GB2367815A - Clays for treating contaminants - Google Patents

Abstract

A modified inorgano-organoclay or organoclay incorporates reactive intercalates for the chemicorption and immobilitation of organic and inorganic contaminants, the clays supporting the growth of microorganisms in a biofilm capable of bioremediation. The intercalation additives preferably comprise a combination of an aluminium hydroxide polymer, a quaternary ammonium salt, and a transition metal salt. Modified clays treated with a transition metal salt and/or a pillaring agent are also disclosed. Typically, the transition metal salt is ferric chloride and the pillaring agent may comprise a metal hydroxide polymer, oxides of silicon and titanium, or transition metal clusters. A method of treating contaminated material using a modified clay is also claimed.

Description

Title:-"MODIFIED CLAY SUPPORTED BIOFILMS" This invention provides a remedial technology for the treatment of contaminated land, ground water and other contaminated materials. In particular, this invention provides a range of modified pillared organoclays and inorgano-organoclays incorporating reactive intercalates which have the capability to chemically bond with a diverse range of organic, inorganic and heavy metal pollutants. This invention is a further embodiment of a previous patent application appertaining to"modified organoclays" incorporating pillaring agents and other intercalatants (refer to UK patent application No. 9612755.0) in that the stoichiometric addition rates and order of intercalation have been altered to encourage the proliferation of a biofilm on the external surfaces of the clay matrix. It is an embodiment of the invention that an organophilic environment is generated on the external surfaces of the modified pillared clay matrix by stoichiometric treatment with an agent selected from the group consisting of a quaternary ammonium salt and a polar organic compound to form a modified pillared organoclay or inorgano-organoclay having external organophilic properties. The external organophilic environment of the modified clay provides an adsorptive surface for organic pollutants to associate with the external surface of the clay in addition to intercalation as taught in UK patent application No. 9612755.0. It should be noted that this prior invention does not teach biodegradation of pollutants within the clay matrix as the interlamellar spacing is not conducive to incorporation of microbes. The advancement as taught herein facilitates adsorption and subsequent biodegradation of organic pollutants amenable to biodegradation by formation of a biofilm on the external clay surfaces associated with the external organophilic environment. The biodegradation enables the clay to be partially regenerated thereby prolonging the life of the clay for the intended application. It is a further embodiment of the invention that recalcitrant and persistent organic pollutants are absorbed and chemically bonded/immobilised within the internal surfaces of the clay matrix.

Background to Invention The number of contaminated sites and their diverse nature poses a serious threat to the environment and health. Hazardous wastes and other forms of pollution present a similar challenge. There is an identified need to develop cost-effective treatment solutions to environmental problems which have the potential for sustainable application.

There are a number of treatment technology approaches (both abiotic and biotic) which have been developed to address land and ground water contamination.

A commonly employed solution for the disposal of contaminated soils and hazardous wastes is the excavation and removal of the contaminated soils and pre-treatment of hazardous wastes for subsequent disposal at landfill sites. Stabilisation and/or solidification of materials before disposal is an accepted practice for the disposal and control of primarily inorganic contamination. The incorporation of modified organophilic clays enables organically contaminated material (or predominantly inorganic material also contaminated with organic pollutants) of varying hydrophobicity, polarity and molecular structure to be effectively stabilised before disposal.

In a number of countries the landfilling approach is being discouraged (and thereby becoming less economical as an acceptable remedial approach) due to the recent introduction of landfill taxes and other punitive measures intended to encourage the use of alternative technologies.

Consequently, there is an ever-increasing need to develop new and innovative technologies that can be applied in a cost-effective manner for the remediation of contaminated sites and/or hazardous material contaminated with a range of pollutants. This invention provides an advanced modified pillared clay technology which chemically absorbs and immobilises pollutants incorporating an external biofilm for biological mineralisation of organic pollutants amenable to such a process. The technology can effect the permanent reduction in volume, toxicity and mobility of hazardous materials. This advanced technology is a permanent treatment methodology, which essentially detoxifies the pollutants without transferring the problem to another area or to another medium. The addition of a biotic influence ensures that the treatment matrix is potentially regenerative which may offer significant potential advantages over other remediation technologies.

Technical Background Bioremediation of contamination in subsurface environments (in situ) involves the utilisation of microorganisms to convert contaminants and intermediary compounds to less harmful products. Biological treatment of contamination in soils is achieved by enhancing the indigenous microbial population able to degrade the pollutants through the stimulation and management of these communities to such a degree that any remaining concentrations of contaminants and degradation products are below the applicable standard. Ideally, the ultimate goal is to achieve complete mineralisation of the contaminants, that is degradation to carbon dioxide, water and mineral salts.

Soil is a favourable habitat for the existence and proliferation of microorganisms and the numbers found are often far greater than that of freshwater or marine habitats.

The most extensive microbial growth however, takes place on the surfaces of soil particles; a small soil aggregate can have many differing environments. It is this aspect of the technology that is exploited by this invention.

It is difficult to scribe generalised adaptive features to most indigenous soil microorganisms as soil has many differing physiochemical properties. The terrestrial environment contains a great number of ecological niches, which are commonly separated spatially or temporally which may permit occupancy by microorganisms competing for common resources. As a result, a typical community of soil microorganisms may be characterised by robust genetic diversity and therefore, extensive physiological and catabolic capabilities. Due to their diverse enzymatic activities and ubiquitous distribution, microorganisms play a major role in biogeochemical cycling (the movement of materials via biochemical reactions through the global atmosphere). It is the aim of this invention to exploit this natural recycling of elements to achieve efficient and cost-effective remediation of hazardous wastes and contaminated land (either soil or ground water).

Laboratory Treatment Trials Laboratory trials were proved to be effective at substantiating the efficacy of the treatment system in enhancing the degradation rates of priority pollutants amenable to biodegradation. From the results of this confidential investigation, it is apparent that there was a higher level of contaminant degradation within the microcosm utilising insitu mixing and injection techniques. One such technique involves the use of a specially modified auger system. These results advocate the beneficial effects of the treatment system in aiding the bioremediation of pollutants amenable to biodegradation within a terrestrial environment A model version of the in-situ mixing and injection system was set up under laboratory conditions in order to test the efficacy of the system in aiding the microbial degradation of contaminants/pollutants.

As a result, treatment scenarios were developed for incorporation as part of an active containment system i. e. the development of a semi-permeable zone combining abiotic and biotic processes for the treatment of contaminated soil and ground water.

Background to Treatment Systems A new passive approach for source and plume containment that offers considerable cost savings is active containment technology using either impermeable or permeable in situ treatment zones (refer to previous UK patent application no. 9610350.2).

This invention is part of an engineered system comprising physical (passive) barriers to isolate contaminated material (i. e. soil and ground water) from surrounding areas and/or active barriers to chemically and biologically prevent the continued migration of contaminants through the barrier.

Essentially the passive barrier is impervious to the migration of contaminants on or off-site. The treatment materials used in the physical barrier comprise of a mixture of unmodified smectite clay and cementitious/pozzolanic materials. The above materials/reagents are applied at a pre-determined addition rate to create an impermeable, low hydraulic conductivity barrier.

The active barriers incorporate modified pillared smectite clays which can effectively treat and immobilise (chemically fixate) both organic and inorganic/heavy metal waste pollutants. The desired treatment chamber is composed primarily of permeable material (i. e. the intercalated modified pillared clays) which is often placed across the contaminant plume. Once the clays are intercalated, the reactive properties of the clay and the presence of reactive species will effectively immobilise the waste material within the clay material matrix. The pillars facilitate the passage of contaminated water through the clay bringing the pollutants into direct contact with the reactive intercalated species. The biologically active film established on the external surfaces of the clay matrix provides a regenerative aspect to the invention. Once established, the microbes are able to biologically degrade organic pollutants which are amenable to bioremediation. Once the contaminant has been degraded, potential active sites are freed for further adsorption and subsequent biodegradation. Residence times are controlled via natural processes. The proliferation of the biofilm will in itself reduce the permeability of the barrier whilst the attraction force of the organophilic agent situated in close proximity to the degrading microorganisms will optimise environmental conditions for the biofilm in turn reducing permeability.

The introduction of organic groups to the external surfaces creates an organophilic environment with an affinity for organics. Specialist microorganisms with the ability to degrade certain organic contaminants are introduced to the external surfaces of the clay matrix. The prime function of the externally attached organic groups is to provide an effective mechanism for attracting organic compounds thereby retaining the pollutants in close proximity to the degrading microbes.

The installation of active barriers/walls as part of an active containment system provides a means for chemical immobilisation and biological degradation of the pollutants as they come into contact with the active barrier. The siting of each integral part of the system is an important stage of the process. In this case, water is the main medium for the transport of contaminants across the site and for bringing them into contact with the chemically reactive barrier incorporating the biofilm.

Active barriers may be installed across the contaminant plume (i. e. situated in the path of ground water flow) or alternatively, active and passive barriers may be installed around the periphery of the site to completely isolate the contamination. Low hydraulic conductivity passive walls can be installed to focus the flow of ground water if necessary. An example of a sequential In situ treatment chamber system is illustrated in Figure 9. This invention can be applied ondlor nstalled in a number of ways according to the individual logistics and requirements of each site. Several means of installing the system have been identified including utilising auger systems or similar, jet grouting or slurry walling.

Summary of Invention Modified pillared organoclays and inorgano-organoclays are based on stoichiometrically controlled intercalation and combination of three groups of reactive intercalatants comprising of metallic and hydroxy-polymer pillaring agents, transition metal salt (s) and organophilic agents. The stoichiometric addition rate will vary up to a maximum of 100% of the available cationic exchange capacity of the base clay.

The combination of the reactive intercalatants provides reactive sites within the interlamellar spaces of the clay matrix enabling the pollutants to be absorbed and chemically bonded within the matrix. The modified clays are primarily intended to treat both inorganic and organic pollutants. Once intercalated, the pollutants are retained in close proximity to the other intercalated reactive agents (a multifunctional property of the agents).

The pillaring effect of the clay is also an integral aspect of this technology.

Contaminated ground water is the general medium for bringing the contaminants into contact with the attached organic groups for the chemical immobilisation of the pollutants.

It is an embodiment of the present invention that modified pillared transition metal organoclays and inorgano-organoclays are further modified by the transformation of the external surfaces from an inorganic nature to an organophilic environment by controlled stoichiometric addition of an organophilic agent selected from the group consisting of a quaternary ammonium salt and a polar organic compound. It is a further embodiment of this invention that bioremediation can be earned out In situ by the creation of a biofilm on the external organophilic surfaces.

The internal sites are exchanged initially with the pillaring reagents and the transition metal salts. Organophilic agents are subsequently applied in controlled excess of stoichiometric balance exchanging for cationic groups on the external surfaces of the clay matrix in addition to exchanging for residual hitherto unexchanged cations at the internal exchange sites. The stoichiometric variation of the intercalatants will vary depending on the nature of the contamination.

The introduction of organic groups to the external surfaces creates an organophilic environment with an affinity for organics. Specialist microorganisms with the ability to degrade certain organic contaminants are introduced to the external surfaces of the clay matrix thereby creating a biofilm. The prime function of the externally attached organic groups is to provide an effective mechanism for attracting organic compounds thereby retaining the pollutants in close proximity to the degrading microbes.

Diagrammatic Descriptions of the Invention Preferred embodiments of the present invention will be described in more detail, by way of example, with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic representation of a modified inorgano-organoclay. The clay structure is modified by the intercalation (treatment) of the clay with an agent selected from the group consisting of a quaternary ammonium salt (1) and a polar organic compound inducing organophilic properties into the clay, and a salt of a transition metal (2) in quantities corresponding to no more than 100% stoichiometric exchange of the exchangeable cations of the clay. Figure 2 is a diagrammatic representation of a modified pillared organoclay. The clay structure is modified by the intercalation (treatment) of the clay with an agent selected from the group consisting of a quaternary ammonium salt (1) and a polar organic compound inducing organophilic properties into the clay, and a pillaring agent selected form the group consisting of aluminium chlorhydrol (3), metal hydroxide polymers, transition metal clusters, silicon oxides, titanium oxides, and mixtures thereof in quantities corresponding to no more than 100% stoichiometric exchange of the exchangeable cations of the clay.

Figure 3 is a diagrammatic representation of a modified pillared inorgano-organoclay.

An embodiment of an earlier invention: UK patent application no. 9612755.0 European patent application no. 96307987.6 USA patent application no. 08/753228 Australia patent application no. 56258/96; Figure 4 is a diagrammatic representation of a modified pillared inorgano-organoclay illustrating its multireactivity with chlorobenzene. There are many chemical bonding processes and reactions that occur within the clay matrix ranging from Van Der Waals attraction forces and dipole reactions to full covalent bonding and/or molecular interaction. Quaternary ammonium salts (1) are intercalated into the clay to create an organophilic environment in order to attract and absorb organic molecules.

Intercalated transition metals (2) have the capability to chemically react with organics by ligand bonding processes. The presence of aluminium ions as naturally substituted cations provide effective sites for Lewis acid/base reactions with chlorinated hydrocarbons such as chlorobenzene. Aluminium ions are also available for Lewis type reactions in the pillars (3). The stoichiometric ratio of the three intercalatants can be varied to a maximum of 100% of the cation exchange capacity of the clay. Figure 5 is a diagrammatic representation of a modified pillared inorgano-organoclay with both external and internal (intercalated) organophilic properties Quaternary ammonium salts (1) or polar organic molecules are added both internally and externally to the clay to create an organophilic environment in order to attract and absorb/adsorb organic molecules.

Figure 6 is a diagrammatic representation of a modified pillared inorgano-organoclay illustrating the organic bonding potential of the external organic reactive groups with chlorobenzene. The external surfaces of the clay are coated with quaternary ammonium or polar organic molecules thereby rendering the external surface organophilic. In the example illustrated, the chlorobenzene molecule associates with the organophilic surface of the clay in addition to intercalation as illustrated in Figure 4. Organic molecules which are amenable to biodegradation are then held in a position for gradual degradation to component constituents by degrading microorganisms in the biofilm. The relationship between the attached organic groups and the biofilm is a further embodiment of this invention and discussed in greater detail below.

Figure 7 is a diagrammatic representation of a modified pillared inorgano-organoclay illustrating the reactivity of the biofilm (4) on targeted organic substrates (i. e. chlorobenzene) and the association of the biofilm with the clay matrix.

Soil microenvironments are subject to the strong properties of clays and organic particles where present. The microenvironment of the microorganism is also subject to the electrostatic and natural forces of clay particles. As a consequence, microorganisms and their reactmts (e. g. substrates, metabolites, enzymes, inorganic ions) tend to accumulate in the vicinity of charged clay and organic matter surfaces, rather than being freely diffusible in the soil aqueous phase. Microorganism freely attach themselves to a clay or soil particle eventually forming a biofilm (4) and will continue to resist elution from the soil profile. Clay particles are essentially anionic with a high cationic exchange capacity unlike humic particles which tend to be cationic (depending upon composition etc). As a consequence, clay and humic particles will tend to associate to form organo-clay complexes. This association between reactive organic groups on the external surfaces of the clay matrix concentrating numerous organic molecules (i. e. for example, chlorobenzene) will form a number of chemical bonds with the organic molecules which in turn will associate with the degrading microorganisms present. This association is intensified as clays tend to have larger spheres of influence, extending greater distances from the colloidal surfaces.

The strength of sorption processes within a clay matrix vary considerably, affected by substrate exposure and the ability of the microorganisms to degrade the pollutants (i. e. the presence of correct degrading enzymes or at least the ability for synthesis of relevant degradative enzymes). It is therefore imperative that trials are conducted prior to remediation to determine the viable population present. It may be necessary to incorporate'specialist'microbes for the degradation of specific contaminants or alternatively indigenous acclimated microbes isolated'on-site'can be incorporated as part of the reactive biofilm.

Soil microenvironments and consequently microbial microenvironments are affected by hydrogen ion accumulation arising at clay and organic particle surfaces. A change in hydrogen ion concentration is usually a direct consequence of microbial activity in the area. This however, is detrimental to further microbial activity. It is therefore imperative that the pH of the system is monitored ; a necessary precaution to prevent the repulsion of microbes from negatively charged particles, such as clay and also to prevent re-solubilisation of heavy metal contaminants which precipitate out of solution under highly alkaline conditions. Controlled addition of cementitious materials and careful monitoring of biological activity will ensure a high pH is maintained. The design of the clay and consequently the acclimated and/or indigenous degrading microbes introduced will vary depending upon the nature and concentration of the contamination. The hydraulic conductivity of the clay may need to be finely adjusted to allow for longer residence times within the treatment zone. This can also be achieved by finely adjusting the addition rates of the cementitious materials and/or the reactive species incorporated within the slurry.

Figure 8 is a diagrammatic representation of a typical arrangement of soil columns in the formation of an active containment barrier also illustrating the treatment of'hot spots' (i. e. severe areas of isolated contamination) : this is an embodiment of an earlier invention as taught in UK patent application no. 9610350.2. Figure 8 is an illustration of an area of contaminated land (A) enclosed by barrier (B) by the formation of treatment columns to arrest the further migration of contaminants. The treatment columns (C) are formed by boring into the ground whilst injecting a slurry containing reactive treatment reagents. The said materials undergoing boring are selected to react with or bind with the pollutants identified in the contaminated zone. Treatment of hot-spots (D), isolated areas of severe contamination can be achieved by forming overlapping treatment columns in and around the isolated zone of contamination.

In some cases the treatment columns may contain materials used only for the containment of contaminated ground water. The said materials may comprise a slurry of bentonite and appropriate cementitious or pozzolanic materials in concentrations specially designed for each application. A mixture of reactive agents and containment reagents can be incorporated into each treatment column to chemically immobilise the contaminants as well as to physically encapsulate them.

Oxygen and essential nutrients may also be introduced to the treatment zone to enhance the conditions needed for bioremediation. Enzymes can also be added into the treatment zone to enhance bioremediation. Figure 9 is a diagrammatic representation of sequential reactive in situ treatment chambers (E). The treatment chambers are utilised in combination with an external physical/passive containment barrier. Reactive materials in the respective treatment chambers chemically immobilise both inorganic and organic molecules within groundwater channelled through the treatment chambers. Sequential treatment chambers can be designed to incorporate different treatment materials for specific/targeted contaminants.

Claims (17)

1. CLAIMS 1. A range of modified inorgano-organoclays and organoclays incorporating reactive intercalates for the chemical sorption and subsequent immobilisation of a range of organic, inorganic and heavy metal contaminants which support the attachment and growth of microorganisms in a biofilm enabling further degradation of organic molecules amenable to biodegradation processes.
2. 2. A range of modified inorgano-organoclays and organoclays incorporating reactive intercalates for the chemical sorption and subsequent immobilisation of a range of organic, inorganic and heavy metal contaminants wherein the modified clay is treated by a salt of a transition metal.
3. 3. A range of modified inorgano-organoclays and organoclays incorporating reactive intercalates for the chemical sorption and subsequent immobilisation of a range of organic, inorganic and heavy metal contaminants wherein the modified clay is treated by a suitable pillaring agent.
4. 4. A range of modified inorgano-organoclays and organoclays incorporating reactive intercalates for the chemical sorption and subsequent immobilisation of a range of organic, inorganic and heavy metal contaminants wherein the modified clay is treated by a pillaring agent and a salt of a transition metal.
5. 5. A range of modified inorgano-organoclays and organoclays incorporating reactive intercalates for the chemical sorption and subsequent immobilisation of a range of organic, inorganic and heavy metal contaminants wherein the modified clay is treated by a pillaring agent and a salt of a transition metal in quantities corresponding to no more than 100% stoichiometric exchange of the exchangeable cations of the clay.
6. 6. A range of modified inorgano-organoclays and organoclays according to Claim 5 wherein the modified clay is further treated with an agent selected from the group consisting of a quaternary ammonium salt and a polar organic compound to controlled excess of stoichiometric balance to create an external organophilic surface suitable for adsorption of organic molecules.
7. 7. A range of modified inorgano-organoclays and organoclays according to Claim 6 wherein the external organophilic surface provides a biodegradation capability through the creation of a biofilm.
8. 8. A range of modified inorgano-organoclays and organoclays according to Claim 2 wherein the transition metal salt comprises ferric salt.
9. 9. A range of modified inorgano-organoclays and organoclays according to Claim 2 wherein the transition metal salt comprises ferric chloride.
10. 10. A range of modified inorgano-organoclays and organoclays according to Claim 3 wherein the pillaring agent creates interlamellar spacing sufficient to provide access for larger molecules such as polychlorinated biphenyls and polyaromatic hydrocarbons.
11. 11. A range of modified inorgano-organoclays and organoclays according to Claim 3 wherein the interlamellar spacing di is at least 15A (15 x 10'mm).
12. 12. A range of modified inorgano-organoclays and organoclays according to Claim 3 wherein the pillaring agent comprises an aluminium or other metal hydroxide polymer.
13. 13. A range of modified inorgano-organoclays and organoclays according to claim 3 wherein the pillaring agent comprises transition metal clusters.
14. 14. A range of modified inorgano-organoclays and organoclays according to Claim 3 wherein the pillaring agent comprises appropriate silicon and titanium oxides.
15. 15. A range of modified morgano-organoclays and organoclays according to Claim 1 including intercalation additives comprising a combination of aluminium hydroxide polymer, a quaternary ammonium salt and a salt of a transition metal.
16. 16. A range of modified inorgano-organoclays and organoclays according to Claim I including intercalation additives comprising a combination of an aluminium hydroxide polymer, a quaternary ammonium salt and a salt of a transition metal combined with external addition of a quaternary ammonium salt.
17. 17. A method of treating materials contaminated by a range of hazardous organic and inorganic molecules and heavy metal pollutants, comprising the formulation of a modified inorgano-organoclay or organoclay including one or more selected organophilic materials and one or more pillaring agents, and one or more transition metal salts, to provide a modified inorgano-organoclay or organoclay tailored to interact with the contaminant molecule or pollutant to be treated, and then treating the contaminated material with such modified inorgano-organoclay or organoclay by which the contaminant is either chemically immobilised within the internal clay structure or biodegraded on the external surface through the association of a biofilm.