WO2009000967A1

WO2009000967A1 - A method for cleaning polluted soil

Info

Publication number: WO2009000967A1
Application number: PCT/FI2008/050328
Authority: WO
Inventors: Olli MÄENTAUSTA; Kari Steffen
Original assignee: Mzymes Oy
Priority date: 2007-06-27
Filing date: 2008-06-04
Publication date: 2008-12-31
Also published as: FI119501B; EP2158046A1; EP2158046A4; FI20070507A0

Abstract

The invention relates to a method for cleaning polluted soil, in which method, mycelial filaments are used in cleaning the polluted soil which filaments are added in substrate suitable for mycelial filaments and transferred to the soil to be cleaned. The method according to the invention is characterised in that the substrate containing mycelial filaments is dosed inside a filament tube (3; 9; 10), after which the filament tubes (3; 9; 10) are closed with an air-tight protective film and in the soil (1) to be cleaned are formed at least one planting hole (2) and at least one aeration hole (4) at a suitable distance from it. After this, the protective film is removed from around the filament tube (3; 9; 10) and the filament tube is fitted in the planting hole (2) made in the soil (1), after which an air feed channel (5) of an air feed device is installed in the aeration hole (4) and air is conveyed by the air feed device in the soil, whereby mycelial filaments start to grow from the planting hole (2) towards the aeration hole (4) simultaneously cleaning impurities in the soil (1) and rotting organic matter in the soil.

Description

A METHOD FOR CLEANING POLLUTED SOIL

The invention relates to a method for cleaning polluted soil (1), in which method, mycelial filaments are used in cleaning the polluted soil (1) which filaments are added in substrate suitable for mycelial filaments and transferred to the soil (1) to be cleaned.

Polychlorinated dibenzo-p-dioxins and dibenzofurans (together dioxins i.e. PCDD/Fs) are toxic organic chlorine compounds found almost everywhere in nature which are mainly generated from industrial and traffic emissions as a result of chlorination and incomplete combustion. In Finland, the most important sources of dioxin are anti-sapstain agents used at sawmills in which chlorophenols have been used as the effective agent and dioxins occur as impurities. Extremely high dioxin concentrations have been found at many sawmills.

Being liposoluble, dioxins closely combine in the organic matter of soil. Hence, high dioxin concentrations mostly occur in the surface layer of soil. The migration of these detrimental substances in surface and ground waters is insignificant at many sites. Dioxins are, however, extremely toxic even at low concentrations (in long-term exposure, even the concentration of 20 ng/kg in the environment can cause health hazards). They are developmentally and reproductively toxic and can affect, inter alia, the metabolism, enzyme production, hormone activity and cause changes in the nervous and immune systems. Thus, dioxins being carried along with dust from the sawmill topsoil or exposing through direct contact can cause a health and environmental risk.

The harmfulness of dioxins is partly based on their persistence and undecomposability. This property also impedes developing repair methods suitable for dioxins. At present, the most utilised repair method of dioxins is digging and transporting to a reception centre of polluted soil where the masses are sited at landfills. Part of masses polluted by dioxins can be disposed at a landfill of conventional waste. These masses are often slightly polluted and they fulfil the placement requirements set for a landfill of conventional waste of the European Council decision 2003/33/EC of 19 December 2002. Alternatively, the masses can be placed at a landfill of hazardous waste.

At present, the only usable and environmentally-friendly treatment method of masses extremely polluted by dioxins is, however, thermal treatment. This method also supports international guidelines and measures and national regulations (Finnish Council of State 22 August 2002/735) created for limiting and controlling environmental problems caused by persistent organic pollutants (POP compounds). According to the Council of State decree, persistent organic pollutants have to be decomposed or removed rather than placed at a landfill. Combustion can be considered the best usable technique in treating soils polluted by dioxins.

The largest source of dioxins in Finland is sawmill areas. The soil of sawmill areas often contains a lot of wood material and thus organic matter. At present, the only recommended and environmentally-friendly treatment method of masses polluted by dioxins is combustion. The treatment capacity of a combustion plant decreases in direct ratio as the amount of organic matter increases. When combusting organic matter, the gas cleaning system of the combustion apparatus clogs. Hence, the amount of material to be combusted has to be decreased for maintaining the operational capacity of the apparatus when treating masses containing great amounts of organic matter. This considerably increases the treatment costs of polluted soil with the combustion method and prevents the best usable method from becoming common as the treatment method of masses containing persistent organic pollutants.

The object of the invention is to provide a method by means of which the above- mentioned problems related to the cleaning methods of polluted soil are eliminated. Particularly, the object of the invention is to introduce a method by means of which polluted soils can be cleaned without combusting the polluted soil. Furthermore, the object of the invention is to introduce a cost-effective method by means of which e.g. ground polluted by dioxin can be cleaned without removing soil from the ground, and by means of which intensively polluted soils can be pre-treated so that the combustion treatment of such soils is provided simpler and more cost-effective.

The object of the invention is achieved with a method for cleaning polluted soil which is characterised by what is presented in the claims.

The method according to the invention is characterised by

- dosing substrate containing mycelial filaments inside a filament tube, after which closing the filament tubes with an air-tight protective film,

- forming in the soil to be cleaned at least one planting hole and at least one aeration hole at a suitable distance from it,

- removing the protective film from around the filament tube and fitting the filament tube in the planting hole made in the soil, - installing an air feed channel of an air feed device in the aeration hole, - conveying air by the air feed device in the soil, whereby the mycelial filaments start to grow from the planting hole towards the aeration hole simultaneously cleaning impurities occurring in the soil and rotting organic matter in the soil.

With such a method, it is possible to clean soil in a considerably simpler and cost- effective way than with recently known cleaning methods based on combusting the polluted soil because, when using such a method, it is not necessary to shift the polluted soil to a different place for the time of the treatment but the treatment can be realised on the spot by embedding filament and air feed tubes in the ground of the polluted soil. The method is also in practice extremely simple to implement because it is sufficient that a required number of holes of suitable depth are sunk in the ground of the land area in which holes the filament and air feed tubes are installed. Furthermore, growing mycelial filaments in the filament tubes and pumping air in the ground/soil in a heap are simple and low-cost measures in relation to the use and the operating costs of a waste combustion plant. Such a method can additionally be used in the treatment of intensively polluted ground/soil as pre-treatment by means of which the concentrations of harmful substances, such as dioxins, in the soil are reduced so much that the combustion treatment can be implemented in mass combustion plants in a considerably simpler and cost-effective way than with recent combustion methods. In an embodiment of the method according to the invention, as the substrate is used substrate manufactured of cleaned straw and bark and as the filament tube a perforated tube manufactured of stainless steel. In such substrate, it is possible to make the mycelial filaments grow as quickly and evenly as possible. The advantage of the filament tube manufactured of stainless steel is good resistance of corrosion and endurance of mechanical load (inter alia, soil pressure). In addition, filament tubes manufactured of stainless steel can be recycled, because they are durable and they can be easily cleaned of used mycelial filaments and substrate.

In an embodiment of the method according to the invention, as the protective film is used a plastic film from which is formed a closed air- and steam-tight package around the filament tube. By means of such a protective film, the filament tube is simply and cost-effectively provided inside a tight package preventing the evaporation of moisture. The substrate being inside a filament tube protected this way, it is easy to maintain suitable moisture in it for providing growth conditions as advantageous as possible during the growth stage of the mycelial filaments. In an embodiment of the method according to the invention, around one planting hole are made several aeration holes. When a filament tube is installed in such a planting hole and air feed tubes in aeration holes, mycelial filaments start to grow from the filament tube in the direction of all aeration tubes. Hence with such an arrangement, it is possible to make the mycelial filaments of one filament tube to spread in an area as large as possible. This is naturally advantageous when e.g. there is a lot of soil to be cleaned and/or the acreage of the land area is extensive.

In an embodiment of the method according to the invention, a planting hole is formed in the soil the depth of which is about 50-80 cm. Typically, the living conditions of fungal species suitable for cleaning soil are at their best close to the ground surface. Due to this, such a depth of the planting hole is extremely suitable for many fungal species. Furthermore, e.g. dioxin most often accumulates in organic soils in the vicinity of the ground surface. Then with the tube embedded in the depth of 50-80 cm, it is possible to clean the most part of impurities in the soil. Furthermore, if making holes deeper than this, the making of planting holes becomes slower and the costs increase, because more effective and expensive devices are required for making the holes.

In an embodiment of the method according to the invention, when cleaning soil piled up in a stack, in the upper part of the stack are formed several mainly horizontal planting holes and aeration holes are made below the planting holes. This way, it is possible to make the mycelial filaments grow effectively also from top downwards. In addition, this kind of an arrangement is easy to implement in practice when cleaning soil to be piled up in stacks.

In an embodiment of the method according to the invention, the planting holes are made in several rows and/or layers on top of each other. With such an arrangement, soil piled up in a stack can be cleaned very effectively when there is a lot of soil to be cleaned in relation to the area in use for cleaning, because then the cleaning can be performed in stacks which are small of their cross area but relatively tall.

In an embodiment of the method according to the invention, when cleaning polluted soil, planting holes are sunk in the soil and aeration holes around them at the distance of about 50 cm. This way, it is possible to make the mycelial filaments spread as evenly as possible in the soil of the area to be cleaned, whereby the area is treated throughout evenly and extensively. The invention will now be described in more detail with reference to the accompanying drawings in which

Fig. 1 shows a cross section of polluted soil in which are formed planting holes in which are installed planting tubes containing mycelial filaments grown in substrate and air feed tubes,

Fig. 2 shows a top plan view of the layout of planting and air feed tubes in accordance with Fig. 1,

Fig. 3a shows the layout of air feed and planting tubes in a second embodiment of the method according to the invention, Fig. 3b shows the layout of air feed and planting tubes in a third embodiment of the method according to the invention, and

Fig. 3c shows the layout of air feed and planting tubes in a fourth embodiment of the method according to the invention.

In a method according to the invention, soil 1 polluted by dioxin is cleaned. For this, substrate is manufactured of cleaned straw and bark in which are added mycelial filaments belonging to the fungal group of (name of the fungal group?) suitable for cleaning. The fungi belonging to this group have a non-specific manner based on peroxidase enzymes to decompose complex and awkwardly decomposing compounds. Hence, they are able to decompose many laboriously decomposing compounds, such as chlorophenols and polyaromatic hydrocarbons. After this, substrate containing mycelial filaments of this kind is dosed in filament tubes 3. The filament tubes are perforated tubes manufactured of stainless steel the outer diameter of which is about 100-150 mm. Next, the filament tubes are closed in air- and steam-tight plastic packages for about two weeks to grow mycelial filaments before installing the filament tubes in the soil 1 to be cleaned.

For embedding the filament tubes in the ground, several planting holes 2 have been sunk in the soil 1 of the land area to be cleaned and between them aeration holes 4 clearly smaller of their diameter than the planting holes. The distance of the planting holes 2 from the aeration hole 4 is in this case about 0.5 m and the depth about 50-80 cm. After sinking the planting and aeration holes, the plastic packages of the filament tubes 3 are removed and the filament tubes are fitted in the planting holes 2. Next, in the aeration holes 4 are conveyed air feed tubes 5. The air feed tubes are hoses manufactured of plastic or rubber, of the thickness of about 10-20 mm of their diameter, the ends of which to be fitted in the aeration holes 4 are obstructed and on the walls of which to be fitted inside the aeration holes are formed several, evenly distributed holes. Air to be fed in the air feed tubes is provided with e.g. a suitable air compressor (not shown in the figures) or by some other suitable air feed device by means of which pressure of about 2 bar suitable for the purpose and sufficient air flow are provided. In one air feed device, there are usually connected several air feed tubes. The air feed tubes are so long that they can be conveyed from the aeration holes to a pumping station to be located in a suitable place, in which station there can be one or more air feed devices depending on the size of the area to be cleaned and the number of required air feed tubes.

When the filament tubes 4 are installed in the aeration holes 3, air pumping is commenced which is maintained for the whole time of the growth stage. After the pumping of air has started, the mycelial filaments slowly start to grow towards air- containing soil coming into the ground via aeration holes. At the same time as the mycelial filaments grow, they decompose organic matter in the soil and clean and split impurities in the soil. Usually, this takes about 2-4 weeks depending on soil quality and weather conditions. After a suitable growth stage, the filament tubes are removed from the planting holes, whereby the filaments remaining in the ground further continue rotting the organic matter and cleaning the soil. The amount of impurities contained by the soil can be observed by taking samples of the soil. When treating slightly and moderately polluted land areas, it is usually possible to repair the area with the method so well that no after-treatment is required. When treating intensively polluted areas, the soil of the area can be after-treated with known ways e.g. by burning the pre-treated soil in a mass combustion plant. Then by mycelial filament treatment, it is possible to decrease the amount of organic matter combusted so much that the clogging of the combustion gas cleaning devices decreases substantially. This considerably decreases the repair costs of intensively polluted land areas. In the treatment of slightly and moderately polluted soils, most often combustion treatment is totally avoided. Then in such a situation, the method can save in costs incurring of, inter alia, earth moving and transport.

Figs. 3 a-c show some other embodiments of the method according to the invention. In these, polluted soil is treated piled up in a stack 6 or a space 7 closed with walls, open from the top. Such embodiments of the method are well suitable e.g. as the pre-treatment method of intensively polluted soil to be treated by combustion, because in them the polluted soil is removed from the ground and piled up on top of aeration tubes 8 set in the ground in a stack 6 (Figs. 3a and 3c) or in a box-like space 7 surrounded by walls (Fig. 3b). In these embodiments, after a soil layer of certain thickness, on top of the aeration tubes 8 are made one or more filament tube layers 9 in accordance with Figs. 3a and 3b or several single filament tubes 10 are set in the soil above aeration tubes 11 in each direction at even intervals in accordance with Fig. 3c.

The method according to the invention can naturally further differ in many aspects from the above-described embodiments. The position and order of the filament tubes and aeration tubes, the materials and diameters of the tubes and the materials of the substrate can vary, inter alia, in accordance with the type of the soil to be cleaned and with harmful substances contained by it. Also the fungal species utilised in the method can vary. In some embodiment of the method, it is possible to use two or more fungal species belonging to the same or different fungal group simultaneously, if feasible.

The invention is not limited to the described advantageous embodiments, but it can vary within the scope of the inventive idea presented in the claims.

Claims

1. A method for cleaning polluted soil (1), in which method, mycelial filaments are used in cleaning the polluted soil (1) which filaments are added in substrate suitable for mycelial filaments and transferred to the soil (1) to be cleaned, ch ara c t e ri s e d by

- dosing substrate containing mycelial filaments inside a filament tube (3; 9; 10), after which closing the filament tubes (3; 9; 10) with an air-tight protective film,

- forming in the soil (1) to be cleaned at least one planting hole (2) and at least one aeration hole (4) at a suitable distance from it,

- removing the protective film from around the filament tube (3; 9; 10) and fitting the filament tube in the planting hole (2) made in the soil (1),

- installing an air feed channel (5) of an air feed device in the aeration hole (4),

- conveying air by the air feed device in the soil, whereby the mycelial filaments start to grow from the planting hole (2) towards the aeration hole (4) simultaneously cleaning impurities occurring in the soil (1) and rotting the organic matter in the soil.

2. A method according to claim 1, ch arac teri s e d in that as the substrate is used substrate manufactured of cleaned straw and bark and as the filament tube (3; 9; 10) is used a perforated tube manufactured of stainless steel.

3. A method according to claim 2, ch ara c teri s e d in that as the protective film is used a plastic film from which is formed a closed air- and steam- tight package around the filament tube (3; 9; 10).

4. A method according to any one of claims 1-3, ch ar act eri s e d in that around one planting hole (2) are made several aeration holes (4).

5. A method according to any one of claims 1-4, ch ar a ct e ri s e d in that in the soil is formed a planting hole (2) the depth of which is about 50-80 cm.

6. A method according to any one of claims 1-5, by which method soil (1) piled up in a stack is cleaned, ch ar a c t e ri s e d in that in the upper part of the stack are formed several mainly horizontal planting holes (2) and that aeration holes (4) are made below the planting holes.

7. A method according to claim 5, c h a r a c t e r i s e d in that the planting holes (2) are made in several rows and/or layers on top of each other.

8. A method according to any one of claims 1-7, in which method, polluted soil (1) is cleaned by mycelial filaments, c h a r a c t e r i s e d in that in the ground are sunk planting holes (2) and around them aeration holes (4) at the distance of about 50 cm.

9. A method according to claim 8, c h a r a c t e r i s e d in that the holes (2, 4) are sunk in a mainly vertical position.

10. A method according to claim 8 or 9, c h a r a c t e r i s e d in that around one aeration hole (4) are sunk several planting holes (2).