FIELD OF THE INVENTION

This invention relates to biological treatment of waste, and particularly to the degradation of organo-halides contained in liquid wastes.

BACKGROUND

Industrial processes that use or generate toxic organic compounds has lead to the contamination of nearby water and land. Most approaches to decontamination or "remediation" involve stopping the local dumping of such compounds and transport of the waste to another area for containment. This is costly and does not eliminate the hazard.

As a remediation technology, bioremediation is considerably more attractive. Rather than merely transporting wastes, it offers the possibility of degrading toxic compounds to harmless reaction products by the use of biologicals.

Bioremediation field trials have involved both in-situ and ex-situ treatment methods. Typically, ex-situ treatment involves the transfer of contaminated waste from the site into a treatment tank designed to support microbial growth, i.e., a "bioreactor" . The reactor provides for effective mixing of nutrients and control over temperature, pH and aeration to allow optimum microbial growth. In-situ treatment involves adding biologicals directly to the waste. This avoids the problems associated with handling (e.g., pumping) toxic compounds. However, in-situ treatment has its own problems. Unlike bioreactors, where microbial growth can be monitored and adjusted, in-situ environmental conditions are difficult to measure and control.

Bioremediation technologies being developed to deal with waste differ further in their ability to handle specific types of compounds. For example, the effluents from most pulp or paper-making operations contain lignin or its degradation products. Lignin is an extremely complex polymer, constituting up to 35% of dry wood weight. During pulping processes, cellulose fibers must be liberated from the surrounding lignin matrix so that they can be associated with one another. The resulting free lignin is highly resistant to degradation.

Chang et al. describe the degradation of the complex lignin polymer by direct addition of cultures of the white- rot fungus, P. chrysosporiim. See U.S. Patent No. 4,655,926, hereby incorporated by reference. They describe the induction of lignin degradation in response to carbon and nitrogen starvation.

This fungal lignin metabolism is a secondary metabolic event. Lignin degradation allows the fungus to expose the cellulose contained within the lignin matrix as its primary food source. Indeed, lignin alone will not support P. chrysosporium growth.

Since cellulose fibers are the primary food source, degradation of lignin by adding the fungus directly to the wood results in reduced pulp yield and an inferior pulp product. Farrell has proposed, therefore, an improvement in lignin degradation. See U.S. Patents Nos. 4,687,745 and 4,690,895, hereby" incorporated by reference. She describes the use of fungal enzymes rather than fungal cultures. The enzymes degrade lignin without degrading cellulose fibers. The mechanism by which these enzymes degrade lignin has been investigated. Glenn et al. have characterized the enzyme manganese peroxidase. See Arch. Biochem. Biophys. 251:688 (1986) . By separating the enzyme from the substrate using a membrane, they showed that Mn(III) complexed to

lactate or other hydroxy acids are intermediates capable of oxidizing organic compounds. This work was confirmed by Lackner et al., Biochem. Biophys. Res. Comm. 178:1092 (1991) . Lignin is but one by-product of paper making operations. The bleaching of paper with chlorine generates effluents that are a serious health concern. Many of these compounds are known to cause cancer in humans. Most importantly, these compounds are not degraded rapidly in the natural environment.

Chang et al. teaches that chloro-organics contained in liquid waste can also be degraded by the white-rot fungus. See U.S. Patent No. 4,554,075, hereby incorporated by reference. In the method proposed, the fungus is immersed in the liquid containing chloro-organics and periodically exposed to an oxygen enriched atmosphere. The chloro- organics are converted from aromatics to aliphatics.

Unfortunately, the rate of chloro-organic degradation is slow since the degradation activity must be induced by starvation of the organism. To avoid the necessity for this starvation step, Aust et al. teach the direct addition of fungal enzymes rather than whole organisms. See U.S. Patent No. 4,891,320, hereby incorporated by reference. They suggest the direct addition of a fungal peroxidase. This, however, requires the continually mixing of the enzyme with hydrogen peroxide. This is difficult whether done in an open environment or a closed reactor.

Indeed, the commercial use of fungal degradation is hampered by complex technical and engineering issues. Growth of the organism and/or enzyme production may be inhibited by waste components. See generally, Mileski et al., Appl. Environ. Microbiol. 54:2885 (1988). Furthermore, the enzyme is a protein and, as such, can undergo proteolysis by any number of proteases in the waste stream,

and be rendered thereby inactive. See Dosoretz et al., Appl. Environ. Microbiol. 56:3429 (1990). In sum, the degrading ability of P. chrysosporium is not practically maintained for a very long period of time. See Lin et al. , Biotechnology and Bioengineering 35:1125 (1990).

There remains a need to develop a bioremediation procedure that can be operated economically on a commercial scale. Such a procedure must be able to deal with diverse waste streams without significant inhibition of the degradation process.

SUMMARY OF THE INVENTION

This invention relates to biological treatment of waste, and particularly to the degradation of organo-halides contained in liquid wastes. In one embodiment, the present invention contemplates a method of degrading compounds contained in a liquid or solid waste stream, comprising the steps of: a) providing, i) a reaction containing means having a semi-permeable membrane partition, ii) at least one enzyme for which the membrane is not permeable, and iii) at least one substrate for the enzyme; b) adding to the containing means on one side of the partition, the enzyme and substrate to create a reaction mixture, thereby generating a reaction intermediate for which the membrane is permeable; c) adding to the containing means on the other side of the partition, the compounds contained in said waste stream, d) applying a pressure to the reaction mixture so as to force the reaction intermediate across said membrane into the compound-containing waste stream, thereby degrading the compounds.

In another embodiment, the present invention contemplates a method of degrading compounds contained in a liquid or solid waste stream, comprising the steps of: a) providing, i) a first reaction containing means having a semi-permeable membrane partition, ii) at least one enzyme for which the membrane is not permeable, and iii) at least one substrate for the enzyme, and iv) a second reaction containing means; b) adding to the first containing means on one side of the partition, the enzyme and substrate to create a reaction mixture, thereby generating a reaction intermediate for which the membrane is permeable; c) applying a pressure to the reaction mixture so as to force the reaction intermediate across said membrane and so as to collect the reaction intermediate on the other side of the partition; and, d) adding the reaction intermediate to the second containing means wherein the compounds to be degraded are contained, thereby degrading the compounds. In one embodiment, the reaction intermediate is added in step (d) by pumping the intermediate from the first reaction containing means to the second reaction containing means.

In one embodiment said enzyme is derived from white-rot fungus. In one embodiment, the fungus is selected from the group comprising Phanerochaete chrysosporiu , Dichromitus sgualens, Phlebia radiata , Lentinula edodes, Tra etes versicolor, Coriolopsis occidentalis, and Rigidoporus lignosus .

It is preferred that the enzyme is a peroxidase. In one embodiment, the substrate is Mn(ll). It is preferred that Mn(II) is added in the presence of an α-hydroxy acid and H ₂ 0 ₂ . In such a case the reaction intermediate is a

Mn(III) - α-hydroxy acid complex. In one embodiment, the α- hydroxy acid is selected from the group comprising lactic, malonic, malic, oxalic, pyruvic and tartaric acid.

It is not intended that the present invention be limited to the compounds exemplified below. The compounds to be degraded may be selected from the group comprising olefins, diols, organic acids, halogenated and non- halogenated aromatics and polyaromatics, dyes and lignin, including halogenated lignin such as chlorolignin. Halogenated aromatics of particular importance are the chlorinated aromatics, including but not limited to pentachlorophenol, trichlorophenol, and dichlorophenol. Important dyes decolorized by peroxidase include crystal violet, bromothylmol blue, methyl green, arsenazo, phenol red, methylene blue, brilliant blue G, brilliant blue R, thymol blue and ethidium bromide. A representative hydroxy ketone is cyclohexanone. Other compounds of some importance in waste include toluene and formaldehyde.

The present invention is also useful for decolorization of waste. In particular, the method of the present invention is useful for the decolorization of paper mill effluent and waste containing dyes.

DESCRIPTION OF THE DRAWINGS

Figure 1 schematically shows the membrane feature of the present invention.

Figure 2 schematically shows the membrane feature of the present invention in the context of a preferred enzyme for degradation.

Figure 3 is an instrumentation diagram schematically showing one embodiment of the device of the present invention in the context of a preferred enzyme for degradation. Figure 4A is a graph showing the absorption spectra of a waste stream.

Figure 4B is a graph showing the absorption spectra of a waste stream following treatment according to one embodiment of the method of the present invention.

Figure 5A is a graph showing the absorption spectra of a waste stream.

Figure 5B is a graph showing the absorption spectra of a waste stream following treatment according to a preferred embodiment of the method of the present invention.

DESCRIPTION OF THE INVENTION This invention relates to biological treatment of waste, and particularly to the degradation of organo-halides contained in liquid wastes. The present invention contemplates both a method and device for degrading a diverse group of compounds contained in a solid or liquid (e.g., paper pulp, pulp mill effluent, sludge, wastewater, etc. ) .

The invention employs enzymes in combination with a semi-permeable membrane system in a reaction containing means, such that the enzyme, substrate and supporting reagents are separated by a partition from the compounds to be degraded (see Figure 1) . It is contemplated that an enzyme, incapable of passing through the membrane, will undergo a reaction with a substrate on the "clean side" of the partition so as to generate a reactive intermediate capable of passing through the semi-permeable membrane to the "application side" of the partition into the compound- containing liquid or "application stream", thereby degrading the compounds.

Unlike prior approaches, the approach of the present invention allows the enzyme to remain localized in an environment where it is stable and productive for much longer periods of time. In this configuration, the enzyme is not inhibited by waste components. Consequently, far

less of the enzyme is consumed, yielding a major savings. Further, the concentrations of the different reagents in the reaction mixture can be monitored and controlled more easily to achieve optimal concentrations and conditions (e.g., pH) to generate the best rates and yields.

While the present invention contemplates that the reactive intermediate may passively travel through the membrane, this approach is inefficient. Indeed, in large scale systems, passive transfer is very slow and largely ineffective. It is preferred, therefore, that the intermediate be subjected to a force to drive it across the membrane. In one embodiment, the present invention contemplates applying a pressure to the reaction mixture so as to force the reaction intermediate across the membrane. There are significant advantages to using a force to drive the intermediate. First, since the mass flux is toward the application stream, there is little or no fouling of the membranes for long periods of time since oils and particulates are continuously swept from the application side of the membrane by the pressure differential. To further exploit this advantage, a counter-current mass transfer may be achieved, if the nature of the application stream allows, by pumping the material to be treated in the opposite direction of the intermediate generating stream, thus exploiting pressure and concentration differences between both streams to the fullest advantage. In the event of high viscosity, chemical incompatibilities or large particulates in the application stream, the flux may be collected from the filtration device and introduced to the stream separately upstream from static or agitated mixing.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In one embodiment the enzyme used is derived from the white-rot fungus P. chrysoεporium. It is preferred that the enzyme is a peroxidase such as a manganese peroxidase. In one embodiment, the substrate is Mn(II) that is added in the presence of an α-hydroxy acid and hydrogen peroxide. In such a case the reaction intermediate is a Mn(III) - α- hydroxy acid complex (see Figure 2) . Where lactic acid is employed, the intermediate is a Mn(lll) -lactate complex. A semi-permeable membrane provides a practical method of keeping the Manganese (III) generating system separate from the application matrix while allowing the Mn(III) complex to reach the eventual point of use. In one embodiment, this is accomplished by performing the reaction on the high pressure side of a membrane device and allowing the Mn(IIl) complex to flux through the membrane and into the application stream. Importantly, the membrane is sized so as to retain the enzyme while allowing the Manganese (III) complex to pass into the application stream. The conditions of the reaction involving the enzyme are monitored and controlled. The optimal pH is 5.0 for enzymatic Mn (III) production. This is in contrast to the optimal pH (pH 2.5 - 3.0) for Mn(III) oxidation of compounds in the application stream. This embodiment is adaptable to any application where aqueous Mn(IIl) complexes are useful for degradation of compounds and particularly organo-halides contained in liquid wastes. This approach to bioremediation represents a significant advance over the current state of the art. Figure 3 schematically shows one embodiment of the device of the present invention. In this embodiment, manganese peroxidase derived from white-rot fungus is provided via providing means (100) , along with other reagents (water, hydrogen peroxide and Mn(II) substrate), to

a reaction containing means or reservoir (200) to create a reaction mixture, thereby generating a reaction intermediate. The reservoir (200) is connected via a flowing means (300) to a chamber (400) having a semi- permeable membrane partition (500) . The membrane (500) is not permeable to the peroxidase but is permeable to the reaction intermediate Mn(III) . A pressure is applied to one side of the membrane via a pressure applying means (600) so as to force the reaction intermediate across the membrane. At this point the reaction intermediate can be collected and added to a second containing means wherein the compounds to be degraded are contained, thereby degrading the compounds. In one embodiment, the reaction intermediate is added by pumping the intermediate from the first reaction containing means to the second reaction containing means. The enzyme can then be recirculated back from the chamber (400) to the reservoir (200) via the flowing means (300) for further reactions.

The reaction mixture is monitored and controlled to provide the best possible Mn(III) production rate per unit volume, factoring in allowances for enzyme stability, Mn(II) to Mn(III) conversion efficiencies, and flux of non- converted reactants. The soluble enzyme remains stable and active for many hours of continuous operation. A typical reaction occurs at 20°C (there can be an in-line heat exchanger for temperature adjustments) at pH 4.5-5.5 under controlled conditions, with constant feeding of hydrogen peroxide, an α-hydroxy acid, and Mn{II) . This generates a yield of Mn(III) of approximately 5-10 mM/hr/mg enzyme or 300-500 mg/hr/mg enzyme.

The bioremediation system of the present invention need not be large. A protein concentration of 1.0-2.0 mg per liter in a reservoir (200) of ten liters, connected to a chamber (400) with a holdup volume of five liters having a

membrane (500) of twenty-five square feet of surface area is capable of generating enough reaction intermediate to process 750 - 10,000 liters per hour of contaminated water. The volume of the reservoir (200) , and consequently the recirculation and reactant volumes, should be kept to a minimum to maintain the enzyme concentration as high as possible for purposes of stability and complete conversion. On the high pressure side of the membrane (500) , there should be monitoring and/or control elements for a) enzyme, peroxide and Mn(II) concentrations, b) pH, c) flow rate, and d) transmembrane pressure differential. On the low pressure side of the membrane (500) , there should be monitoring and/or control elements for a) Mn(III) concentration, and b) flux rate. The entire system can be placed conveniently under the control of individual loops or cascaded into a local batch controller or minicomputer for more exacting applications.

Experimental

The following examples serve to illustrate certain preferred embodiments and aspects of the present invention and are not to be construed as limiting the scope thereof.

In the experimental disclosure which follows, the following abbreviations apply: eq (equivalents) ; M (Molar) ; μM (micromolar) ; N (Normal) ; mol (moles) ; mmol (millimoles) ; μmol (micromoles) ; nmol (nanomoles) ; g (grams) ; mg

(milligrams) ; μg (micrograms) ; L (liters) ; ml (milliliters) ; μl (microliters) ; cm (centimeters) ; mm (millimeters) ; μm (micrometers) ; nm (nanometers) ; °C (degrees Centigrade) .

Unless otherwise indicated, enzyme was obtained from P. chrysoεporium strain BKM-F-1767 (ATCC #24725) which was maintained and grown essentially according to Tien & Kirk Meth. Enz. 161:238 (1988). Production of spores was done in tissue culture flasks (Corning 25160-225) containing 100ml

of the following (per L) lOg glucose; lOg malt extract; 2g peptone; 2g yeast extract; Ig asparagine; 2g KH ₂ P0 ₄ ; Ig MgS0 ₄ ^• 7H ₂ 0; Img thiamine • HC1; 20g agar. After three days to several weeks, the spores are washed out with sterile water and kept at 4 ^a C until use.

Growth conditions can be selected to either produce predominantly Lignin peroxidase or Manganese peroxidase, respectively, by varying the MnS0 ₄ concentration. In both cases, the fungus was grown under nitrogen-limiting conditions to induce secondary metabolism. The growth media is shown in Table 1. The list of trace elements is shown in Table 2.

MnS0 ₄ concentration was either 10 ppm (180μM) for predominant Lignin peroxidase production or 40 ppm (740μM) for exclusive Manganese peroxidase production.

The cultures were inoculated with 5x10 ^s spores / ml either in 2.8L Fernbach flasks with 1L medium or in a 15L stirred tank (New Brunswick FS 314 with F-14 100 tanks) with 12L medium. After two days of growth, veratryl alcohol and MnS0 ₄ was added and the cultures were flushed (1L) or sparged (12L) with pure oxygen twice daily. Manganese peroxidase was excreted into the medium after five to seven days. Depending on the growth conditions, the white rot fungus produces Manganese peroxidase (MnP) to about 80% purity, based on protein concentration. After filtration and concentration of the extracellular fluid, the crude enzyme can be used without further purification. However, proteases that are present in the concentrate could degrade the enzyme and, therefore, decrease the activity during application. To separate the enzymes of interest from proteases, a simple DEAE cellulose column chromatography step gives a 50-70% yield of partially purified, active and stable enzyme.

The crude enzyme concentrate is dialyzed against lOmM of a suitable equilibration buffer, pH 7.0-8.0, loaded on an appropriate sized column and eluted with a linear NaCl gradient 0-->0.5M. MnP elutes at around 0.1M NaCl and LiP (predominantly isozyme H ₂ ) at around 0.15M NaCl. The active peak fractions are concentrated by ultrafiltration (Amicon PM30 or equivalent) and stored frozen until use.

The crude Manganese peroxidase is stable for several days at room temperature. In one example, the crude enzyme had lost less that 10% of its activity after 24 hours at 20 ^β C. The stability of the enzyme at 20 ^a C can be greatly increased by the elimination of contaminating proteases.

Enzyme which had been purified by the method above, retained over 93% of its activity after storage at room temperature for 77 days.

EXAMPLE 1 Using the purified enzyme, a number of model organic compounds were screened to determine which could be oxidized

by the enzymatically produced Mn(III) . Table 3 shows that Mn(III) is the reactive species generated by Manganese

peroxidase which is responsible for the oxidation of organics. Note that "+" indicates a positive reaction as measured by disappearance of a peak, marked color change and/or shift in absorbance. Note further that " (+) " indicates a less pronounced positive reaction.

Some reactions shown in Table 3 are pH-dependent, e.g., 2,4,6-Trichlorophenol reacts fast at pH 3.0 and slow at pH 5.0.

EXAMPLE 2 In this example, the use of Manganese peroxidase and a semi-permeable membrane system is examined to degrade 2,4,6- Trichlorophenol. In the first experiment, a 50 liter starting solution (lOmM Na-lactate, pH 5.0; 0.50mM MnS0 ₄ ; 0.25mM H ₂ 0 ₂ > was prepared. Manganese Peroxidase (6,000 units) was added to 4 liters of this start solution to make a reaction solution. A 50 liter treatment solution (50mM Na-acetate, pH 3.0; 60ppm(3g) 2,4,6-Trichlorophenol) was employed.

The starting solution was pumped into the reaction solution at a rate of approximately 0.8 liters per minute and the reaction solution was filtered through three cassettes (15 sq. ft.) of Millipore Pellicon 10K MWCO at a rate of 0.8 liters per minute. Thereafter, the flux was added to the treatment solution which was mixed by a diaphragm pump for a faster reaction.

When the reaction was monitored by spectral change of the treatment solution, there was only a 25% change (see Figures 4 and 4B) (Δ A ₂₇₄ was a factor of 2.6) . Measurement of the reaction intermediate indicated that the Mn(III) lactate concentration was 16 to 50% of the expected value. Interestingly, the flow rate was only about 0.5 liters per minute.

From the result, it appeared that the Na-lactate concentration was too low and that Mn(III) precipitated in the reaction solution, resulting in a suspension unable to cross the filtration membrane. This suspension also decreased the flux rate. Clearly, the concentration of lactate, MnS0 ₄ , enzyme and H ₂ 0 ₂ have to be balanced to provide the maximum delivery of Mn(lll) -lactate to the substrate to be oxidized.

To solve the problem, a new 50 liter start solution (50mM Na-lactate, pH 5.0; 0.50mM MnS0 ₄ ; 0.25mM H ₂ 0 ₂ ) was prepared. Manganese Peroxidase (5,400 units) was added to 4 liters of this start solution to make a reaction solution. A new 50 liter treatment solution (50mM Na-lactate, pH 3.0; 30ppm(1.5g) 2,4,6-Trichloro-phenol) was employed. The solutions were pumped and filtered as before except that the treatment solution was equipped with a pH probe to adjust the pH to below 4.0. During the experiment, the pH did not rise above 3.4.

When the reaction was monitored by spectral change of the treatment solution, there was approximately a 100% change (see Figures 5A and 5B) (Δ A ₂₇₄ was a factor of 11.5) . Measurement of the reaction intermediate indicated that the Mn(III) lactate concentration was 84-100% of the expected value. The flow rate was a satisfactory 0.7 liters per minute.

EXAMPLE 3 In this example, the impact of membrane size on flux rate was demonstrated. Three membranes were employed: 1) an Amicon PM 10 with a 10,000 MW cut-off; 2) an Amicon PM 30 with a MW cut-off of 30,000 Daltons; and 3) an Amicon YM 30 with a MW cut-off of 30,000 Daltons and having low protein binding characteristics. A 100 ml starting solution was prepared (25mM Na-lactate, pH 5.0; ImM MnS0 ₄ ; 0.5mM

H ₂ 0 ₂ ) . Manganese Peroxidase (1.5 units per ml) was added and pressure was applied to the reaction mix. The flux was collected and the time was recorded (see Table 4) .

Note that the 30,000 MW membranes clearly show a better flux rate than the published 10,000 MW membranes.