NL8602985A - Removing organic contaminants from soil - by homogenising and breaking down soil, and treating with microorganisms - Google Patents

Abstract

In cleaner soil contaminated with organic substances, the soil is continuously homogenised and kept in motion, with comminution of the soil particles, and is exposed to the action of microorganisms which can break down the organic matter. Bioconversion reactor suitable for process is also claimed.

Description

'1 "Τ' Ν.0. 33957 ν *

Method for cleaning soil contaminated with organic substances and apparatus suitable for carrying out such a method.

The invention relates to a method for cleaning soil contaminated with organic substances.

The biotechnological cleaning of soil, which is contaminated with organic substances of many kinds and properties, is a high priority in many industrialized countries. Namely, the costs associated with physico-chemical treatment methods are often high and often deliver soil systems, which are not suitable for agricultural or recreational purposes for a long time. On the other hand, the aforementioned biotechnological cleaning has the advantage that it is a so-called "mild" treatment method, whereby the ecological value of the soil to be purified is kept at the highest possible value and the cost aspect compared to that of the energy-intensive physico-chemical treatment methods can be considered acceptable.

More in particular, the so-called "land-farming" is known from the prior art as a biological reactor system, which type of reactor system is simple and relatively inexpensive to implement (Veerkamp W., and Zewald CA, Land + Water - nu / Milieutechniek, October 1985 and Zewald CA et al, PT / Civil Engineering 39 (1984) No. 6 and the book "Petroleum Microbiology", RM Atlas (ed.), Macmillan Publishing Company, New York, 1984) biz. 569-570.

According to this "land-farming" method, contaminated soil is spread evenly over a plastic film in the open air or covered with a plastic film. Usually the drainage water from the system is collected and, if necessary, treated. Active microorganisms capable of decomposing the organic contaminants may already be present in the contaminated soil or may be added thereto. To optimize the treatment conditions, the soil can be cultivated, the surface of the contaminated soil can be vegetated and its water content and temperature controlled. The advantage of such a system is the associated low costs. An important drawback of this method, however, is the variable reliability in view of the problems regarding the control / management of the soil homogeneities and their treatment as well as the ecological parameters.

40 A second system involves the composting of contaminated soil 8602985 6 * 2 (Zewald CA et al. PT / Civil Engineering 39 (1984) No. 6. The main differences from the above-described "land-farming" method are an elevated temperature and greater processing intensity The advantage of the latter system seems to lie in an increased biodegradation rate, but the main drawback, however, lies again in the problems regarding the control / management of the soil homogeneities. the organic substances present in the contaminated soil are at the elevated temperature used, which in turn results in air pollution problems.

Hexachlorocyclohexane (HCH) is mentioned as a characteristic example of a substance that is fairly difficult to remove from contaminated soil. Indeed, it has been found that significant amounts of HCH are still present in high concentrations in soil contaminated by a chemical plant 30 years ago (Slange, J, M.S. Thesis, LH Wageningen, 1984). Although HCH has been shown to be biodegradable using mixed and pure microorganism cultures (Hill and McCarty, Water Pollution Control Federation Meeting, Kansas City, 1966; Haider, K., et al. Arch. Microbiol. 104, 1975, biz. 113-121 and Tu, CM, 20 Arc, Microbiol. 108, 1976, 259-263), the microbial conversion of HCH in a natural environment has been found to be severely limited by non-ideal conditions.

A semi-continuous or batchwise process has been found which has the advantages of the simplicity of the "land-farming" system 25 without its drawbacks in terms of limited controllability. More particularly, the invention relates to a method for cleaning soil contaminated with organic substances, wherein the contaminated soil is continuously homogenized and kept in motion by comminution of the soil particles, during which operation the contaminated soil is exposed to the action of microorganisms, which can break down the organic substances. The process conditions are preferably adjusted in such a way that optimum conditions are obtained for the microorganisms. Examples of such favorable conditions are a temperature in the range of from 20 to 30 ° C, for example, and the addition to the contaminated soil of the amount of air (oxygen) required for aerobic microbial conversion, preferably of more than 5% by volume, as well as amount of water required or any nutrients required for the microorganisms, such as N and P in the form of ammonia and phosphate.

40 By homogenizing the contaminated soil, the clumps and the like contained therein 8692985 3 are greatly reduced. · In such soil, the contaminants present are also distributed as homogeneously as possible and their accessibility to microorganisms capable of decomposing these contaminants is reduced, optimal. Among other things, the toxicity of the pollutants, which will often be present in concentrated form in non-homogenised soil, has greatly decreased due to the spread of the contaminants over the total amount of soil, so that the action of microorganisms is often only good now. is possible · 10 By setting optimal conditions for the microorganisms in question, optimal growth of the microorganisms is possible on the one hand and optimal degradation of the contamination (s) on the other hand. On the basis of the optimum growth of the microorganisms, these will increase in number. increase strongly so that a very rapid decomposition of the organic pollution (s) occurs. Compared to that of the known methods discussed above ("land-farming" and composting), this degradation is particularly good in terms of speed.

Due to the very good homogenization of the contaminated soil, which is (almost) continuously continued during the treatment, the mass transport factor is no longer the limiting factor as in the above known methods.

In the method according to the invention, use is made of microorganisms already present in the soil or, if necessary, the contaminated soil is inoculated with soil microorganisms or activated sludge (cultivated in a laboratory), etc. In this way, cleaned soil is obtained , which is ecologically acceptable and possibly valuable. An important advantage of the method according to the invention is the complete absence of by-products, which are often obtained in the physiochemical treatment systems.

As examples of organic contaminants, which can be broken down by micro-organisms, the substances listed in Table A below with the associated micro-organisms can be mentioned. · 8602985 * 4 _TABLE A_

Substances Organisms Condition3)

Hydrocarbons soil, water and sea organisms ae (petroleum) such as Pseudomonas, Achromobacter,

Arthrobacter, Micrococcus, Nocardia,

Vibrio, Acinobacter, Brevibacterium,

Candida, Trichosporon cutaneum,

Cunninghamella, Flavobacterium,

Corynebacterium, Mycobacterium,

Cladosporium, Aspergillus,

Penicillium

Branched alkanes P. aeruginosa, Corynebacterium, Breviae bacterium

Cyclic aliphatic Pseudomonas, soil microorganisms, ae hydrocarbons mixed culture of Mycobacterium and Arthrobacter, Nocardia, Acinetobacter

Aromatic hydrocarbon- Soil micro-organisms, Pseudomonas, ae substances Arthrobacter, Nocardia, Candida

Polycyclic flavor- Pseudomonas, Flavobacterium, as well as aetic hydrocarbons various yeasts, fungi and algae N-butylbenzene, Pseudomonas ae n-propylbenzene

Phenol, toluene, Trichosporon cutaneum ae cresolen

Phenol, cresols Bacillus stearothermophilus ae

Phenol, benzoate anaerobic microorganisms an

Phenol, benzoate, anaerobic sludge, Moraxella, an cresols, monohydroxy- Pseudomonas benzoates

Benzoate, hydroxy-Rhodopseudomonas an benzoates

Phthalate esters Pseudomonas acidovorans, various soil microorganisms

Phthalate esters and Micrococcus, Nocardia, aphthalic acids Arthrobacter, Pseudomonas 8602985 »5 (Table A continued)

Stoffen_Organismen_ Condition3)

Phthalic acids Mixed cultures an

Trichloromethane, Activated sludge, groundwater and bromodichloromethane, dibromochloromethane, tribromomethane

Dichloromethane Mixed culture, Pseudomonas, ae

Hyphomicrobium, activated sludge 3-Chlorobenzoate, Pseudomonas ae 4-chlorobenzoate, 4-chlorophenol, 3-5-dichlorobenzoate, 4-Fluorobenzoate 2-Fluorobenzoate Pseudomonas, Alcaligenes ae 4-Fluorobenzoate Pseudomonas ae 2-Chlorophenol, Pseudomonas , ae 4-chlorophenol, 2,4-di-Alcaligenes chlorophenol, 2,6-dichlorophenol, 2,4,6-trichlorophenol

Pentachlorophenol Mixed culture ae 1,2,3- and 1,2,4-Tri- Soil organisms, mixed ae chlorobenzene culture

Monochlorobenzoates, Sewage ae 3.4- dichlorobenzoate 2-, 3-, 4-Chlorobenzoate Methanogenic consortia, 2-, 3-, 4-iodobenzoate, 2,4-, 2,5-, 3,4-, 3.5 - Dichlorobenzoate, and 2,3,6-Trichlorobenzoate 2,4-Dichlorophenoxy-Achromobacter, Flavobacterium, ae acetate, 3 * methyl ~ 4-Arthrobacter, Pseudomonas chlorphenoxyacetate

Chlorophenoxybutyrates Nocardia opaca ae 8602985 6 (Table A continued)

Substances Organisms Condition3) 2,4,5-Trichlorophenoxy-Pseudomonas cepacia ae acetate DDT Various bacteria, fungi an (ae) and algae; Pseudomonas and Fusarium

Lindane (gamma-HCH) Soil ecosystems, soil micro-ae, organisms; Pseudomonas, Clostridium

Aldrin Soil microorganisms ae

Dieldrin Pseudomonas, Bacillus, Trichoderma ae

Arthrobacter, Nocardia, soil organisms 2,2-Dichloropropionate Pseudomonas ae

Chloroacetate, Fluorine Pseudomonas, Moraxella ae Acetate

Parathion Pseudomonas, mixed cultures ae

Triazines Pseudomonas, lebsiella ae

Phenylurea Bacillus, Fusarium ae

Carbamates Several microorganisms ae

Dioxins, e.g. dibenzo-Beyerinckia ae-p-dioxin »1- and 2-chlorodibenzo-p-dioxin, 2,3-, 2,7- and 2,8-dichlorodibenzo-p-dioxin TCDD Several microbial cultures ae

Chlorinated Biphenyls Alcaligenes, Acinetobacter, ae

Achromobacter, activated sludge 8602985 7 »(Table A continued)

Fabrics_Organisms_Condition3)

Cyanides Bacillus, Chromobacterium, ae

Stemphilium, activated sludge

Ntril, e.g., aceto-Pseudomonas, Corynebacterlum, ae nitrile, propionitrile Nocardia, Brevibacterium and acrylonitrile a) ae = aerobic; an * anaerobic 8602985 8

The method according to the invention is carried out in a bioconversion reactor, which is characterized by a container, which is provided with at least one detachable lid serving as a filling and discharge opening, as well as a series of baffles, which are placed on the inner wall of the The container is provided with the baffles on the side remote from the container wall in the form of cutting or inserting members as well as of a drive device which serves to rotate the container.

Fig. 1 shows an embodiment of a reactor to be used for carrying out the method 10 according to the invention. More particularly, this reactor is characterized by a cylindrical container (1), provided with at least one detachable lid (2) serving as a filling and discharge opening, as well as a spiral series of baffles (3), mounted on the inner wall of the container . This container further comprises supply openings (4) and. (5) for supplying water, air, chemical additives, etc. In addition, these openings are also suitable for sampling, so that the progress of the process can be adequately monitored. Furthermore, the reactor according to the invention is provided with a drive device 20 (6), which serves to rotate the cylindrical container about the longitudinal axis.

Fig. 2 illustrates a side view of a baffle plate (3), which has a knife shape (7) on the side remote from the container wall and, moreover, is provided on at least one side with wing-like members 25 (8).

Fig. 3 illustrates a top view of part of the baffle (3), clearly depicting the wing-shaped members (8).

With regard to the dimensions of the reactor according to the invention, it is noted that, depending on the desired capacity, it can be large or small. The baffles present in the container have a height depending on the internal diameter of the container, which is preferably 5-20% of the internal container diameter. The height of the baffles is advantageously about 10% of the internal diameter of the container. The top of the baffle plates is advantageously designed in the form of knives or a saw, the height of the knife-shaped tips having a value of approximately d / 25 (d = internal diameter of the container). The wing-shaped members arranged on the side of the baffle plates, which serve to optimally mix the contaminated soil, have a length of about 8602985 9 d / 10 and are advantageously at an angle of 10-45 ° with respect to the container wall fitted · The pitch of the baffle spiral is about 0.5-2 m / 360 °, preferably about 1 m / 360 °.

The above dimensions for the dimensions of reap, versions of the 5 baffles and elements arranged thereon for optimum mixing and reduction of the contaminated soil can be adapted, if necessary or desired, to the properties of the soil to be cleaned.

The favorable results of the process according to the invention or the use of the above-discussed reactor according to the invention are further elucidated with reference to Figs. 4-7 indicated in Examples I-III.

EXAMPLE I

Fig. 4 shows the degradation rate for hexachlorocyclohexane (HCH) in contaminated soil at a temperature of 30 ° C for the land-farming method and the method according to the invention. In the method according to the invention, the contaminated soil is kept moving in a closed container and is homogenized partly by comminuting the soil particles. With regard to the parameters of both processes, reference is made to Table B below.

20

TABLE B

Parameters Reactor System Land-farming system 25 Amount of treated soil Kilos Kilos

Moisture content suspension of 100 g 20 vol.% Dry matter / 1

Oxygen content 22 vol.% (Air) 22 vol.% (Air); lower soil layers 30 may have a lower oxygen content.

From this Fig. 4 it can be deduced that the HCH has been completely removed in a period of 20-30 days by means of the method according to the invention. In comparison with the degradation rate of HCH for the land-farming system, also shown in Fig. 4, it appears that a considerably better result is achieved with the aid of the method according to the invention.

40 EXAMPLE II

In Fig. 5 the conversion rate of HCH at the more realistic temperature of 10 ° C for Dutch standards is shown in accordance with the manner described in Example I 8602985, 10. With regard to Fig. 4, it appears that the conversion rate of HCH for both systems has decreased considerably. However, the method according to the invention is far superior to the "land-farming" system.

From the above it also appears that an average temperature of more than 10 ° C is necessary for the degradation of HCH. Such a temperature control can easily be realized in a reactor according to the invention. On this basis, it can therefore be stated that the process according to the invention, carried out in a reactor according to the invention, is far superior to the land-farming system.

EXAMPLE III

In Figures 6 and 7, in addition to a high degree of homogenization and a temperature of 30 ° C, the influence of other parameters such as redox conditions, ie the amount of oxygen, is present in the contaminated soil (see Figure 6; oxygen content of 22 vol.%). for the aerobic microorganisms and 0 vol.% for the anaerobic microorganisms), as well as adding all kinds of microorganisms (see fig. 7; 20 oxygen content of 22 vol.% for the aerobic microorganisms and 0 vol.% for the anaerobic microorganisms). . From these Figures 6 and 7 it can be deduced that such parameters are important for a successful cleaning of contaminated soil. It is clear in this connection that the control resp. controlling such parameters is easier in a reactor according to the invention than in a landfarming system.

For illustrative purposes, Table C below lists some optimal conditions for HCH degradation.

30 TABLE C

Parameters Value

Temperature 20-30 ° C

Oxygen content 10-20 vol.% (Air) 35 Water content 40-60 vol.% 8602985

Claims (14)

Method for cleaning soil contaminated with organic substances by means of microorganisms, characterized in that the contaminated soil is continuously homogenized and kept in motion while the soil particles are reduced, the soil being exposed to the action of microorganisms which substances can break down, is exposed 2. Process according to claim 1, characterized in that the process conditions for the microorganisms are optimized. Method according to claim 2, characterized in that the contaminated soil is heated to a temperature in the range of 20-30 ° C. 4. Process according to claim 2 or 3, characterized in that the optimum amount of oxygen is supplied to the contaminated soil for an aerobic microbial conversion. Method according to one or more of claims 2-4, characterized in that the optimum amount of water is added to the contaminated soil for the microbial conversion. Process according to one or more of claims 2-5, characterized in that nutrients for the micro-organisms such as nitrogen and phosphorus in the form of, for example, ammonia and phosphate are added to the contaminated soil. 7. Process according to one or more of claims 1-6, characterized in that the contaminated soil is inoculated with additional cultures of soil microorganisms. 8. Bioconversion reactor, characterized by a container, provided with at least one detachable lid serving as a filling and discharge opening, and with a series of baffles mounted on the inner wall of the container, which baffles on the side remote from the container wall. in the form of cutting or insertion members as well as by a driving device suitable for rotating the container. Reactor according to claim 8, characterized by a horizontal cylindrical container (1) provided with at least one detachable lid (2) serving as a filling and discharge opening, as well as a spiral series of baffles (3) mounted on the inner wall of the container, said baffles on the side remote from the container wall being in the form of cutting or insertion members and by a drive device (6) suitable for rotating the container about the longitudinal axis. 8602985 t Reactor according to claim 8 or 9, characterized in that the baffles (3) present therein are provided with knife-shaped tips (7). Reactor according to one or more of claims 8-10, characterized in that the baffles (3) present in the container are provided on at least one side, substantially perpendicular to the baffle, with a wing-shaped member (8). Reactor according to claim 11, characterized in that the wing-shaped member (8) is arranged at an angle of 10-45 ° to the container wall. Reactor according to one or more of claims 8-12, characterized in that the height of the baffle plate is a value of 5-20% of the internal container diameter, the height of the knife tips (7) a value of 2-10% of the internal container diameter and the length of the wing-shaped member (8) is 5-15% of the internal container diameter. Reactor according to one or more of claims 8-13, characterized in that the container wall is provided with sample / supply openings (4) and (5). ***** 8602985