Long term monitoring of trichloroethylene degradation indicator parameters using sensors

Past operations at Savannah River Site (SRS) have resulted in significant amount of groundwater contamination with trichloroethylene. Natural attenuation of chlorinated solvents via reductive dechlorination is one of the most important processes occurring at SRS, which requires monitoring. Many traditional monitoring techniques require manual sampling and analysis at an onsite or offsite laboratory, which is costly and time consuming. Therefore the need for a system, which can accurately and cost-effectively conduct real-time analysis using automated sensors, is important. There are several characteristics of groundwater like pH, ORP, conductivity and chloride that may be monitored to assess the TCE degradation. To evaluate the effectiveness of the sensors to measure the required parameters, a series of tests were conducted by varying the parameters that can affect the performance of the sensors. Interference by the other ions is neither strong nor permanent but can cause interference during measurement. So a thorough testing of the ISE is necessary to obtain reliable data

DEGRADATION OF 1,2-DICHLOROETHANE WITH NANO-SCALE ZERO VALENT IRON PARTICLES

The application of nanoscale zero-valent iron particles (nZVI) for abiotic remediation of chlorinated compounds is proving among the most viable technologies for environmental remediation. However, although most polychlorinated C2 compounds are easily dechlorinated by nZVI, 1,2-dichloroethane (1,2-DCA), has shown resistance to dechlorination by this nanomaterial. The present contribution shows how a combination of a catalyst and nZVI together with the addition of a hydrogen donor can be used to; achieve dechlorination of 1,2-DCA under aqueous conditions similar to those found in the field. The best results for dechlorination were observed using formic acid as a H2 donor and Pd as catalyst doped onto CMC stabilized nanoscale zero-valent iron particles at a temperature of 45°C. This leads to significant degradation (close to 18%) of 1,2-DCA at the end of seven days. As degradation products, evolution of ethane and propane were observed from the very first day of reaction

Electrochemical methods for the dechlorination and detection of chilorinated ethenes

Chlorinated ethenes in the environment are dechlorinated by accepting electrons from electron donors found in nature. Such reductive dechlorination forms the basis of this research into remediation and detection of these compounds in the environment. The reducing abilities of one of the strongest electron donors known, tetraki s(dimethylamino)ethylene (TDAE), were used to abiotically simulate reductive dechlorination. TDAE was found to form an electron donor-acceptor complex with tetrachloroethene, and to very rapidly reduce trichloroethene and cis-dichloroethene via removal of the most positive chlorine. Microbiological studies of bacteria utilising chlorinated ethenes in their metabolic systems established that Vitamin B,2 (cyanocobalamm) is of great importance to the dechlorination process, acting as a cofactor for the organism's dehalogenase enzyme. The dechlorination mechanism involves cobalt (I) as the active transition metal in extremely reducing conditions. A series of analytical experiments were undertaken to establish the reductive capability of cobalt (I), both in a simple cobalt salt and in vitamin 812, under reducing conditions. Molasses was used as a hydrogen source and an electron donor in simulation of the biotic process. Results indicate that Vitamin B12 is more successful at dechlorination than simple cobalt salts, but neither system presents an ideal method for commercial dechlorination based on current experimental process. Remediation of environmental tetra- and trichloroethene contamination would be improved by the development of on-line sensors. Glutathione, an intracellular sulfhydryl tripeptide comprising glutamyl, cysteinyl, and glycinyl, bonds with alkyl halides via the thiol group in its cysteine moeity, and displays characteristic redox behaviour, presenting an ideal prospective system for development of a relevant biosensor. Potentiometric and amperometric studies have been carried out to determine the efficacy of the proposed system; results indicate that response to and selectivity for alkyl halides at environmental concentrations can be achieved

Electron donor and acceptor utilization by halorespiring bacteria

Chlorinated ethenes are widespread soil and groundwater pollutants. Over the last 2 decades a lot of effort has been made to understand the degradation mechanisms for these pollutants. In the early eighties reduction of tetrachloroethene (PCE) was observed in anaerobic soil samples, which was shown to be mediated by microorganisms. The first microorganism able to couple the anaerobic reduction of PCE to growth in a process called halorespiration (alternative terms are chlororespiration, chloridogenesis or dehalorespiration) was isolated in 1993. Since then, about 15 bacteria able to reduce PCE metabolically have been isolated. This thesis describes research on different aspects influencing the reductive dechlorination of chlorinated ethenes by anaerobic halorespiring bacteria.A new halorespiring bacterium is described in chapter 1. This bacterium, Sulfurospirillum halorespirans PCE-M2, was isolated from a polluted soil near Rotterdam harbor. Strain PCE-M2 is a metabolically versatile bacterium able to use a variety of electron acceptors and electron donors. This new strain is closely related to Dehalospirillum multivorans, but more detailed studies indicated that strain PCE-M2 belongs to the genus Sulfurospirillum, It also appeared that Dehalospirillum multivorans had to be included in this genus. Consequently, it was reclassified to Sulfurospirillum multivorans.Members of the genus Sulfurospirillum were originally known for their sulphur, selenate and arsenate respiring properties. Therefore, we screened a number of halorespiring and related bacteria for their metal reducing properties (Chapter 2). It was shown that the reduction of metals such as ferric iron, manganese, selenate and arsenate is a common property amongst halorespiring bacteria. We also investigated the quinone reducing and oxidizing abilities. AU tested bacteria are able to reduce AQDS7 a quinone-bearing humic acid analogue. Some of the tested bacteria (Desulfitobacterium hafniense DP7, Sulfurospirillum barnesii, S. deleyianum and S. arsenophilum) are also able to oxidize AEbQDS coupled to nitrate reduction.The influence of some alternative electron acceptors on the reductive dechlorination is discussed in chapter 3. Sulfurospirillum halorespirans preferably reduces nitrate (to ammonium) and then PCE. In contrast, Sulfurospirillum multivorans reduces nitrate only to nitrite, and PCE reduction is blocked irreversibly in the presence of nitrate. In Desulfitobacterium frappieri TCEl, PCE and nitrate are reduced simultaneously in excess of electron donor. Under electron donor limitation PCE reduction was inhibited (Gerritse Bt al., AppI. Environ. Microbiol. 1999, 65, 5212-5221). The influence of nitrate on the reduction of chlorinated ethenes by halorespiring bacteria differs between species and may also depend on the availability of electron donor. Sulphate, which is not used as electron acceptor by chlorinated ethenes respiring bacteria is often found at polluted sites. We have tested the influence of sulphate on halorespiring bacteria (Chapter 3). It appeared that sulphate does not influence these microorganisms. Sulphite however, a possible electron acceptor for Desulfitobacterium species, inhibits the reduction of PCE. This inhibition may be the result of a chemical interaction between sulphite and cobalamine containing dehalogenases. We also studied the adaptation of Sulfurospirillum halorespirans PCE-M2 to different alternative electron acceptors (Chapter 3). Both nitrate and arsenate are reduced by cells pre-grown on PCE, nitrate, arsenate and selenate. This indicates that the enzymes responsible for the reduction of nitrate and arsenate are constitutiveiy present in S, halorespirans. In contrast, PCE and selenate are only reduced by cells pre-grown on PCE or selenate respectively.Halorespiring bacteria have a high affinity for hydrogen (H2). H2 may even be the most important electron donor for these organisms in natural environments. We have studied H2^thresh0ld concentrations in pure cultures of halorespiring bacteria (Chapter 4). H2-threshold values between 0.05 and 0.08 nM under PCE-reducing and nitrate-reducing conditions were measured. Furthermore, we measured H2 concentrations at a field site polluted with chlorinated ethenes. PCE and trichloroethene (TCE) reduction can occur at H2 concentrations below 1 nM. However, for the reduction of lower chlorinated ethenes a higher H2 concentration seems to be required.Accumulation of cis-l,2-dichloroethene (cis-l,2-DCE) and vinyl chloride (VC) under anaerobic conditions is often observed. The enrichment of two cultures (DCE-I and DCE-2) able to reduce VC at relative high rates is described in chapter 5. Cis-l,2-DCE is reduced at approximately 20-30 fold lower rates than VC. Our results suggest that these two enrichment cultures are able to gain energy from the reduction of lower chlorinated ethenes. When we performed these studies, no microorganisms had been isolated able to grow by the reduction of VC. However, recently He et al. (Nature. 2003, 424, 62-65) isolated Dehalococcoides strain BAVl, which is able to couple the reduction of DCE and VC to ethene to growth.Finally, the results obtained are combined with available literature data to obtain a state-of-the-art on chlorinated ethenes respiring microorganisms, the influence of alternative electron acceptors on these microorganisms and the role of H3 and H?-threshold values in halorespiration

The Role of Hydroxyl Surface Groups on the Dechlorination Activity of Iron Bearing Nanoparticles

Dechlorination of groundwater contaminants by nano zero valent iron (nZVI) has been successfully utilized for a wide range of halogenated hydrocarbons. At the same time incorporation of noble metals such as Pd to nZVI has shown to result in a catalytic effect in the dechlorination reaction. Despite the extensive research to improve nZVI reactivity, 1,2-DCA remains recalcitrant to dechlorination by nZVI. These dechlorination processes are known to occur as a surface mediated reactions. However, a complete understanding of the surface composition and the role of the species present on the nZVI surface in the dechlorination adsorption/reaction mechanisms still needs to be achieved. -FeOOH, -Fe2O3, Fe2O3 are the most frequently observed species present in the surface of the nZVI particles. In this thesis, the mechanisms through which 1,2-DCA and TCE interact with these iron species are studied by means of in situ spectroscopic techniques. Experimental results demonstrate that surface hydroxyl groups play a critical role in the adsorption processes and that interaction of both 1,2 DCA and TCE with these hydroxyl groups results in the formation of an ethoxide surface complex. From temperature program experiments it was found that surface morphology, crystalline structure and surface speciation can lead to the existence of nonequivalent adsorption sites, with different chemical environments. This surface heterogeneity has a direct effect in the adsorption/reaction mechanisms, resulting in the formation of different observed desorption products. A reaction mechanism is proposed to rationalize all these observations

Sanační technologie s využitím molekulárně- genetických analýz

Předkládaná dizertační práce řešila dva hlavní cíle. Prvním byl monitoring a hodnocení bioremediačních procesů in situ pomocí molekulárně genetických metod. Druhým cílem byla příprava nanovlákených nosičů biomasy, které by měly sloužit k odběru a izolaci DNA ze vzorků získaných na reálné lokalitě. Výzkum byl cílený na problematiku chlorovaných ethenů patřících mezi nejčastější kontaminanty s prokázaným negativním vlivem na životní prostředí i lidské zdraví.Kombinace chemické a biologické sanace patří k častým strategiím odstranění chlorovaných ethenů. V disertační práci byl zkoumán vliv těchto technik na přítomná bakteriální společenstva pomocí molekulárně genetických metod. Použité markery zahrnovaly 16S rRNA gen specifických degradérů i geny pro reduktivní dehalogenázy. Dále byly testovány markery charakterizující denitrifikační a síru redukující bakterie. Monitoring hladin jednotlivých testovaných markerů dovoloval hodnotit průběh a efektivitu probíhajících sanačních procesů.Metody molekulární genetiky spolu s hydrogeochemickými analýzami byly také použité při hodnocení biologických dějů v kvartérním aluviálním podloží nacházejícím se v blízkosti historického zdroje rozsáhlé kontaminace tetrachlorethylenem. Relativní hladiny specifických degradérů byly měřené metodou polymerázové řetězové reakce v reálném čase (real-time PCR). Detailní charakterizace zkoumané lokality, respektive autochtonní mikroflóry, byla prováděná metodou sekvenace nové generace. Výsledky obou metod potvrdily hypotézu zonace aktivní reduktivní dechlorace v souladu s hydrogeochmickými parametry.Druhým cílem dizertační práce bylo vyvinout nanovlákenné nosiče, které by bylo možné opakovaně použít při dlouhodobém sledování kontaminované lokality, protože odběr vzorků podzemních vod, jejich transport a zpracování je komplikovaný. Podobně pravidelný odběr vzorků půdy není možný nejen z důvodu finančních, ale i sporné reprodukovatelnosti. Vyvinuté nanovlákenné nosiče jsou kompaktní, dostatečně malé, snadno přenositelné, a především vhodné pro izolaci DNA. Dlouhodobé testy in situ potvrdily funkčnost pro využití nanovlákenných nosičů pro molekulárně genetické analýzy autochtonní mikroflóry. Jednotlivé varianty nanovlákenných nosičů byly patentovány.This thesis focuses on bioremediation, molecular genetic methods and the preparation of nanofibre carriers for actual microbial community sampling. The research was focused exclusively on chlorinated ethenes with severe negative effects on both the environment and human health. The combination of chemical and biological methods, along with application of Fenton's reagent and enhanced reductive dechlorination, are the most common remediation strategies for removal of chlorinated ethenes. In this thesis study, the influence of such techniques on indigenous bacteria was assessed using a wide spectrum of molecular genetic markers, including the 16S rRNA gene, specific chlorinated ethene degraders and reductive dehalogenase genes, together with sulphate-reducing and denitrifying bacteria. Bioremediation was monitored through the level of individual enzymes or bacterial strains. Molecular genetics and hydrochemical tools were also used to evaluate natural attenuation of chlorinated ethenes in a Quaternary alluvial aquifer located close to a historical source of large-scale tetrachloroethylene contamination. Next generation sequencing of the middle and/or lower zones served as a tool for detailed characterisation. The relative abundance of specific degraders was identified using real-time PCR. The combined results confirm the hypothesis that there is significant potential for reductive dechlorination by natural attenuation.At present, sampling and processing of groundwater for DNA analysis is complicated and influenced by transport and filtration in the laboratory. Regular soil sampling is not always possible due to the financial costs and reproducibility. The aim of this research was to develop a system of nanofibre carriers that could be used repeatedly for long-term monitoring of contaminated localities. The newly developed nanofibre carrier displayed non-preferential growth, is small thus easily transportable, and the material meets the requirement for DNA isolation. Long-term testing in situ proved that the nanofibre carriers are more than suitable for molecular genetic analysis. Individual composition and the arrangement of the nanofibre carriers were patented

Investigation into the Potential Toxicity of Zero-Valent Iron Nanoparticles to a Trichloroethylene-Degrading Groundwater Microbial Community

The microbiological impact of zero-valent iron remediation of groundwater was investigated by exposing a trichloroethylene-degrading anaerobic microbial community to bare and coated iron nanoparticles. Changes in population numbers and metabolic activity were analyzed using qPCR and were compared to those of a blank, negative, and positive control to assess for microbial toxicity. Additionally, these results were compared to those of samples exposed to an equal concentration of iron filings in an attempt to discern the source of toxicity. Statistical analysis revealed that the three iron treatments were equally toxic to total Bacteria and Archaea populations, as compared with the controls. Therefore, toxicity appears to result either from the release of iron ions and the generation of reactive oxygen species, or from alteration of the redox system and the disruption of microbial metabolisms. There does not appear to be a unique nanoparticle-based toxicity

Enhanced Dechlorination of 1,2-Dichloroethane by Coupled Nano Iron-Dithionite Treatment

1,2-dichloroethane (1,2-DCA) is a chlorinated solvent classified as a probable human carcinogen. Due to its extensive industrial applications, widespread contamination and recalcitrance towards abiotic dechlorination, 1,2-DCA remains a challenging compound for the remediation community and one of the great research interests. Batch experiments combining bimetallic or monometallic nZVI (stabilized or non-stabilized) with sodium dithionite were conducted for the degradation of 1,2-DCA. These experiments have yielded up to 92 % degradation of the initial 1,2-DCA concentration over the course of a year. Observed pseudo-first order rate constants (kobs) range from 3.8 x 10-3 to 7.8 x 10-3 day-1. Degradation was also achieved using magnetite and iron sulfide as the metal surface, with kobs values of 6.2 x 10-3 and 4.7 x 10-3 day-1, respectively. Characterization analysis of the nZVI/dithionite nanoparticles shows that zero valent iron as such remains in solution after more than one year of reactivity and that iron sulfide is formed in solution. This novel treatment represents the first nZVI-based formulation to achieve nearly complete degradation of 1,2-DCA