyte. After a reaction time of 90 min under a current density of 50 mA/cm², ethanethiol could be thoroughly destructed by the successive attack of hydroxyl radicals (·OH) electrogenerated on the surface of the β-PbO₂ anode, while the sulfur atoms in ethanethiol were ultimately converted to sulfate ions [Formula: see text]. The reaction mechanism is proposed, and the operating condition is also estimated with a kinetic model. This hybrid process could be a promising way to remove thiol compounds from municipal waste landfill gases.

Non-ureolytic calcium carbonate precipitation by Lysinibacillus sp. YS11 isolated from the rhizosphere of Miscanthus sacchariflorus

Although microbially induced calcium carbonate precipitation (MICP) through ureolysis has been widely studied in environmental engineering fields, urea utilization might cause environmental problems as a result of ammonia and nitrate production. In this study, many non-ureolytic calcium carbonate-precipitating bacteria that induced an alkaline environment were isolated from the rhizosphere of Miscanthus sacchariflorus near an artificial stream and their ability to precipitate calcium carbonate minerals with the absence of urea was investigated. MICP was observed using a phase-contrast microscope and ion-selective electrode. Only Lysinibacillus sp. YS11 showed MICP in aerobic conditions. Energy dispersive X-ray spectrometry and X-ray diffraction confirmed the presence of calcium carbonate. Field emission scanning electron microscopy analysis indicated the formation of morphologically distinct minerals around cells under these conditions. Monitoring of bacterial growth, pH changes, and Ca²⁺ concentrations under aerobic, hypoxia, and anaerobic conditions suggested that strain YS11 could induce alkaline conditions up to a pH of 8.9 and utilize 95% of free Ca²⁺ only under aerobic conditions. Unusual Ca²⁺ binding and its release from cells were observed under hypoxia conditions. Biofilm and extracellular polymeric substances (EPS) formation were enhanced during MICP. Strain YS11 has resistance at high pH and in high salt concentrations, as well as its spore-forming ability, which supports its potential application for self-healing concrete.

Non-ureolytic calcium carbonate precipitation by Lysinibacillus sp. YS11 isolated from the rhizosphere of Miscanthus sacchariflorus

Although microbially induced calcium carbonate precipitation (MICP) through ureolysis has been widely studied in environmental engineering fields, urea utilization might cause environmental problems as a result of ammonia and nitrate production. In this study, many non-ureolytic calcium carbonate-precipitating bacteria that induced an alkaline environment were isolated from the rhizosphere of Miscanthus sacchariflorus near an artificial stream and their ability to precipitate calcium carbonate minerals with the absence of urea was investigated. MICP was observed using a phase-contrast microscope and ion-selective electrode. Only Lysinibacillus sp. YS11 showed MICP in aerobic conditions. Energy dispersive X-ray spectrometry and X-ray diffraction confirmed the presence of calcium carbonate. Field emission scanning electron microscopy analysis indicated the formation of morphologically distinct minerals around cells under these conditions. Monitoring of bacterial growth, pH changes, and Ca²⁺ concentrations under aerobic, hypoxia, and anaerobic conditions suggested that strain YS11 could induce alkaline conditions up to a pH of 8.9 and utilize 95% of free Ca²⁺ only under aerobic conditions. Unusual Ca²⁺ binding and its release from cells were observed under hypoxia conditions. Biofilm and extracellular polymeric substances (EPS) formation were enhanced during MICP. Strain YS11 has resistance at high pH and in high salt concentrations, as well as its spore-forming ability, which supports its potential application for self-healing concrete.

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.

Characterization of the novel dimethyl sulfide-degrading bacterium Alcaligenes sp. SY1 and its biochemical degradation pathway

Recently, the biodegradation of volatile organic sulfur compounds (VOSCs) has become a burgeoning field, with a growing focus on the reduction of VOSCs. The reduction of VOSCs encompasses both organic emission control and odor control. Herein, Alcaligenes sp. SY1 was isolated from active sludge and found to utilize dimethyl sulfide (DMS) as a growth substrate in a mineral salt medium. Response surface methodology (RSM) analysis was applied to optimize the incubation conditions. The following conditions for optimal degradation were identified: temperature 27.03°C; pH 7.80; inoculum salinity 0.84%; and initial DMS concentration 1585.39 μM. Under these conditions, approximately 99% of the DMS was degraded within 30 h of incubation. Two metabolic compounds were detected and identified by gas chromatography-mass spectrometry (GC-MS): dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). The DMS degradation kinetics for different concentrations were evaluated using the Haldane-Andrews model and the pseudo first-order model. The maximum specific growth rate and degradation rate of Alcaligenes sp. SY1 were 0.17 h(-1) and 0.63 gs gx(-1)h(-1). A possible degradation pathway is proposed, and the results suggest that Alcaligenes sp. SY1 has the potential to control odor emissions under aerobic conditions.

A newly isolated Pseudomonas putida S-1 strain for batch-mode-propanethiol degradation and continuous treatment of propanethiol-containing waste gas

Pseudomonas putida S-1 was isolated from activated sludge. This novel strain was capable of degrading malodorous 1-propanethiol (PT). PT degradation commenced with no lag phase by cells pre-grown in nutrition-rich media, such as Luria-Bertani (LB), and PT-contained mineral medium at specific growth rates of 0.10-0.19 h(-1); this phenomenon indicated the operability of a large-scale cell culture. A possible PT degradation pathway was proposed on the basis of the detected metabolites, including dipropyl disulfide, 3-hexanone, 2-hexanone, 3-hexanol, 2-hexanol, S(0), SO4(2-), and CO2. P. putida S-1 could degrade mixed pollutants containing PT, diethyl disulfide, isopropyl alcohol, and acetaldehyde, and LB-pre-cultured cells underwent diauxic growth. Waste gas contaminated with 200-400 mg/m(3) PT was continuously treated by P. putida S-1 pre-cultured in LB medium in a completely stirred tank reactor. The removal efficiencies exceeded 88% when PT stream was mixed with 200 mg/m(3) isopropanol; by contrast, the removal efficiencies decreased to 60% as the empty bed residence time was shortened from 40 s to 20 s.

Cometabolic degradation of ethyl mercaptan by phenol-utilizing Ralstonia eutropha in suspended growth and gas-recycling trickle-bed reactor

The degradability of ethyl mercaptan (EM), by phenol-utilizing cells of Ralstonia eutropha, in both suspended and immobilized culture systems, was investigated in the present study. Free-cells experiments conducted at EM concentrations ranging from 1.25 to 14.42 mg/l, showed almost complete removal of EM at concentrations below 10.08 mg/l, which is much higher than the maximum biodegradable EM concentration obtained in experiments that did not utilize phenol as the primary substrate, i.e. 2.5 mg/l. The first-order kinetic rate constant (kSKS) for EM biodegradation by the phenol-utilizing cells (1.7 l/g biomass/h) was about 10 times higher than by cells without phenol utilization. Immobilized-cells experiments performed in a gas recycling trickle-bed reactor packed with kissiris particles at EM concentrations ranging from 1.6 to 36.9 mg/l, showed complete removal at all tested concentrations in a much shorter time, compared with free cells. The first-order kinetic rate constant (rmaxKs) for EM utilization was 0.04 l/h for the immobilized system compared to 0.06 for the suspended-growth culture, due to external mass transfer diffusion. Diffusion limitation was decreased by increasing the recycling-liquid flow rate from 25 to 65 ml/min. The removed EM was almost completely mineralized according to TOC and sulfate measurements. Shut down and starvation experiments revealed that the reactor could effectively handle the starving conditions and was reliable for full-scale application.

Degradation pathway and kinetic analysis for p-xylene removal by a novel Pandoraea sp. strain WL1 and its application in a biotrickling filter

In this study, a novel Pandoraea sp. strain WL1 capable of mineralizing p-xylene as sole carbon and energy source was isolated from the activated sludge of a pharmaceutical wastewater treatment plant. A nearly complete degradation of 16.6∼99.4 mg L(-1)p-xylene in the liquid-phase was achieved within 6∼18 h accompanied by 15.9∼56.3 mg dry cell weight (DCW)L(-1) for bacterial growth. A complete pathway for p-xylene degradation by strain WL1 was presented through identification of a major intermediate (p-toluic acid) and final products (2.193 gCO2 gp-xylene(-1) of CO₂ production and 0.215 g DCW gp-xylene(-1) of bacterial yield). Kinetics of bacterial growth and p-xylene degradation were evaluated using Haldane-Andrews model and pseudo first-order model, respectively. Furthermore, a biotrickling filter (BTF) was employed to evaluate the application of strain WL1 on the removal of gas-phase p-xylene under gas flow rates of 0.41∼1.98 m(3)h(-1) for inlet loading rates of 5∼248 gm(-3)h(-1). The BTF inoculated with strain WL1 proved to be robust against fluctuations of gas flow rates and inlet p-xylene concentrations. All the results obtained highlight the potential of strain WL1 for the treatment of p-xylene.

Efficient bio-deodorization of thioanisole by a novel bacterium Brevibacillus borstelensis GIGAN1 immobilized onto different parking materials in twin biotrickling filter

Biological treatment of odorous gas is an alternative to conventional physicochemical processes. A newly-isolated and identified Brevibacillus borstelensis GIGAN1 was seeded on active carbon (AC) and ceramic particle (CP) in a twin biotrickling filter (BTF) to comparatively probe the removal performance of gaseous thioanisole, respectively. At empty bed residence time (EBRT) of 66 s, 100% of thioanisole (⩽ 3mg L(-1)) could be removed on AC; while 100% of thioanisole could only be achieved for ⩽ 1.2 mg L(-1) on CP. Further increase thioanisole concentration to 3 mg L(-1), higher elimination capacity was obtained on AC (162.51 g m(-3)h(-1)) than CP (139.93 g m(-3)h(-1)). Further, longer EBRT was also beneficial to thioanisole removal. Additionally, the biomass accumulation did not lead to the column clogging. The bio-deodorization mechanism of thioanisloe were also tentatively proposed. Overall, an unprecedented performance could be achieved by the novel GIGAN1 in BTF for thioanisole biodegradation.

Aerobic biodegradation of odorous dimethyl disulfide in aqueous medium by isolated Bacillus cereus GIGAN2 and identification of transformation intermediates

A novel, flagellated, rod-shape, Gram-positive facultative aerobe, was isolated and identified as Bacillus cereus GIGAN2. It can effectively remove model odorous organics dimethyl disulfide (DMDS) in aqueous solution under aerobic conditions. Initial concentration, pH value and temperature played important role in DMDS biodegradation, and up to 100% of 10mgL(-1) of DMDS could be removed within 96h under the optimum conditions (30°C, pH 7.0 and 200rpm) with a maximum biodegradation rate constant of 0.0330h(-1) and minimum half-life of 21.0h, respectively. Three main intermediates were identified using gas chromatography-mass spectrometry during this biodegradation process. Further, a reaction scheme is also proposed to explain the possible DMDS biodegradation mechanism by GIGAN2 based on the above-identified intermediates. Overall, this is the first report to demonstrate a newly isolated strain using high concentrated DMDS as the sole carbon and energy source with high efficiency.

Isolation, identification and cyfluthrin-degrading potential of a novel Lysinibacillus sphaericus strain, FLQ-11-1

Strain FLQ-11-1, isolated from sewage sludge, was able to degrade cyfluthrin and was identified as Lysinibacillus sphaericus based on its morphology, 16S rRNA sequence and fatty acid methyl ester (FAME) analyses. This strain could use cyfluthrin as its carbon or nitrogen source. Response surface methodology (RSM) analysis showed that the optimum conditions for degradation were at pH 7.0 and 35 °C, using an inoculum amount with an OD600nm value of 1.6. Under these conditions, approximately 80.4% of cyfluthrin (50 mgl(-1)) was degraded within five days (d) of incubation. Four metabolic compounds were detected during cyfluthrin degradation and identified as methyl-3-(2,2-dichlorovinyl)-2,2-dimethyl-(1-cyclopropane)-carboxylate, 4-fluoro-3-phenoxy-benzoic acid methyl ester, methyl-3-phenoxybenzoate, 3-phenoxy-benzaldehyde by gas chromatography-mass spectrometry (GC-MS) and tandem mass spectrum (MS/MS) analysis and no cyfluthrin was detected after seven days of incubation. A possible degradation pathway was proposed, and our data showed that cyfluthrin could be efficiently degraded by FLQ-11-1, indicating that this strain could potentially be used to eliminate the contamination of pyrethroid herbicides.

Pollution profiles, health risk of VOCs and biohazards emitted from municipal solid waste transfer station and elimination by an integrated biological-photocatalytic flow system: a pilot-scale investigation

Volatile organic compounds (VOCs) and biohazards air pollution in municipal solid waste transfer station were investigated. As compressor working, the concentrations of almost all quantified 14 VOCs (0.32-306.03 μg m(-3)) were much higher than those as compressor off (0-13.31 μg m(-3)). Comparatively, only 3 VOCs with extremely low concentrations could be detected at control area. Total microorganism was 7567 CFU m(-3) as compressor working, which was 1.14 and 6.22 times higher than that of compressor off and control area, respectively. Bacteria were the most abundant microorganism at all three sampling places. At pilot-scale, during whole 60-day treatment, for VOCs, the average removal efficiencies were over 92% after biotrickling filter-photocatalytic (BTF-PC) treatment. Although non-cancer and cancer risks of some VOCs were over the concern level before treatment, almost all VOCs were removed substantially and both potential risks were below the concern after BTF-PC treatment. Additionally, biohazard concentrations decreased dramatically and air quality was purified from polluted to cleanness after PC treatment. All results demonstrated that the integrated technology possessed high removal capacity and long stability for the removal of VOCs and biohazards at a pilot scale.

Startup and long-term performance of biotrickling filters packed with polyurethane foam and poplar wood chips treating a mixture of ethylmercaptan, H2S, and NH3

Treatment of a mixture of NH3, H2S, and ethylmercaptan (EM) was investigated for more than 15 months in two biotrickling filters packed with poplar wood chips and polyurethane foam. Inlet loads ranging from 5 to 10 g N-NH3 m-3 hr-1, from 5 to 16 g S-H2S m-3 hr-1, and from 0 to 5 g EM m-3 hr-1 were applied. During startup, the biotrickling filter packed with polyurethane foam was re-inoculated due to reduced biomass retention as well as a stronger effect of nitrogen compounds inhibition compared with the biotrickling filter packed with poplar wood. Accurate pH control between 7 and 7.5 favored pollutants abatement. In the long run, complete NH3 removal in the gas phase was achieved in both reactors, while H2S removal efficiencies exceeded 90%. EM abatement was significantly different in both reactors. A systematically lower elimination capacity was found in the polyurethane foam bioreactor. N fractions in the liquid phase proved that high nitrification rates were reached throughout steady-state operation in both bioreactors. CO2 production showed the extent of the organic packing material degradation, which allowed estimating its service lifetime in around 2 years. In the long run, the bioreactor packed with the organic packing material had a lower stability. However, an economic analysis indicated that poplar wood chips are a competitive alternative to inorganic packing materials in biotrickling filters.

IMPLICATIONS

We provide new insights in the use of organic packing materials in biotrickling filters for the treatment of H2S, NH3, and mercaptans and compare them with polyurethane foam, a packing commonly used in biotrickling filters. We found interesting features related with the startup of the reactors and parameterized both the performance under steady-state conditions and the influence of the gas contact time. We provide relevant conclusions in the profitability of organic packing materials under a biotrickling filter configuration, which is infrequent but proven reliable from our research results. The report is useful to designers and users of this technology.

Co-treatment of single, binary and ternary mixture gas of ethanethiol, dimethyl disulfide and thioanisole in a biotrickling filter seeded with Lysinibacillus sphaericus RG-1

The work reports the aerobic co-treatment characteristics of single, binary and ternary mixture gas of ethanethiol, dimethyl disulfide (DMDS) and thioanisole in a biotrickling filter seeded with Lysinibacillus sphaericus RG-1. 100% removal efficiency (RE) was achieved for sole ethanethiol, DMDS and thioanisole at inlet concentration below 1.05, 0.81 and 0.33 mg/L, respectively, at empty bed resident time 110 s. In addition, 100% RE was also obtained with binary ethanethiol and DMDS (1:1) and ternary ethanethiol, DMDS and thioanisole (3:2:1). Michaelis-Menten equation was modified to incorporate the plug flow behavior of the bioreactor. The maximum removal rate (V(max)) was calculated as 56.18, 57.14 and 22.78 g/m(3)/h for sole ethanethiol, DMDS and thioanisole, respectively, while the V(max) was 41.84 and 14.56 g/m(3)/h for DMDS and thioanisole in binary and ternary systems, respectively. Overall, these suggest that not only sole but also binary and ternary mixture can be efficiently removed in this system.

Comparison of the removal of ethanethiol in twin-biotrickling filters inoculated with strain RG-1 and B350 mixed microorganisms

This study aims to compare the biological degradation performance of ethanethiol using strain RG-1 and B350 commercial mixed microorganisms, which were inoculated and immobilized on ceramic particles in twin-biotrickling filter columns. The parameters affecting the removal efficiency, such as empty bed residence time (EBRT) and inlet concentration, were investigated in detail. When EBRT ranged from 332 to 66 s at a fixed inlet concentration of 1.05 mg L(-1), the total removal efficiencies for RG-1 and B350 both decreased from 100% to 70.90% and 47.20%, respectively. The maximum elimination capacities for RG-1 and B350 were 38.36 (removal efficiency=89.20%) and 25.82 g m(-3) h(-1) (removal efficiency=57.10%), respectively, at an EBRT of 83 s. The variation of the inlet concentration at a fixed EBRT of 110 s did not change the removal efficiencies which remained at 100% for RG-1 and B350 at concentrations of less than 1.05 and 0.64 mg L(-1), respectively. The maximum elimination capacities were 39.93 (removal efficiency=60.30%) and 30.34 g m(-3) h(-1) (removal efficiency=46.20%) for RG-1 and B350, respectively, at an inlet concentration of 2.03 mg L(-1). Sulfate was the main metabolic product of sulfur in ethanethiol. Based the results, strain RG-1 would be a better choice than strain B350 for the biodegradation of ethanethiol.