WO2004080620A2

WO2004080620A2 - Bio-reactive permeable barrier for the degradation of organic contaminants

Info

Publication number: WO2004080620A2
Application number: PCT/EP2004/002549
Authority: WO
Inventors: Rodolfo Vignola; Adriano Bernardi; Pasquale Sacceddu; Raffaello Sisto
Original assignee: Enitecnologie S.P.A.
Priority date: 2003-03-13
Filing date: 2004-03-10
Publication date: 2004-09-23
Also published as: WO2004080620A3; ITMI20030477A1

Abstract

A reactive system is described for the treatment of contaminated water, comprising an inert permeable carrier medium consisting of pumice or expanded clay on which a high number of microorganisms are laid, as a bio-film, selected for their capacity of bio-transforming the contaminants found in water.

Description

BIO-REACTIVE PERMEABLE BARRIER FOR THE DEGRADATION OF ORGANIC CONTAMINANTS

The present invention relates to a reactive permeable barrier for the degradation of organic contaminants.

More specifically, the invention relates to a permeable bio-reactive barrier wherein the remediation system consists of a particular inert permeable medium on which microorganisms are laid, at high concentration, suitable for the degradation of organic contaminants which are transformed into C0₂ and H₂0 or non-toxic products.

The presence of aromatic hydrocarbons and chlorinated solvents in groundwater beneath industrial sites is a common situation, due to leakages or the spilling of liquid products on the ground and their subsequent percolation.

The elimination of these contaminants through conventional techniques, such as the "pump and treat" system which consists in sucking the water from the groundwater, and subjecting it to a remediation treatment on the sur- face, has a number of drawbacks which restrict their use. High energy and labour costs are among the most relevant drawbacks . The technical problems to be faced during the treatment are also important, such as, for example, the transfer of the contaminant from one point to another in the site, due to adsorption and desorption phenomena (Cat- wright, GC . 1991. Limitations of pump and treat technology. Pollution Eng. November, pages 64-68; Hasbach, A. 1993. Moving beyond pump and treat. Pollution Eng. March pages 36-7, 8) . An emerging technique for the treatment of groundwater consists in the use in situ of permeable barriers, placed perpendicular to the direction of the groundwater flow, capable of removing the contaminants .

The most relevant advantages of this technique lie in the substantial reduction in the energy and labour costs, the possibility however of using the site for other purposes, during the treatment, thanks to the lack of surface structures, is not of lesser importance.

The most efficient mechanisms for functioning of bar- riers are based on the use of adsorbing materials or on systems capable of promoting degradation through a chemical or biological approach. The most widely used chemical approach consists in the reduction, on the part of the metal iron, of compounds such as, for example, aliphatic organo- chlorinated products or metals with a high oxidation num- ber, such as chromium Cr⁺⁶.

The biological approach, generally more favourably accepted by public opinion, makes use of the capacity of particular microorganisms of destroying contaminants . This in situ bioremediation technique has been usefully employed for groundwater contaminated by petroleum hydrocarbons (Hutchins, S.R. 1995. In situ bioremediation of a pipeline spill using nitrate as electron acceptor In; Hinchee R.E. (Ed) Applied Bioremediation of petroleum hydrocarbons pages 143-153. Battelle Press., Columbus, Ohio).

In general the bio-barriers described in literature are based on the utilisation of high degradation activity microorganisms .

It is also described that the efficacy of biological barriers can be enhanced by immobilizing the microorganisms selected for the bio-transformation on particular inert, permeable mediums. In this way, a higher stability and the control of the biological process are guaranteed (US 6,337,019) . The organic contaminants present in water are transformed, when they pass through the barrier, into C0 and H₂0 or less toxic compounds and more easily attacked by the other microbial populations of the site.

Numerous materials can be used as inert mediums for the production of permeable bio-barriers, their selection however is extremely important for reducing the initial investment costs and to avoid establishing unfavourable conditions during the running of the degradation system.

For example, although microorganisms carried by granu- lar peat or steel balls (Yerushalmi, L. 1999. Biodegrada- tion, 10, 341-352), show a good initial performance, they subsequently reveal bio-fouling conditions which lead to a progressive decrease in the barrier permeability.

In the case of peat, this phenomenon is linked to the production of organic substances of interest to other microorganisms in the groundwater.

It has now been found that by using pumice or expanded clay as carrier medium for microorganisms, and by making use of these reactive systems for the formation of bio- barriers, stable systems are obtained, capable of operating with a high efficiency in removing contaminants from groundwater and capable of avoiding bio-fouling.

Pumice and expanded clay granules assure an optimum adhesion of the microorganisms, have a good mechanical re- sistance, an optimum surface/volume ratio, a low density together with a high permeability. In addition to all these characteristics useful for preparing a good biological reactive system stable for a long period of time, there is also a wide availability at low cost. In accordance with the above, an object of the present invention relates to a reactive system for the treatment of contaminated water, comprising an inert permeable carrier medium consisting of pumice or expanded clay on which a high number of microorganisms is immobilized, selected for their capacity of bio-transforming the contaminants present in water .

A further object of the present invention relates to a permeable bio-reactive barrier for the treatment of contaminated water wherein the decontamination system consists of the reactive system previously defined.

The system described can be inserted in groundwater as a reactive zone or as a gate (the point where the plume of contaminants is directed) of a barrier, in the configuration called "funnel and gate" schematised in figure 1. In particular, the figure shows a schematisation of a bio-barrier in the funnel and gate configuration inserted in a containment system prepared for the safety of ground- water beneath an industrial site on the coast, but it definitely has a more general meaning. This system has particular advantages due to the fact that the microorganisms immobilized in the form of a bio- film, and therefore constantly present, selected from the autochthonous species, are the most active in the degradation of the contaminants present in the site to be re- claimed. These microorganisms are also present in a large number and in the most suitable place, i.e. at the interception of the plume of contaminants .

The bio-barrier object of the present invention is particularly useful for the treatment of water contaminated by organic and chlorinated organic compounds . In particular, the organic products of environmental importance which can be bio-degraded, according to an oxidative mechanism operating under aerobic and icro-arophilic conditions, are: benzene, ethyl benzene, styrene, toluene, o-, m- and p-xylene, methyl terbutyl ether, naphthalene, alkyl naphthalenes, and the chlorinated organic products are: 1,2- dichloroethane, chlorobenzene, di-chlorobenzene, tri- chlorobenzene, dichloromethane. The chlorinated organic products which can be biode- graded through a reduction mechanism operating under anaerobic conditions are: tetrachloro ethylene (PCE) , tri- chloro ethylene, 1,2-dichloro ethylene, vinyl chloride, 1, 1, 1-trichloroethane, carbon tetrachloride, chloroform, dichloromethane, chloromethane. In the former case, the treatment is more effective if oxygen is added to the water to be treated, which can be effected by the insufflation of air, air enriched with oxygen and in the presence of other electron-acceptors, complementary or alternative to oxygen, such as nitrates, or by the addition of hydrogen or magne- sium peroxides.

The autochthon icrobial populations capable of degrading aromatic hydrocarbons under aerobic or micro- arophilic conditions, and organo-chlorinated solvents under anaerobic conditions, were isolated from the water removed from two different contaminated industrial sites, one similar to a refinery, due to the presence of aromatic hydrocarbons and the other to a landfill as a result of the presence of organo-chlorinated compounds in addition to other types of products.

These populations were then grown under suitable cultural conditions and the kinetic parameters of the degradation activities were determined, in order to verify their efficacy. The microorganisms were then immobilized on inert carrier mediums by means of techniques normally used for the adhesion of microorganisms. In practice, the microorganisms were cultivated in batch, with direct contact of the carrier, in the columns filled with the pumice or expanded clay carrier medium, respectively, by the inoculation of 10-20% (vol/vol) of a saline medium (MSM) (Nielsen R.B. & Keaseling J.D., 1999, Biotechnol . Bioeng. 62, 161-165) containing one of the contaminants to be treated, which also represents the sole source of carbon for the aerobic/micro- arophilic microorganisms. The culture thus obtained was left to slowly recirculate in the column, with an up-flow inside each column, using the most suitable conditions, at room temperature, for the cellular multiplication. The immobilization operation lasted a week for the aerobic bio- barriers and a month for the anaerobic bio-barrier. The possibility of using pumice as carrier medium, having a particle size ranging from 0.3 to 50 mm and a density between 0.5 and 1.5 g/ml, or clay with a particle size of between 0.5 and 30 mm and a density ranging from 0.5 and 1.5 g/ml, was verified.

In accordance with the present invention, the best carrier medium consists of pumice with a particle size ranging from 0.4 to 0.6 mm and a density of 0.48 g/ml, or clay with a particle size ranging from 1.8 to 2 mm and a density of 0.56 g/ml.

The inoculum used (10⁷-10⁹ cells/ml) for the preparation of the bio-film on the inert material of the bio- barrier, both aerobic and anaerobic, can vary from 1 to 20% of the empty volume of the column, according to the reac- tivity of the microorganisms.

The aerobic inoculum used was obtained by the enrichment of the groundwater associated with the refinery through a procedure which consisted in diluting 10-20% of groundwater in MSM containing 20 mg/1 of toluene as sole carbon source. The anaerobic inoculum was, in turn, obtained through the enrichment of groundwater associated with the landfill by means of a procedure analogous to the previous one, which consisted in diluting 10-20% of groundwater in MSM containing 130 mg/1 of PCE and 450 mg/1 of sodium lactate as electron-donor and carbon source.

The stock cultures used for the inoculum and the kinetic characterization tests of the microorganisms, were produced by subsequent sub-cultivations of bi-weekly en- richment, wherein 20% of the culture was transferred to a fresh medium. These operations were effected for about three months for the aerobic culture and six months for the anaerobic culture, at room temperature and under the most suitable operative conditions for each type of consortium. The degradation activity of the microbial populations, both suspended and immobilized on carrier mediums, confirmed the possibility of using autochthon populations in the barrier for the degradation of contaminants present in groundwater . The K_m values, the semi-saturation constant for the uptake of the substrate-contaminant, which indicates the affinity towards the substrate, and V_max, the maximum specific velocity of the substrate uptake, for the aerobic degradation of toluene, proved to be 1.66 mg/1 and 3.70 mg/h-mg, respectively, of dry biomass . The data obtained for the anaerobic degradation of PCE were: K_m 33.3 mg/1 and V_max 0.634 mg/h-mg of dry biomass .

The populations were characterized from a morphological and physiological point of view. As far as the anaerobic species are concerned, the characterization of the bacterial phenotypes showed, as predominant morpho-types, the sporigenous strains of the genus SRB Desulfotomaculum and the vibrioid strains belonging, most probably, to the Desulfovibrio genus. As far as the aerobic species is concerned, the tolu- ene-oxidant bacterial population proved to almost completely consist of mobile bacillary cells, lophotrichous , pigment producers which can be diffused on King medium, forming fluorescent colonies at the Wood lamp, to be at- tributed to the Pseudomonas genus.

Bacteria belonging to the actinomicete gram-positive Rhodococcus erythropolis species, were also found in a significant quantity.

The genera Pseudomonas and Rhodococcus are known in literature for their capacity of degrading toluene (Har- wood, C.S., Parales, R.E. 1996. The beta-ketoadipate pathway and the biology or self-identity Annu. Rev. Microbiol . 50: 553-90) .

The presence of denitrifying bacteria characterized as Pseudomonas Stutzeri, capable of oxidizing toluene in i- cro-aerophilia, using nitrate as electron acceptor, was also detected in the bio-mass .

The autochthonous microorganisms were immobilized on pumice or expanded clay inside columns conceived so as to have minimum wall effects and preferential channels, using suitable ratios between the particle size and diameters of the columns .

The degradation of toluene and para-xylene, while passing through the aerobic column/bio-barrier, was fol- lowed, and different conditions were simulated. In particular, concentrations and flows were examined in order to enable the abatement of the concentrations of contaminants to values lower than 15 and 10 μg/1, for toluene and para- xylene, respectively. The bio-barrier of the invention, de- veloped in laboratory simulation apparatuses, proved to be capable of carrying out a bio-degradation activity for a period not shorter than 18 months. The treatment of water contaminated by aromatic hydrocarbons was effected under aerobic conditions, by operating at different operative conditions, experimenting critical parameters such as the linear flow rate, the contaminant concentration, the effect of the presence of different quantities of salt in the water treated. The experiments were also effected with real groundwater . The results showed a high efficiency in removing the contaminating hydrocarbons, higher than 99% under the different conditions tested, and a complete absence of problems due to bio-fouling.

As far as the degradation of aliphatic organo- chlorinated products is concerned, the bio-barrier prepared in the laboratory, carried out under anaerobic conditions, showed its efficiency for a period of six months, during which PCE levels below the law limits (1.1 μg/1) were reached in the process developed. EXAMPLES

Chemical analyses

GC/MS analyses for the identification of compounds in the reference groundwater:

The analyses were carried out on water samples, in particular on products extracted with CH₂C1₂ or on products as such, with the head-space technique.

The system used was GC/MS Mod. MAT/90 of Finnegan; the gas chromatographic column used was a PONA (length 50 m x

0.21 I.D. and 0.5 μm of film) of Hewlett-Packard. The car- rier (Helium) flow rate measured at 35°C proved to be 0.6 ml/ in. 500 μl of the head space were injected for each sample, by drawing with a gas syringe (heated) , from the phial kept under equilibration for 2 h at 70°C. The mass spectrometer operated in E.I. (electronic impact) at 70 eV. and at a resolution of 1500 in the mass interval 30-120 (a.m.u.) and at a scanning rate which was such as to acquire a spectrum every 0.8 sec. Detection limit: about 20

μg/1.

Qualitative analysis of the products detected in groundwater of the reference site for the treatment of chlorinated solvents in anaerobiosis (landfill)

The analytical investigation effected on the water samples collected in and around the site, showed a heterogeneous concentration, coherent with the "landfill" func- tion covered in recent times. The results of the tests are indicated below.

GC-Mass (head space) Cyclopentene, cyclopentane, methyl cyclopentane, methyl terbutyl ether (MTBE)*, benzene*, cyclohexane, toluene, m- xylene*, p-xylene, o-xylene*, trimethyl benzene (blend of isomers)*, tetramethyl benzene, naphthalene, indane, in- dene,

* most abundant compounds GC (CH₂C1₂ extract) in addition to all the compounds identified in the head space, the following products were found:

2-methyl-naphthalene; 1-methyl-naphthalene; blend of dimethyl-naphthalenes; phenanthrene; phthalates; tetrachloro ethylene (PCE) ; trichloro ethylene (TCE) . Quantitative analysis of the main contaminants Quantitative analysis of organic compounds (μg/1) : MTBE 713; benzene 299; toluene 10; ethyl benzene 4; p-xylene

148; m-xylene 48; o-xylene 764; tri ethyl benzene 251; naphthalene 252; methyl naphthalene 74; PCE 30; TCE 40; Quantitative analysis of ions (mg/1) : Cl^~ 4034; SO₄ ⁼80; Na⁺ 2847; Ca⁺⁺ 178; Mg⁺⁺ 348; Fe⁺⁺ 1; Pb⁺⁺ 6.

The analysis showed traces of the industrial refinery activity (aromatic hydrocarbons, diesel) and the treatment of exhausted oils. GC analysis of the products found in the groundwater of the reference site for the treatment of aromatic hydrocarbons in aerobiosis (refinery)

Hydrocarbons: toluene 300 μg/1; benzene 10 μg/1; ethyl benzene 4 μg/1; p-xylene 950 μg/1; trimethyl benzene 25 μg/1; naphthalene 272 μg/1; methyl naphthalene 74 μg/1.

Inorganic ions: Cl^" 15.6 g/1; S0₄ ⁼ 2 g/1; N0₃ ^" 0.8 g/1; Na⁺

9.5 g/1; Ca⁺⁺ 0.31 g/1; Mg⁺⁺ 1.07 g/1.

In view of a possible insertion of the bio-barrier in the groundwater considered, it is important to have the presence of sufficient amounts of inorganic nutrients, in particular nitrogen, which should otherwise be adequate for keeping the microorganisms .

EXAMPLE 1

Preparation of the stock anaerobic culture Groundwater samples were collected in one litre con- tainers, completely full, and immediately sent to the laboratory.

50 ml portions of water were introduced into 160 ml phials (Weathon) containing 50 ml of the MSM medium, ad- justed to pH 7, consisting of:

Na₂S0 1 g/1; NH₄C1 0.2 g/1; K₂HP0₄ 0.1 g/1; KH₂P0₄ 0.055 g/1; MgCl₂ • 6 H₂0 0.2 g/1; MhCl₂- 4 H₂0 0.1 g/1; CoCl₂ 0.17 g/1; ZnCl₂ 0.1 g/1; CaCl₂ 0.2 g/1; H₃B0₃ 0.01 g/1;

NiCl₂ ^• 6 H₂0 O.05 g/1; Na₂M0₄ ^• 2 H₂0 0.02 g/1; Yeast extract 0.05 g/1.

Resazurine (redox indicator): 4 ml of an 0.2% solution. The phials were insufflated with N₂ in the head space, immediately before the addition, to the culture medium, of Na₂S (0.5 g/1) and Cisteine-HCl (0.5 g/1) as reducing agents .

130 mg/1 of PCE (from a 2% mother solution) were added as electron-acceptor contaminant. Sodium lactate in a concentration of 450 mg/1 was added as carbon, energy and electron source. The phials, sealed with a butyl rubber plug and aluminum ring-nut, were incubated in an oven, under static conditions, at 28°C. The head space of the phials was de- spaced with nitrogen, and new quantities of PCE and sodium

lactate were added by means of a syringe, every 7÷10 days, after a bacterioscopica_l control of the culture (at the O.M. in phase contrast at 400x) and dosage of PCE at the GC.

The blowdown and batch fed was repeated until a growth (a density) of the microbial cells was observed, adequate for use as stock culture. EXAMPLE 2 Preparation of the aerobic stock culture.

Aliquots of groundwater of 100 ml together with 100 ml of saline sterile solution according to the Harms &_ Zehnder formula (Alvarez, P.J.J. and T.C.O.M. Vogel . 1995. Wat. Sci . Tech. 31: 15-28), were introduced into 500 ml ampoules .

After insufflation of sterile air into the head space, the ampoules were sealed using ring-nut nippers; quantities of toluene equal to 20 mg/1 were introduced through the rubber plug. The ampoules were incubated at 24÷25°C, the contents being maintained under stirring by means of a magnetic anchor (400 rpm) on a Variomag stirrer. The contents of the ampoules were subjected daily to bacterioscopic con- trol and toluene dosage with GC, in order to intervene with new insufflations of filtered air (by means of a gassing- manifold) and repeat the toluene addition, by means of a syringe, as carbon and energy source. The formation of micro-flakes of bacterial cells, suspended in the stock, was assumed as indicating that the mineralization of the hydro- carbon substrate had taken place. In order to maintain the aerobic stock culture over a period of time, a portion (25%) of each culture was transferred to a new system on

fresh saline medium, consisting of: a₂HP0₄ • 2 H₂0 1.75 g/1; KH₂P0 0,5 g/1; (NH₄)₂S0 0.5 g/1; MgCl₂ ^• 6 H₂0 0.1 g/1; Ca(N0₃) • 4 H₂0 0.05 g/1; Solution of oligo-elements 1 ml . EXAMPLE 3 Characterization of microbial populations The activity related to: isolation and characterization of the main strains forming the consortium of microorganisms of the groundwater, kinetic verification of their degradation efficacy, adhesion of the biomass to the carrier medium and verification of the activity on the colo- nized carrier medium.

The groundwater associated with the refinery was used for preparing the aerobic culture by adopting as growth medium the saline solution prepared according to Harms & Zehnder: Na₂HP0₄ • 2 H₂0 1.75 g/1; K₂HP0₄ 0,5 g/1; (NH₄)₂S0 0.5 g/1; MgCl₂ ^■ 6 H₂0 0.1 g/1; Ca(N0₃)₂ ^• 4 H₂0 0.5 g/1. 1 ml/1 of the following solution for micro-nutrients was

added to the above solution: Co(N0₃)₂ • 6 H₂0 0,291 g/1;

A1K(S0₄)₂ • 12 H₂0 0.474 g/1; CuS0₄ 0.16 g/1; ZnS0₄ ^• 7 H₂0

0.288 g/1; FeS0₄ ^• 7 H₂0 2.78 g/1; MnS0₄ ^• H₂0 1.69 g/1; Na₂Mo0₄ • 2 H₂0 0.482 g/1; Ca(N0₃)₂ ^• 4 H₂0 2.36 g/1. The fi- nal pH was 6 . 8-7 .

The estimate on Tryptone Soy Agar (SA) of the overall aerobic microbial charge present in the groundwater, gave a value corresponding to 4.0 • 10⁴ colonial units (UFC/ml) af- ter 72 h of incubation at 25°C.

A fraction of the microbial community present, measured as 1.0 • 10² Most Probable Number (MPN)/ml, proved to consist of bacterial strains capable of developing also under anoxia, as reducers of the nitrate ion. A screening operation, effected in order to examine the aerobic phenotypes, showed the presence of four main phenotypes, carrying oxidative metabolic predispositions

(they are capable of using gas oil for motor vehicles as C source) . The colonial units consist of mobile bacillary cells, which are gram-negative, nitrate-reducers, producers of green pigment which can be diffused on King medium. They can be ascribed to strains of the Pseudomonas genus. Other isolated products, of minor importance, belonging to systematic heterogeneous gram-variable groups (Artrobacter) also oleo-oxidant, were isolated from an enrichment culture prepared with mineral salts and gas oil .

The microbial populations shown in the following table, were found in samples of the groundwater associated with the landfill, collected in duplicate at different heights of the groundwater Microbial populations in groundwater

The number of colonial units grown after 72 h of incubation at 28°C was used for calculating the total microbial charges (aerobic on TSA and anaerobic on Reinforced Clos- tridial Agas) . An estimate of the denitrifiers (as MPN on Nitrate Stock) was effected after 120 h from the inoculum. The amounts of sulphate reducing (SRB) and hydrocarbon oxidizing bacteria (on Bushnell-Haas Stock + 5 μg/1 of gas oil) were registered after 20 days of incubation at 25°C.

The quantity of microorganisms, in terms of total aerobic microbial charge and distinct physiological groups, is representative of an environment which, on the whole, must be defined as being vertically homogeneous . The substantial homogeneity of the biological system, from which the nine samples were collected, was also confirmed by the results of a screening effected for the morphological examination of the phenotypes, which found a limited number of types forming colonies, in amounts well distributed among each other.

The population of the strict aerobic germs - capable of forming colonies on a solid medium, in the absence of oxygen and nitrates, during three days of incubation, estimated as being in the order of ten thousand units/g of sample - is represented by a sole phenotype. This evidence makes it possible to consider the existence of a selective pressure, due to phenomena deriving from previous contaminations, or underway, in the eco-system object of the survey.

The morphotypes of sulphate-reducing anaerobic bacteria can mainly be ascribed to sporigenous genera. More specifically, the characterization of the bacterial phenotypes indicated, as predominant morphotypes, the sporigenous strains assignable to the SRB Desulfotomaculum genus and vibrioid strains belonging, most probably, to the genus Des ul fovibri o . EXAMPLE 4

Determination of the microbial biomass .

The biomass was determined as "total suspended solids" (TSS) dried at 103÷105°C.

Aliquots of 10÷30 ml of the culture were collected un- der stirring and filtered under vacuum with the Millipore system using a Whatman 934 AH filter; the filter was put in an oven at 105°C for one hour. The TSS values were determined as weight difference between the filter treated with the culture and the untreated filter. EXAMPLE 5

Degradation activity test of toluene in batch.

10 ml of culture medium are added to 1 mg of TSS biomass collected from the stock growth culture, in a 130 ml bottle. Increasing quantities of a saturated solution of

toluene in water, up to a maximum of 100 μl, were added with a syringe, up to a final concentration of toluene ranging from 0.1 to 5 mg/1, leaving 100 ml as head space; the sample was incubated under stirring at 25°C. The toluene was determined, at suitable times, by analysis of the head space.

Controls were effected on samples without cells and samples consisting of saline medium with cells without toluene.

All cell samples used in the determination of K_m and V_max were collected simultaneously from the mother growth culture, at such a concentration as to have 1 mg TSS of cells in the test.

The initial rate, for each toluene concentration, was determined by measuring the concentration of the substrate

at least 4 times, during a total period of 1÷2 h; during this period of time there were no significant changes in the biomass (<5%) . EXAMPLE 6

Degradation activity test of PCE in batch. Two weeks before the determination of the degradation kinetics, the growth culture was left to sediment and the suspended portion was separated from the solid portion (particles of sulphides precipitated with microorganisms attached) , in order to eliminate or reduce the heterogene- ity of the system. 35 ml of culture medium with 12 mg (TSS) of biomass, collected from the stock growth culture, were added to a 60 ml bottle. Sodium lactate at a concentration of 450 mg/1 was used as electron donor. Increasing amounts

(up to a maximum of 250 μl) of a saturated aqueous solution of PCE, were added with a syringe to have final concentrations ranging from 100 to 1000 μg/1; the sample was incubated at room temperature. The samples were subjected, at suitable times, to PCE dosage, by collecting 100 μl from the head space. Controls were effected with samples without cells and with samples consisting of saline medium with cells without PCE.

The cell samples (1 mg TSS) used for the determination of K_m and V_max, were collected contemporaneously from the mother growth culture. The initial rate was determined, for each PCE concen- tration, using at least 4 dosages every 30 min. , during a total period of 2 h; during this period of time there were no significant changes in the biomass (<5%) . EXAMPLE 7 Preparation of the simulation equipment of aerobic bio- barriers in the laboratory. Pumice columns

The dimensions of the carrying particles and the diameter of the columns were chosen so as to avoid wall effects and preferential channels (diameter of columns/diameter of particles > 50) (Martin, H. 1978. Chem. Eng. Sci . 33, 913).

A glass column of 2.5 x 30 cm (diameter x length) was packed with pumice (particle size 0.4-0.6 mm; density 0.48 g/ml) forming a free space of about 66%, see fig. 2. The column was connected, by means of Teflon fittings and tubes, to the peristaltic pump for the water feeding. All the system components, tubes, columns and reservoirs, were covered with silver paper to reduce the production of phototrophic microorganisms . The column was subjected for 4 days to water conditioning with a flow rate of 8 ml/h and for further 4 days with saline medium only.

30 ml of aerobic culture at a concentration of 10⁹ cells/ml (about 8 mg TSS/ml) were charged into the column together with a saline medium containing 20 mg/1 of tolu- ene, for the preparation of the reactor; the stock-culture was recycled for 7 days. After this period, the concentration of the cells eluted from the column became stabilized at about 10⁴-10⁵ cells/ml, the recycle was interrupted, the feeding of fresh substrate being continued and also the elution at a flow rate of 16 ml/h, corresponding to a linear rate of 1.1 m/day. The elution was continued and the concentration of toluene at the inlet was varied every 4 days, reducing first to 15, then to 10, to 5 to 1.5 and fi- nally 0.7 mg/1. This latter concentration was used, the following month, to stabilize the colonization of the material contained in the columns . EXAMPLE 8 Expanded clay columns An expanded clay column was prepared analogously to the pumice column.

The glass column 10 x 60 cm was filled with expanded clay (with a particle size of about 1.8-2 mm and a density of 0.56 g/ml) forming a free space in the column of about 57%.

The column structure, carrier mediums, tubes and pumps, the adhesion technique and stabilization of the biomass were completely similar to those used for the pumice column. EXAMPLE 9 Preparation of the simulation equipment of the anaerobic bio-barrier in the laboratory. Pumice column

The simulation equipment consisted of a glass column of 2.5 x 5 cm, filled with pumice. The column was fed with a solution of nourishing medium MSM, adjusted to pH 7, consisting of: Na₂S0 1 g/1; NH₄C1 0.2 g/1; K₂HP0₄ 0.1 g/1;

KH₂P0₄ 0.055 g/1; MgCl₂ • 6 H₂0 0.2 g/1; MnCl₂ ^• 4 H₂0 0.1 g/1; CoCl₂ 0.17 g/1; ZnCl₂ 0.1 g/1; CaCl₂ 0.2 g/1; H₃B0₃

0.01 g/1; NiCl₂ • 6 H₂0 0.05 g/1; Na₂M0₄ ^• 2H₂0 0.02 g/1; Yeast extract 0.05 g/1; Resazurine (redox indicator): 4 ml of a solution at 0.2% of Na₂S (0.5 g/1) and Cisteine-HCl

(0.5 g/1) as reducing agents.

An electron donor was added to the medium, sodium lac- tate, initially at 450 mg/1 and subsequently reduced in order to have, in the final step, a sodium lactate/PCE molar ratio = 2. This solution was continuously insufflated with N₂.

The immobilization of the anaerobic biomass, collected from the stock culture deriving from the groundwater of the reference site for the treatment of chlorinated solvents under anaerobic conditions (landfill) , on the pumice carrier medium of the bio-barrier was effected through a batch phase and subsequently a feed-batch phase. The batch phase consisted of the cultivation of the inoculated biomass, 10⁸-10⁹ cells/ml, on the carrier medium.

The elute containing the microorganisms still in suspension, was recycled in up-flow onto the column until an equilibrium phase was reached, verified by the cellular concentration in the elute, which stabilised at 10⁴ cells/ml .

The feed-batch phase consisted of the substitution of an aliquot of exhausted stock with fresh stock. The complete preparation including the batch and feed-batch phase lasted one month. EXAMPLE 10 Tests in bio-barrier simulation apparatuses .

The aerobic bio-barrier simulation apparatuses consist of two columns, one 30 cm long, with a diameter of 2.5 cm, filled with pumice, and the other 60 cm long, with a diameter of 10 cm, filled with expanded clay.

The columns were fed with a solution of nourishing medium, continuously insufflated with air, to which suitable amounts of an aqueous solution of contaminants were added - by means of a peristaltic pump and a three- path mixing system - contained in a defor able tedlar bag in order to avoid head space problems in the container and allow a constant feed of contaminant.

The experimentation was carried out at room te pera- ture. The effect of passing through the bio-barrier simula- tion apparatus , on the removal of contaminants was evaluated by analysing the eluted sample, collected in a test tube equipped with an aluminum ring-nut with a Teflon septum, completely full, to avoid head space. The analysis was effected by means of gas-chromatography, associated with a purge and trap system, which allow the dosage of contami¬

nants directly in water, in amounts lower than 10 μg/1. The results obtained in a series of tests carried out by varying the feeding flow and the composition, are indicated in the following examples. The column for the bio-barrier simulation under anaerobic conditions, 5 cm long and with a diameter of 2.5 cm, filled with pumice, was handled in the same way, with the only difference that the saline nourishing medium was insufflated with N₂ instead of air. EXAMPLE 11

Determination of the toluene biodegradation in the pumice bio-barrier.

The degradation of contaminants at different concentrations and water flow rates, was determined after condi- tioning the column for at least 5 days, allowing the elution of at least 20-30 volumes of column. At the end of the conditioning time, samples were collected for the following two days, for the determination of the contaminants.

The samples to be analyzed at the GC were collected in 40 ml tubes, equipped with a Teflon plug with a gastight metal ring-nut. For the determination of the organic compounds a GC was used with a FID or ECD detector, equipped with "purge and trap", which allows the direct dosage of the contaminants without manipulation. Low boiling compounds contained in aqueous solutions can be directly analyzed with this method; the use of large volumes to be treated allows an accurate analysis of samples at low concentrations, < 10 μg/1.

The method envisages an amount of sample ranging from 15 to 40 ml.

The analysis is carried out with a purge and trap system, consisting of an 0-1 Analytical 4551-A and a 4560-PC, with a transfer line connected to a Gas-Chromatograph HP- 6890, having a split-splitless injector and a FID and/or ECD detector, according to the method described hereunder. 5 ml of sample are collected by the system and subjected to counter-current extraction with helium at a flow rate of 20 ml/min, for a period of 11 minutes at 25°C; the substance is fixed in a tenax and active carbon trap, this is a Purge mechanism.

The trap is subsequently heated to 180°C during 60", for a time of 8' and, still under a helium flow, all the matter released from the trap is quantitatively transferred to the GC HP-6890 through the transfer line. ' At the same moment, the GC is started and the gas- chromatographic analysis is carried out.

The method for the gas-chromatographic analysis envisages:

an isotherm step of 7' at 36°C: o a programmed step of 10°C/min up to 70°C followed by 1 minute under isothermal condition;

a programmed step of 17°C/min up to 120°C followed by 2 minutes under isothermal condition;

a programmed step of 30°C/min up to 220°C followed by 1 minute under isothermal condition;

• (off)

BACK INLET (SPLIT/SPLITLESS) FRONT DETECTOR (FID)

Mode: Split Temperature: 300°C

Initial temp. : 300°C Hydrogen flow; 40 ml/min

Pressure: 8.92 psi Air flow: 450 ml/min Split ratio: 50:1 Mode: Constant column + makeup flow

Split flow: 99.1 ml/min Combined flow: 45 ml/min Total flow: 104.2 ml/min Makeup flow: on Gas saver: off Makeup gas type: Helium Gas type: Helium Flame: on

Capillary column: HP 19091J-413, HP-5 5% Phenyl methyl siloxane (30 meters) x (320 μm) x (0.25 μm) . Table 1 shows the toluene concentrations at the pumice bio- barrier outflow, run under different operative conditions . Table 1 Functioning of the pumice bio-barrier in the biodegradation of toluene under different operative conditions .

EXAMPLE 12

Determination of the biodegradation of p-xylene in the pum- ice bio-barrier.

P-xylene was used as contaminant, in the same pumice bio-barrier as example 1; the results obtained under different operative conditions are indicated in table 2.

Table 2 Functioning of the pumice bio-barrier in the biodegradation of p-xylene under different operative conditions .

EXAMPLE 13

Determination of the biodegradation of toluene/p-xylene blends in the pumice bio-barrier.

A blend of toluene/p-xylene was used as contaminant in the same pumice barrier as example 1; the results obtained under different operative conditions are indicated in table 3.

Table 3 Functioning of the pumice bio-barrier in the biodegradation of toluene/p-xylene blends under different operative conditions .

The removal of hydrocarbons under the conditions examined is higher than 99%. EXAMPLE 14

Determination of the toluene biodegradation in the expanded clay bio-barrier.

The carrier medium of expanded clay substantially confirmed the results obtained with the pumice; the results of the bio-barrier with expanded clay as carrier medium (10x67 cm) are indicated in the table 4 below.

Table 4 Functioning of the expanded clay bio-barrier in the biodegradation of toluene

The results obtained, which are of particular importance for the concentrations examined, show the removal of contaminants, according to the results of the gas- chromatographic analysis .

The possible mechanism, at contaminant concentrations which are not compatible with the concentration of dissolved oxygen, could be the partial oxidation of the con- taminants, with transformation into non toxic products, together with the contribution of microorganisms capable of using nitrates as electron-acceptors under the conditions of micro-aerophilia generated in the bio-barrier. EXAMPLE 15 Stability of the bio-barriers

The simulation apparatuses for the aerobic degradation were run for six months, in order to collect information on the stability of the bio-film and on its degradation capability with respect to toluene and p-xylene. The results obtained during six months are indicated in table 5 below.

Table 5 Bio-barrier stability, linear rate 100 cm/day (Pumice 2.5 x 30 cm; expanded clay 10 x 30 cm)

The results demonstrate not only that the aerobic bio- reactive system is capable of lowering the concentration of aromatic hydrocarbons well below the groundwater specifications established by the Italian regulations, but also that, when immobilized on both the inert carrier mediums used (pumice and expanded clay) , it keeps its degradation capacities unaltered for a long period of time. It should be pointed out that the above performances are obtained at a linear rate of 1 m/day, which are generally at the upper limit of applicability of the permeable barriers with a reactivity which is not only biological The hydraulic properties of the simulation apparatuses also remained stable with time, indicating that the growth of the biomass is under control, and bio-fouling phenomena, which would cause a reduction in the permeability of the reactive medium and the formation of preferential paths, do not intervene. EXAMPLE 16 Saline effect on the bio-barrier efficacy

The data found in the groundwater of the reference site for the treatment of aromatic hydrocarbons under aero- bic conditions (refinery) showed the high concentration of NaCl close to 15 g/1. The possible saline effect on the bio-barrier activity was therefore examined.

The nourishing solution was brought to this NaCl concentration by means of monthly additions of 5 g/1. The data shown in the table refer to the results obtained three months after reaching the concentration of 15 g/1.

Table 6 Saline effect on the degradation of toluene/p-xylene contaminants in the bio-barriers, linear rate 100 cm/day.

The bio-degradation capacity was tested under suitable conditions which mainly interested the use of sodium lactate as electron-donor. A 10 month experimentation was effected using a 2.5 x 5 cm column, at a linear rate of 40 cm/day. The concentration at the column inlet was about 2 mg/1 PCE. The sodium lactate/PCE ratio was changed during the experimentation until a molar ratio of 2 was reached in the final step, with lactate at 3 mg/1.

Table 7 Stability of anaerobic bio-barrier.

The results obtained showed the efficacy of the bio-barrier even at reduced concentrations of sodium lactate, with linear rates and PCE concentrations in line with what is normally found in groundwater described in literature.

Claims

1. A reactive system for the treatment of contaminated water, comprising an inert permeable carrier medium consisting of pumice or expanded clay on which a high number of microorganisms capable of bio-transforming the contaminants found in water, is laid, in the form of bio-film.

2. The reactive system for the treatment of contaminated water according to claim 1, wherein the inert permeable carrier medium consists of pumice having a particle size ranging from 0.3 to 50 mm and a density of between 0.5 and 1.5 g/ml or of clay having a particle size ranging from 0.5 to 30 mm and a density ranging from 0.5 to 1.5 g/ml.

3. The reactive system according to claim 2 , wherein the pumice has a particle size ranging from 0.4 to 0.6 mm and a density of 0.48 g/ml and the clay has a particle size ranging from 1.8 to 2 mm and a density of 0.56 g/ml.

4. A bio-reactive permeable barrier for the treatment of contaminated water, whose decontamination system consists of the reactive system according to any of the previous claims.

5. A process for the treatment of contaminated water wherein the water is sent through the reactive system of claim 1 or the barrier of claim 4.

6. The process according to claim 5 , wherein the treat- ment is carried out on water contaminated by organic or chlorinated organic compounds, under aerobic conditions, through a reactive system comprising microorganisms selected from aerobic microorganisms of the genus Pseudomonas.

7. The process according to claim 6 , wherein the treatment is effected with the addition of oxygen and in the presence of electron-acceptor compounds .

8. The process according to claim 6, wherein the organic compounds consist of benzene, ethyl benzene, styrene, tolu- ene, o- , m- and p-xylene, methyl terbutyl ether, naphthalene, alkyl naphthalenes, and the chlorinated organic products which are degradable under aerobiosis consist of tricoloro ethylene (TCE) , 1,1-dichloro ethylene, 1,2-dichloro ethylene, 1, 1-dichloroethane 1, 2-dichloroethane.

9. The process according to claim 5, wherein the treatment is carried out on water contaminated by chlorinated organic compounds, in anaerobiosis, with a reactive system which comprises microorganisms selected from anaerobic microorganisms of the genus SRB Desulfotomaculum and the ge- nus Desulfovibrio .

10. The process according to claim 9, wherein the chlorinated organic compounds consist of vinyl chloride, 1,2- dichloro ethane, chlorobenzene, dichloro benzene, trichloro benzene, tetrachloro ethylene, trichloro ethylene, 1,2- dichloro ethylene, 1, 1, 1-trichloroethane, carbon tetrachlo- ride, chloroform, dichloromethane, chloromethane .

11. The process according to claim 9, wherein the treatment is carried out by feeding an adequate electron-donor to the reactive system, in a molar ratio of between 3 and 0.5 for each chlorine atom present in the molecule of chlorinated organic compound.

12. A process for the preparation of the reactive system of claim 1, comprising: preparation of a column with an inert permeable carrier medium consisting of pumice or expanded clay: feeding to the column a culture of microorganisms together with a nourishing medium and the contaminant to be bio-degraded; - recycling the microorganism culture until the number of cells eluted from the column is constant, running the column in a batch and feed-batch phase, wherein an aliquot of exhausted stock is substituted with fresh stock.

13. The process for the preparation of a permeable reactive barrier according to claim 4, which comprises the preparation of a channel and the filling of the same with the reactive system of claim 1.