Optimizing aerobic biodegradation of dichloromethane using response surface methodology

Response surface methodology （RSM） was employed to evaluate the optimum aerobic biodegradation of dichloromethane （DCM） in pure culture. The parameters investigated include the initial DCM concentration, glucose as an inducer and hydrogen peroxide as terminal electron acceptor （TEA）. Maximum aerobic biodegradation efficiency was predicted to occur when the initial DCM concentration was 380 mg/L, glucose 13.72 mg/L, and H202 115 mg/L. Under these conditions the aerobic biodegradation rate reached up to 93.18%, which was significantly higher than that obtained under original conditions. Without addition of glucose degradation efficiencies were ≤ 80% at DCM concentrations ≤ 326 mg/L. When concentrations of DCM were more than 480 rag/L, the addition of hydrogen peroxide did not help to significantly increase DCM degradation efficiency. When DCM concentrations increased from 240 to 480 rag/L, the overall DCM degradation efficiency decreased from 91% to 60% in the presence of HaO2 for 120 mg/L.

Removal of dichloromethane from waste gases by a biotrickling filter

Dichloromethane is harmful to human health and hazardous to atmospheric environment. In this study, two strains were isolated which were identified as Pseudomonas sp. and Mycobacterium sp., and utilized dichloromethane （DCM） as sole carbon and energy sources. The optimal culture conditions were temperature of 28℃ and pH of 6.5 for obtaining the two mixed bacterial strains. The investigation on the purification of DCM-contaminated gas was carried out in a bench-scale biotrickling filter which was inoculated with the two strains and operated under these optimal conditions. The DCM removal efficiencies varied between 72% and 99% in the biotrickling filter when empty-bed residence time was 9.6 s with the inlet concentrations ranged fi＇om 0.7 to 3.12 g/m^3 under the conditions ofpH of 6.5 ±0.5 and temperature of 28℃. It was also found that NaCl accumulation in the broth would inhibit the DCM biodegradation dramatically when the accumulated NaCl concentration was over 35.1 g/L.

GC/GCMS analysis of the petroleum ether and dichloromethane extracts of Moringa oleifera roots

Objective:To explore the phytochemical constituents from petroleum ether and diehloromethane extracts of Moringa oleifera(M.oleufera)roots using GC/GC—MS.Methods:A total of 5.11 kg fresh and undried crashed root of M.oleifera were cut into small pieces and extracted with petroleum ether and diehloromethane(20 L.each) at room temperature for 2 d.The concentrated extracts were subjected to their GC—MS analysis.Results:The GC-MS analysis of the petroleum ether and diehloromethane extracts of M.oleifern roots,which showed promising biological activities,has resulted in the identification 102 compounds.These constituents belong to 15 classes of compounds including hydrocarbons,fatty acids,esters,alcohols,isolhioeyanate.thiocyanale,pyrazine,aromalics.alkamides.cyanides,steroids,halocompounds.urea and N-hydroxyimine derivatives,unsaturated alkenamides.alkyne and indole.GC/GC-MS studies on petroleum ether extraet of the roots revealed that it contained 39 compounds,belonging to nine classes.Cyclooctasulfur S8 has been isolated as a pure compound from the extract.The major compounds identified from petroleum ether extract were trans-13-clocosene(37.9%).nonacosane(32.6%).cycloartenol(28.6%) nonadecanoic acid(13.9%) and cyclooctasulfur S8(13.9%).Dichloromethane extract of the roots was composed of 63 compounds of which nasimizinol(58.8%) along with oleic acid(46.5%),N—benzyl-N-(7—cyanato heptanamide(38.3%),N—benzyl-N—(1—chlorononyl) amide(30.3%),bis[3—benzyl prop-2-ene]-1-one(19.5%) and N.N-dibeuzyl—2-ene pent 1.5—diamide(11.6%) were the main constituents.Conclusions:This study helps to predict the formula and structure of active molecules which can be used as drugs.This result also enhances the traditional usage of M.oleifera which possesses a number of bioactive compounds.

High-efficiency Extraction of Bitumen from Oil Sands Using Mixture of Ionic Liquid [Emim][BF_(4)] and Dichloromethane

An ionic liquid(IL),1-ethyl-3-methyl imidazolium tetrafluoroborate([Emim][BF_(4)]),was used to enhance bitumen recovery from oil sands by dichloromethane solvent extraction.A multiphase system could be formed by simply mixing the components at ambient temperature,consisting of sands and clays,mixtures of ionic liquid and dichloromethane,and concentrated bitumen layer.The results demonstrated that[Emim][BF_(4)]increased the bitumen recovery up to 92%.Much less clay fines were found in the recovered bitumen than those formed by using dichloromethane solvent extraction alone,and the dichloromethane residue was not detected in the spent sands.We proposed that[Emim][BF_(4)]had an ability to reduce the adhesion of bitumen to sand,resulting in an improved separation efficiency.Furthermore,[Emim][BF_(4)]could facilitate the transfer of the extracted bitumen to the surface interface,and then the bitumen was auto-partitioned to a separate immiscible phase for ease of harvesting.This technology circumvented the issue of high consumption of distillation energy due to separation of bitumen phase and low boiling point of dichloromethane.[Emim][BF_(4)]and dichloromethane could be readily recycled through the system and used repeatedly.After ten cycles,the bitumen recovery remained above 88%.Initial scale-up work suggested that this approach would form the basis for a viable large-scale process.

Analysis of compounds in dichloromethane extractives for Sawara Falsecypress （Chamaecyparis pisifera） outer heartwood

The chemical components of dichloromethane extractives for Sawara Falsecypress heartwood were analyzed with GC/MS except for basic chemical composition analysis for heartwood with Chinese standard method. 14 kinds of compounds were idenfifjed according to the computer compounds library data. The major compounds in dichloromethane extractives comprised of terpene and naphthalene derivafives. The experiments of antifungal effects of the dichloromethane extractive on Aspergillus niger were also carded out. The result showed that the dichloromethane extractive from Sawara Falsecypress has no or weak antifungal capability.

Efficient degradation of aqueous dichloromethane by an enhanced microbial electrolysis cell:Degradation kinetics,microbial community and metabolic mechanisms

Dichloromethane(DCM)has been listed as a toxic and harmful water pollutant,and its re moval needs attention.Microbial electrolysis cells(MECs)are viewed as a promising alterna tive for pollutant removal,which can be strengthened from two aspects:microbial inocula tion and acclimation.In this study,the MEC for DCM degradation was inoculated with the ac tive sludge enhanced by Methylobacterium rhodesianum H13(strain H13)and then acclimated in the form of a microbial fuel cell(MFC).Both the introduction of strain H13 and the initi ation in MFC form significantly promoted DCM degradation.The degradation kinetics were fitted by the Haldane model,with V_(max),K_(h),K_(i)and v_(max)values of 103.2 mg/L/hr,97.8 mg/L268.3 mg/L and 44.7 mg/L/hr/cm^(2),respectively.The cyclic voltammogram implies that DCM redox reactions became easier with the setup of MEC,and the electrochemical impedance spectrogram shows that the acclimated and enriched microbes reduced the charge transfe resistance from the electrode to the electrolyte.In the biofilm,the dominant genera shifted from Geobacter to Hyphomicrobium in acclimation stages.Moreover,Methylobacterium played an increasingly important role.DCM metabolism mainly occurred through the hydrolytic glutathione S-transferase pathway,given that the gene dcmA was identified rather than the dhlA and P450/MO.The exogenous electrons facilitated the reduction of GSSG,directly o indirectly accelerating the GSH-catalyzed dehalogenation.This study provides support fo the construction of an efficient and stable MEC for DCM removal in water environment.

Enhanced catalytic oxidation of dichloromethane by a surfactant-modified CeO_(2)@TiO_(2) core-shell nanostructured catalyst

Surfactant-modified CeO_(2)@TiO_(2) core-shell nanostructure catalysts were prepared by coprecipitation with the addition of sodium dodecyl sulfonate(SDS),and their catalytic oxidation of dichloromethane(DCM) was studied.A 90% DCM conversion efficiency is obtained at 300℃ with the CeO_(2)@TiO_(2)SDS catalyst,and its catalytic stability in the 55 h test period is better than that of Ce/TiO_(2) and CeO_(2)@TiO_(2).Based on the characterization of CeO_(2)@TiO_(2)SDS,the dispersion of active components is promoted due to the inhibition of crystal growth with the introduction of SDS.The improvement of surface acidity and redox capacity is beneficial to the enhancement of catalytic activity.The higher adsorbed oxygen content on the surface of the CeO_(2)@TiO_(2)SDS catalyst is responsible for the better catalytic stability.Generally,a novel method was developed to design catalytic oxidation catalysts for the treatment of chlorinated volatile organic compounds in future applications.

Controllable cross-coupling of thiophenols with dichloromethane mediated by consecutively paired electrolysis

Chloroalkanes are important building blocks in the synthesis,but their use in redox chemistry is limited by their negative reduction potentials.Electrosynthesis can precisely control the reaction energy just by adjusting the current or voltage to achieve the selectivity of regulation.In this study,the consecutively paired electrolyticmediated controllable radical cross-coupling of thiophenols with dichloromethane was developed to deliver the dithioacetals,sulfides,and sulfoxides in the absence of electrochemical mediator conditions.It features broad substrate scope,simple operation,gram-scale synthesis,and is eco-friendly.Mechanistic studies reveal that this electrochemical reaction is radical-induced cross-coupling of thiophenols with dichloromethane.

Individual stages of bacterial dichloromethane degradation mapped by carbon and chlorine stable isotope analysis

The fractionation of carbon and chlorine stable isotopes of dichloromethane(CH_2Cl_2,DCM)upon dechlorination by cells of the aerobic methylotroph Methylobacterium extorquens DM4 and by purified DCM dehalogenases of the glutathione S-transferase family was analyzed.Isotope effects for individual steps of the multi-stage DCM degradation process,including transfer across the cell wall from the aqueous medium to the cell cytoplasm,dehalogenase binding,and catalytic reaction,were considered.The observed carbon and chlorine isotope fractionation accompanying DCM consumption by cell supensions and enzymes was mainly determined by the breaking of C\Cl bonds,and not by inflow of DCM into cells.Chlorine isotope effects of DCM dehalogenation were initially masked in high density cultures,presumably due to inverse isotope effects of non-specific DCM oxidation under conditions of oxygen excess.Glutathione cofactor supply remarkably affected the correlation of variations of DCM carbon and chlorine stable isotopes(Δδ^(13)C/Δδ^(37)Cl),increasing corresponding ratio from 7.2–8.6 to 9.6–10.5 under conditions of glutathione deficiency.This suggests that enzymatic reaction of DCM with glutathione thiolate may involve stepwise breaking and making of bonds with the carbon atom of DCM,unlike the uncatalyzed reaction,which is a one-stage process,as shown by quantum-chemical modeling.

Conversion characteristics and mechanism analysis of gaseous dichloromethane degraded by a VUV light in different reaction media

The photodegradation of gaseous dichloromethane （DCM） by a vacuum ultraviolet （VUV） light in a spiral reactor was investigated with different reaction media and initial concentrations. Through the combination of direct photolysis, O3 oxidation and HO. oxidation, DCM was ultimately mineralized into inorganic compounds （such as HC1, CO2, H20, etc.） in the air with relative humidity （RH） of 75%-85%. During the photodegradation process, some small organic acids （including formic acid, acetic acid） were also detected and the intermediates were more soluble than DCM, providing a possibility for its combination with subsequent biodegradation. Based on the detected intermediates and the confirmed radicals, a photodegradation pathway of DCM by VUV was proposed. With RH 75%- 80% air as the reaction medium, the DCM removal followed the second-order kinetic model at inlet concentration of 100-1000 mg/m3. Kinetic analysis showed that the reaction media affected the kinetic constants of DCM conversion by a large extent, and RH 80% air could cause a much lower half-life for its conversion. Such results supported the possibility that VUV photodegradation could be used not only for the mineralization of DCM but also as a pretreatment before biodegradation.

Enzyme-electrolytic degradation of dichloromethane: Efficiency, kinetics and mechanism

Enzymatic electrolysis cell(EEC)has advantages over microbial electrolysis cell(MEC)due to the needless of microbe inoculation and high-efficiency of enzymatic reaction.In this study,an EEC was first applied to achieve the effective degradation of halogenated organic pollutants and dichloromethane(CH2Cl2)was utilized as a model pollutant.The results indicate that the degradation efficiency of CH2Cl2 after 2 hr reaction in the EEC was almost100%,which was significantly higher than that with enzyme(51.1%)or current(19.0%).The current induced the continuous regeneration of reduced glutathione(GSH),thus CH2Cl2 was degraded under the catalysis of GSH-dependent dehalogenase through stepwise dechlorination,and successively formed monochloromethane(CH3Cl)and methane(CH4).The kinetic result shows that with a current of 15 mA,the maximum specific degradation rate of CH2Cl2(3.77×10-3 hr-1)was increased by 5.7 times.The optimum condition for CH2Cl2 dechlorination was also obtained with pH,current and temperature of 7.0,15 mA and 35°C,respectively.Importantly,this study helps to understand the behavior of enzymes and the fate of halogenated organic pollutants with EEC,providing a possible treatment technology for halogenated organic pollutants.

Effect of Ni-V loading on the performance of hollow anatase TiO2 in the catalytic combustion of dichloromethane

A catalyst based on mixed V-Ni oxides supported on TiO2(Ni-V/TiO2)was obtained using the sol-gel method.Its catalytic performance relative to dichloromethane(DCM)degradation was investigated.Characterization and analysis were conducted using transmission electron microscopy,H2 temperature-programmed reduction,pyridine-Fourier transform infrared spectroscopy(FTIR)characterization,and X-ray diffraction.Results showed that the original hollow anatase structure of pure TiO2 was well-maintained after Ni-V loading.The loading of NiO-VOx not only significantly improved the stability of pure TiO2 but also inhibited the formation of the by-product monochloromethane(MCM).Among the series of Ni-V/TiO2 catalysts,4%Ni-V/TiO2 possessed the highest catalytic activity,with 90%DCM conversion at only 203℃.No by-products and no significant changes in the catalytic activity were observed during combustion of DCM after 100 hr of a continuous stability test.Furthermore,thermogravimetric analysis(O2-TG)and energy dispersive spectrometer(EDS)characterization of the used 4%Ni-V/TiO2 catalyst revealed that no coke deposition or chlorine species could be detected on the catalyst surface.

Antitumor Activity of Dichloromethane Extract from Salvia plebeia and Induction of Apoptosis on K562 Cells

Objective To study the antitumor activity of extract from Salvia plebeia and investigate whether the extract induce apoptosis of K562 cells.Methods The aqueous,petroleum ether,dichloromethane(CH2Cl2),ethyl acetate,and butanol extracts were prepared from the aerial parts of S.plebeia.Taking fluorouracil as reference,the cytotoxic activities of these extracts on HeLa,A549,SGC-7901,HCT-116,K562,LoVo,DU-145,and HepG2 cells were evaluated.To clarify the apoptosis of K562 cells induced by CH2Cl2 extract,the methods of Hoechst 33258 staining,flow cytometry assay,and DNA ladder assay were investigated.Results The CH2Cl2 extract showed the most potent cytotoxic effect against K562 cells,with an IC50<15μg/mL for 3 d treatment.The characteristic apoptotic symptoms such as DNA fragmentation and chromatin condensation were also observed in the K562 cells.Conclusion The CH2Cl2 extract from S.plebeia may inhibit the cancer cell proliferation by inducing cell apoptosis.

Degradation of dichloromethane by an isolated strain Pandoraea pnomenusa and its performance in a biotrickling filter

A strain Pandoraea pnomenusa LX-1 that uses dichloromethane （DCM） as sole carbon and energy source has been isolated and identified in our laboratory. The optimum aerobic biodegradation of DCM in batch culture was evaluated by response surface methodology. Maximum biodegradation （5.35 mg/（L.hr）） was achieved under cultivation at 32.8℃, pH 7.3, and 0.66% NaC1. The growth and biodegradation processes were well fitted by Haldane＇s kinetic model, yielding maximum specific growth and degradation rates of 0.133 hr^-1 and 0.856 hr^-1, respectively. The microorganism efficiently degraded a mixture of DCM and coexisting components （benzene, toluene and chlorobenzene）. The carbon recovery （52.80%-94.59%） indicated that the targets were predominantly mineralized and incorporated into cell materials. Electron acceptors increased the DCM biodegradation rate in the following order： mixed 〉 oxygen 〉 iron 〉 sulfate 〉 nitrate. The highest dechlorination rate was 0.365 mg C1-/（hr.mg biomass）, obtained in the presence of mixed electron acceptors. Removal was achieved in a continuous biotrickling filter at 56%-85% efficiency, with a mineralization rate of 75.2%. Molecular biology techniques revealed the predominant strain as P. pnomenusa LX-1. These results clearly demonstrated the effectiveness of strain LX-1 in treating DCM-containing industrial effluents. As such, the strain is a strong candidate for remediation of DCM coexisting with other organic compounds.

Acid modified carrier on catalytic oxidation of dichloromethane over CeO_(2)/HZSM-5 catalysts

In this study,a series of Hydrogen-Zeolite Socony Mobil-5-X(HZSM-5-X) catalysts were prepared by acid modification,then Ce/HZSM-5-X(X=0,0.2,0.4,1.0,2.0) catalysts were prepared by impregnation method.The catalytic performance of the catalysts on dichloromethane(DCM) oxidation was investigated.Through different characterizations,HZSM-5-X exhibit high specific surface area,good redox ability,rich acidity and much suitable acidic site distribution after acid treatment.Among them,Ce/HZSM-5-0.4 shows better catalytic activity with the lowest by-product and the best CO_(2) yield.Its T_(90) is 302℃ and the CO_(2) yield of T_(90) is more than 80 wt%,which demonstrates that the acid modification of carrier plays the positive effect on the catalytic capacity for DCM oxidation.

Dichloromethane as a methylene synthon for regioselective linkage of diverse carboxylic acids:Direct access to methylene diesters under metal-free conditions

A metal-free cross coupling between common CH2Cl2 and carboxylic acids has been achieved with K2CO3 as the sole additive. This simple protocol is a convenient and cost-effective route to synthesize methylene diesters from a wide scope of carboxylic acids substrates with good functional group tolerance. Several gram-scale reactions have been performed to evaluate the effectiveness and practicality of this protocol.

Mechanism of dichloromethane disproportionation over mesoporous TiO2 under low temperature

Mesoporous TiO2 was synthesized via nonhydrolytic template-mediated sol-gel route.Catalytic degradation performance upon dichloromethane over as-prepared mesoporous TiO2,pure anatase and rutile were investigated respectively.Disproportionation took place over as-made mesoporous TiO2 and pure anatase under the presence of water.The mechanism of disproportionation was studied by in situ FTIR.The interaction between chloromethoxy species and bridge coordinated methylenes was the key step of disproportionation.Formate species and methoxy groups would be formed and further turned into carbon monoxide and methyl chloride.Anatase(001)played an important role for disproportionation in that water could be dissociated into surface hydroxyl groups on such structure.As a result,the consumed hydroxyl groups would be replenished.In addition,there was another competitive oxidation route governed by free hydroxyl radicals.In this route,chloromethoxy groups would be oxidized into formate species by hydroxyl radicals transfering from the surface of TiO2.The latter route would be more favorable at higher temperature.

Comparative study of Co_(3)O_(4)-ZSM-5 catalysts synthesized by different hydrothermal methods for the catalytic oxidation of dichloromethane

In this work,various Co_(3)O_(4)-ZSM-5 catalysts were prepared by the microwave hydrothermal method(MH-Co_(3)O_(4)@ZSM-5),dynamic hydrothermal method(DH-Co_(3)O_(4)@ZSM-5),and conventio nal hydrothermal method(CH-Co_(3)O_(4)/ZSM-5).Their catalytic oxidation of dichloromethane(DCM)was analyzed.Detailed characterizations such as X-ray diffractometer(XRD),scanning microscopy(SEM),X-ray photoelectron spectroscopy(XPS),Brunauer-Emmett-Teller(BET),H2 temperature-programmed reduction(H2-TPR),temperature-programmed desorption of O_(2)(O_(2)-TPD),temperature-programmed desorption of NH_(3)(NH_(3)-TPD),diffuse reflectance infrared Fourier-transform spectra with NH_(3)molecules(NH_(3)-DRIFT),and temperature-programmed surface reaction(TPSR)were performed.Results showed that with the assistance of microwave,MH-Co_(3)O_(4)@ZSM-5 formed a uniform core-shell structure,while the other two samples did not.MH-Co_(3)O_(4)@ZSM-5 possessed rich surface adsorbed oxygen species,higher ratio of Co^(3+)/Co^(2+),strong acidity,high reducibility,and oxygen mobility among the three Co_(3)O_(4)-ZSM-5 catalysts,which was beneficial for the improvement of DCM oxidation.In the oxidation of dichloromethane,MH-Co_(3)O_(4)@ZSM-5 presented the best activity and mineralization,which was consistent with the characterizations results.Meanwhile,according to the TPSR test,HCl or Cl_(2)removal from the catalyst surface was also promoted in MH-Co_(3)O_(4)@ZSM-5 by their abundant Bronsted acid sites and the promotion of Deacon reaction by Co_(3)O_(4)or the synergistic effect of Co_(3)O_(4)and ZSM-5.According to the results of in situ DRIFT studies,a possible reaction pathway of DCM oxidation was proposed over the MH-Co_(3)O_(4)@ZSM-5 catalysts.

Prescreening teratogenic potential of chlorinated drinking water disinfection by-products by using Hydra regeneration assay

Practicability of method for the Hydra regeneration assay on the prescreening teratogenic potential of chlorinated drinking water disinfection by products was studied through both the assays of toxicity of adult Hydra (T) and inhibition of the growth of regeneration Hydra (I) by using chloroform, dichloromethane and chloroacetic acid. The results showed that T 50 / I 50 ratios of chloroform and chloroacetic acid were 2 77 and 6 16 respectively, with teratogenic potential. T 50 / I 50 ratio of dichloromethane was 1.69, with weaker teratogenic potential. These experimental results indicated preliminarily that the Hydra regeneration assay has certainly applied value as a prescreening assay for developmental toxicity.

CAPILLARY GAS CHROMATOGRAPHIC ANALYSES OF THE PETROLEUM HYDROCARBONS IN COASTAL SEAWATER

This study of the petroleum hydrocarbons in coastal seawater, using dichloromethane extraction withO-terphenyl and n-C20 as internal standards, and gas chromatography with silica-capillary-column showedthat the recovery of petroleum hydrocarbons reaches 87.8% and that the lowest detection limit is 0.96μg.This method is reproducible, highly accurate, and applicable for determining the petroleum hydrocarbonsin coastal seawater.