Cometabolic Degradation Of Trichloroethylene Research Articles

Alternated phenol and trichloroethylene biodegradation in an aerobic granular sludge reactor

Co-metabolic removal of a synthetic solvent, trichloroethylene (TCE) was conducted. Phenol was used as the primary substrate, and aerobic granules as the biocatalyst. An airtight reactor was designed and constructed with glass, and the configuration was verified of its applicability with volatile solvent. Phenol and TCE were fed into the reactors alternately, and both were efficiently removed during 6 weeks of operation. Compared with the control reactor receiving no TCE, biomass in the TCE-fed reactors had lower phenol-dependent specific oxygen utilization rate, but higher concentration, bigger size, and better settling ability. The morphology of the biomass in TCE and control reactors exhibited distinct characteristics. Granules in the TCE reactors slightly broke up early in the operation, but generally retained their shape and structure throughout. The biomass in the control reactor, however, lost its granular structure and totally disintegrated into flocs. Therefore, TCE co-metabolism likely improved the structural integrity of aerobic granular sludge, and co-metabolic degradation of TCE by phenol-grown aerobic granules showed long term stability.

Acclimation of aerobic-activated sludge degrading benzene derivatives and co-metabolic degradation activities of trichloroethylene by benzene derivative-grown aerobic sludge

The acclimation of aerobic-activated sludge for degradation of benzene derivatives was investigated in batch experiments. Phenol, benzoic acid, toluene, aniline and chlorobenzene were concurrently added to five different bioreactors which contained the aerobic-activated sludge. After the acclimation process ended, the acclimated phenol-, benzoic acid-, toluene-, aniline- and chlorobenzene-grown aerobic-activated sludge were used to explore the co-metabolic degradation activities of trichloroethylene (TCE). Monod equation was employed to simulate the kinetics of co-metabolic degradation of TCE by benzene derivative-grown sludge. At the end of experiments, the mixed microbial communities grown under different conditions were identified. The results showed that the acclimation periods of microorganisms for different benzene derivatives varied. The maximum degradation rates of TCE for phenol-, benzoic acid-, toluene-, aniline- and chlorobenzene-grown aerobic sludge were 0.020, 0.017, 0.016, 0.0089 and 0.0047 mg g SS−1 h−1, respectively. The kinetic of TCE degradation in the absence of benzene derivative followed Monod equation well. Also, eight phyla were observed in the acclimated benzene derivative-grown aerobic sludge. Each of benzene derivative-grown aerobic sludge had different microbial community composition. This study can hopefully add new knowledge to the area of TCE co-metabolic by mixed microbial communities, and further the understanding on the function and applicability of aerobic-activated sludge.

Cometabolic degradation of trichloroethylene by Burkholderia cepacia G4 with poplar leaf homogenate.

Trichloroethylene (TCE), a chlorinated organic solvent, is one of the most common and widespread groundwater contaminants worldwide. Among the group of TCE-degrading aerobic bacteria, Burkholderia cepacia G4 is the best-known representative. This strain requires the addition of specific substrates, including toluene, phenol, and benzene, to induce the enzymes to degrade TCE. However, the substrates are toxic and introducing them into the soil can result in secondary contamination. In this study, poplar leaf homogenate containing natural phenolic compounds was tested for the ability to induce the growth of and TCE degradation by B. cepacia G4. The results showed that the G4 strain could grow and degrade TCE well with the addition of phytochemicals. The poplar leaf homogenate also functioned as an inducer of the toluene-ortho-monooxygenase (TOM) gene in B. cepacia G4.

Enhancing trichloroethylene degradation using non-aromatic compounds as growth substrates

The effect of non-aromatic compounds on the trichloroethylene (TCE) degradation of toluene-oxidizing bacteria were evaluated using Burkholderia cepacia G4 that expresses toluene 2-monooxygenase and Pseudomonas putida that expresses toluene dioxygenase. TCE degradation rates for B. cepacia G4 and P. putida with toluene alone as growth substrate were 0.144 and 0.123μg-TCE/mg-proteinh, respectively. When glucose, acetate and ethanol were fed as additional growth substrates, those values increased up to 0.196, 0.418 and 0.530μg-TCE/mg-proteinh, respectively for B. cepacia G4 and 0.319, 0.219 and 0.373μg-TCE/mg-proteinh, respectively for P. putida. In particular, the addition of ethanol resulted in a high TCE degradation rate regardless of the initial concentration. The use of a non-aromatic compound as an additional substrate probably enhanced the TCE degradation because of the additional supply of NADH that is consumed in co-metabolic degradation of TCE. Also, it is expected that the addition of a non-aromatic substrate can reduce the necessary dose of toluene and, subsequently, minimize the potential competitive inhibition upon TCE co-metabolism by toluene.

Cometabolic Degradation of Trichloroethylene by Single- and Two-Phase Systems

The cometabolic degradation of trichloroethylene (TCE) by Pseudomonas putida F1 (strain ATCC 700007) at different concentrations was studied in single- and two-phase systems using 2-undecanone as the second organic phase. Toluene vapors were used as the primary growth substrate for Pseudomonas putida F1. The effects of the biomass concentration and the phase ratio on the biodegradation process were investigated. The best biomass concentration and the most suitable phase ratio were found to be 0.462 and 0.025 g/L (vorg/vaq), respectively. In the single-phase system, 36.5 mg/L TCE was degraded completely in 15 hours and only 78% of 55 mg/L TCE was degraded in 27 hours, while in the two-phase system 55 mg/L TCE was degraded completely in 14 hours. The use of the two-phase system not only decreased the biodegradation time of TCE but also prevented the inhibition effect of high concentrations of TCE on the microbial biomass.

Trichloroethylene and tetrachloroethylene elimination from the air by means of a hybrid bioreactor with immobilized biomass

Two-phase bioreactors consisting of bacterial consortium in suspension and sorbents with immobilized biomass were used to treat waste air containing chlorinated ethenes, trichloroethylene (TCE) and tetrachloroethylene (PCE). Synthetic municipal sewage was used as the medium for bacterial growth. The system was operated with loadings in the range 1.48-4.76 gm(-3)h(-1) for TCE and 1.49-5.96 gm(-3)h(-1) for PCE. The efficiency of contaminant elimination was 55-86% in the bioreactor with wood chips and 33-89% in the bioreactor filled with zeolite. The best results were observed 1 week after the pollutant loading was increased. However, in these conditions, the stability of the process was not achieved. In the next 7 days the effectiveness of the system decreased. Contaminant removal efficiency, enzymatic activity and the biomass content were all diminished. The system was working without being supplied with additional hydrocarbons as the growth-supporting substrates. It is assumed that ammonia produced during the transformation of wastewater components induced enzymes for the cometabolic degradation of TCE and PCE. However, the evaluation of nitrogen compound transformations in the system is difficult due to the sorption on carriers and the combined processes of nitrification and the aerobic denitrification. An applied method of air treatment is advantageous from both economic and environmental point of views.

Cometabolic degradation of trichloroethylene in a hollow fiber membrane reactor with toluene as a substrate

Contamination of air by volatile organic components (VOCs) is a serious health concern in the present industrial age. To address this issue, a study was devoted to the development of a hollow fiber membrane bioreactor (HMBR), where microorganisms immobilized on the outside of a polyvinylidene fluoride (PVDF) membrane contribute to removing toluene and trichloroethylene (TCE) from air passing through the filter. Waste gas containing toluene and TCE as contaminants was passed through the membrane and shifted to a liquid phase. The performance of fibrous-bed biofilm was evaluated with toluene as carbon source. After over 9 months of continuous operation, long-term performance was demonstrated. The hollow fiber membrane provided a large gas–liquid interface which enabled the efficient removal of the pollutants. Under inlet concentrations of 450–2400 mg m −3 for toluene and 100–160 mg m −3 for TCE, the maximum elimination capacity of toluene and TCE were 0.275 g m −2 h −1 and 0.0016 g m −2 h −1, corresponding to a volumetric of toluene membrane removal rate of 1479 g m −3 h −1 and 8.5 g m −3 h −1, respectively. During the experiments, 95% of toluene as well as 22.1% of TCE removal efficient were observed. No intermediate products such as dichloroethylenes (DCE) and vinyl chloride (VC) were detected during cometablism. Overall, the feasibility of sustained higher anaerobic biotreatment of toluene and TCE in a HFMR was approved.

Cometabolic degradation of TCE in enriched nitrifying batch systems

The aim of this study was to evaluate the effect of the trace pollutant trichloroethylene (TCE) on the nitrification process and to assess its cometabolic degradation. Nitrification was accomplished in batch suspended growth systems containing an enriched nitrifier culture. The presence of TCE resulted in both the inhibition of specific oxygen uptake rate (SOUR) and specific ammonium utilization rate (qNH 4–N). In both SOUR and qNH 4–N a 50% decrease was observed in a TCE concentration range of 1000–2000 ppb. TCE was cometabolically degraded by this enriched nitrifier culture. The cometabolic degradation of TCE was found to be dependent on initial TCE concentration. The results may be applicable in the treatment of TCE containing industrial wastewaters and contaminated groundwaters and soils.

Co-metabolic degradation of trichloroethylene by Pseudomonas putida in a fibrous bed bioreactor

Co-metabolic degradation of trichloroethylene (TCE) by Pseudomonas putida F1 was investigated in a novel bioreactor with a fibrous bed. A pseudo-first-order rate constant for TCE degradation was 1.4 h−1 for 2.4 to 100 mg TCE l−1. Competitive inhibition of toluene on TCE removal could be prevented in this bioreactor. 90% TCE was removed over 4 h when 95 mg toluene l−1 was presented simultaneously.

Effect of Trichloroethylene on the Competitive Behavior of Toluene-Degrading Bacteria

The influence of trichloroethylene (TCE) on a mixed culture of four different toluene-degrading bacterial strains (Pseudomonas putida mt-2, P. putida F1, P. putida GJ31, and Burkholderia cepacia G4) was studied with a fed-batch culture. The strains were competing for toluene, which was added at a very low rate (31 nmol mg of cells [dry weight] h). All four strains were maintained in the mixed culture at comparable numbers when TCE was absent. After the start of the addition of TCE, the viabilities of B. cepacia G4 and P. putida F1 and GJ31 decreased 50- to 1,000-fold in 1 month. These bacteria can degrade TCE, although at considerably different rates. P. putida mt-2, which did not degrade TCE, became the dominant organism. Kinetic analysis showed that the presence of TCE caused up to a ninefold reduction in the affinity for toluene of the three disappearing strains, indicating that inhibition of toluene degradation by TCE occurred. While P. putida mt-2 took over the culture, mutants of this strain which could no longer grow on p-xylene arose. Most of them had less or no meta-cleavage activity and were able to grow on toluene with a higher growth rate. The results indicate that cometabolic degradation of TCE has a negative effect on the maintenance and competitive behavior of toluene-utilizing organisms that transform TCE.

地下水におけるトリクロロエチレンの挙動及びコメタボリズム分解に関する数値モデル

地下水におけるトリクロロエチレンの挙動及びコメタボリズム分解に関する数値モデル

Cometabolic Degradation of TCE and DCE without Intermediate Toxicity

Trichloroethylene (TCE) and cis-1,2-dichloroethylene (DCE) cometabolic degradation by a filamentous, phenol-oxidizing enrichment from a surface-water source were investigated in batch tests. No intermediate toxicity effects were evident during TCE or DCE degradation for loadings up to 0.5 mg TCE/mg VSS or 0.26 mg DCE/mg VSS. Phenol addition up to 40 mg/L did not inhibit TCE or DCE degradation. TCE specific degradation rates ranged from 0.28 to 0.51 g TCE/g VSS-d with phenol present, versus an average endogenous rate of 0.18 g TCE/g VSS-d. DCE specific degradation rates ranged from 0.79 to 2.92 g DCE/g VSS-d with phenol present, versus 0.27 to 1.5 g DCE/g VSS-d for endogenous conditions. There was no inhibition of DCE degradation rates at concentrations as high as 83 mg/L. TCE degradation rates declined between 40 and 130 mg/L TCE. Perchloroethylene, 1,1,1-trichloroethane, and chloroform were not degraded.

Continuous degradation of trichloroethylene by Xanthobacter sp. strain Py2 during growth on propene.

Propene-grown Xanthobacter sp. strain Py2 cells can degrade trichloroethylene (TCE), but the transformation capacity of such cells was limited and depended on both the TCE concentration and the biomass concentration. Toxic metabolites presumably accumulated extracellularly, because the fermentation of glucose by yeast cells was inhibited by TCE degradation products formed by strain Py2. The affinity of the propene monooxygenase for TCE was low, and this allowed strain Py2 to grow on propene in the presence of TCE. During batch growth with propene and TCE, the TCE was not degraded before most of the propene had been consumed. Continuous degradation of TCE in a chemostat culture of strain Py2 growing with propene was observed with TCE concentrations up to 206 microns in the growth medium without washout of the fermentor occurring. At this TCE concentration the specific degradation rate was 1.5 nmol/min/mg of biomass. The total amount of TCE that could be degraded during simultaneous growth on propene depended on the TCE concentration and ranged from 0.03 to 0.34g of TCE per g of biomass. The biomass yield on propene was not affected by the cometabolic degradation of TCE.

A Gas Lift Bioreactor for Removal of Contaminants from the Vapor Phase

The cometabolic degradation of trichloroethylene (TCE) as a vapor by two aromatic-metabolizing pseudomonads was evaluated in an airlift reactor. These microorganisms were able to degrade 90 to 95% of TCE in air at concentrations at the reactor inlet of 300 to 4,000 mug/liter. Although exposure of the cells to high inlet concentrations of TCE (4 mg/liter) caused a decline in enzyme-specific activity and TCE removal efficiency, this loss in activity could be prevented or delayed by increasing the rate of cosubstrate addition. Under the appropriate operating conditions, the microorganisms were able to degrade even high concentrations of TCE and activity of the cells in the reactor could be maintained for periods of at least 2 weeks.