DE WINDT, Wim (Schoolstraat 44, Sint-amandsberg, BE-9040, BE)
MARIAGE, Pierre-Antoine (GALACTIC SA, Place d'Escanaffles 23, Escanaffles, BE-7760, BE)
GALACTIC SA (Place d'Escanaffles 23, Escanaffles, BE-7760, BE)
LAKAYE, Frédéric (BIOREM ENGINEERING SARL, Avenue de la Concorde 847, Stella Plage, FR-62780, FR)
DE WINDT, Wim (Schoolstraat 44, Sint-amandsberg, BE-9040, BE)
MARIAGE, Pierre-Antoine (GALACTIC SA, Place d'Escanaffles 23, Escanaffles, BE-7760, BE)
| Claims 1. Remediation composition, having catalytic dehydrohalogenation properties, for contaminated soil and sediments, which comprises a mixture of slurry of a biodegradable polymer dissolved in a biodegradable solvent and a powder of zerovalent nano particles of metal having catalytic hydrogenation properties, dispersed therein. 2. Remediation composition according to claim 1 wherein the biodegradable polymer is a polyester of hydrocarboxylic acid and preferably lactic acid. 3. Remediation composition according to claims 1 or 2 wherein the biodegradable solvent is selected from ester of lactic acid, and preferably ethyllactate . 4. Remediation composition according claims 1 to 3 wherein the metal is selected among metals of Group VI to VIII. 5. Remediation composition according to claim 4, wherein the metal is preferably selected from Pd, Ni, Pt and Rh. 6. Remediation composition according to claims 1 to 5, wherein the zerovalent nano particles of metal have a size comprised between lnm and 500 nm. 7. Process for the catalytic dehydrohalogenation of PCB and other contaminants in soil and sediments which comprises the steps of : Preparing a remediation composition under the form of a slurry, as described in any one of claims 1 to 6 ; Injecting or pumping said remediation composition into the soil and sediments Achieving the biodegradation of the biodegradable polymer present in the slurry of remediation composition so that hydrogen is generated through enzymatic reaction while simultaneously zerovalent metal nano particles are dispersed in soil and sediment to be treated Achieving dehydrohalogenation at temperature comprised between 0° and 600C - Recovering the treated soil substantially freed from contaminants. 8. Process according to claim 7, wherein the powder of zerovalent metal nano particles, as described in any one of claims 1 to 6 is obtained by : Fermenting of Shewanella in the presence of a C-source and salt of metal having catalytic hydrogenation properties ; Achieving reduction of said metal salt in the presence of an electron donor at ambiant temperature by incubation ; Recovering the cells containing the zerovalent metal nano particles Processing the so-recovered cells into a powder |
Domain of the invention
The present invention provides for a remediation composition for injection into environmental substances such as groundwater, soil material or underwater sediment. More particularly the invention relates to such remediation composition comprising a mixture in a solvent of biologically degradable monomers, oligomers and polymers of hydroxycarbolylic acid which are combined with catalytic hydrogenation zero valent metallic nanoparticles for treatment of recalcitrant environmental contaminants contained in sediments and soils such as PCB, metals and volatiles organochlorines .
The present invention also relates to a process for the treatment of contaminated soils and sediments with such remediation composition as well as a process to prepare such remediation composition.
Prior art
When environmental substances are contaminated with low or high concentrations of halosubstituted organic molecules, particularly polychlorinated biphenyl molecules, or with certain metals, treatment with known remediation composition does not result in decontamination of these substances under ambient environmental conditions even in the course of a few months, depending on the nature and concentration level of the contaminants. It is also known in the art that such type of treatment needs to excavate the soil or sediment to treat it ex-situ by heating and stirring. These treatments are not generally operated under ambient environmental conditions and in-situ. The composition's mode of action is a microbiologically driven physico- chemical catalytic degradation of halosubstituted organic molecules .
It has already been described in the prior art biodegradable compositions and formulations for environmental remediation purposes, often in the form of slow-release substrates that release organic acids slowly over time, as for example in US Patent 6,420,594 which describes a composition that releases hydroxy acid slowly over time, and Wood and Huang (2006) which describe bioremediation of chlorinated solvent using a hydrogen release compound. The preferred use of the compositions described in the prior art is for bioremediation purposes, wherein they provide a time-release source of lactic acid to support growth and reductive activity of microbes present in a system or medium, such as an aquifer, bioreactor, soil, industrial process, wastestream, body of water, river or well. The microbes use the reducing equivalents, such as short-chain organic acid or molecular hydrogen, originating from the depolymerized composition, as a source of energy to drive the metabolic conversion of compounds which are capable of being reduced, such as nitrogen-containing organic compounds, oxygen-containing organic compounds, polyaromatic hydrocarbons, and halogen-containing organic compounds. All of these examples are aimed at stimulating a (micro-) biological action as an end-point in the reaction chain. Although various studies have reported efficient degradation of pollutants by microorganisms due to metabolic pathways and degradative genes responsible for enzyme production, biosorption, co-metabolism, bioaccumulation, and biotransformation (Ju, 1997 and Davis, 2002), it is however of common knowledge that biological degradation is not always possible. Limitations exist in the case of toxic components that are very persistent to biological degradation. For example, it is well known from the art that only a very limited number of polychlorinated biphenyl congeners are susceptible for (micro-) biological degradation. There is a wide variety of the rate, extent and specificity towards flanked and unflanked meta, para and ortho microbial dechlorinations (reviewed by Wiegel and Wu, 2000) .
Furthermore, it is also of common knowledge that biological degradation may result in very long removal processes for the contaminants or even in certain cases biological degradation may not be observed, due to limited mass transfer, limited biological activity, limited bio-availability of the contaminants, toxicity of the environment, non-ideal physicochemical parameters for the conversion (such as redox potential, pH, temperature, ... ) and so on .
It is also known from the art to use, catalytic zero valent iron particles for chemical degradation of environmental contaminants in soil, but such particles need to be protected from unwanted physicochemical processes during the conversion of reactants by contacting these particles by a polymer or by polymers. For that purpose, we noted that it is described in EP 1,151,807 that a hydrophilic binder can be coated onto the surface of fine iron particles to protect the surface from oxidation, and other processes. In all of these processes, it is the purpose of the polymer to protect the catalyst but not take part in the catalytic reaction. While it is generally also known that zero valent iron is a catalyst for dehalogenation organic haloginated molecules at elevated temperatures of 300 0 C (Varnasi et al, 2007). Chuang et al . (1995) observed that reductive dechlorination of PCBs using Fe 0 as reductant was only happening at 400 0 C, whereas there was no dechlorination at room temperature. It is sometimes described that rapid reductive dechlorination can be achieved while using bimetallic materials, such as palladized FeO (Pd/Fe) as a reductant (Korte et al . , 1997). But of course, bimetallic catalyst are needed that is known as not being an easy way to solve the decontamination problem, since it involves incomplete decontamination of the soil and sediments associated to the well known difficulty of homogeneously distribution of the Pd/Fe catalyst. On top of that, it is also well known that the redox potential cannot be controlled by the Pd/Fe catalyst.
It is therefore a need to have a remediation composition which enable to remedy the drawbacks of the prior art, hereabove mentioned.
An object of the present invention is to provide a remediation composition to remedy these drawbacks in order to improve remediation of soils and contaminants. Another object of the invention is to provide a remediation composition for the in situ decontamination of soil and sediments contaminated with halogenated organic molecules.
Another object of the present invention is to provide a remediation composition containing only one catalytic metal and in the absence of iron particles.
Still another object of the present invention is to use as mode of action of the remediation composition, a microbiologically-driven physic-chemical catalytic degradation of halosubstituted organic molecules.
Still another object of the present invention is a process using such remediation composition to achieve a complete decontamination of soils and sediments in reasonable times.
A further object is also a process to prepare such remediation composition.
Summary of the invention
The Applicant has now unexpectedly found that by using as remediation composition a product consisting of a mixture of biodegradable, viscous, semi-polar polymers, oligomers and monomers of carboxylic acid dissolved in a biodegradable solvent containing a limited amount of a well-dispersed solid metallic hydrogenation catalyst selected from the group comprising metals of Group VIb or Group VIIIb, and more particularly platinum or palladium where the catalytic particles are either nano- or micron- sized, halogenated organic molecules, and especially PCB' s can be dechlorinated to hydrocarbon that can be further biodegraded by soil's or sediment's microflora. The mode of action of this remediation composition is by a combined action of microbiological metabolic conversion of the biodegradable polymers, oligomers, monomers and solvent and chemical catalytic conversion of halogenated molecules on the metallic catalyst without the need of the presence of iron as a source of electrons or hydrogen. The redox potential in the soil or sediment where such a product is injected or mixed is reduced to negative values by the presence of biodegradable components, enhancing the reductive dehalogenation driven by the catalyst. Furthermore, during metabolic conversions of the biodegradable part of the remediation composition, electrons are released, which are combined with the halogenated organic molecules in order to be reduced on the catalyst surface. Hence, the biodegradable polymer is then metabolized by indigenous bacteria to produce hydrogen and to create ideal redox conditions for reductive dechlorination.
According to the present invention the remediation composition is injected in low concentrations in-situ under the form of a liquid, pumpable composition, in order to bring about complete decontamination under ambient environmental conditions (redox potential, temperature, pH and other environmental parameters) .
Description of the invention
More specifically, the remediation composition of the invention is a mixture consisting of:
(i) a polyester of hydrocarboxylic acid, which may also contain oligomers and monomers of said polyester
(ii) a biodegradable solvent; said polyester of hydrocarboxylic acid is preferentially lactic acid, while the biodegradable solvent is preferentially an ester of said hydrocarboxylic acid, and particularly ethylactate when polyester of lactic acid is selected,
(iii) nanoparticles of a metal of Group VIb or VIIIb, particularly palladium, as hydrogenation catalyst which are then easily dispersed in the mixture of polyester and solvent
The biodegradable solvent is generally used in a concentration in the range of in between 2 % and 50 % (w/w) , and preferably in a range between 7 and 15% (w/w) This solvent has two functions: i) to extract the contaminating compounds (PCBs and other) from the soil or sediment matrix and liberate these contaminants for catalytic degradation, and ii) to serve as a source of hydrogen through biodegradation .
To illustrate this second function, hydrogen release, we use the example of ethyl lactate:
While the biodegradable solvent may be used alone, it may also be used in conjunction with a surfactant, to allow penetration of the solvent into the core of the contaminated aggregates.
The Applicant have surprisingly found that such remediation composition was a performant reductive catalyst for polychlorinated biphenyls and other recalcitrant environmental contaminants when mixed into water-submerged or non-submerged sediment of a lake or when mixed into soil samples or sediment samples in the presence or absence of air. With the remediation composition of the invention it was unexpectedly found that the chlorinated molecules are completely dechlorinated to hydrocarbons that can be further degraded biocatalytically . The catalytic remediation composition (polymer mixture and nanoparticles) of the invention has a viscous character and can be transported by pumping action or gravity. The catalytic remediation composition is heavier than water and will remain mixed into the sediment when a water column is present above it. Due to the presence of a semi-polar ester of lactic acid with an alcohol such as ethyl lactate in the product, hydrophobic contaminants such as polychlorinated biphenyls, which are strongly adsorbed to organic material inside of the sediment matrix, can be desorbed and made available for reductive dechlorination inside of the product matrix.
The present invention also comprises a process for the catalytic dehydrohalogenation of PCB and other contaminants in soils and sediments which comprises the steps of:
Preparing a remediation agent under the form of a slurry comprising a biodegradable polymer dissoved in a solvent and a powder of zerovalent Pd or Pt nanoparticles dispersed therein ;
Injecting or pumping the remediation agent into the soil and sediments
Achieving the biodegradation of the biodegradable polymer present in the slurry of remediation agent so that hydrogen is generated through enzymatic reaction while simultaneously zerovalent Pd or Pt nano particles are dispersed in soil and sediment to be treated Achieving dehydrohalogenation at temperature comprised between 0° and 60 0 C
Recovering the treated soil substantially freed from contaminants.
The present invention also comprise a process to prepare the remediation catalytic composition which comprises the steps of preparing the powder of zerovalent Pd or Pt nano particles is obtained by :
Fermenting of Shewanella in the presence of a
C-source and salt of Pd or Pt
Achieving reduction of the Pd or Pt salt in the presence of an electron donor at ambiant temperature by incubation
Recovering the cells containing the zerovalent Pd or Pt nano particles
Processing the so-recovered cells into a powderAccording to an embodiment of the process of the present invention, the remediation composition is mixed and injected at ambient temperature into a contaminated soil or sediment, the polymer is partially hydrolyzed into monomers and monomers are oxidized into end-products by enzymatic (biocatalytic) action from the autochtonous microbial population present inside the sediment or soil matrix. The hydrogen thus generated through the enzymatic reaction, then reacts with the contaminant, such as a polychlorinated biphenyl molecule, through a reductive halosubstitution or other reductive reaction mechanism catalyzed at ambient temperatures by the hydrogenation catalyst, constituted by the nanoparticles of metal selected from Group VIb or VIIIb, generally Pd, Ni, Pt, Rh, and particularly Pd or Pt, dispersed in small quantities inside of the catalytic composition. By small quantities, it is understood quantities comprised between
(10 mg/kg mixture) and (10000 mg/kg mixture) . The powder of zero valent nanoparticles of Pd or Pt may be prepared by a method described in "De Windt et al . 2005". It has been found that a continuous significant decrease of PCB concentrations over time inside of sediments treated with this remediation composition reaching a reduction between 69% and 98% after 53 days. Hence, the Applicant has unexpectedly found that the composition lowers the redox potential of the surrounding environments to values below 0 mV, and typically to values between -100 mV and -400 mV. An advantage of the process of the present invention is there is no need for external hydrogen source for the decontamination, since the hydrogen is formed out of the product itself by biocatalysis .
The catalyst is preferably a heterogeneous catalyst, which is in separate phase than the contaminants (i.e. a solid phase catalyst and contaminants in a gaseous or liquid phase) . This catalyst is a usual hydrogenation catalyst that catalyzes reactions at low to medium range temperatures (0-60 0 C), such as metals of Group VIb or VIIIb and particularly Pt or Pd; while bimetallic or trimetallic alloys of precious metals may be used, but with well known drawback of non-homogeneous distribution in the remediation composition. According to the process of the invention, the contaminants to be degraded combined with molecular hydrogen can be reduced at ambient temperature at the surface of the hydrogenation catalyst through a reductive reaction, for example a hydrodechlorination reaction. The low to medium temperature range allows the system to perform its function of decontamination under ambient environmental temperature ranges. The catalyst is present as a component of the described composition, in a concentration between 10 and 10,000 mg/kg mixture (dry weight) . This composition is mixed into the contaminated sediment or soil in a concentration of about 10 to 10,000 μg of catalyst/kg sediment or soil (dry weight) .
Some PCB congeners are more resistent towards Pd- catalyzed hydrodechlorination, as is evidenced by the results for PCB 118 removal.
Further, the mixture of oligomers and polymers of hydro carboxylic acid can be produced through usual condensation reactions at industrial scale; according to the present invention, it is preferred to use a polylactic acid polymer in admixture with its oligomer and monomer; it is common knowledge that polylactic acid is a well-known component in food and feed market applications .
The Invention furthermore brings the following advantages to the field of environmental remediation: (1) limited need for excavation or dredging of substances, since the composition is injected in situ; (2) limited need for transport of substances, for the same reason; (3) limited need for landfilling of contaminated substances, since a technology is proposed to decontaminate these substances to below threshold levels suggested by national environmental authorities; (4) limited energy consumption for the decontamination, since no heating or transportation is required; (5) limited risk since end- concentrations of contaminants after treatment by the method described in this invention are low, and since the reaction products are biodegradable and environmentally benign molecules
Detailed Description of the Preferred Embodiments
Example 1: Production of the remediation composition
A remediation composition was produced by mixing at temperature of 60 0 C, 980 kg of polylactic acid of degry of polymerization about 5 units, obtained by polycondensation of lactic acid at 97% with 158 kg of ethyl-lactate 98.5% as biodegrable solvent and 120 kg of lactic acid at 97%. The temperature was decreased at 25°C before the drumming. The catalytic palladium nanoparticles were produced by a protocol described in "De Windt et al . , 2005". The palladium nanoparticles were examined by X-Ray Diffraction analysis and Scanning and Transmission Electron Microscopy, and found to exist out of individual, non-agglomerated metallic PdO nanoparticles with a size between 1 and 50 nm, on average 10 nm.
This palladium suspension was then further processed by spray-drying and atomized into a powder. Spray drying was done with a Niro Production Minor atomizer with an inlet temperature of 180 0 C and an outlet temperature of 60 0 C. After the atomization process, a palladium containing powder was obtained.
The powder was mixed and homogenized into the remediation composition by mixing in a heated mixing tank with anchor agitator. An equivalent of 250 mg/kg of palladium was mixed into the remediation composition liquid to result in the final dispersion . The product was heated to maximum 30 0 C in order to limit viscosity and to allow good dispersion of the nanopowder into the liquid.
Example 2: Pilot-scale testing with in situ PCB degradation by injection of catalytically active remediation composition into sediment In Table 1, results are shown for the in situ application of the catalytic remediation composition of this invention, in PCB contaminated sediment. The catalytic remediation composition as prepared in Example 1 was applied in a concentration of 3 g/kg sediment dry weight in the top 15 cm of contaminated sediment by mechanical mixing .
Three sediment zones were treated: zone S8 and zone S9, two zones which served as independent replicates, and zone C which served as a control zone where only the polymeric compound comprising polylactic acid and ethyl lactate as prepared in Example 1 was injected without the presence of the catalytic particles.
The results in Table 1 show a continuous significant decrease of indicator PCB concentrations inside of the treated sediments S8 and S9 over time. Fifty three days after the initial application, between 69% and 98% of the indicator PCB congeners had been removed from the sediment, resulting in residual concentrations as low as 36μg/kg. In the control zone, no significant reduction of
PCB congeners was observed, although some of lower chlorinated PCBs may have been dechlorinated by the increased microbiological activity in the sediment due to addition of carbon source.
In all of the zones, the redox potential dropped to values below -100 mV, and even a value of -400 mV was observed. These results indicate the redox-lowering characteristic of the micture of biodegradable polymers, oligomers, monomers and solvent.
Table 1: Results of treatment with 5 g/kg of the remediation composition in Zone Marnage area, from 10
September until 13 november (S8 and S9) and from treatment with the mixture in Zone Control (C) area, from
11 September until 8 november (C) . Concentrations of the sum of 7 indicator PCBs are expressed in function of time (days) after treatment, in μg PCB/kg sediment dry weight.
Cone ( dw) 7
Ballschmitter
Day (μg/kg)
Zone S8 0 1600
13 1148,7
33 679
53 36
Zone S9 0 440
13 226,4
33 147
53 137
Zone C 0 269,0
10 210, 0
23 273,8
48 202,0