Dechlorination Conditions Research Articles

Dechlorination ability of municipal waste incineration fly ash for polychlorinated phenols

Pathways of pentachlorophenol dechlorination have been investigated on municipal waste incineration fly ash at 200 °C under nitrogen atmosphere. Thermodynamic calculations have been carried out for these dechlorination conditions using the method of total Gibbs energy minimization for the whole system consisting of gaseous components, i.e., chlorinated phenols, phenol, hydrogen chloride and the Cu 3Cl 3 trimer and of solid Cu 2O and CuCl 2 components. The effects of water, temperature and of the amounts of the reaction components on the thermodynamic equilibrium have been discussed and the experimental results compared with the calculated thermodynamic data.

Synthesis, characterization, and thermal properties of poly(methylvinylsilylene‐co‐styrene)

AbstractThe copolymerization of methylvinyldichlorosilane (MVDCS) and styrene was carried out with various monomer feed ratios under dechlorination conditions with sodium in toluene at 110°C. The copolymers were obtained in 84–95% yields. The copolymerization of MVDCS and styrene with monomer feed ratios of 1 : 0.25 and 1 : 0.5 mainly gave insoluble polymers. The copolymers synthesized with monomer feed ratios of 1 : 1, 1 : 3, and 1 : 7 contained soluble fractions of 3, 26, and 47%, respectively. The copolymers were characterized with infrared, 1H‐NMR, gel permeation chromatography, thermogravimetric analysis, pyrolysis/gas chromatography (PGC), X‐ray diffraction, and elemental analysis (silicon content). 1H‐NMR and PGC studies suggested that the soluble fractions were mainly polystyrene. PGC studies indicated that the copolymers obtained with monomer feed ratios of 1 : 0.25 and 1 : 0.5 did not have any significant amount of polystyryl blocks, whereas the copolymers obtained with higher styrene feed ratios contained appreciable amounts of polystyryl blocks. The composition of the insoluble fractions of the copolymers was obtained from PGC data and was in good agreement with the composition calculated from the silicon content of the copolymers.© 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3774–3784, 2004

Dechlorination of Concentrated Monochloroalkanes under Various Hydrothermal Conditions

Fundamental reaction behavior in dechlorination of concentrated monochloroalkanes (methyl, ethyl, n-propyl, and iso-propyl chloride), whose concentrations were set at as high as 15–20 times the solubility at room temperature, was investigated at various hydrothermal conditions under a saturated vapor pressure up to 380°C. The optimum conditions for the dechlorination treatment and solvent effects on the reactions have been discussed based on the results obtained under specific conditions of temperature, reaction time, stirring rate, solvent states (e.g., volume ratio of chloride to solvent, concentration of additive alkali or alcohol, filling ratio of solution in a vessel) on the dechlorination ratio. All the chlorides studied in the present work were easily dechlorinated by hydrolysis, and the alkyl groups were preserved under hydrothermal conditions in the “subcritical” region. These results indicate the optimum conditions for hydrothermal dechlorination and that the products can be controlled in the yield and ether formation by the concentration of the additives in the solvent.

Dechlorination of polychlorinated biphenyls in industrial transformer oil by radiolytic and photolytic methods.

Used electrical transformer oils containing low or high concentrations of polychlorinated biphenyls (PCBs) were treated using electron, gamma, and ultraviolet radiation, and the conditions for complete dechlorination were developed. Dechlorination was determined by analysis of the inorganic chloride formed and the concentrations of remaining PCBs. Transformer oil containing approximately 95 microg g(-1) PCB (approximately 3.5 mmol L(-1) Cl) is completely dechlorinated by irradiation with 600 kGy after the addition of 10% triethylamine (TEA). Transformer oil containing >800,000 microg g(-1) PCB (17.7 mol L(-1) Cl) requires an additional solvent to prevent solidification. When this oil is diluted with 2-propanol (2-PrOH) and TEA (v/v/v, 1/79/20), complete dechlorination is achieved with a dose of 2500 kGy. Ultraviolet photolysis of the same oil/2-PrOH/TEA solutions led to 90% dechlorination after exposure for 120 h in our experimental setup. Such yields were obtained by radiolysis with a dose of 2000 kGy (300 h in our Gammacell). Replacing TEA with KOH in 2-PrOH solutions greatly increases the yield of dechlorination in both the radiolytic and the photolytic experiments, demonstrating that a chain reaction plays a role in both of these treatment methods and suggesting that both methods deserve further consideration for large-scale application.

Thermal degradation kinetics of poly(methylvinylsilylene-co-styrene)

Thermal degradation kinetics of poly(methylvinylsilylene-co-styrene) copolymers, viz., PMVSS-I to PMVSS-V obtained by reacting methylvinyldichlorosilane (MVDCS) and styrene in 1:0.25, 1:0.5, 1:1, 1:3 and 1:7 mole ratios under dechlorination conditions, using sodium, was studied by thermogravimetry. The homopolymer, poly(methylvinylsilane) (PMVS), synthesized from MVDCS using sodium was also subjected to the above study for comparative evaluation. The kinetic parameters for thermal degradation, viz., activation energy ( E) and pre-exponential factor ( A) for the above polymers were estimated by non-isothermal kinetic methods such as Mac Callum–Tanner (M–T), Horowitz–Metzger (H–M), Madhusudhanan–Krishnan–Ninan (MKN) and Coats–Redfern (C–R). The order for thermal degradation of PMVS was found to be almost 0. In the case of the copolymers, the order was 1 for PMVSS-I and 2 for PMVSS-II to PMVSS-V. The observed difference in the order for thermal degradation of PMVSS-I when compared to the other copolymers is attributed to the presence of polysilyl linkages in PMVSS-I. It was found that the activation energy and pre-exponential factor showed an increase in trend with increase in concentration of styrene in the copolymer system.

Non-point source pesticide removal by a mountainous wetland

Non-point source (NPS) pollution is believed to be one of the major causes of impairment of water bodies. Among NPS pollution, agricultural NPS pollution is considered to be the largest single category resulting in water quality deterioration. Pesticides are some the most ubiquitous of these agricultural NPS pollutants. In this study, a mountainous wetland was selected to investigate the effects of the natural wetland system on the NPS pesticide (atrazine) removal to maintain the surface water quality. The selected wetland receives water from two unnamed creeks, which drain primarily upgradient agricultural lands. Wetland investigation and monitoring were conducted from November 1999 to March 2001. Major storm events and baseline water quality samples were analyzed. Field results indicate that the wetland was able to remove NPS atrazine flushed from the upgradient agricultural lands after the occurrence of storm events. Laboratory aerobic and anaerobic bioreactor experiments were conducted to evaluate the biodegradation of atrazine under the intrinsic conditions of the wetland system. Microbial enumeration was conducted for a quick screen of bacterial activity in the studied wetland. Results from the study suggest that the methanogenesis process was possibly the dominant biodegradation pattern, and atrazine can be degraded under reductive dechlorinating conditions when sufficient intrinsic organic matter was provided. Results from this study can provide us with further knowledge on pesticide removal mechanisms in natural wetlands and evaluate the role of wetlands in controlling pesticide pollutants from stormwater runoff.

Oligomerization pathways of dichlorodifluoromethane hydrodechlorination catalyzed by activated carbon supported Pt-Cu, Pt-Ag, Pt-Fe, and Pt-Co

Activated carbon-supported Pt-Cu, Pt-Ag, Pt-Co, Pt-Fe, and Pt catalyze the formation of oligomerization products from CF2Cl2 and H2 mixture (1:1 ratio) at 523K. All catalysts deactivate with time on stream. The Pt-Co/C catalyst exhibits the highest selectivity toward C2–C3 hydrocarbons (∼50%), whereas Pt-Cu/C is the most selective toward tetrafluoroethylene (∼20%). The other catalysts (Pt, Pt-Ag, Pt-Fe) exhibit negligible oligomerization activity, CH4 and partially halogenated C1 molecules are the main products. The performance of each catalyst is understood in terms of the difference in the stability of bimetallic particles toward segregation under dechlorination conditions.

Microbial dechlorination of three PCB congeners in river sediment

We investigated the potential for the anaerobic degradation of three PCB congeners (2,3,5,6-CB, 2,3,4,5-CB, and 2,3,4,5,6-CB) in sediments collected from five monitoring sites along the Keelung River in northern Taiwan. Optimal conditions for congener dechlorination were 30°C and pH 7.0. Intermediate 2,3,4,5-CB products were identified as 2,3,5-CB, 2,4,5-CB, and 2,5-CB. Intermediate 2,3,4,5,6-CB products were identified as 2,3,5,6-CB, 2,3,6-CB, and 2,5-CB. For 2,3,5,6-CB, intermediate products were identified as 2,3,6-CB and 2,5-CB. Dechlorination rates for PCB congeners were observed as (fastest to slowest): 2,3,4-CB>2,3,4,5-CB>2,3,4,5,6-CB>2,3,5,6-CB>2,2 ′,3,3 ′,4,4 ′-CB>2,2 ′,4,4 ′,6,6 ′-CB>2,2 ′,3,4,4 ′,5,5 ′-CB>2,2 ′,3,3 ′,4,4 ′,5,5 ′-CB. Rates decreased for mixtures of the eight congeners. Dechlorination rates for the three primary congeners under different reducing conditions occurred in the order of (fastest to slowest): methanogenic condition > sulfate-reducing condition > nitrate-reducing condition. Under methanogenic and sulfate-reducing conditions, dechlorination rates were enhanced by the addition of lactate, pyruvate, or acetate, but delayed by the addition of manganese oxide, or ferric chloride. Under nitrate-reducing condition, dechlorination rates were delayed by the addition of lactate, pyruvate, acetate, manganese oxide or ferric chloride. Treatment with such microbial inhibitors as bromoethanesulfonic acid (BESA) or molybdate revealed that methanogen and sulfate-reducing bacteria were involved in the dechlorination of these three PCB congeners.

Evaluation of TCDD biodegradability under different redox conditions

Polychlorinated dibenzo- p-dioxins have been generated as unwanted by-products in many industrial processes. Although their widespread distribution in different environmental compartments has been recognized, little is known about their fate in the ultimate environment sinks. The highly stable dioxin isomer 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) has been called the most toxic compound known to man. In this laboratory microcosm study, TCDD bioavailability was evaluated under five reduction/oxidation (redox) conditions including aerobic biodegradation, aerobic cometabolism, methanogenesis, iron reduction, and reductive dechlorination. Activated sludge and aquifer sediments from a TCDD and a pentachlorophenol (PCP) contaminated site were used as the inocula. Acetate, sludge cake, and cane molasses were used as the primary substrates (carbon sources) in cometabolism and reductive dechlorination microcosms. After a 90-day incubation period, microcosms constructed under reductive dechlorination conditions were the only treatment showing promising remediation results. The highest TCDD degradation rate [up to 86% of TCDD removal (with an initial concentration of 96 μg/kg of soil)] was observed in the microcosms with anaerobic activated sludge as the microbial inocula and sludge cakes as the primary substrates. Except for reductive dechlorination microcosms, no significant TCDD removal was observed in the microcosms prepared under other conditions. Thus, application of an effective primary substrate to enhance the reductive dechlorination process is a feasible method for TCDD bioremediation. Bioremediation expense can be significantly reduced by the supplement of some less expensive alternative substrates (e.g., sludge cakes, cane molasses). Results would be useful in designing a scale-up in situ or on-site bioremediation system such as bioslurry reactor for field application.

Intrinsic bioremediation of trichloroethylene and chlorobenzene: field and laboratory studies

Activities at a former fire training area at Robins Air Force Base in Georgia, USA resulted in contamination of groundwater with a mixture of trichloroethylene (TCE) and chlorobenzene (CB). Results from the field investigation suggest that intrinsic bioremediation process is occurring, which caused the decrease in TCE and CB concentrations, and increase in TCE degradation byproducts [e.g., dichloroethylene isomers (DCEs), vinyl chloride (VC)] concentrations. Contaminated groundwater samples collected from this site were used to conduct microbial enumeration tests, and used as the inocula for microcosm establishment. Results from the microbial enumeration study indicate that methanogenesis was the dominant biodegradation pattern within the source and mid-plume areas, and the aerobic biodegradation process dominated the downgradient area. Laboratory microcosm experiments were conducted to evaluate the feasibility of using CB as the primary substrate to enhance the intrinsic biodegradation of TCE. Microcosm results suggest that CB can serve as the primary substrate (electron donor), and enhance TCE biodegradation to less-chlorinated compounds under both aerobic cometabolism and reductive dechlorination conditions.

Microbial dechlorination of polychlorinated biphenyls in anaerobic sewage sludge

The potential of a chlorophenol (CP)-adapted consortium to dechlorinate polychlorinated biphenyls (PCBs) in sewage sludge was investigated. Results show that dechlorination rates differed significantly depending on sludge source and PCB congener. Higher total solid concentrations in sewage sludge and higher concentrations of chlorine in PCB resulted in slower dechlorination rates. No significant difference was found for 2,3,4,5-CB dechlorination from pH 6.0 to pH 8.0; however, dechlorination did not occur at pH 9.0 during a 41-day incubation period. Results show that at concentrations of 1 to 10 mg/L, the higher the PCB concentration, the faster the dechlorination rate. In addition, dechlorination rates were in the following order: methanogenic conditions > sulfate-reducing conditions > denitrifying conditions. The addition of acetate, lactate, pyruvate, and ferric chloride decreased lag times and enhanced dechlorination; however, the addition of manganese dioxide had an inhibitory effect. Dechlorination rates were also enhanced by the addition of PCB congeners, including 2,3,4-CB, 2,3,4,5-CB and 2,3,4,5,6-CB in mixture. Overall results show that the CP-adapted consortium has the potential to enhance PCB dechlorination. The optimal dechlorination conditions presented in this paper may be used as a reference for feasibility studies of PCB removal from sludge.

Dechlorination of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid in soil

The potential for dechlorinating 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in selected soils with a mixed culture showing stable dechlorinating activity was investigated. Intermediate 2,4,5-T dechlorination products were identified as 2,5-D and 3-CP, while the intermediate 2,4-D dechlorination product was identified as 4-CP. Dechlorination occurred at a faster rate in Shulin clay loam compared to Guishan sandy loam and dechlorination occurred faster for 2,4-D than 2,4,5-T. However, the differences in dechlorination rates of either compound are not significant in either of the two soil types. We found optimal dechlorination conditions for the two compounds to be a temperature of 30°C at pH 8.0 and 100% water content. With the simultaneous presence of 2,4-D and 2,4,5-T, dechlorination rates for both compounds were slower. We also found that the addition of chlorophenolic compounds inhibited dechlorination of both 2,4-D and 2,4,5-T.

Reductive Dechlorination of Hexachlorobenzene by an Anaerobic Mixed Culture

The potential for reductive dechlorination of hexachlorobenzene (HCB) by a 1,2,3-trichlorobenzene (TCB)-adapted mixed culture was investigated. Optimal dechlorination conditions were assessed at 29 °C ∼ 37 °C and pH 6.1 ∼ 6.9. The observed transformation pathway was HCB → pentachlorobenzene (PCB) → 1,2,3,5-tetrachlorobenzene (TeCB) → 1,3,5-TCB. The dechlorination of HCB was delayed by the addition of ferric chloride and manganese dioxide as electron acceptors, but enhanced by the addition of lactate and pyruvate as electron donors. However, we found that the addition of acetate had no significant effect on HCB dechlorination. Following treatment with bromoethanesulfonic acid (BESA) and vancomycin, it was suggested that the methane-producing bacteria was involved in the dechlorination of CBs.

Effects of selected reducing agents on microbiologically mediated reductive dechlorination of aroclor® 1242

AbstractThe effect of various chemical reducing agents on the anaerobic microbial reductive biotransformation of polychlorinated biphenyls (PCBs) was investigated using Aroclor® 1242 at a concentration of 600 μg/g soil and microorganisms eluted from Hudson River sediments. The investigation sought to determine how various reducing agents influenced PCB dechlorination rates, patterns, and acclimation periods. Three reducing agents were incorporated into culture media: amorphous ferrous sulfide, sodium sulfide with sodium thioglycollate, and sodium sulfide with amorphous ferrous sulfide. All cultures were incubated statically under methanogenic conditions and ambient incubation temperatures of about 20°C. Cultures utilizing both sodium sulfide and ferrous sulfide together demonstrated the most extensive removal of meta‐ and para‐chlorines, the highest average dechlorination rate, the greatest dechlorination of tri‐ and tetrachlorinated biphenyls, and the greatest accumulation of dichlorobiphenyl homologues. Overall, treatments incorporating ferrous sulfide, alone or in combination with sodium sulfide, demonstrated the ability to more effectively dechlorinate tri‐ortho‐substituted tetrachlorobiphenyls and pentachlorobiphenyls which had commonly positioned chlorines. Under these same conditions, dichlorobiphenyls, which are more amenable to aerobic dechlorination conditions, increased from 25% (molar basis) initially to levels greater than 60%.

Effect of temperature, pH and electron donor on the microbial reductive dechlorination of chloroalkenes

In order to elucidate the effect of environmental conditions such as pH, temperature, and electron donor on the microbial reductive dechlorination of tetrachloroethylene and its transformation products, batch, acetate-fed methanogenic cultures were developed from a field contaminated soil and incubated within a pH range of 4 to 9.5 and a temperature range of 5 to 45°C. Optimum conditions for reductive dechlorination were achieved at pH and temperature values of around 7 and 35°C, respectively. Methane production was more affected by pH and temperature than was the rate of dechlorination. Increased levels of electron donor (acetate) resulted in faster rates of both methanogenesis and reductive dechlorination. The effect of pH and temperature on the dechlorination rate and methane production were simulated by using previously established relationships pertaining to the activation and deactivation of enzymatic processes.

Anaerobic biodegradation of 2,4, 6‐trichlorophenol and pentachlorophenol by dichlorophenol‐adapted river sediment

We investigated the anaerobic degradation of 2,4,6‐trichlorophenol (2,4,6‐TCP) and pentachlorophenol (PCP) by, 2,4‐ and 3,4‐dichlorophenol (DCP)‐adapted river sediment. The dechlorination rate of 2,4,6‐TCP and PCP by DCP‐adapted sediment was observed to be higher than by river sediment which was not adapted to DCP. For the DCP‐adapted sediment, optimal dechlorination conditions for both 2,4,6‐TCP and PCP were 40°C and pH 8.0. The dechlorination of 2,4,6‐TCP was inhibited by nitrate and enhanced by lactate and pyruvate, but no significant influence was observed for the addition of acetate and sulfate. PCP dechlorination was inhibited by pyruvate and nitrate and enhanced by lactate and acetate, but no significant influence was observed from sulfate. Treatment with 2‐bromoethane sulfonate (BES) and vancomyin showed eubacteria to be the major microbial population. The addition of chloramphenicol showed that 2,4,6‐dechlorination is probably regulated by an inducible enzyme.