摘要:

Bioremediation of groundwater contaminated with chlorinated solvents, such as perchloroethylene (PCE) or carbon tetrachloride, can be accomplished by adding nutrients to stimulate a microbial community capable of reductive dechlorination. However, biotransformation of these solvents, especially PCE, typically occurs very slowly or not at all. Experiments were conducted to evaluate whether the addition of transition metal tetrapyrrole catalysts would increase the reductive transformation of PCE to trichloroethylene (TCE) by sulfate-reducing enrichment cultures. Batch assays were used to test vitamin B12and two synthetic sulfonatophenyl porphine catalysts for the stimulation of reductive dechlorination of PCE by sulfate-reducing bacteria (SRB) enriched from aquifer sediments from two locations at Dover Air Force Base. Cells from the enrichments were concentrated and added to batch assay vials. Vials containing SRB cells amended with vitamin B12 exhibited enhanced transformation of PCE to TCE compared with reactors amended with either synthetic catalysts or reactors containing cells alone. Methane production was observed in reactors that exhibited maximum levels of dechlorination. Storage of aquifer sediments between enrichments led to decreased levels of PCE dechlorination in subsequent assays.

ISSN:1088-9868    

DOI:10.1080/10889860091114167

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Bioremediation of munitions-contaminated soil requires effective transformation and detoxification of high concentrations of 2,4,6-trinitrotoluene (TNT).Pseudomonas aeruginosastrain MX, isolated from munitions-contaminated soil, aerobically transformed TNT (100 mg/L) in culture medium within 15 h, causing transient accumulation of hydroxylaminodinitrotoluenes (HADNTs). The predominance of 2-hydroxylamino-4,6-dinitrotoluene (2HADNT), as well as 2-amino-4,6-dinitrotoluene (2ADNT) and 4,4′,6,6′ -tetranitro-2,2′ -azoxytoluene (2,2′AZT), indicated preferential reduction of the TNTorthonitro group. While only 12% of the TNT was transformed to 2ADNT, up to 65% was transformed to tetranitroazoxytoluenes (AZTs), which accumulated as a precipitate. The precipitate was formed by microscopic particles adhering to bacterial cells, which subsequently formed clusters containing lysed cells. Toxicity toward bacteria was primarily attributed to 2ADNT, because pure AZTs preincubated with sterile medium had little effect on the strain. While the culture medium containing TNT exhibited toxicity toward corn (Zea maysL.) and witchgrass (Panicum capillareL.), little phytotoxicity was observed after incubating withP. aeruginosastrain MX for 4 d. Strong binding of HADNTs to soil and low AZT bioavailability may further promote the detoxification of TNT in soil.

ISSN:1088-9868    

DOI:10.1080/10889860091114176

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Comparative studies were conducted with benzoate, propionate, oleate, tetrabutyl orthosilicate (TBOS), and biomass as substrates for dehalogenation ofcis-1,2-dichloroethene (cDCE). All five substrates supported dehalogenation. Sufficient calcium was required to precipitate oleate and thus reduce its toxicity to the dehalogenating microorganisms. More cDCE was dehalogenated with TBOS than with benzoate, although TBOS initially had an inhibitory effect. The most efficient dehalogenation was associated with biomass, 20% of which was used for dehalogenation, even higher than the 17% obtained with propionate. The advantages and disadvantages of these organic substances for introduction into an aquifer as electron donors for in situ dehalogenation were examined in terms of efficiency of electron use for reductive dehalogenation, and method and ease of introduction into the aquifer. Benzoate and propionate are useful for recirculation systems, while TBOS, oleate, and biomass are appropriate for more passive approaches.

ISSN:1088-9868    

DOI:10.1080/10889860091114185

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

White-rot fungi are known to degrade a wide range of xenobiotic environmental pollutants, including the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT). TNT is first reduced by the fungal mycelium to aminodinitrotoluenes and diaminonitrotoluenes. In a second phase, reduced TNT metabolites are oxidatively transformed and mineralized. The extracellular oxidative enzyme of the ligninolytic system of these fungi includes the lignin peroxidases (LiP) and the manganese-dependent peroxidases (MnP). In the present study, we have shown that a cell-free enzymatic system containing fast protein liquid chromatography (FPLC)-purified LiP (H8) from the white-rot fungusPhanerochaete chrysosporiumwas able to completely transform 50 mg/L of 2,4-diamino-6-nitrotoluene (2,4-DA-6-NT) and 2-amino-4,6-dinitrotoluene (2-A-4,6-DNT) in 1 and 48 h, respectively. Veratryl alcohol (VA), often described as a mediator in the LiP-catalyzed oxidative depolymerization of lignin, was not required for the enzymatic transformation of 2,4-DA-6-NT or 2-A-4,6-DNT. 2,4-DA-6-NT was also shown to be a competitive inhibitor of the LiP activity measured through the oxidation of VA. Experiments using14C-U-ring labeled compounds showed that 2-A-4,6-DNT was converted to 2,2′-azoxy-4,4′,6,6′-tetranitrotoluene. No significant mineralization, measured by the release of14CO2, was observed over 5 d.

ISSN:1088-9868    

DOI:10.1080/10889860091114194

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Experiments were conducted to delineate the applicability and limitations of biologically active Fe(0) barriers to remove nitrate under various geochemical and hydraulic conditions. Microcosm studies showed that, while no Fe(0) treatment was needed to remove nitrate from a high-carbon soil, adding Fe(0) to a low-carbon soil supplemented the electron donor pool and enhanced nitrate removal. Montmorillonite, an acidic aluminosilicate mineral, enhanced Fe(0) corrosion and nitrate removal (from about 1 to 3 mg/L NO3-N per day), and reduced the transient accumulation of nitrite. Combining autotrophic denitrifiers (e.g.,Paracoccus denitrificans) with Fe(0) significantly reduced the amount of nitrite eluted from aquifer columns, from up to 7 to less than 1 mg/L NO2∼-N. Bacteria were observed to preferentially colonize the Fe(0) surface, which produces cathodic H2when corroded by water. The preferential colonization of Fe(0) suggests that hydrogenotrophic consortia are likely to develop around Fe(0) walls to exploit cathodic depolarization as a metabolic niche.

ISSN:1088-9868    

DOI:10.1080/10889860091114202

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

The primary objective of this study was to evaluate the impact of substrate interactions on the biotransformation rates and mineralization potentials of gasoline monoaromatics and methyltert-butyl ether (MTBE), compounds that commonly co-exist in groundwater contaminant plumes. A mixed culture was derived from gasoline-contaminated aquifer material using toluene as the enrichment substrate. Two pure cultures,Rhodococcussp. RR1 and RR2, were isolated from the mixed culture. The three toluene-grown cultures were shown to biotransform all of the six BTEX compounds (benzene, toluene, ethylbenzene,o-xylene,m-xylene, andp-xylene), both individually and in mixtures, over a broad range of concentrations. The mixed culture was shown to degrade all of the BTEX compounds to14CO2, while the two isolates mineralized BTE(m-/p-)X, but biotransformedo-xylene without production of carbon dioxide. Studies to evaluate substrate interactions caused by the concurrent presence of multiple BTEX compounds during their biodegradation revealed a number of patterns,including competitive inhibition and cometabolism. Ethylbenzene was shown to significantly inhibit BTX degradation in mixtures. MTBE was not biodegraded by any of the three toluene-grown cultures over a range of MTBE concentrations. Furthermore, the presence of MTBE at concentrations of 2 to 100 mg/L had no effect on BTEX biotransformation rates.

ISSN:1088-9868    

DOI:10.1080/10889860091114211

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor