Two parallel pilot experiments were performed at Kurivody (Czech Republic) in order to compare two reductive remedial technologies for chlorinated ethenes - microbial dehalogenation assisted by lactate and chemical dehalogenation with zero-valent iron (nZVI) nanoparticles. The methods were applied at a site contaminated by tetrachlorethylene (PCE) and trichlorethylene (TCE), with total concentrations from 10 to 50 mg/l. Concentrations of chlorinated ethenes, inorganic components of interest, pH and oxidation reduction potential (ORP) were monitored at the site for a period up to 650 days. The method of biological reductive dechlorination supported by lactate showed a considerable removal of PCE and TCE, but temporary accumulation of transient reaction product 1,2-cis-dihloroethene. Reductive dechlorination with nZVI showed a significant reduction in the concentration of chlorinated ethenes without a formation of intermediate products. The development of pH showed only small changes due to the high buffering capacity of the aquifer. Both methods differ in the initial development of ORP, but over the long term showed similar values around 100 mV. Significant differences were observed for chemical oxygen demand, where groundwater after the application of nZVI showed no change in comparison to the application of lactate. The reductive effects of both agents were verified by changes in inorganic compound concentrations.
- MeSH
- Chlorine isolation & purification MeSH
- Hydrocarbons, Chlorinated chemistry MeSH
- Hydrogen-Ion Concentration MeSH
- Lactic Acid chemistry MeSH
- Environmental Pollutants chemistry MeSH
- Oxidation-Reduction MeSH
- Pilot Projects MeSH
- Environmental Restoration and Remediation methods MeSH
- Iron chemistry MeSH
- Publication type
- Journal Article MeSH
- Evaluation Study MeSH
- Research Support, Non-U.S. Gov't MeSH
- Comparative Study MeSH
Electric field assisted remediation using nano iron has shown outstanding results as well as economic benefits during pilot applications (Černíková et al., 2020). This method is based on donating electrons to the zero-valent iron that possess an inherently strong reductive capacity. The reduction of chlorinated hydrocarbons may be characterized by a decrease in contaminants or better still by the evolution of ethene and ethane originating from the reduction of chlorinated ethenes. The evolution of ethene and ethane was observed predominantly in the vicinity of the anode despite reduction processes being expected near the cathode - the electron donor. The reduction near the anode occurred due to dissolved Fe2+ ions, whose presence was suggested by a Pourbaix diagram that combines Eh/pH values to characterize electrochemical stabilities between different species. No products of dechlorination were observed in the area of the cathode due to presence of oxidized Fe in the form of Fe3+ or Fe(OH)4-. The experimental work described in this research provides a deeper view of the processes of electrochemical reductive dechlorination using zero-valent iron and DC. It also showed an increase in the efficiency compared to the method using zero-valent iron only.
- MeSH
- Water Pollutants, Chemical * analysis MeSH
- Hydrocarbons, Chlorinated * MeSH
- Thermodynamics MeSH
- Iron MeSH
- Publication type
- Journal Article MeSH
Application of Fenton's reagent and enhanced reductive dechlorination are currently the most common remediation strategies resulting in removal of chlorinated ethenes. In this study, the influence of such techniques on organohalide-respiring bacteria was assessed at a site contaminated by chlorinated ethenes using a wide spectrum of molecular genetic markers, including 16S rRNA gene of the organohalide-respiring bacteria Dehaloccocoides spp., Desulfitobacterium and Dehalobacter; reductive dehalogenase genes (vcrA, bvcA) responsible for dechlorination of vinyl chloride and sulphate-reducing and denitrifying bacteria. In-situ application of hydrogen peroxide to induce a Fenton-like reaction caused an instantaneous decline in all markers below detection limit. Two weeks after application, the bvcA gene and Desulfitobacterium relative abundance increased to levels significantly higher than those prior to application. No significant decrease in the concentration of a range of chlorinated ethenes was observed due to the low hydrogen peroxide dose used. A clear increase in marker levels was also observed following in-situ application of sodium lactate, which resulted in a seven-fold increase in Desulfitobacterium and a three-fold increase in Dehaloccocoides spp. after 70 days. An increase in the vcrA gene corresponded with increase in Dehaloccocoides spp. Analysis of selected markers clearly revealed a positive response of organohalide-respiring bacteria to biostimulation and unexpectedly fast recovery after the Fenton-like reaction.
- MeSH
- Bacteria metabolism MeSH
- RNA, Bacterial genetics MeSH
- Biodegradation, Environmental MeSH
- Water Pollutants, Chemical metabolism MeSH
- Chlorine metabolism MeSH
- Hydrocarbons, Chlorinated metabolism MeSH
- Genetic Markers genetics MeSH
- Catalysis * MeSH
- Sodium Lactate administration & dosage metabolism MeSH
- Oxidation-Reduction MeSH
- RNA, Ribosomal, 16S genetics MeSH
- Publication type
- Journal Article MeSH
Biomolecular and hydrochemical tools were used to evaluate natural attenuation of chlorinated ethenes in a Quaternary alluvial aquifer located close to a historical source of large-scale tetrachloroethylene (PCE) contamination. Distinct stratification of redox zones was observed, despite the aquifer's small thickness (2.8 m). The uppermost zone of the target aquifer was characterised by oxygen- and nitrate-reducing conditions, with mixed iron- to sulphate-reducing conditions dominant in the lower zone, along with indications of methanogenesis. Natural attenuation of PCE was strongly influenced by redox heterogeneity, while higher levels of PCE degradation coincided with iron- to sulphate reducing conditions. Next generation sequencing of the middle and/or lower zones identified anaerobic bacteria (Firmicutes, Chloroflexi, Actinobacteria and Bacteroidetes) associated with reductive dechlorination. The relative abundance of dechlorinators (Dehalococcoides mccartyi, Dehalobacter sp.) identified by real-time PCR in soil from the lower levels supports the hypothesis that there is a significant potential for reductive dechlorination of PCE. Local conditions were insufficiently reducing for rapid complete dechlorination of PCE to harmless ethene. For reliable assessment of natural attenuation, or when designing monitoring or remedial systems, vertical stratification of key biological and hydrochemical markers should be analysed as standard, even in shallow aquifers.
- MeSH
- Biodegradation, Environmental MeSH
- Water Pollutants, Chemical analysis MeSH
- Chloroflexi MeSH
- Ethylenes analysis MeSH
- Halogenation MeSH
- Environmental Monitoring * MeSH
- Groundwater chemistry MeSH
- Tetrachloroethylene chemistry MeSH
- High-Throughput Nucleotide Sequencing MeSH
- Iron analysis MeSH
- Publication type
- Journal Article MeSH
Iron-based materials used in water treatment and groundwater remediation-especially micro- and nanosized zerovalent iron (nZVI)-can be more effective when modified with lower-valent forms of sulfur (i.e., "sulfidated"). Controlled sulfidation for this purpose (using sulfide, dithionite, etc.) is the main topic of this review, but insights are derived by comparison with related and comparatively well-characterized processes such as corrosion of iron in sulfidic waters and abiotic natural attenuation by iron sulfide minerals. Material characterization shows that varying sulfidation protocols (e.g., concerted or sequential) and key operational variables (e.g., S/Fe ratio and sulfidation duration) result in materials with structures and morphologies ranging from core-shell to multiphase. A meta-analysis of available kinetic data for dechlorination under anoxic conditions, shows that sulfidation usually increases dechlorination rates, and simultaneously hydrogen production is suppressed. Therefore, sulfidation can greatly improve the efficiency of utilization of reducing equivalents for contaminant removal. This benefit is most likely due to inhibited corrosion as a result of sulfidation. Sulfidation may also favor desirable pathways of contaminant removal, such as (i) dechlorination by reductive elimination rather than hydrogenolysis and (ii) sequestration of metals as sulfides that could be resistant to reoxidation. Under oxic conditions, sulfidation is shown to enhance heterogeneous catalytic oxidation of contaminants. These net effects of sulfidation on contaminant removal by iron-based materials may substantially improve their practical utility for water treatment and remediation of contaminated groundwater.
- MeSH
- Water Pollutants, Chemical MeSH
- Water Purification * MeSH
- Halogenation MeSH
- Groundwater MeSH
- Sulfides MeSH
- Iron * MeSH
- Publication type
- Journal Article MeSH
- Review MeSH
ISCO using activated sodium persulphate is a widely used technology for treating chlorinated solvent source zones. In sensitive areas, however, high groundwater sulphate concentrations following treatment may be a drawback. In situ biogeochemical transformation, a technology that degrades contaminants via reduced iron minerals formed by microbial activity, offers a potential solution for such sites, the bioreduction of sulphate and production of iron sulphides that abiotically degrade chlorinated ethenes acting as a secondary technology following ISCO. This study assesses this approach in the field using hydrochemical and molecular tools, solid phase analysis and geochemical modelling. Following a neutralisation and bioaugmentation, favourable conditions for iron- and sulphate-reducers were created, resulting in a remarkable increase in their relative abundance. The abundance of dechlorinating bacteria (Dehalococcoides mccartyi, Dehalobacter sp. and Desulfitobacterium spp.) remained low throughout this process. The activity of iron- and sulphate-reducers was further stimulated through application of magnetite plus starch and microiron plus starch, resulting in an increase in ferrous iron concentration (from
- MeSH
- Water Pollutants, Chemical analysis metabolism MeSH
- Chlorine metabolism MeSH
- Chloroflexi metabolism MeSH
- Water Purification methods MeSH
- Desulfitobacterium metabolism MeSH
- Ethylenes metabolism MeSH
- Halogenation MeSH
- Oxidation-Reduction MeSH
- Peptococcaceae metabolism MeSH
- Groundwater analysis chemistry microbiology MeSH
- Environmental Restoration and Remediation methods MeSH
- Solvents metabolism MeSH
- Sulfates metabolism MeSH
- Sodium Compounds MeSH
- Tetrachloroethylene analysis metabolism MeSH
- Trichloroethylene analysis metabolism MeSH
- Iron metabolism MeSH
- Publication type
- Journal Article MeSH
- Geographicals
- Czech Republic MeSH
The removal efficiencies and the kinetics of disinfection byproducts (DBPs) were studied in six greenhouse laboratory-scale SSF CWs. Cattail (Typha latifolia) and its litter (collected from the aboveground samples of cattail in autumn) were used as a potential phytoremediation technology and as a primary substrate, respectively, for DBP removal. Results showed that most of the 11 DBPs (except chloroform and 1, 1-dichloropropanone) were efficiently removed (>90%) in six SSF CWs with hydraulic retention time of 5 d and there were no significant differences among the systems. Under the batch mode, the removal of DBPs in SSF CWs followed first-order kinetics with half-lives of 1.0-770.2 h. As a primary DBP in wastewater effluent, removal efficiencies for chloroform were higher in planted systems than in unplanted ones and plant uptake accounted for more than 23.8% of the removal. Plant litter greatly enhanced the removal of trihalomethanes (THMs) by supplying primary substrates and reducing conditions, and the formation of dichloromethane supported the anaerobic biodegradation of THMs via reductive dechlorination in SSF CWs. Trichloroacetonitrile was completely removed within 10 h in each system and hydrolysis was considered to be the dominant process as there was a rapid formation of the hydrolysis byproduct, trichloroacetamide.
- MeSH
- Bacteria, Anaerobic metabolism MeSH
- Biodegradation, Environmental MeSH
- Water Pollutants, Chemical analysis metabolism MeSH
- Water Purification methods MeSH
- Disinfection methods MeSH
- Kinetics MeSH
- Wetlands * MeSH
- Waste Products analysis MeSH
- Typhaceae MeSH
- Groundwater chemistry MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Cis-1,2-dichloroethylene (cDCE), which is a common hazardous compound, often accumulates during incomplete reductive dechlorination of higher chlorinated ethenes (CEs) at contaminated sites. Simple monoaromatics, such as toluene and phenol, have been proven to induce biotransformation of cDCE in microbial communities incapable of cDCE degradation in the absence of other carbon sources. The goal of this microcosm-based laboratory study was to discover non-toxic natural monoaromatic secondary plant metabolites (SPMEs) that could enhance cDCE degradation in a similar manner to toluene and phenol. Eight SPMEs were selected on the basis of their monoaromatic molecular structure and widespread occurrence in nature. The suitability of the SPMEs chosen to support bacterial growth and to promote cDCE degradation was evaluated in aerobic microbial cultures enriched from cDCE-contaminated soil in the presence of each SPME tested and cDCE. Significant cDCE depletions were achieved in cultures enriched on acetophenone, phenethyl alcohol, p-hydroxybenzoic acid and trans-cinnamic acid. 16S rRNA gene sequence analysis of each microbial community revealed ubiquitous enrichment of bacteria affiliated with the genera Cupriavidus, Rhodococcus, Burkholderia, Acinetobacter and Pseudomonas. Our results provide further confirmation of the previously stated secondary compound hypothesis that plant metabolites released into the rhizosphere can trigger biodegradation of environmental pollutants, including cDCE.
- MeSH
- Acetophenones metabolism MeSH
- Aerobiosis MeSH
- Bacteria genetics metabolism MeSH
- Biodegradation, Environmental MeSH
- Cinnamates metabolism MeSH
- Dichloroethylenes metabolism MeSH
- Phenylethyl Alcohol metabolism MeSH
- Phenols metabolism MeSH
- Phylogeny MeSH
- Hydroxybenzoates metabolism MeSH
- Soil Pollutants metabolism MeSH
- Microbial Consortia genetics MeSH
- Soil Microbiology MeSH
- RNA, Ribosomal, 16S MeSH
- Plants metabolism MeSH
- Secondary Metabolism MeSH
- Toluene metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
A low-permeability locality with heterogeneous geology contaminated primarily by tetrachloroethene (PCE) present partially in the free phase in the unsaturated zone was treated on a pilot scale via direct push pneumatic fracturing combined with the hydraulic delivery of a remediation suspension consisting of milled iron, sulphidated nanosized zerovalent iron and sand in guar gum solution. Afterwards, a whey solution was injected into the fractures as a carbon source for bacteria. The unsaturated and saturated zones were treated. Long-term monitoring of the groundwater revealed that the abiotic reduction of PCE and trichloroethene was the dominant remediation processes for several months after the injections. A complex microbial consortium was developed that was capable of effective, long-term chlorinated ethenes (ClE) dechlorination. The consortium consisted mainly of Dehalococcoides but also of other anaerobic bacterial strains capable of partial dechlorination of ClE, including the sulphate-reducing bacteria; Geobacter and Desulfitobacterium. The average chlorine number in the groundwater decreased from 3.65 to 1.38 within 2.5 years after the injections, while the average ClE concentration increased from 13.5 to 31.5 mgL-1 because of the substantial acceleration of the ClE mass-transfer to the groundwater caused by the treatment. The remediation processes remained fully active for 2.5 years.
Polychlorinated biphenyl (PCB) organohalide-respiring communities from the efflux channel of a former Delor manufacturer in Eastern Slovakia were assessed using metagenomic, statistical and cultivation-adapted approaches. Multivariate analysis of environmental factors together with terminal restriction fragment length polymorphisms of the bacterial communities in the primary sediments revealed both temporal and spatial heterogeneity in the distribution of microbial populations, which reflects the dynamic pattern of contamination and altered conditions for biodegradation activity along the channel. Anaerobic microcosms were developed from eight sediments sampled along the channel, where high concentrations of PCBs - from 6.6 to 136mg/kg dry weight, were measured. PCB dehalorespiring activity, congruent with changes in the microbial composition in all microcosms, was detected. After 10 months of cultivation, the divergently evolved consortia achieved up to 35.9 percent reduction of the total PCB concentration. Phylogenetic-analysis of the active Chloroflexi-related organohalide-respiring bacteria by partial sequencing of 16S rRNA genes in cDNA from microcosms with the highest PCB dechlorination activity revealed diverse and unique complexity of the populations. The predominant organohalide respirers were either affiliated with Dehalococcoides sp. and Dehalococcoides-like group (DLG) organisms or were composed of currently unknown distant clades of DLG bacteria. The present study should encourage researchers to explore the full potential of the indigenous PCB dechlorinating populations to develop effective bioremediation approaches that can perform the complete mineralization of PCBs in polluted environments.
- MeSH
- Bacteria, Anaerobic classification isolation & purification metabolism MeSH
- RNA, Bacterial genetics MeSH
- Biodegradation, Environmental MeSH
- Water Pollutants, Chemical analysis MeSH
- Chloroflexi isolation & purification metabolism MeSH
- DNA, Bacterial genetics MeSH
- Phylogeny MeSH
- Geologic Sediments chemistry microbiology MeSH
- Halogenation MeSH
- Cloning, Molecular MeSH
- Hydrogen-Ion Concentration MeSH
- Microbial Consortia * MeSH
- Environmental Monitoring MeSH
- Multivariate Analysis MeSH
- Polychlorinated Biphenyls analysis MeSH
- RNA, Ribosomal, 16S genetics MeSH
- Sequence Analysis, DNA MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Geographicals
- Slovakia MeSH
