Nocardioides, Sediminibacterium, Aquabacterium, Variovorax, and Pseudomonas linked to carbon uptake during aerobic vinyl chloride biodegradation

Vinyl chloride (VC) is a frequent groundwater contaminant and a known human carcinogen. Bioremediation is a potential cleanup strategy for contaminated sites; however, little is known about the bacteria responsible for aerobic VC degradation in mixed microbial communities. In attempts to address this knowledge gap, the microorganisms able to assimilate labeled carbon ((13)C) from VC within a mixed culture capable of rapid VC degradation (120 μmol in 7 days) were identified using stable isotope probing (SIP). For this, at two time points during VC degradation (days 3 and 7), DNA was extracted from replicate cultures initially supplied with labeled or unlabeled VC. The extracted DNA was ultracentrifuged, fractioned, and the fractions of greater buoyant density (heavy fractions, 1.758 to 1.780 g mL(-1)) were subject to high-throughput sequencing. Following this, specific primers were designed for the most abundant phylotypes in the heavy fractions. Then, quantitative PCR (qPCR) was used across the buoyant density gradient to confirm label uptake by these phylotypes. From qPCR and/or sequencing data, five phylotypes were found to be dominant in the heavy fractions, including Nocardioides (∼40 %), Sediminibacterium (∼25 %), Aquabacterium (∼17 %), Variovorax (∼6 %), and Pseudomonas (∼1 %). The abundance of two functional genes (etnC and etnE) associated with VC degradation was also investigated in the SIP fractions. Peak shifts of etnC and etnE gene abundance toward heavier fractions were observed, indicating uptake of (13)C into the microorganisms harboring these genes. Analysis of the total microbial community indicated a significant dominance of Nocardioides over the other label-enriched phylotypes. Overall, the data indicate Nocardioides is primarily responsible for VC degradation in this mixed culture, with the other putative VC degraders generating a small growth benefit from VC degradation. The specific primers designed toward the putative VC degraders may be of use for investigating VC degradation potential at contaminated sites.

Reductive dehalogenation of trichloroethene vapors in an anaerobic biotrickling filter

Until now, it has not been possible to use biofiltration to treat trichloroethene (TCE) from waste gases generated by soil vapor extraction or dual-phase extraction at remediation sites because aerobic biodegradation of TCE is possible only via cometabolism, which is difficult to engineer on a large scale. This study looks at the possibility of conducting anaerobic gas-phase biotreatment of TCE vapors. The vision is that nitrogen sparging could be substituted for air sparging, resulting in TCE contaminated oxygen-free gas streams which require treatment A lab-scale anaerobic biotrickling filter inoculated with a mixed culture containing multiple Dehalococcoides strains was used for the proof of concept TCE vapors were removed via reductive dechlorination and converted to ethene, cis-1,2-dichloroethene (cis-DCE), and vinyl chloride (VC). Sodium lactate, a fermentable substrate, was provided to the reactor through the recirculating liquid as a source of hydrogen, the electron donor for Dehalococcoides strains. The biotrickling filter was able to remove >90% TCE at loadings of up to 4 g m(bed)(-3) h(-1) and sustained performance for over 200 days. The distribution of the intermediates of TCE biological reduction was found to be affected by the pH of the recirculating liquid. At pH 8.3, the primary accumulating productwas cis-DCE (approximately 92% of the TCE removed); while at pH 6.85-6.9, conversion to ethene, the intended end product, was 50-67% of the TCE removed. Kinetic determinations using batch biotrickling filter operation showed that VC reduction and not cis-DCE reduction was the sloweststep. Overall, the study shows that sustained anaerobic biotreatment of TCE vapors in biotrickling filters is possible.

Density functional theory studies of chloroethene adsorption on zerovalent iron

Adsorption of perchloroethene (PCE), trichloroethene (TCE), and cis-dichloroethene (cis-DCE) on zerovalent iron is investigated using density functional theory (DFT) to evaluate hypotheses concerning the relative reactivity of these compounds on zerovalent iron. Four different chloroethene adsorption modes on the Fe(110) surface were studied using periodic DFT and the generalized gradient approximation (GGA). Of the adsorption sites examined, the atop site, where the chloroethene C==C bond straddles a surface iron atom, was the most energetically favorable site for the adsorption of all three chloroethenes. Electronic structure and property analyses provide an indication of the extent of sp2-sp3 hybridization. The strong hybridization of the pi-bonding orbital between the chloroethene C==C bond and the iron surface suggests that adsorbed chloroethenes are strongly activated on Fe(110) and are likely precursors for subsequent chloroethene dissociation on the Fe surface. When the effect of solvation is indirectly taken into account in the DFT simulations by considering the hydration energies of chloroethenes in bulkwater,the ordering ofthe adsorption energies of chloroethenes from the aqueous phase onto Fe(110) is in agreement with experimental observation (PCE > TCE > cis-DCE). Electronic properties of the adsorbed configurations of chloroethenes are also presented.

Selective adsorption of volatile organic compounds in micropore aluminum methylphosphonate-alpha: a combined molecular simulation-experimental approach

Results concerning the adsorption capacity of aluminum methylphosphonate polymorph alpha (AlMePO-alpha) for pure ethyl chloride and vinyl chloride by measured individual adsorption isotherms of these pure compounds are presented and discussed here. The experimental data supports the idea of using these materials as selective adsorbents for separating these compounds in mixtures. To explore this possibility further, we have performed grand canonical Monte Carlo simulations using a recently proposed molecular simulation framework for gas adsorption on AlMePO, and the results are presented here. The molecular model of the material was used in a purely transferable manner from a previous work (Herdes, C.; Lin, Z.; Valente, A.; Coutinho, J. A. P.; Vega, L. F. Langmuir 2006, 22, 3097). Regarding the molecular model of the fluids, an existing model for ethyl chloride was improved to capture the experimental dipole value better; an equivalent force field for the vinyl chloride molecule was also developed for simulation purposes. Simulations of the pure compounds were found to be in excellent agreement with the measured experimental data at the three studied temperatures. Simulations were also carried out in a purely predictive manner as a tool to find the optimal conditions for the selective adsorption of these compounds prior experimental measurements are carried out. The influence of the temperature and the bulk composition on the adsorption selectivity was also investigated. Results support the use of AlMePO-alpha as an appropriate adsorbent for the purification process of vinyl chloride, upholding the selective adsorption of ethyl chloride.