WO1998046311A1

WO1998046311A1 - Bioremediation of organic and metallic contaminants

Info

Publication number: WO1998046311A1
Application number: PCT/GB1998/000900
Authority: WO
Inventors: Harry Eccles
Original assignee: British Nuclear Fuels Plc
Priority date: 1997-04-15
Filing date: 1998-04-15
Publication date: 1998-10-22
Also published as: GB9707589D0; AU7056098A

Abstract

The invention provides a method, and apparatus for implementing the same, for treating materials comprising one or more metallic and one or more organic contaminants in a liquid stream, the method comprising contacting the contaminants with one or more microbial species in a reactor vessel, one or more of the microbial species at least in part causing one or more of the organic contaminants to be chemically altered and one or more of the microbial species at least in part causing one or more of the metallic contaminants to be chemically altered. The technique is particularly beneficial in that the treatment is possible under naturally occurring conditions of low pH and in that complex organic forms are degraded.

Description

BIOREMEDIATION OF ORGANIC AND METALLIC CONTAMINENTS

This invention concerns improvements in and relating to treatment, and particularly but not exclusively to the treatment of materials contaminated with heavy metal and organic pollutants by microbial means, for instance bioremediation .

Organic and metallic contamination of a wide variety of materials (for instance, soils, ground water and process waste streams) occur in many instances. The contamination may have been caused by past activities in that environment or on-going activities. The treatment or remediation of these materials to remove the contaminants they contain or the processing of waste streams from ongoing processes to treat such contaminants is highly desirable. The limits on waste stream contents which can be discharged and the condition in which contaminated water or land can be left are the subject of increasingly stringent legislation.

A wide variety of techniques for treating such materials have been proposed, but all face problems in terms of the capital costs involved; operating costs; technical difficulties or a limited range of materials which can be treated; limited scale on which the techniques can be put into effect; or undesirable by-products.

It is known, for instance, to use microbial agents to precipitate metals in aqueous solutions as metallic sulphides. However, the successful operation of such systems rely on microbial friendly conditions. For instance, it is necessary to feed the microbes with simple carbon feed sources, normally provided in a purified form. Additionally, the conditions under which such microbes can be successfully used tends to be limited, for instance in terms of relatively neutral pH's.

The present invention aims to provide alternative systems which feed on more complex carbon sources with a beneficial effect and/or to provide a more widely ranging tolerance for conditions and/or to address organic and metallic contaminations within a single system.

According to a first aspect of the invention we provide a method for treating materials comprising one or more metallic and one or more organic contaminants, the method comprising contacting the contaminants with one or more microbial species, one or more of the microbial species at least in part causing one or more of the organic contaminants to be chemically altered and one or more of the microbial species at least in part causing one or more of the metallic contaminants to be chemically altered.

The material to be treated is preferably a liquid and most preferably an aqueous liquid. The material may comprise solids, for instance particulate matter.

The material may comprise a waste or byproduct stream from a process. The material may comprise a leachate or other stream from a recycling, remediation or bioremediation process. The material may have a pH of less than 6 and is preferably between pH 1 and 5, more preferably pH 1.5 to 3.5.

Preferably the metallic contaminants are dissolved ions, such as sulphate but not necessarily chromate counter ions, with sulphate counter ions being particularly preferred. Aqueous dissolved forms are preferred. A plurality of different species may be present. A plurality of different metals may be present.

The metallic species may particularly comprise transition metals or metalloids and/or radioactive species and/or actinides and their decay products and/or fission products and their daughter products. Particular metals include uranium, plutonium, neptunium, americium, lead, zinc, nickel, cadmium, technecium, copper, mercury and cobalt.

Preferably the organic contaminants are in^' dissolved or suspended form. The organic components may be present as a distinct phase within an aqueous stream. The organic phase may be dispersed within the aqueous phase, for instance as discrete droplets. The organic contaminants may include one or more different compounds. The invention relates to all organic compounds, that is carbon based, but is particularly concerned with xenobiotics, aromatic, cyclic, phenolic, halogenated, nitro incorporating or polymerised compounds. The organics may particularly include chlorinated xenobiotics, benzene, toluene, ethyl benzene, xylene, dioxins, polyaromatic hydrocarbons and polychlorinated biphenyls and/or benzoic acid, m-hydroxybenzoate, p- hydroxybenzoate, salicylic acid, vanilic acid, benzyl alcohol, benzaldehyde, phenol, phenylacetic acid, napthalene, hexadecane and hexadecanoic acid.

The material is preferably contacted with the one or more microbial species in a reactor vessel . Preferably the contaminants are brought into contact with the microbial species within the reactor. Alternatively or additionally the contaminants may be contacted with a product of the microbial species .

Preferably the material is free to pass through the reactor vessel . Preferably the microbial species are restrained within the confines of the reactor vessel.

The material may be pre-treated prior to entering the microbial treatment stage. The pre-treatment may include the addition of an electron donor or addition of a supplemental electron donor. The pre-treatment may similarly include the addition of an electron acceptor and/or supplemental electron acceptor and/or nutrients and/or supplemental nutrients for ^"the microbial species . Preferably the organic contaminants at least partially provide a food source and/or electron donor for the microbial species. The pre-treatment, may, however, include the addition of additional . carbon sources as feed or supplemental feed. Such carbon sources may include ethanol, lactose, formate or the like. The additional feed may additionally function as an electron donor. ^' Additional electron acceptors may be provided as sulphate ions. The pre- treatment may include the addition of phosphorous and/or nitrogen based nutrients for the microbial species.

The pre-treatment may include a pH adjustment, preferably to increase the pH. This adjustment may be used to avoid extremely low pH's system. Preferably the pH is adjusted to 1.5, or more preferably 2.0, or greater.

The treatment of the metallic contamination may principally or exclusively occur in one stage. The treatment of the organic contamination may occur principally or exclusively in one stage, preferably a different reactor stage to the principal stage for the metallic treatment.

Preferably a microbial treatment is provided to cause conversion of metallic contaminants from soluble to substantially insoluble form, which microbial treatment consumes as a foodstuff . at least part of the organic contaminants present. Preferably the organic contaminant microbial treatment includes the degradation of one or more of the organic components in the material. Preferably the organic contaminant microbial treatment assists in providing the organic contaminants in a form suitable for use as a feedstuff by the metallic contaminant treating microbial species.

The first stage may provide for the treatment of metallic species. The first stage may convert the metallic species to insoluble form. Preferably the first stage also provides for at least partial degradation of one or more of the organic contaminants. Preferably the first stage is anaerobic. Preferably the same microbial species is responsible for both metallic contaminant conversion and organic contamination degradation. Preferably the microbial species uses one or more of the organic components as electron donor. Preferably the microbial species uses sulphate or chromate ions or high valency metal ions as electron acceptors. Preferably the second stage provides for the degradation of one or more of the remaining organic contaminants ^' or fragments thereof. Preferably the second stage completes the degradation of one or more of the components . The second stage may be aerobic or anaerobic. The organic components may be incorporated within the biomass due to growth. The organic components may be used as electron donors.

Alternatively the first stage may provide for the at least partial degradation of one or more of the organic contaminants . The first stage may use one or more of the organic components as an electron donor. Preferably the degradation arises as a result of this function of the organic component . Preferably the first stage renders one or more of the contaminants to a form assimilable by the microbial species of the second stage. The first stage may leave the metallic contaminants substantially or completely unaltered. The first stage may be aerobic or anaerobic. The first stage may be performed at a pH of between 1.5 and 4 , more preferably 2 and 3.5. The second stage may provide for the complete degradation of one or more of the organic contaminants, most preferably as a food stuff. The second stage may-provide for the conversion of one or more of the metallic contaminants to an insoluble form. The second stage is preferably anaerobic. Preferably the conversion occurs due to the reduction of sulphate ions to sulphide ions . Preferably the sulphate ions act as electron acceptor to the biomass growth process. Preferably the degraded organic components act as electron donors to the microbial species.

A pre-treatment may be provided between the first and second stage. The pre-treatment may include the addition of one or more of an electron donor, an electron acceptor, or nutrients for the microbial species. Preferably carbon based materials are used as the electron donor and/or supplemental feed. Preferably sulphate are provided as the electron acceptor. Additional nutrients may include supplemental carbon food sources and/or phosphorous • sources and/or nitrogen sources. The pre-treatment may include a pH adjustment stage.

The second stage may be provided by a first reactor in which the microbes act to produce a reduced sulphur form and a second reactor to which the reduced sulphur from is fed and in which the metallic species is treated. The reduced sulphur form may be HS^" and/or H₂S . The first reactor of the second stage may be fed by a stream leaving the second reactor of the second stage. In this case nSRB's may be used in the first reactor and/or the pH of the stream may be between 7 and 9. The first reactor of the second stage may be fed by a stream leaving the first stage. In this case acidophilic SRB's may be used in the first reactor and/or the pH of the stream may be between 1.5 and 4. Feed to the first reactor may be continuous or periodic. Carbon sources may be added to the first reactor.

The treatment of one or more organic contaminants and one or more metallic contaminants may be achieved in a single stage. The partial degradation of one or more of the organic contaminants may be effected by a microbial species, with the complete degradation being achieved by a microbial species which also causes one or more of the metallic contaminants to be converted to insoluble form. The microbial species may be different or the same. Preferably the stage is anaerobic.

One or more of the stages may involve variation of the electron donor and/or electron acceptor present over time. Preferably the variation is caused by the addition of supplemental forms over time. The supplemental addition may be in the form of a series of pulses. Preferably electronic acceptor additional is varied over time to boost activity of the microbial species.

Preferably one or more of the organic contaminants are degraded by one or more of the microbial species. Degradation may be taken to include removal of functional groups, substitution of functional groups, a decrease in molecular weight, breaking of carbon chains, cleavage of aromatic rings, oxidation, reductive dehalogenation or more than one of these.

Preferably one or more of the organic contaminants act as an electron donor for a chemical function performed by one or more of the microbial species. Preferably one or more of the organic contaminants comprise a food source for one or more of the microbial species. Most preferably one or more of the organic contaminants are incorporated and/or used in the microbial biomass as a result of biomass growth/ One or more of the organic contaminants may be degraded by one or more of the microbial species and comprise a food stuff for one or more microbial species in degraded form.

Preferably one or more of the metallic contaminants are altered to a less soluble species form, compound form or state by one or more of the microbial species. Preferably one or more of the metallic contaminants are converted to sulphide form. Preferably the conversion to sulphide form arises as a result of conversion of sulphate ions to sulphide ions by one or more of the microbial species. The conversion of sulphate to sulphide may arise as a byproduct of the growth of the biomass. The reduction of the sulphate ions may arise as a result of oxidation of the microbial species food source. Preferably the precipitate is present in the liquid phase. Preferably the precipitate does not ^"adhere to the cell walls of the biomass .

Preferably a one microbial species effects the treatment of one or more of the metallic contaminants . Preferably sulphate reducing bacteria are used on the metallic contaminants. Preferably one microbial species effects the initial degradation of one or more of the organic contaminants. Preferably acidophillic bacteria are used on the organic contaminants. Preferably the species for treating metallic and organic contaminants are different. Preferably the microbial species effecting the treatment of the metallic contaminants also degrades one or more of the organic contaminants. Preferably this species completes the degradation of the partially degraded organic contaminants.

The microbial species for metallic contaminant treatment may be selected from Desulfovibrio ^'and/or Desulfomonas and/or Desulfomaculum species and/or related sulphate reducing bacteria .

The organic contaminant treating species may be selected from one or more of pseudomonaas, nocardias, mycobacteria, flavobacteria, alcaligenes, corynebacteria, Bacilli, Arthrobecters and clostridia species, amongst others.

The treated material may be further processed following the first and/or second stage. The further processing may include a solid/liquid separation. The solid /liquid separation may separate the metallic contaminant precipitate from the remaining liquid or liquids. Gravity sedimentation may be used. The treated material may be further processed following the first and/or second stage to ^'remove any gases, such as hydrogen sulphide, present. The gases may be recycled.

The treated material from the first and/or second stage may be treated to remove unmetabolised organic components, these may be returned to earlier parts of the process or treated elsewhere.

According to a second aspect of the invention we provide apparatus for contacting a material comprising one or more metallic and one or more organic contaminants with one or more microbial species, the one or more microbial species at least in part causing one or more of the organic contaminants to be chemically altered and one or more of the microbial species at least in part causing one or more of the metallic contaminants to be chemically altered and means for separating the microbial species from the material and/or for separating the chemically altered metallic contamination from the material.

The apparatus may comprise one or more reactor vessels. Where a plurality of reactor vessels are provided preferably they are provided in series. The first reactor vessel may provide for the partial degradation of the organic contaminants present and/or provide for the chemical alteration of the metallic contaminants present. The second stage may provide for the further degradation of the organic contaminants and/or provide for the chemical alteration of the metallic contaminants present .

The second aspect of the invention should be taken to include means and apparatus for performing or embodying any of the possibilities and options for the invention discussed elsewhere in this application, including the first aspect of the invention.

Various embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: -

Figure 1 illustrates a process route according to a first embodiment of the invention; -Si- Figure 2 illustrates a process route for a second embodiment of the invention;

Figure 3 illustrates a process route according to a third embodiment of the present invention;

Figure 4 illustrates a further embodiment of the invention;

Figure 5 illustrates a still further embodiment of the invention; and

Figure 6 illustrates a yet further embodiment of the invention.

The process routes described in the latter part of this description addresses the processing of aqueous streams containing both organic and metallic contaminants. Such aqueous streams can originate in a wide variety of ways and from a wide variety of sources .

The aqueous streams may arise merely as a waste product stream from one or more stages of an overall processing system.

In alternative forms the aqueous stream may comprise a leach liquor arising from the treatment of contaminated soils in a way intended to leach metallic and organic contaminants within that soil out into the liquid form. Such techniques might include the leaching of soils with acidic solutions, for instance sulphuric acid containing solutions. The leaching process may be based on chemical conditions applied to the area by the introduction of the leacha e, and/or may arise as a result of microbial or other actions within the area being leached. The sulphuric acid, for instance, may be produced by microbial action on elemental sulphur or other sulphur sources. Such systems successfully leach metallic contamination into solution, generally in sulphate form.

The stream to be treated may even arise from combining separate waste streams to create the desired oV acceptable contaminant content suitable for feed to the present invention.

The organic contaminants which may be present may include benzene, toluene, ethyl benzene, xylene, polyaromatic hydrocarbons, polychlorinated biphenyls, dioxines, halogenated xenobiotics, phenolics, nitro based compounds and a wide variety of other carbon based molecules.

The metallic forms of contamination may derive from elemental metal,- metalloid, metal containing compound, metal containing complex, alloy or metal salt forms. Particular metals of interest include those having a toxological effect in the environment such as nickel, zinc, cadmium, copper, mercury, cobalt and lead. The treatment of radioactive metallic elements and fission products arising therefrom, i.e. strontium to cesium in the periodic table, is also envisaged.

The metallic contamination is most likely present as dissolved species, although fine suspensions of particulate contamination can also be considered. The organic contamination may be present as dissolved species or as small amounts of an organic phase intermingled with the aqueous phase .

The nature of waste streams containing such species is that they will generally have a relatively low pH, ie less than 3.

The present invention is aimed at treating any input stream having the basic characteristic of containing organic and metal contamination, what ever its origins and particular form.

In the process route according to the first embodiment of the invention, illustrated in Figure 1, the input stream 1 contains the organic and metallic contamination to be treated. This input is subjected to an optional pre-treatment stage 3 designed to alter the conditions of the feed as required.

The pre-treatment stage 3 may include the addition of agents needed for the subsequent _ reactions or intended to facilitate their progress. The addition of a supplemental sulphate feed 5 and/or a supplemental electron donor source 7 and/or nutrients source 8, including phosphorous or nitrogen are envisaged and discussed in more detail below.

The pre-treatment stage 3 may include pH adjustment, although it is desirable to treat the waste under its natural pH, typically 3 or less, rather than incur the cost of neutralising the pH. An additional problem with neutralisation is that metal hydroxides may form and the resulting precipitate has poor bulking properties. A very high volume and difficult to de-water sludge generally results. Limited pH adjustment to avoid the most extreme pH's may be preferred.

The addition of additional sulphate ions may be necessary to act as electron acceptors in the subsequent microbial stages if the existing concentration in solution is not already high enough. Particularly where sulphuric acid is used in the initial leaching process to form the stream however, this may not be a problem. Where additional sulphate ions are required sulphuric acid and/or other cheap sulphate forms may be the preferred addition form.

An electron donor is also imperative for a successful microbial treatment . The electron donor form can vary significantly and to an extent depends on the microbial activity to be used. The electron donor, may comprise or consist of hydrogen gas or formate. Ideally the carbon source acts as electron donor too.

Following the pre-treatment stage 3 the stream containing all the necessary agents for the subsequent treatment is fed to microbial treatment stage 9. In this embodiment of the invention the microbial treatment stage is initially principally concerned with treatment of the metallic contamination present. The bioreactor used contains the sulphate reducing bacteria, such as species Desulfovibrio, Desulfotomaculum and Desulfomonas used to achieve the treatment. These organisms use a carbon food source to derive energy and growth, the growth of the organisms also resulting in the reduction of sulphates present to sulphides. As metal sulphides have a far lower solubility in aqueous solutions than the sulphate forms, metallic ions present will tend to precipitate as metallic sulphides.

An important aspect of the present invention is that the organisms partially feed on the complex organic materials present within the product stream. As a result, even though additional simple food sources such as ethanol need to be added, a significant degree of degradation of the complex organics present occurs. The nature of the degradation will vary from organic to organic under attack, but may include reductive de-halogenation, oxidation (for instance using itiono- oxygenase type enzymes) , conversion of fatty acids to aldehydes and carboxylic acids, hydration, epoxidation, ring breakage and ring clearage.

The microbial treatment proposed uses the necessary added food source to control the process. Thus whilst the process is not self-sustaining the growth of the bio-mass can be controlled and the level of certain by-products, i.e. H₂S, can be regulated.

The sulphate reducing bacter-ia also have a beneficial effect in terms of the result of their action on the pH of the solution. In general a pH 2 feed to the microbial stage might be expected to leave it as a pH 5 to 6 solution. The neutralisation of the solution in this way by the SRB's is useful in avoiding costly chemical neutralisation, or neutralisation prior to the metallic contaminations precipitation in sulphide form.

The processed stream from the microbial stage 9 is then fed to separation stage 10. It is important that as much as possible of the precipitate forms arising are in free suspension and unconnected with the biomass as possible. It is preferred therefore to avoid precipitation on cell walls in the biomass. The separation stage may include one or more separations intended to remove the various components of the system. The separation may occur .within the bioreactor. A solid/liquid separation, for instance, precipitation and then gravity sedimentation, may be used to extract the sulphides from the stream as product 11. The product may be further processed to recover its constituents for reuse or may be further processed to render its components to a form suitable for long term storage or disposal .

In certain cases the product stream may also include hydrogen sulphide, dissolved or in gaseous form, which originates from the microbial process. Hydrogen sulphide can originate where growth decoupled reduction occurs, but it is highly toxic to the microbial systems and its removal by air stripping or membrane extraction it is desirable to avoid poisoning the subsequent microbial step. The off gas product 13 may be recycled to other stages in the process, for instance following further processing, stage 15 as the sulphate source for the pre-treatment stage 3 or the H₂S may be direct to the pre-treatment stage. Alternatively the hydrogen sulphide may be turned to another process, such as the feed for a leaching process, not shown.

Following separation of the solid and any gaseous components of the product stream, the remaining liquid is fed to a further microbial stage 17 designed to increase the degradation of the organic components.

In stage 17 microbes present consume the remaining organic materials and previously broken fragments of organic materials as a feed stock in their growth. The growth of the organisms results in the substantive degradation of the organics to forms which can be more readily taken up by the organisms in growth. Any remaining fragments should be sufficiently degraded as to be readily processed elsewhere or discarded as tolerable waste 19.

In the event that the microbial treatment 17 leaves incompletely degraded organics these can be extracted by a separation stage to form stream 21 which can then be returned, with intervening pre-treatment if appropriate, to an earlier stage in the overall process, for instance, microbial treatment 9. On additional passes through the apparatus further degradation can be expected.

The overall system provides for the successful treatment of both metallic and organic contaminants in an input stream, whilst beneficially using the organics as a part contributor to the feed material necessary for the microbial growth stage and whilst benefitting from the SRB's part neutralisation of the input stream to produce a pH more readily disposable.

In certain circumstances, an alternative process stream may be desirable, as illustrated in Figure 2. In certain circumstances the combination of organic and metallic components in the input stream 31 may be prejudicial to initial microbial treatment of the metallic constituents. Such a case might occur where the metals present complex with the organic materials so restricting the biological availability of the organic materials as a feedstock to the sulphate reducing bacteria.

In this alternative process, therefore, a pre-treatment stage 33 may be employed to present the input stream in the desirable manner, for instance in terms of components or pH, prior to feeding to microbial treatment stage 35. In this microbial treatment stage the microbes present concentrate their attack on the organic components and may have no activity with regard to the metallic components present . The stage may be conducted under anaerobic or aerobic conditions. As a result of this preferential attack the organic components are broken down into fragments by degradation and their ability to complex with the metal ions is removed as a result . The carbon fragments arising from this treatment stage 35 are also more readily suited to forming feedstuffs for the subsequent treatment stage as a result .

The process stream exiting microbial treatment stage 35 contains the substantially unaltered metallic contamination, but in conjunction with an organic contamination which has been significantly degraded. In its degraded form complexes with the metal species no longer form.

Further pre-treatment scage 37 allows the conditions of the product stream to be adjusted to those most suitable for the metal treatment stage. This adjustment may include introducing a supplemental sulphate ion source 39 or supplemental nutrient source 41 to provide other nutrients to the carbon already in the process stream, ror instance phosphorous and nitrogen, to assist in the subsequent microbial treatment .

The adjusted feed is fed to microbial treatment stage 43 in which the microbes discussed above employ the carbon fragments produced from the degradation of the organic components as their foodstuffs. As a result the carbon fragments are consumed and the stream is largely cleaned of organic components. As previously discussed this process also results in the sulphate forms present being reduced to sulphide. These combine with the metallic contamination to give largely insoluble sulphide forms. The separation process stages 45 following this treatment allow the precipitates 47 to be separated out from any gases 49, principly hydrogen sulphide, which may be recycled and the cleaned liquid output 51.

As the organics are sufficiently degraded by the second stage 43 they form the whole of the food stuff requirement so rendering the process self-sustaining.

In certain circumstances a singular microbial treatment stage may be employed as illustrated in Figure 3. In this case input stream 61 is pre-treated to ensure the desired components and conditions are present in pre-treatment stage 63 prior to feeding to microbial treatment stage 65.

This microbial treatment stage 65 includes, microbes intended both to attack the organic components present by using them as a feedstuff and breaking them into fragments; and also microbial components which result in the reduction of the sulphate species to sulphide, and hence precipitate the metals as sulphides . The sulphate reducing bacteria may employ the complicated organic components as their feedstuff, or more readily, use the fragmented carbon components originating from the other microbes as their food source . The microbial treatment may be presented as a single stage or double stage, one process following straight on from the other.

The products from this process stage 65 can then be subject to a series of separation stages 67 to remove precipitate 69 and any gases 71 from the cleaned product stream 77. Any unmetabolised organic materials may be recycled from a further separation stage or stages 73.

The process illustrated in Figure 4 represents a derivation of the process of Figure 2. In this alternative process, however, a pre-treatment stage is avoided as the pH, below 4, is acceptable to the microbial treatment stage 100 as that stage uses acidophilic organic degrading bacteria. Cost and the level of interference are thus minimised as only inorganic nutrients, such as nitrogen or phosphorous forms, need be added.

In the microbial treatment stage 100 the microbes present concentrate their attack on the organic components under aerobic conditions. As a result of this preferential attack, for instance on aliphatic and aromatic components of the effluent, the organic components are broken down into fragments by degradation. The carbon fragments arising from this treatment stage 100 are more readily suited to forming feedstuffs for the subsequent treatment stage 102 and are less likely to be toxic to the microbes of that stage 102 too. The process stream exiting microbial treatment stage 100 contains the substantially unaltered metallic contamination, but in conjunction with an organic contamination which has been significantly degraded. The pH is also substantially unaltered from that at which it is fed to the stage 100.

In the second stage 102 SRB's are employed to treat the metallic constituents. Acidophillic SRB's may be used with benefits in terms of reduced pH adjustment necessary or neutrophillic SRB's with potentially greater treatment efficiency may be used.

The conditions of the second stage may need to be adjusted to those most suitable for the metal treatment stage. This adjustment may include introducing a supplemental sulphate ion source or supplemental food source, for instance ethanol, to provide other food sources to the carbon already in the process stream, or nutrients, for instance phosphorous and nitrogen, to assist in the subsequent microbial treatment.

As a result of the second stage the carbon fragments are consumed and the stream is largely cleaned of organic components and the metallic sulphate forms present are reduced to sulphide forms and hence precipitated.

In the system set out in Figure 5 the effluent is fed to an initial feed tank 200 where nutrients, such as nitrogen or phosphorous may be added. No adjustment of the pH is needed, as described above for Figure 4, and the first reactor 202 works to degrade the complex organic forms present, as described for Figure 4.

The effluent stream 204 is then fed to a precipitation tank 206 to which HS^" is also added. The precipitation of the metals is performed in the manner previously described.

The HS^" for the precipitation tank is produced in an offline bioreactor vessel 208. In this stage 208 neutrophillic SRB's act on input stream 210 to generate HS^" which forms stream 212. The input stream 210 is formed by the effluent draining from the precipitation tank 206 and is substantially neutral in pH due to the preceeding action of the SRB's and/or sulphide addition. Ethanol or other simple carbon forms can be added to the stage 208. This technique has advantages in terms of the isolation of the nSRB reactor from other parts of the process stream.

In the system of Figure 6 equivalent feed tank 300 and first reactor stages 302 are provided to the Figure 5 set up.

Off-line bioreactor 304 contains acidophillic SRB's which act on the sulphate ions in stream 306 and/or added sulphate ions 308 under the prevailing pH conditions, 3-4, to produce hydrogen sulphide. The hydrogen sulphide can be separated and fed to precipitation tank 310 where it gives metal precipitaion in the manner described above.

In both the Figure 5 and Figure 6 set ups flow to the second biorectors may be periodic with the flow proceding from the first reactor to the precipitation tank at other times. The final effluent from the precipitation tank may be recycled back to a stage of the process and/or an equivalent process.

Tests on a variety of neutrophilic SRB's have established their ability to cope with the levels of metallic contamination to be treated, to survive in the presence of a variety of metal ions and a variety of organic constituents and to grow under pH conditions of practical value. The results for the growth of a variety of samples, presented as % protein compared with a control, of nSRB's in ImM of the listed species are : -

TABLE 1

COPPER CADMIUM NICKEL ZINC

Mixed Culture 105.8 114.5 43.0 82.6

Isolate 1 110.1 67.1 80.7 130.0

Dv vulgaris 80.8 62.4 12.7 68.4

Dc multivorans 26.1 61.3 60.6 78.2

The results for the effectiveness of metal precipitation, % of ImM, growing in 5mM of the listed species are :-

TABLE 2

COPPER CADMIUM NICKEL ZINC

Mixed Culture 93.4 50.6 92.7 54.2

Isolate 1 99.9 99.9 99.3 99.7

Dv vulgaris 100 99.9 99.4 99.8

Dc multivorans 94.7 79.3 61.1 96.2

The mixed culture of nSRB's grew and reduced sulphate at pH 4.9 and greater; pH 4 and greater when glass bead supported in batch culture; pH 4.2 and greater in continuous culture; pH 3.7 and greater in continuous biofilm culture. In all cases the nSRB's increased the pH to approximately 8 at the outflow end.

The growth of the various nSRB's was shown to be possible under many of the conditions anticipated.

When grown in the presence of ImM benzoic acid, m- hydroxybenzoate, p-hydroxybenzoate, salicylic acid, vanilic acid, benzyl alcohol, benzaldehyde, phenol, phenylacetic acid, napthalene, hexadecane and hexadecanoic acid, the mixed culture and isolate 1 were only inhibited by napthalene and Dv vulgaris was only inhibited by vanillic acid and phenylacetic acid.

When grown for 8 weeks in the presence of lOOOmg/l chlorobenzene, hexadecane, phenanthrene, napthalene, phenol, little inhibition of Dv vulgaris or the nixed culture was found with all bar phenol.

Claims

1. A method for treating materials comprising one or more metallic and one or more organic contaminants in a liquid stream, the method comprising contacting the contaminants with one or more microbial species in a reactor vessel, one or more of the microbial species at least in part causing one or more of the organic contaminants to be chemically altered and one or more of the microbial species at least in part causing one or more of the metallic contaminants to be chemically altered.

2. A method according to claim 1 in which the organic contaminants at least partially provide a food source and/or electron donor for the microbial species .

3. A method according to claim 2 in which the food source includes one or more of xenobiotics, aromatic, cyclic, phenolic, halogenated, nitro incorporating or polymerised compounds .

4. A method according to claim 3 in which the food source includes one or more of chlorinated xenobiotics, benzene, toluene, ethyl benzene, xylene, dioxins, polyaromatic hydrocarbons, polychlorinated biphenyls, benzoic acid, m- hydroxybenzoate, p-hydroxybenzoate , salicylic acid, vanilic acid, benzyl alcohol, benzaldehyde, phenol, phenylacetic acid, napthalene, hexadecane, chlorobenzene, phenol, phenanthrene and hexadecanoic acid.

5. A method according to any preceeding claim 1 in which the material is a liquid and has a pH of between pH 1 and 5.

6. A method accroding to any preceeding claim in which the material is pre-treated prior to entering the microbial treatment stage by the addition of an electron donor or addition of a supplemental electron donor and/or the addition of an electron acceptor and/or supplemental electron acceptor and/or the addition of nutrients and/or supplemental nutrients for the microbial species.

7. A method according to any preceeding claim in which the treatment of the metallic contamination principally or exclusively occurs in one reactor stage.

8. A method according to any preceeding claim in which the treatment of the organic contamination principally or exclusively occurs in one reactor stage.

9. A method according to any of claims 1 to 8 in which the first stage is areobic and provides for the at least partial degradation of one or more of the organic contaminants, the first stage rendering one or more of the contaminants to a form assimilable by the microbial species of the second stage.

10. A method according to claim 9 in which the second stage is anerobic and provides for the complete degradation of one or more of the organic contaminants and for the conversion of one or more of the metallic contaminants to an insoluble form.

11. A method according to any preceeding claim in which the treatment of one or more of the metallic contaminants is provided by sulphate reducing bacteria and acidophillic bacteria are used on the organic contaminants .

12. A method according to any preceeding claim in which the microbial species for metallic contaminant treatment is selected from Desulfovibrio and/or Desulfomonas and/or Desulfomaculum species.

13. A method according to any preceeding claim in which the organic contaminant treating species is selected from one or more of pseudomonads , nocardias, mycobacteria, flavobacteria, alcaligenes, corynebacteria, Bacilli, Arthrobecters and clostridia species.

14. Apparatus for contacting a material comprising one or more metallic and one or more organic contaminants in a liquid stream with one or more microbial species, the one or more microbial species at least in part causing one or more of the organic contaminants to be chemically altered and one or more of the microbial species at least in part causing one or more of the metallic contaminants to be chemically altered and means for separating the microbial species from the material and/or for separating the chemically altered metallic contamination from the material .

15. Apparatus according to claim- 14 in which the apparatus comprises a plurality of reactor vessels in series, the first reactor vessels providing for the partial degradation of the organic contaminants present, the second reactor vessels providing for the further degradation of the organic contaminants and/or providing for the chemical alteration of the metallic contaminants present.

16. A method for treating materials comprising one or more metallic and one or more organic contaminants, the method comprising contacting the contaminants with one or more microbial species, one or more of the microbial species at least in part causing one or more of the organic contaminants to be chemically altered and one or more of the microbial species at least in part causing one or more of the metallic contaminants to be chemically altered.