Assessment of biostimulation and bioaugmentation for removing chlorinated volatile organic compounds from groundwater at a former manufacture plant.

Site in a former chemical manufacture plant in China was found contaminated with high level of chlorinated volatile organic compounds (CVOCs). The major contaminants chloroform (CF), 1,2-dichloroethane (1,2-DCA) and vinyl chloride (VC) in groundwater were up to 4.49 × 104, 2.76 × 106 and 4.35 × 104 µg/L, respectively. Ethene and methane were at concentrations up to 2219.80 and 165.85 µg/L, respectively. To test the hypothesis that the CVOCs in groundwater at this site could be removed via biodegradation, biomarker analyses and microcosm studies were conducted. Dehalococcoides 16S rRNA gene and VC-reductase gene vcrA at densities up to 1.5 × 104 and 3.2 × 104 copies/L were detected in some of the groundwater samples, providing strong evidence that dechlorinating bacteria were present in the aquifer. Results from the microcosm studies showed that at moderate concentrations (CF about 4000 µg/L and 1,2-DCA about 100 µg/L), CF was recalcitrant under natural condition but was degraded under biostimulation and bioaugmentation, while 1,2-DCA was degraded under all the three conditions. At high concentration (CF about 1,000,000 µg/L and 1,2-DCA about 20,000 µg/L), CF was recalcitrant under all the three treatments and 1,2-DCA was only degraded under bioaugmentation, indicating that high concentrations of contaminants were inhibitory to the bacteria. Electron donors had influence on the degradation of contaminants. Of the four fatty acids (pyruvate, acetate, propionate and lactate) examined, all could stimulate the degradation of 1,2-DCA at both moderate and high concentrations, whereas only pyruvate and acetate could stimulate the degradation of CF at moderate concentration. In the microcosms, the observed first-order degradation rates of CF and 1,2-DCA were up to 0.12 and 0.11/day, respectively. Results from the present study provided scientific basis for remediating CVOCs contaminated groundwater at the site.

Diverse Reductive Dehalogenases Are Associated with Clostridiales-Enriched Microcosms Dechlorinating 1,2-Dichloroethane.

The achievement of successful biostimulation of active microbiomes for the cleanup of a polluted site is strictly dependent on the knowledge of the key microorganisms equipped with the relevant catabolic genes responsible for the degradation process. In this work, we present the characterization of the bacterial community developed in anaerobic microcosms after biostimulation with the electron donor lactate of groundwater polluted with 1,2-dichloroethane (1,2-DCA). Through a multilevel analysis, we have assessed (i) the structural analysis of the bacterial community; (ii) the identification of putative dehalorespiring bacteria; (iii) the characterization of functional genes encoding for putative 1,2-DCA reductive dehalogenases (RDs). Following the biostimulation treatment, the structure of the bacterial community underwent a notable change of the main phylotypes, with the enrichment of representatives of the order Clostridiales. Through PCR targeting conserved regions within known RD genes, four novel variants of RDs previously associated with the reductive dechlorination of 1,2-DCA were identified in the metagenome of the Clostridiales-dominated bacterial community.

Polyhydroxyalkanoate (PHB) as a slow-release electron donor for advanced in situ bioremediation of chlorinated solvent-contaminated aquifers.

During the last two decades permeable reactive barriers (PRBs) established as robust alternatives to traditional pump & treat approaches for groundwater remediation. Zero-valent iron (ZVI) is currently the most frequently employed reactive media, especially for treating plumes polluted by chlorinated hydrocarbons. However PRB-ZVI technology is affected by some problems such as the long-term performance decrease, loss of porosity and no applicability to some important compounds, such as 1,2-dichloroetane (1,2-DCA). In this study we wanted to investigate whether the coupling of ZVI with a long-lasting slow-release substrate (i.e. poly-hydroxybutyrate, PHB) could be a strategy to enhance the degradation performance of ZVI barriers towards chlorinated ethanes especially stimulating biological reductive dechlorination downgradient the PRB. Results here presented clearly demonstrate the feasibility of the proposed approach and the possibility that a biodegradable polymer, usually produced for different commercial sectors, could be advantageously used in the groundwater remediation market.

Electrochemical degradation of 1,2- dichloroethane (DCA) in a synthetic groundwater medium using stainless-steel electrodes.

The electrochemical degradation of 1,2-dichloroethane (DCA) was examined in a synthetic groundwater medium. An undivided electrolytic reactor constructed with 304 L-type stainless-steel plate electrodes was employed in all experiments. The removal of total organic carbon (TOC) content during the electrolysis of DCA was experimentally examined. Stainless-steel plate electrodes were effective in degrading DCA under experimental conditions including varying initial concentrations, chloride concentrations, electrolyte conductivities and applied current densities. A half-life method demonstrated TOC removal followed zero-order kinetics under the experimental conditions examined. Chlorides concentration and applied current affected the TOC removal rates. An increase in current density increased the rate of TOC removal but caused a reduction in mineralization current efficiency. Increase in electrolyte conductivity had no effect on TOC removal rates but it decreased the energy consumption by reducing the cell voltage. Reaction temperature was shown to affect the TOC removal and was modeled by the Arrhenius equation.

Extraction and biodegradation of a toxic volatile organic compound (1,2-dichloroethane) from waste-water in a membrane bioreactor.

An extractive membrane bioreactor has been used to treat a synthetic waste-water containing a toxic volatile organic compound, 1,2-dichloroethane (DCE). Biofilms growing on the surface of the membrane tubes biodegrade DCE while avoiding direct contact between the DCE and the aerating gas. This reduces air stripping by more than an order of magnitude (from 30-35% of the DCE entering the system to less than 1%) relative to conventional aerated bioreactors. Over 99% removal of DCE from a waste-water containing 1600 mg l-1 of DCE was achieved at waste-water residence times of 0.75 h. Biodegradation was verified as the removal mechanism through measurements of CO2 and chloride ion evolution in the bioreactor. No DCE was detected in the biomedium over the operating period. The diffusion-reaction phenomena occurring in the biofilm have been described by a mathematical model, which provides calculated solutions that support the experimental results by predicting that all DCE is biodegraded within the biofilm. Experimentally, however, the rate of DCE degradation in the biofilm was found to be independent of O2 concentration, while the model predictions point to O2 being limiting.

Increased removal capacity for 1,2-dichloroethane by biological modification of the granular activated carbon process.

The removal of 5 mg l-1 1,2-dichloroethane [(CH2Cl)2] was studied in two granular activated carbon (GAC) reactors run with hydraulic retention times of below 1 h. One reactor was operated abiotically. The other one was inoculated with microorganisms able to degrade (CH2Cl)2. While the (CH2Cl)2-adsorption capacity of the non-inoculated GAC reactor was exhausted after 20 days, it apparently did not exhaust for at least 170 experimental days in the biologically activated system because (CH2Cl)2 was removed to over 95% as a result of the microbial degradation. The biodegradation was quantified: during the passage through the biologically activated GAC reactor, (CH2Cl)2 (5 +/- 1 mg l-1) disappeared, chloride ions (3.3 +/- 0.2 mg l-1) were produced, and oxygen (4 to 6 mg l-1) was consumed. Removal of 30% of GAC at the entrance of the reactor, which visibly carried most of the biomass, and its replacement by virgin GAC at the end of the column did not change the apparent (CH2Cl)2 removal capacity of the GAC column, indicating that still enough biomass was available to degrade most of the chemical fed. After the addition of the virgin carbon, the effluent concentration fell for a short period of time from about 200 micrograms l-1 to below 100 micrograms l-1, indicating partial adsorption of the non-degraded (CH2Cl)2 at the end of the reactor by the virgin carbon. Thus, the modification of the adsorption process by inoculation and maintenance of bacteria with special degradation capabilities resulted in a lower consumption of GAC and thus led to an extended service life of the GAC columns.