Anaerobic Biodegradation of Tetrachloroethylene with Acetic Acid as Cometabolism Substrate under Anaerobic Condition

A series of batch-type experiments with acetate acid as the primary substrate were performed using enrichment cultures developed from the anaerobic sludge to investigate the effect of acetate acid on tetrachloroethylene （PCE） biodegradation. Experimental results indicated that acetate acid was an efficient electron donor in affecting the biotransformability of PCE. Trichloroethylene （TCE） was the primary dehalogenation product, and small amounts of dichloroethylenes （DCEs） were also detected. No significant further DCEs degradation was detected. PCE degradation rate in the experiment was 36.6 times faster than background rate in natural groundwater.

Anaerobic Degradation of Tetrachloroethylene Using Different Co-substrates as Electron Donors

Objective To investigate the biodegradation of tetrachloroethylene （PCE） by acclimated anaerobic sludge using different co-substrates, i.e., glucose, acetate, and lactate as electron donors. Methods HP-6890 gas chromatograph （GC） in combination with auto-sampler was used to analyze the concentration of PCE and its intermediates, Results PCE could be degraded by reductive dechlorlnation and the degradation reaction conformed to the first-order kinetic equation. The rate constants are klaetate〉kglucose〉kacetate. The PCE degradation rate was the highest in the presence of lactate as an electron donor. Conclusion Lactate is the most suitable electron donor for PCE degradation and the electron donors supplied by co-metabolic substrates are not the limiting factors for PCE degradation,

Influence of Rain on Tetrachloroethylene's Multiphase Migration in Soil

For the increasingly serious soil and groundwater pollution by volatile organic compounds, tetrachloroethylene（PCE） was selected as the research object in this study. With the in-situ soil column physical simulation experiments, migration law of PCE in soil under rain conditions was studied by monitoring precipitation and soil parameter as well as sampling and analyzing soil and soil gas, and influence of rain on the multiphase migration process of PCE was preliminarily discussed. Research shows that migrations of PCE and soil moisture were not synchronous, and the rate of the former was speeded up by the latter caused by rain. Preliminary analysis indicates that migration of volatile chlorohydrocarbon in soil was not only driven by soil moisture, but also controlled by the nature of volatility of their own, that is to say, volatilization into gas phase was an important way of migrating and diffusing in pore medium, and the rate of migration and diffusion of gaseous PCE was faster than that of solid, resulting in more abroad distribution of gas phase than that in solid phase.

A reactor system combining reductive dechlorination with co-metabolic oxidation for complete degradation of tetrachloro-entylene

A laboratory sequential anaerobic aerobic bioreactor system, which consisted of an anaerobic fixed film reactor and two aerobic chemostats, was set up to degrade tetrachloroethylene (PCE) without accumulating highly toxic degradation intermediates. A soil enrichment culture, which could reductively dechlorinate 900 μM (ca. 150 mg/L) of PCE stoichiometrically into cis 1,2 dichloroethylene ( cis DCE), was attached to ceramic media in the anaerobic fixed film reactor. A phenol degrading strain, Alcaligenes sp. R5, which can efficiently degrade cis DCE by co metabolic oxidation, was used as inoculum for the aerobic chemostats consisted of a transformation reactor and a growth reactor. The anaerobic fixed film bioreactor showed more than 99 % of PCE transformation into cis DCE in the range of influent PCE concentration from 5 μM to 35 μM at hydraulic retention time of 48h. On the other hand, efficient degradation of the resultant cis DCE by strain R5 in the following aerobic system could not be achieved due to oxygen limitation. However, 54% of the maximum cis DCE degradation was obtained when 10 μmol of hydrogen peroxide (H 2O 2) was supplemented to the transformation reactor as an additional oxygen source. Further studies are needed to achieve more efficient co metabolic degradation of cis DCE in the aerobic reactor.

Biodegradation of Tetrachlorothylene Using Methanol as Co-metabolic Substrate

Objective To investigate the biodegradation of tetrachloroethylene （PCE） using methanol as electron donor by acclimated anaerobic sludge. Methods HP-6890 gas chromatograph （GC）, together with HP-7694 autosarnpler, was used to analyze the concentration of PCE and intermediates. Results PCE could be decholrinated reductively to DCE via TCE, and probably further to VC and ethylene. The degradation of PCE and TCE conformed to first-order reaction kinetics. The reaction rate constants were 0.8991 d^-1 and 0.068 d^-1, respectively, and the corresponding half-life were 0.77 d and 10.19 d, respectively. TCE production rate constant was 0.1333 d^-1, showing that PCE was degraded more rapidly than TCE. Conclusion Methanol is an electron donor suitable for PCE degradation and the cometabolic electron donors are not limiting factors for PCE degradation.

Hexachlorobutadiene emissions from typical chemical plants

Hexachlorobutadiene(HCBD)was classed as a persistent organic pollutant under the Stockholm Convention in 2015.HCBD is mainly an unintentionally produced by-product of chlorinated hydrocarbon(e.g.,trichloroethylene and tetrachloroethylene)synthesis.Few studies of HCBD formation during chemical production processes have been performed,so HCBD emissions from these potentially important sources are not understood.In this study,HCBD concentrations in raw materials,intermediate products,products,and bottom residues from chemical plants producing chlorobenzene,trichloroethylene,and tetrachloroethylene were determined.The results indicated that HCBD is unintentionally produced at much higher concentrations in trichloroethylene and tetrachloroethylene plants than chlorobenzene plants.The sum of the HCBD concentrations in the samples from all of the trichloroethylene and tetrachloroethylene production stages in plant PC was 247000µg/mL,about three orders of magnitude higher than the concentrations in the tetrachloroethylene production samples(plant PB)and about six orders of magnitude higher than the concentrations in the chlorobenzene production samples(plant PA).The HCBD concentrations were highest in bottom residues from all of the plants.The concentrations in the bottom residue samples contributed 24%–99%of the total HCBD formed in the chemical production plants.The bottom residue,being hazardous waste,could be disposed of by incineration.The HCBD concentrations were much higher in intermediate products than raw materials,indicating that HCBD formed during production of the intended chemicals.The results indicate the concentrations of HCBD unintentionally produced in typical chemical plants and will be useful in developing protocols for controlling HCBD emissions to meet the Stockholm Convention requirements.