Biodegradation Of Trichloroethylene Research Articles

Strategies and mechanisms for improving groundwater remediation efficiency of chlorinated ethenes by controlling the particle size of polyhydroxyalkanoate

The efficacy of in-situ bioremediation of chlorinated ethenes (CEs)-contaminated groundwater is heavily contingent upon the provision of exogenous electron donors to facilitate reductive dechlorination by dechlorinating bacteria. Nonetheless, methanogenic archaea have been reported to engender competition for the limited electron donor supply, thereby diminishing dechlorination efficiency. This study proposes a novel strategy to enhance reductive dechlorination by reducing the particle size of polyhydroxyalkanoate (PHA) to the micrometer scale, thereby inhibiting methanogenic competition for electron donors. The results demonstrate that trichloroethylene (TCE) biodegradation efficiency peaked at a PHA particle size of 500 μm, significantly surpassing the efficiency observed in groups with particle sizes of 50 and 2000 μm. Furthermore, the electron utilization efficiency of dechlorinating bacteria (represented by Geobacter, Dehalobacter, Anaerolinea, etc in this study) was as high as 94.82 % over methanogenic archaea (represented by Methanobacterium) in the 500 μm group. Mechanistic analyses revealed that the 500 μm PHA particles activated dark oxygen, leading to the generation of reactive oxygen species that decreased the abundance of the methanogenic functional gene McrA and increased the abundance of dechlorinating functional gene TceA relative to the total microbial genome gene (in terms of 16S rRNA). In contrast, PHA particles of 50 μm exhibited lower TCE biodegradation efficiency due to particle aggregation, while particles of 2000 μm exhibited reduced efficiency due to lower specific surface area. This study moves a step for the in-situ microbial remediation of CEs-contaminated groundwater.

Uncovering the microbial community structure and physiological profiles of terrestrial mud volcanoes: A comprehensive metagenomic insight towards their trichloroethylene biodegradation potentiality

Mud volcanoes are dynamic geological features releasing methane (CH4), carbon dioxide (CO2), and hydrocarbons, harboring diverse methane and hydrocarbon-degrading microbes. However, the potential application of these microbial communities in chlorinated hydrocarbons bioremediation purposes such as trichloroethylene (TCE) has not yet been explored. Hence, this study investigated the mud volcano's microbial diversity functional potentiality in TCE degradation as well as their eco-physiological profiling using metabolic activity. Geochemical analysis of the mud volcano samples revealed variations in pH, temperature, and oxidation-reduction potential, indicating diverse environmental conditions. The Biolog Ecoplate™ carbon substrates utilization pattern showed that the Tween 80 was highly consumed by mud volcanic microbial community. Similarly, MicroResp® analysis results demonstrated that presence of additive C-substrates condition might enhanced the cellular respiration process within mud-volcanic microbial community. Full-length 16 S rRNA sequencing identified Proteobacteria as the dominant phylum, with genera like Pseudomonas and Hydrogenophaga associated with chloroalkane degradation, and methanotrophic bacteria such as Methylomicrobium and Methylophaga linked to methane oxidation. Functional analysis uncovered diverse metabolic functions, including sulfur and methane metabolism and hydrocarbon degradation, with specific genes involved in methane oxidation and sulfur metabolism. These findings provide insights into the microbial diversity and metabolic capabilities of mud volcano ecosystems, which could facilitate their effective application in the bioremediation of chlorinated compounds.

Biodegradation of Trichloroethylene by Trametes versicolor and its Physiological Response to Contaminant Stress.

Trichloroethylene (TCE) poses a potentially toxic threat to humans and the environment and widely exists in contaminated sites. White rot fungi effectively degrade refractory pollutants, while a few research studies use white rot fungi to degrade TCE. In this study, we investigated TCE biodegradation by white rot fungi and the potential influencing factors in the environment and attempted to research the effect of TCE on the physiological characteristics of white rot fungi. White rot fungi (Trametes versicolor, Pseudotrametes gibbosa, Pycnoporus sanguines and Pleurotus ostreatus) were added to the liquid medium for shock culture. The results revealed that T. versicolor exhibited the most pronounced efficacy in removing TCE, with a degradation rate of 81.10% within a 7 d period. TCE induces and is degraded by cytochrome P450 enzymes. High pH and Cr(VI) adversely affected the effectiveness of the biodegradation of TCE, but the salinity range of 0-1% had less effect on biodegradation. Overall, the effectiveness of degradation of TCE by T. versicolor has been demonstrated, and it provides a reference for the application prospects of white rot fungi in TCE-contaminated soils.

Highly efficient bioregeneration of high temperature-pyrolyzed biochar after trichloroethylene adsorption through biodegradation of Dehalococcoides

Biochars was widely employed to immobilize chlorinated aliphatic hydrocarbons (CAHs) in groundwater. Biodegradation of adsorbed CAHs may be able to regenerate biochars, but was scarcely explored. In this study, therefore, biodegradation of trichloroethylene (TCE) adsorbed on a biochar prepared at 700 °C (WBC700) by Dehalococcoides mccartyi 195 (Dhc 195) was investigated. Aqueous TCE was completely degraded to ethene by Dhc 195 within 28 days, while 87.5 % of WBC700-adsorbed TCE was degraded to ethene within 63 days. The slower biodegradation of WBC700-adsorbed TCE could be attributed to its lower accessibility to Dhc 195 caused by the steric effects of WBC700. The adsorption capacity of WBC700 for TCE remained 80.4 % after five adsorption-bioregeneration cycles, indicating that the microbial degradation could be a highly efficient method to regenerate biochars. The microbial degradation was mainly through the electron transfer from Dhc 195 to TCE mediated by biochars as electron conductor or shuttle, but was not assisted by desorption or extracellular redox active species. Compared with biodegradation of aqueous TCE, the biodegradation of WBC700-adsorbed TCE by Dhc 195 had a wider pH tolerance and required more VB12, due to the buffer effect and adsorption of WBC700, respectively. The obtained results could provide a cost-effective method of biochar regeneration for CAHs removal in groundwater.

Enhanced trichloroethylene biodegradation: The mechanism and influencing factors of combining microorganism and carbon‑iron materials

Trichloroethylene (TCE) is one of the most prevalent contaminants with long-term persistence and a strong carcinogenic risk. Biological dechlorination has gradually become the mainstream method due to its advantages of low treatment cost and high environmental friendliness. However, microorganisms are easily restricted by environmental factors, such as an insufficient energy supply and a slow biological dechlorination process. This study focused on the coupled degradation of TCE with the combination of microorganisms and assistant materials (biochar, nZVI, nZVI modified biochar, HPO3 modified biochar), and set up microorganisms (alone) and materials (alone) as separate controls. Biochar provided nutrients, increased contact with pollutants, and promoted electron transfer to improve TCE degradation, although it did not change the pathway of degradation. The coupled treatment with anaerobic microorganisms (Micro) and 1 g/L unmodified biochar (BC) had the strongest degradation capacity. Compared with microorganisms alone, the addition of biochar resulted in the complete removal of TCE within 4 days. The influence of ambient temperature was mainly related to microbial activity, and 35 °C showed better degradation than 20 °C. Under 20 °C, 1 g/L of nZVI significantly promoted microbial dechlorination. As the dosage increased to 2 g/L and 4 g/L, nZVI showed a strong toxic effect. After 16 days, TCE was completely converted to ethylene by Micro-BC with C3H5O3Na, while 4.40 μmol dichloroethane (DCE) and 1.48 μmol vinyl chloride (VC) remained in the treatment with Micro-BC alone. As an electron acceptor, NaNO3 directly competed with TCE in the reduction process, which decreased the reduction efficiency of TCE. These findings provide a better understanding of the mechanism of the chemical materials coupling microbial dechlorination process and an optimal treatment method for trichloroethylene degradation.

Artificial neural network modeling on trichloroethylene biodegradation in a packed-bed biofilm reactor and its comparison with response surface modeling approach

An artificial neural network (ANN) model was developed for predicting trichloroethylene (TCE) biodegradation via co-metabolism in a packed-bed biofilm reactor using Pseudomonas putida F1 as the bio-catalyst and toluene as the primary substrate. The model uses an architecture with three hidden layers (3–2–1) and resilient back-propagation algorithm to obtain optimal weights for the associated neurons. ANN model predictions of TCE degradation efficiency have not only successfully validated those obtained from a Response Surface Model (RSM), but the model also outperformed RSM with a better predicting power that the ANN showed a lower root mean square error (RMSE) 9.07 and a higher determination of coefficient (R2) 80.32 % than those of RSM (RMSE=9.93, 10.88 after corrected for model degree of freedom; R2 = 76.4 %). Further model analysis revealed that this ANN model correctly interpreted the experimental data with the underlying biological mechanisms and would be able to provide guidance on local operations to achieve optimal TCE degradation. Sensitivity analysis showed that the ANN model was still a robust model when an extreme TCE data point was added during the model development. A simulation study also indicated that on average, ANN models had better fit to the experimental data than the RSM.

Recent advances and trends of trichloroethylene biodegradation: A critical review.

Trichloroethylene (TCE) is a ubiquitous chlorinated aliphatic hydrocarbon (CAH) in the environment, which is a Group 1 carcinogen with negative impacts on human health and ecosystems. Based on a series of recent advances, the environmental behavior and biodegradation process on TCE biodegradation need to be reviewed systematically. Four main biodegradation processes leading to TCE biodegradation by isolated bacteria and mixed cultures are anaerobic reductive dechlorination, anaerobic cometabolic reductive dichlorination, aerobic co-metabolism, and aerobic direct oxidation. More attention has been paid to the aerobic co-metabolism of TCE. Laboratory and field studies have demonstrated that bacterial isolates or mixed cultures containing Dehalococcoides or Dehalogenimonas can catalyze reductive dechlorination of TCE to ethene. The mechanisms, pathways, and enzymes of TCE biodegradation were reviewed, and the factors affecting the biodegradation process were discussed. Besides, the research progress on material-mediated enhanced biodegradation technologies of TCE through the combination of zero-valent iron (ZVI) or biochar with microorganisms was introduced. Furthermore, we reviewed the current research on TCE biodegradation in field applications, and finally provided the development prospects of TCE biodegradation based on the existing challenges. We hope that this review will provide guidance and specific recommendations for future studies on CAHs biodegradation in laboratory and field applications.

Microbiome reengineering by four environmental factors for the rapid biodegradation of trichloroethylene

Trichloroethylene (TCE) was once a widely applied industrial solvent, but is now an infamous contaminant in groundwater. Although anaerobic reductive dechlorination is considered a greener remediation approach, the accumulation of toxic intermediates, such as vinyl chloride (VC), and a longer remediation period are highly concerning. Biostimulation and bioaugmentation have been developed to solve these problems. The former method may not be effective, and the latter may introduce foreign genes. Here, we propose a new approach by applying environmental stresses to reshape the indigenous microbiome. In this study, by using the Taguchi method, the effects of heating, pH, salinity, and desiccation were systematically examined. The optimum conditions were defined as 50 °C, pH 9, 3.50% salinity (w/v), and 21% volumetric water content (θW). The top performing group, G7, can complete the conversion of 11.81 mg/L TCE into ethene in 3.0 days with a 1.23% abundance of Dehalococcoides mccartyi 195 (Dhc 195). Redundancy analysis confirmed that temperature and salinity were the predominant factors in reorganizing the microbiomes. The microbiome structure and its effectiveness can last for at least 90 d. The repetitive selection conditions and sustainable degradation capability strongly supported that microbiome reengineering is feasible for the rapid bioremediation of TCE-contaminated environmental matrices.

Thermally Enhanced Biodegradation of TCE in Groundwater

In situ remediation is usually restricted by temperature, lack of substrate for reductive dechlorination (anaerobic respiration), the presence of dehalogenating microorganisms, and specific bedrock conditions. In this work, trichloroethene (TCE) degradation was studied by a number of methods, from physical–chemical analyses to molecular biological tools. The abundance changes in dechlorinating bacteria were monitored using real-time PCR. The functional genes vcrA and bvcA as well as the 16S rRNA specific for representatives of genera Dehalococcoides, Dehalobacter, and Desulfitobacterium were monitored. Furthermore, the sulfate-reducing bacteria and denitrifying bacteria were observed by amplifying the functional genes apsA and nirK. The elevated temperature and the substrate (whey) addition significantly affected TCE dechlorination. The chlorine index decreased after nine weeks from 2.5 to 0.1 at 22 °C, to 1.1 at 17 °C and 1.7 at 12 °C and complete dechlorination was achieved at 22 °C with whey addition. The achieved results of this work show the feasibility and effectiveness of biological dechlorination of TCE enhanced with elevated temperature and whey addition.

A Polyhydroxybutyrate (PHB)-Biochar Reactor for the Adsorption and Biodegradation of Trichloroethylene: Design and Startup Phase.

In this work, polyhydroxy butyrate (PHB) and biochar from pine wood (PWB) are used in a mini-pilot scale biological reactor (11.3 L of geometric volume) for trichloroethylene (TCE) removal (80 mgTCE/day and 6 L/day of flow rate). The PHB-biochar reactor was realized with two sequential reactive areas to simulate a multi-reactive permeable barrier. The PHB acts as an electron donor source in the first “fermentative” area. First, the thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses were performed. The PHB-powder and pellets have different purity (96% and 93% w/w) and thermal properties. These characteristics may affect the biodegradability of the biopolymer. In the second reactive zone, the PWB works as a Dehalococcoides support and adsorption material since its affinity for chlorinated compounds and the positive effect of the “coupled adsorption and biodegradation” process has been already verified. A specific dechlorinating enriched culture has been inoculated in the PWB zone to realize a coupled adsorption and biodegradation process. Organic acids were revealed since the beginning of the test, and during the monitoring period the reductive dichlorination anaerobic pathway was observed in the first zone; no chlorinated compounds were detected in the effluent thanks to the PWB adsorption capacity.

A Borehole Test for Chlorinated Solvent Diffusion and Degradation Rates in Sedimentary Rock

AbstractWe present a new field measurement and numerical interpretation method (combined termed “test”) to parameterize the diffusion of trichloroethene (TCE) and its biodegradation products (DPs) from the matrix of sedimentary rock. The method uses a dual‐packer system to interrogate a low‐permeability section of the rock matrix adjacent to a previously contaminated borehole and uses the borehole monitoring history to establish the pretest condition. TCE and its DPs are removed from the groundwater between the packers at the onset of the testing. The parameters estimated by fitting a radial diffusion model to the concentration history and borehole concentration data, also termed back diffusion, are the tortuosity factor and sorption coefficients of TCE and DPs in the rock matrix and the TCE and DP biodegradation rate coefficients in the borehole. We demonstrate the equipment design and the interpretive method using a borehole accessing the gray mudstone at a TCE contaminated site in the Newark Basin. In this test, both nonreactive (bromide) and reactive (trichlorofluoroethene) tracers are used to constrain the estimated parameters; however, the bromide tracer was not needed to estimate the parameters in this test. The parameters estimated from the field test are consistent with values measured independently in laboratory experiments using field samples of similar lithology. From the interpretation, we compute the TCE and DP concentration distributions in the rock matrix prior to the test to illustrate how the results can be used to enhance understanding of contaminant distribution in the rock matrix.

Coupled Adsorption and Biodegradation of Trichloroethylene on Biochar from Pine Wood Wastes: A Combined Approach for a Sustainable Bioremediation Strategy.

Towards chlorinated solvents, the effectiveness of the remediation strategy can be improved by combining a biological approach (e.g., anaerobic reductive dechlorination) with chemical/physical treatments (e.g., adsorption). A coupled adsorption and biodegradation (CAB) process for trichloroethylene (TCE) removal is proposed in a biofilm–biochar reactor (BBR) to assess whether biochar from pine wood (PWB) can support a dechlorinating biofilm by combining the TCE (100 µM) adsorption. The BBR operated for eight months in parallel with a biofilm reactor (BR)—no PWB (biological process alone), and with an abiotic biochar reactor (ABR)—no dechlorinating biofilm (only an adsorption mechanism). Two flow rates were investigated. Compared to the BR, which resulted in a TCE removal of 86.9 ± 11.9% and 78.73 ± 19.79%, the BBR demonstrated that PWB effectively adsorbs TCE and slows down the release of its intermediates. The elimination of TCE was quantitative, with 99.61 ± 0.79% and 99.87 ± 0.51% TCE removal. Interestingly, the biomarker of the reductive dechlorination process, Dehalococcoides mccartyi, was found in the BRR (9.2 × 105 16S rRNA gene copies/g), together with the specific genes tceA, bvcA, and vcrA (8.16 × 106, 1.28 × 105, and 8.01 × 103 gene copies/g, respectively). This study suggests the feasibility of biochar to support the reductive dechlorination of D. mccartyi, opening new frontiers for field-scale applications.

Bioremediation of trichloroethylene-polluted groundwater using emulsified castor oil for slow carbon release and acidification control.

In this study, the emulsified castor oil (ECO) substrate was developed for a long-term supplement of biodegradable carbon with pH buffering capacity to anaerobically bioremediate trichloroethylene (TCE)-polluted groundwater. The ECO was produced by mixing castor oil, surfactants (sapindales and soya lecithin [SL]), vitamin complex, and a citrate/sodium phosphate dibasic buffer system together for slow carbon release. Results of the emulsification experiments and microcosm tests indicate that ECO emulsion had uniform small droplets (diameter = 539 nm) with stable oil-in-water characteristics. ECO had a long-lasting, dispersive, negative zeta potential (-13 mv), and biodegradable properties (viscosity = 357 cp). Approximately 97% of TCE could be removed with ECO supplement after a 95-day operational period without the accumulation of TCE dechlorination byproducts (dichloroethylene and vinyl chloride). The buffer system could neutralize acidified groundwater, and citrate could be served as a primary substrate. ECO addition caused an abrupt TCE adsorption at the initial stage and the subsequent removal of adsorbed TCE. Results from the next generation sequences and real-time polymerase chain reaction (PCR) indicate that the increased microbial communities and TCE-degrading bacterial consortia were observed after ECO addition. ECO could be used as a pH-control and carbon substrate to enhance anaerobic TCE biodegradation effectively. PRACTITIONER POINTS: Emulsified castor oil (ECO) contains castor oil, surfactants, and buffer for a slow carbon release and pH control. ECO can be a long-term carbon source for trichloroethylene (TCE) dechlorination without causing acidification. TCE removal after ECO addition is due to adsorption and reductive dechlorination mechanisms.

Biodegradation of Tetrachloroethene in Batch Experiment and PHREEQC Model; Kinetic Study

Introduction: Bioremediation and biodegradation are considered as environmental friendly techniques for contaminants’ removal in polluted environment. In this study, the removal and kinetics of Tetrachloroethene (PCE) and Trichloroethene (TCE) microbial degradation, their inhibitory effects and the rate of dehalogenation capacity at high concentration of PCE were investigated.Materials and Methods: Dechlorinating culture was provided by Bioclear B.V. from a PCE-contaminated site (Evenblij in Hoogeveen -The Netherlands). The batch apparatuses were placed in an orbital shaker at 150 rpm at room temperature. In all the 18 batches, 6 different concentrations of PCE were measured from 0.1 mM to 0.6 mM. The degradation rate of PCE, Trichloroethene (TCE), and cis-1,2-dichloroethene (cDCE) were determined by the PHREEQC model.Results: The results revealed that the final product was ethene and the rate of dechlorinating of PCE increased gradually. The degradation process started after 3 days in batch modes (0.1 mM). After 10 days, the dechlorination of PCE to TCE was obtained in a low concentration of PCE (0.1 mM). Also, the TCE concentration became close to zero after 10 days. However, the start point was longer than PCE and the rate of biodegradation of TCE was faster than PCE. PCE did not show any progress in the dechlorinating procedure at 13th and 14th batch series and none of the daughter products were observed.Conclusions: It should be concluded that there was no single organism that could dechlorinate PCE to ethene, directly. Therefore, the best consortium of microorganisms to dechlorinate PCE to ethene faster, with less production of VC as the most hazardous compound, should be studied.

Cometabolic biodegradation of chlorinated ethenes with methanotrophs in anaerobic/aerobic simulated aquifer

Aim: This study explores anaerobic/aerobic biodegradation efficiencies of aerobic cometabolism with methanotrophs when contaminants trichloroethylene (TCE) and cis-1,2-dichloroethylene (cDCE) are present individually or in tandem. Methodology: Batch tests and an anaerobic/aerobic column system were used to simulate saturated, contaminated aquifers. A brown glass bottle with an effective volume of 44 m l-1 was prepared for the batch test. An integrated one-dimensional sequential anaerobic/aerobic column system was used to simulate the accumulative intermediates such as TCE, cDCE and VC caused by incomplete degradation of PCE during the upgradient anaerobic stage in the saturated aquifer. In the downgradient aquifer, aerobic cometabolism was employed to degrade the intermediates. Methanotrophs in the aerobic aquifer were inoculated to degrade the by-products of incomplete degradation of PCE by aerobic cometabolism. Results: In the batch test, biodegradation of TCE was significantly inhibited by cDCE. However, biodegradation of cDCE was not significantly inhibited by TCE. In the simulated aquifer test, aerobic cometabolism completely degraded intermediates (TCE, cDCE, and VC) produced by incomplete anaerobic degradation of tetrachloroethylene (PCE). The results showed that methane, a by-product of anaerobic reductive dechorination of PCE, was used as a primary substrate for aerobic degradation, at a utilization rate of almost 100%. Interpretation: Biodegradation of TCE was significantly inhibited by cDCE. Bioremediation should have sufficient oxygen and methane at aerobic stage to ensure that chlorinated ethenes fully mineralize.

Enhanced trichloroethylene biodegradation: Roles of biochar-microbial collaboration beyond adsorption

Trichloroethylene (TCE) is a pollutant widely found in groundwater, especially in the heavily contaminated industrial sites. Biological dechlorination method is environmentally friendly and low-cost. However, microorganisms grow slowly and their activity is susceptible to environmental fluctuations. This study used biochar as an additive to promote anaerobic biodegradation of TCE with mixed culture. Results showed that biochar with dose of 0.1–0.4% (w/v) brought a rapid initial decrease of TCE concentration by 39.4–88.8% in 24 h via adsorption mechanism. Biochar produced at 500 °C pyrolysis temperature (BC500) achieved the highest TCE adsorption in comparison to BC300 and BC700. Subsequently, a significantly shortened microbial stagnation phase (from 85 h to 37 h) was observed in the system with the presence of biochar. During the exponential growth phase, BC700 outperformed BC300 and BC500 in terms of TCE degradation efficiency. Electrochemical analysis demonstrated that BC700 possessed the greatest electron transfer capability. Finally, biochar shortened the time for achieving 100% removal of TCE by 54.5–69.7% (from approximate 330 h to 100–150 h). Even at high concentration of TCE (20–30 mg·L−1) that could lead to serious microbial growth inhibition, the TCE degradation efficiency could be recovered in the presence of BC500. The high-throughput sequencing data revealed that biochar promoted the relative abundance of co-metabolizing dechlorinating microorganisms (Pseudomonas, Burkholderia) in the aqueous solution, and simultaneously led to the selective colonization of reductive dechlorinating microorganisms (Enterobacteriaceae, Clostridium) attached on biochar surface. On the other hand, biochar addition decreased the relative abundance of hydrogen-competing microorganisms, thereby forming an efficient co-metabolism-reductive dechlorination system. These findings allow a better understanding of the promotion mechanism of biochar for microbial dechlorination technology supporting the biochar-assisted bioremediation in practice.

Continuous trichloroethylene biodegradation by Pseudomonas putida F1 in a biofilm reactor and determination of an optimal feeding path via a response surface model

AbstractReactor design and feeding strategies are the key to successful trichloroethylene (TCE) treatment via cometabolism. An easy to maintain and operate laboratory scale packed‐bed biofilm reactor, featuring recycled gas and liquid effluent streams, was developed for continuous aerobic aqueous‐phase TCE biodegradation using Pseudomonas putida F1 as the biocatalyst and toluene as the primary substrate. The impacts of the influent toluene and TCE concentrations, flow rates, and recycle rates on TCE biodegradation were studied. Multivariate factors, including influent toluene and TCE concentrations, their interactions, and flow rates were further analyzed via a response surface model (RSM). Results showed that such bioreactor design eliminated oxygen limitation and removed or substantially reduced toluene competitive inhibition on TCE degradation. A TCE removal efficiency of >90% was achieved at an influent TCE concentration of ≤0.3 mg/L under an ˜8‐min mean hydraulic retention time. Toluene and TCE concentrations, in both linear and quadratic forms, were the most significant factors for TCE degradation, indicating both cell regenerating and inhibiting effects from toluene and a toxic effect from TCE. This RSM analysis has successfully identified an optimal influent toluene concentration path for each influent TCE concentration and provided insight for an extended TCE degradation at higher TCE concentrations.

Microbiome Reengineering by Heat Selection for Rapid Biodegradation of Trichloroethylene with Minimal Vinyl Chloride Formation

Trichloroethylene (TCE) was a widely used industrial solvent but is now regarded as a notorious groundwater contaminant. Both physicochemical and biological methods have been applied to remediate groundwater contaminated by TCE. For medium to low level of TCE contamination, bioremediation could be more cost-effective. However, bioremediation approaches suffer from slow degradation rates and accumulation of vinyl chloride (VC). In addition, bioaugmentation is often highly encouraged but may introduce foreign genes and increase the pace of microbial evolution. In this study, a microbiome reengineering strategy by heat selection is applied to solve these problems. Out of eight heat-treated mixed cultures, two showed a much-improved TCE degradation rate, more than 70 times higher than the untreated. The biodegradation half-life (t1/2) of TCE was 0.0627 d or shorter. No VC was detected by a gas chromatography equipped with flame ionization detector (GC-FID) and only a minimal amount by a GC-mass spectrometer (GC-MS). Ethene achieved a fairly good mass balance. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and next-generation sequencing (NGS) results showed that the heating process did not kill most bacteria, but Dehalococcoides were either not present or very scarce. Acetoanaerobium and Methanosarcina could be the most important species in this reductive dechlorination process. Kinetic study results showed that the maximum specific TCE degradation rate was approximately 1,271 nmole/min/mg cell protein, which are two orders of magnitude higher than that of the mixed cultures reported in literature. These results suggest that apart from biostimulation and bioaugmentation, microbiome reengineering could be a promising approach for rapid bioremediation of TCE-contaminated aquifers.

Simultaneous adsorption and biodegradation of trichloroethylene occurs in a biochar packed column treating contaminated landfill leachate

Trichloroethylene (TCE) is a human carcinogen that is commonly found in landfill leachate. Contaminated leachate plumes may be intercepted prior to reaching groundwater and treated in situ using permeable reactive barriers (PRB). This study used a packed column system containing herbal pomace and spruce biochar, previously shown to have TCE adsorptive capabilities. Influent containing raw or autoclaved landfill leachate was used to investigate the potential for environmental micro-organisms to establish a TCE-dechlorinating biofilm on the biochar, in order to prolong the operational life span of the system. TCE removal ≥ 99.7 % was observed by both biochars. No dichloroethylene (DCE) isomers were present in the column effluents, but cis-1,2 DCE was adsorbed to the biochar treating raw landfill leachate, indicating that dechlorination was occurring biologically in these columns. Known microbial species that are individually capable of complete dechlorination of TCE to ethene were not detected by 16S rRNA gene sequencing, but several species capable of partial TCE dechlorination (Desulfitobacterium spp., Sulfurospirillium spp. and Desulfuromonas spp) were present in the biofilms of the columns treating raw landfill leachate. These data demonstrate that biochar from waste material may be capable of supporting a dechlorinating biofilm to promote bioremediation of TCE.

Batch degradation of trichloroethylene using oleaginous Rhodococcus opacus in a two-phase partitioning bioreactor and kinetic study

In the present study, we present the biodegradation of trichloroethylene (TCE) for the first time using pure bacterial strain of Rhodococcus opacus PD630. TCE utilized as the sole carbon substrate by R. opacus in single phase system and was reached to highest specific growth rate of 0.015 h−1 at the concentration of 75 mg L−1. To further enhance the degradation performance even at high concentration (1000 mg L−1), two-phase partitioning bioreactor (TPPB) was developed. Silicone oil (20%, v/v) was selected as non-aqueous phase solvent to achieve high metabolic activity of bacteria. Furthermore, the experimental results of TCE degradation and specific TCE utilization rate were fitted to various kinetic models. Our experimental results clearly revealed that TPPB system having R. opacus as biological source and silicone oil as solvent was highly efficient and successful for removing high concentrated TCE compared with single phase system.