BE1029690B1 - METHOD FOR CONTROLLING INVASIVE PLANTS BY CONDUCTIVE HEAT TREATMENT - Google Patents

Abstract

The present invention relates to a method for treating soil infested by invasive plants and/or by its underground network (rhizomes, roots, seeds) such as Japanese knotweed. The present invention proposes a process for treating infested soils based on in situ or ex situ conduction heating technology. The infested soils are brought to the temperatures required to destroy the aerial and underground network of invasive plants. The present invention relates to the adaptation of a technology used in soil remediation for the treatment of soil invaded by invasive plants: the invention relates to a heating system consisting of heating units arranged in a regular pattern in the area treat.

Description

1 BE2021/5655

METHOD FOR CONTROLLING INVASIVE PLANTS BY TREATMENT

THERMAL CONDUCTIVE

FIELD OF THE INVENTION

The present invention relates to a method for controlling invasive plants using conductive heat treatment. In particular, the invention relates to a heating system consisting of heating units targeting environments infested by invasive plants and their underground network.

In the same way, the present invention can also be used for the sterilization of soils contaminated by pathogenic microorganisms (bacteria, viruses, fungi, etc.).

BACKGROUND OF THE INVENTION

An invasive plant is defined as any exotic plant introduced into an ecosystem and capable of causing environmental, economic or human health harm. Invasive plants pose a threat to biodiversity. Indeed, they contribute to the disappearance of local species by competition or hybridization and thus disturb the ecosystem in which they establish themselves.

The invasion of environments by exotic plants has a significant economic impact: it contributes to the reduction of agricultural yields, to the erosion of the banks where they settle - which can lead to flooding - and also causes infrastructural damage. Building land with an invasive species suffers a strong depreciation in value. Today, many efforts are being made to restore colonized environments.

An example of an invasive species currently rampant, particularly in Europe, is the

Japanese Knotweed (Fallopia Japonica). Japanese knotweed, native to East Asia, is a herbaceous plant introduced in Europe at the beginning of the 19th century as an ornamental, fodder and bee plant. It was then introduced to North America, Australia and New Zealand. In a new environment without pathogenic, parasitic or phytophagous species capable of regulating its expansion, Japanese knotweed is now one of the 100 most problematic species in the world, listed in the Global Invasive species database.

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The competitive advantage of Japanese knotweed, leading to the disappearance of native species and the reduction of biodiversity, can be explained by various points:

Japanese knotweed is a plant that settles in humid environments and spreads mainly vegetatively, by means of rhizomes. Its root system forms a dense and relatively deep horizontal network, which can go up to 7 m in depth and extend horizontally up to 15-20 m around the foot.

Japanese knotweed has abundant foliage with large leaf areas, 5 to 12 cm long and 5 to 8 cm wide. These thick leaves hardly allow light to pass, which gives it a shading property against competing species.

In addition, Japanese knotweed produces allopathic substances based on phenolic derivatives causing necrosis of neighboring plants.

The existing means of combating invasive plants - and for example against the

Japanese knotweed - are diverse. Most control techniques target aboveground biomass, the most common control being mowing. Other techniques have been developed: deployment of an opaque tarpaulin over the plants to restrict access to light, thermal weeding, biological control by inserting herbivorous predators, etc. However, these techniques have proven to be ineffective due to the plant's ability to regenerate new plants from the developed root and rhizome system.

To overcome these constraints, excavation, a generally costly method, aims to eliminate a population of invasive plants - as well as their root system - in one operation. Nevertheless, techniques for excavating invaded areas have also shown their limits. Indeed, the root and rhizome network being dense, extensive and deep, the area to be excavated is difficult to delimit and all the rhizomes may not be removed. A 1cm long fraction of rhizome is able to regenerate a viable plant and new shoots. Furthermore, the excavation produces waste to be evacuated and stored or treated as well as a risk of dissemination of the said invasive plants.

Other control methods, such as chemical or biological treatment, target the underground parts of the plant. Among examples of the prior art on this subject,

WO2013/023294A1 proposes a saline solution injection technique targeting rhizomes and roots to control the spread of invasive plants.

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In addition, there are maximum and minimum critical temperatures at which the aerial and underground parts of a plant cannot survive. The patent

EP2409566A1 presents an innovative technique for destroying plants and seeds of invasive plants by freezing the infested soil using a cryogen such as nitrogen. Another means of control would be heat treatment. Indeed, the underground parts of invasive plants are sensitive to high temperatures. It has for example been demonstrated that 60° C. was the lethal temperature for a Japanese knotweed rhizome.

The present invention presents a method for controlling invasive plants by heating, thus targeting the underground parts of plants and with the aim of preventing their vegetative and sexual reproduction.

Heating via thermal conduction is one of the techniques used in the field of soil remediation by thermal desorption (WO2001078914A8). With this technique, the energy coming from the heating tubes propagates radially in the ground by conduction.

This technique has the advantage of heating the soil evenly to high temperatures regardless of soil heterogeneity. Indeed, the thermal conductivity has the particularity of not fluctuating by large orders of magnitude with the materials present in the soil. Therefore, thermal conduction is much more efficient than other methods of heat transfer in the case of heterogeneous soils.

This technique is applicable ex situ and in situ. For ex-situ heating, excavated soil is used to form piles or placed in containers which are heat treated. With in-situ heating, the heating tubes are directly inserted into the infested soil, thus avoiding excavation and transport of soil. This also makes it possible to treat soils in restricted places and/or with limited access, such as remote sites, sites in urban areas, along dwellings, etc. In general, this technique is fast and has a reduced environmental impact.

BRIEF DESCRIPTION OF FIGURES

Figure 1: Vertical section of infested soil with heating pits (In situ)

Figure 2: Possible configurations of heating tubes in a soil to be treated

Figure 3: Example of ex situ treatment configuration of soil to be treated

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Figure 4: Example of implementation - external finned tube

The legend of the figures is as follows: 1. Hot air/combustion gas 2. Internal heating tube 3. External heating tube 4. Insulating layer 5. Infested soil 6. Temperature sensor tube 7. Heating well 8. Burner 9. Container 10. Fins

DETAILED DESCRIPTION OF THE INVENTION

The term "infected soil" here describes any type of soil or material presenting an invasive species such as Asian knotweed or others, in the form of plants, seeds, roots or rhizomes. It thus describes any type of soil or material having a pathogenic or toxic compound.

The invention presents a technique used in the depollution of soils (WO2016062757A1 and US7618215B2 are recognized as prior art of the invention), and adapted to the treatment of land infested by invasive plants, based on the increase in the temperature of the land by inserting heating tubes allowing the circulation of hot gases (combustion gas), coming from a burner, in two concentric tubes (BE1024596B1). With this technique, the energy coming from heating tubes propagates radially in the ground by conduction. Thermal conduction heats the ground to temperatures exceeding 350°C.

As part of the treatment of soil infested by invasive plants, the soil is heated to a temperature of between 50°C and 100°C, preferably to a temperature of between 60°C and 80°C.

The thermal conductivity has the particularity of not fluctuating by large orders of magnitude with the materials present in the ground. Because of this, thermal conduction is much more efficient than other methods of heat transfer in the case of heterogeneous soils.

The present invention relates to a system with a number of thermally conductive tubes (2) (3) placed in infested soil (5). The pipes are in communication with a heat source (8) causing the circulation of a heated fluid (1) through the tubes: from the internal heating tube (2) to the external heating tube (3), causing the rise in the temperature of the surrounding ground (5). Tubes, called temperature sensor tubes (6) are placed at regular intervals in the mass of infected soil and monitor the rise in temperature. With an adequate data collection and analysis system, these tubes allow treatment monitoring.

The tubes are laid out in a pattern in the infested soil to achieve the most even heating throughout the pattern. A regular pattern of pipes (7) can be used, such as triangular (Figure 2a), square (Figure 2b), rectangular, hexagonal (Figure 2c), etc. chosen to substantially cover the infested area. Triangular patterns are preferred because they provide the best thermal efficiency. The temperature in the ground is increased by circulating a heated fluid (1) through the pipes (2) (3). The overlapping heat flow from all the pipes results in a more even temperature rise across the pattern. It will be clear that the number of tubes (7) applied in the ground, the spacing, the relative position of the tubes, can vary according to the constraints of the project and / or the time desired to reach the target temperature and / or the type soil and/or economic considerations. In a preferred embodiment, the distance between two adjacent pipes is between 1.5m and 3m.

The tubes (2)(3) preferably comprise tubes of a heat resistant material such as, but not limited to, steel, metal or ceramic. The tubes can have any desired cross-sectional shape, including, but not limited to, triangular, rectangular, square, hexagonal, ellipsoidal, round, or oval. Preferably, the tubes have a substantially ellipsoidal, round or oval transverse shape. In a particularly preferred embodiment, the pipes have a substantially round transverse shape and have a diameter which is between 50 and 200 mm and preferably between 80 and 180 mm. The tubes have a length of between 3 and 30 m, and preferably between 6 and 18 m.

Two modes of operation are presented: in a preferred embodiment, the tubes are placed vertically, directly in the infected area of a = site (In-Situ Operation, Figure 1); in a second preferred embodiment, the horizontal heating elements are disposed on excavated infested material

6 BE2021/5655 and mounted in the form of a stack and/or contained in a container (Ex-situ operation — Figure 3).

In-situ Operation (ISTD) — Figure 1

In ISTD operating mode, no earth excavation is required and the remediation technology is directly integrated into the volume of polluted earth.

A drilling of the required depth is performed in order to be able to insert the heating tubes (2) (3) into the ground. The distribution of the heating wells (7) as well as

The interdistance between them is variable and chosen to optimize the heating of the floor.

Once in the ground, the heating tubes are surmounted by a combustion head or a burner (8) and connected to the fuel network and the electrical network. A central circuit, consisting of an extractor (fan), collects the combustion gases and routes them to a chimney.

An insulating layer (4) can be deployed on the surface of the area to be treated in order to reduce heat losses and increase heating efficiency.

Ex-situ operation (ESTD) — Figure 3

In ESTD operating mode, the infested soil (5) is excavated and then treated on site or moved to a site designated as a depollution site. The earth is then used to form mounds, piles or placed in containers (9) allowing “batch” treatment. The heating tubes (2) (3) are inserted in a horizontal position in rows through the pile with, again, a distribution allowing the best possible heating of the entire volume of infested soil. In a preferred embodiment, the piles of earth will be covered with a layer of concrete and a layer of insulation (4) to consolidate the pile and limit heat loss. In a preferred embodiment, exchanger tubes are placed in the stack between two rows of burners. These tubes make it possible to use the heat of the combustion gases to reinforce the heat exchange by thermal conduction with the ground.

Similar to in-situ operation, the heating tubes are surmounted by a combustion head or a burner (8) and connected to the fuel network and the electrical network. A central circuit, consisting of an extractor (fan), collects the combustion gases and routes them to a chimney.

Compared to the techniques of the prior art used in soil depollution (WO2016062757A1, US7618215B2, BE1024596B1), the present invention is distinguished by the absence of a system for recovering the vapors generated by the

7 BE2021/5655 floor heating. Indeed, in the case of the use of heat to treat polluted soil, tubes called vapor tubes placed under vacuum, have the role of recovering the vapors generated and containing the thermally desorbed pollutants present in vapor form. These tubes are surrounded by gravel, in order to allow a homogeneous suction of soil vapors and are connected to a vapor treatment unit. In the case of using heat to treat infested soil, this device is not necessary.

In a preferred embodiment, the smooth tubes are directly inserted into the ground, with or without a prior drilling step. In another preferred embodiment, the outer tube has fins (10) facilitating direct insertion into the ground and increasing the contact surface present allowing the conduction of heat to the ground (Figure 4).

Claims (2)

8 BE2021/5655 CLAIMS 1. Method, in situ or ex situ, of destroying invasive plants, in particular Japanese knotweed, by conductive heat treatment of infested soils. 2. Method as described in claim 1, characterized by a network of heating tubes arranged in a regular pattern in the area to be treated.