WO2023021057A1

WO2023021057A1 - Method of controlling invasive plants by conductive heat treatment

Info

Publication number: WO2023021057A1
Application number: PCT/EP2022/072898
Authority: WO
Inventors: Jan Haemers; Aline JORDENS
Original assignee: The Soil Research Lab Sprl
Priority date: 2021-08-17
Filing date: 2022-08-17
Publication date: 2023-02-23
Also published as: BE1029690A1; BE1029690B1

Abstract

The present invention relates to a method of treating soil infested by invasive plants and/or their underground network (rhizomes, roots, seeds) such as Japanese Knotweed. The present invention provides a method for treating infested soils based on in situ or ex situ conductive heating technology. The infested soils are heated to the temperatures required to destroy the aerial and subterranean network of invasive plants. The present invention concerns the adaptation of a technology used in soil remediation for the treatment of soils invaded by invasive plants: the invention concerns a heating system consisting of heating units arranged in a regular pattern in the area to be treated.

Description

METHOD OF CONTROLLING INVASIVE PLANTS BY CONDUCTIVE HEAT TREATMENT

FIELD OF THE INVENTION

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

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

CONTEXT OF THE INVENTION

An invasive plant is defined as any exotic plant introduced into an ecosystem that can cause environmental, economic, or human health problems. Invasive plants represent 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 an important economic impact: it contributes to the reduction of agricultural yields, to the erosion of 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 made to restore colonized environments.

An example of an invasive species currently rampant, especially in Europe, is the Japanese Knotweed (Fallopia Japonica). Japanese knotweed, native to East Asia, is an herbaceous plant introduced in Europe at the beginning of the 19th century as an ornamental, forage, and honey plant. It was then introduced in North America, Australia and New Zealand. In a new environment without pathogenic, parasitic, or phytophagous species able to regulate its expansion, the Japanese knotweed is today among the 100 most problematic species in the world, listed in the Global Invasive species database.

The competitive advantage of Japanese knotweed, leading to the disappearance of native species and the reduction of biodiversity, can be explained by different points: Japanese knotweed is a plant that settles in wetlands 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 deep and extend horizontally up to 15-20 m around the foot.

The Japanese knotweed has an abundant foliage with leaves presenting large surfaces, from 5 to 12 cm long and 5 to 8 cm wide. These thick leaves do not allow light to pass through, which gives it a shading property towards competing species. In addition, Japanese knotweed produces allopathic substances based on phenolic derivatives that cause necrosis of neighboring plants.

There are a variety of control methods for invasive plants, such as Japanese knotweed. Most control techniques target the aboveground biomass, the most common control being mowing. Other techniques have been developed: deployment of an opaque tarp over the plants to restrict access to light, thermal weeding, biological control by insertion of herbivorous predators, etc. However, these techniques have not proven to be very effective 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 intervention. Nevertheless, excavation techniques of 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 the totality of the rhizomes may not be removed. A fraction of 1cm long rhizome is capable of regenerating a viable plant and new shoots. In addition, excavation produces waste to be disposed of and stored or treated as well as a risk of dissemination of said invasive plants.

Other control methods, such as chemical or biological treatment, target the subterranean parts of the plant. Among examples of the prior art in this regard, WO2013/023294A1 proposes a saline injection technique targeting rhizomes and roots to control the spread of invasive plants.

Furthermore, there are maximum and minimum critical temperatures at which the aerial and underground parts of a plant cannot survive. 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. For example, 60°C has been shown to be the lethal temperature for a Japanese knotweed rhizome. The present invention presents a method of controlling invasive plants by heating, thereby targeting the underground parts of the 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 (W02001078914A8). With this technique, the energy from the heating tubes propagates radially through the soil by conduction. This technique has the advantage of heating the soil homogeneously to high temperatures regardless of the heterogeneity of the soil. Indeed, the thermal conductivity has the particularity of not fluctuating significantly 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 both ex-situ and in-situ. With ex-situ heating, excavated soil is used to form piles or placed in containers that 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 allows the treatment of soils in restricted areas and/or with limited access such as remote sites, sites in urban areas, along housing, etc. In general, this technique is fast and has a reduced environmental impact.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 : Vertical section of infested soil with heat wells (In situ)

Figure 2: Possible configurations of heating elements in an infested soil to be treated Figure 3: Example of an ex-situ soil treatment configuration Figure 4: Implementation example - 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 wells

8. burner

9. container

10. fins DETAILED DESCRIPTION OF THE INVENTION

The term "infected soil" is used here to describe any type of soil or material with an invasive species such as Asian or other knotweeds in the form of plants, seeds, roots or rhizomes. It thus describes any type of soil or material with a pathogenic or toxic compound.

The invention presents a technique used in soil remediation (WO2016062757A1 and US7618215B2 are recognized as prior art of the invention) and adapted to the treatment of land infested by invasive plants, based on increasing the temperature of the soil by inserting heating tubes allowing the circulation of hot gases (combustion gases), coming from a burner, in two concentric tubes (BE1024596B1). With this technique, the energy coming from the heating tubes is propagated radially in the ground by conduction. Thermal conduction allows the ground to be heated to temperatures more than 350°C.

For the treatment of soils infested with invasive plants, the soil is heated to a temperature between 50°C and 100°C, preferably to a temperature between 60°C and 80°C.

In an embodiment, the infested soil is heated by conduction to a temperature between 40°C and 100°C, preferably between 50°C and 80°C.

Thermal conductivity has the characteristic of not fluctuating significantly with the materials present in the soil. Therefore, thermal conduction is much more efficient than other methods of heat transfer in heterogeneous soils.

The present invention relates to a system with several thermally conductive tubes (2) (3) placed in an infested soil (5). The tubes are in communication with a heat source (8) causing a heated fluid (1) to flow through the tubes from the inner heating tube (2) to the outer heating tube (3), causing the temperature of the surrounding soil (5) to rise. Temperature sensor tubes (6) are placed at regular intervals in the infected soil mass and monitor the temperature rise. With an adequate data collection and analysis system, these tubes allow a follow-up of the treatment.

The pipes are arranged in a pattern in the infested soil to achieve the most uniform 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 offer the best thermal efficiency. The temperature in the soil is increased by circulating a heated fluid (1) through the pipes (2) (3). The superposition of the heat flow from all the pipes results in a more uniform increase in temperature in the pattern. It will be clear that the number of pipes (7) applied in the soil, the spacing, the relative position of the pipes, may vary depending on the project constraints and/or the desired time to reach the target temperature and/or the soil type 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 include tubes of a heat resistant material such as, but not limited to, steel, metal, or ceramic. The tubes may 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 cross-sectional shape. In a particularly preferred embodiment, the tubes have a substantially round cross-sectional shape and have a diameter that is between 50 and 200 mm and preferably between 80 and 180 mm. The pipes have a length of between 3 and 30 m meters, 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 placed on excavated infested materials and mounted as a pile and/or contained in a container (Ex-Situ Operation - Figure 3).

In-situ operation (ISTD) - Figure 1

In the ISTD mode of operation, no excavation of the soil is required, and the remediation technology is directly integrated into the polluted soil volume. A borehole of the required depth is drilled to insert the heating pipes (2) (3) into the soil. The distribution of the heating wells (7) as well as the distance between them is variable and chosen to optimize the heating of the soil. Once in the ground, the heating tubes are surmounted by a combustion head or a burner (8) and connected to the oil network and the electrical network. A central circuit, composed of an extractor (ventilator), collects the combustion gases and conveys 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 loss and increase heating efficiency. Ex-situ operation (ESTD) - Figure 3

In ESTD mode of operation, the infested soil (5) is excavated and then treated on site or moved to a designated cleanup site. The soil is then used to form mounds, piles or placed in containers (9) for batch processing. The heating tubes (2) (3) are inserted in a horizontal position in rows through the pile, again with a distribution that allows the entire volume of infested soil to be heated in the best possible way. In a preferred embodiment, the soil piles 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, heat exchanger tubes are placed in the pile between two rows of burners. These tubes allow to use the heat of the combustion gases to reinforce the heat exchange by thermal conduction with the ground.

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

Compared to the prior art techniques used in soil remediation (WO2016062757A1, US7618215B2, BE1024596B1), the present invention differs from the previous one in that it does not include a system for recovering the vapors generated by the heating of soil. Indeed, in the case of the use of heat to treat a polluted soil, tubes called vapor tubes put under depression, 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 aspiration of the 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 soil and increasing the contact surface present allowing heat conduction to the soil (figure 4).

Claims

7 CLAIMS

1. An in situ or ex situ method of destruction of invasive plants, in particular Japanese Knotweed, by conductive heat treatment of infested soils.

2. A method as described in claim 1, characterized by a network of heating tubes arranged in a regular pattern in the area to be treated.

3. A method as described in claim 1 and 2, where the infested soil is heated by conduction to a temperature between 40°C and 100°C, preferably between 50°C and 80°C.