WO2004040958A2

WO2004040958A2 - Soil treatment

Info

Publication number: WO2004040958A2
Application number: PCT/GB2003/004808
Authority: WO
Inventors: Ivor Gifford Richards; Stephen Mark Blunt
Original assignee: Groundcover D.B.M. Limited
Priority date: 2002-11-06
Filing date: 2003-11-06
Publication date: 2004-05-21
Also published as: AU2003292367A8; GB0225815D0; WO2004040958A3; AU2003292367A1

Abstract

A method of treating soil to eradicate viable underground vegetation parts particularly of Japanese knotweed (Fallopia Japonica), comprises excavating the ground of soil to be treated and grading the soil into a class which is shredded and into a larger class which is ground. The shredding and grinding reduces the size of any underground vegetation parts contained in the soil to a size where they are no longer viable. The treated soil can then be safely returned to the ground.

Description

Soil Treatment

This invention relates to the treatment of soils and more particularly to the treatment of soils such that weeds and other vegetation in the soil do not grow back and persist.

Many types of vegetation comprise tough underground parts, such as roots, bulbs, tubers, stems and rhizomes which, if left in the soil, can regenerate into new growth even if the above ground parts have been removed.

Japanese knotweed ( Fallopia Japonica) is a perennial weed which spreads rapidly to form large dense thickets . Land for new development must be cleared of the weed because it is unsightly and comprises root systems which can damage foundations, drains and other structures. The weed also excludes more desirable vegetation, obstructs sight lines and watercourses, as well as trapping litter and debris. Japanese knotweed is difficult and expensive to control, since it develops deep and wide spreading root systems, from which it regenerates each year. Japanese knotweed has been spread primarily by the movement of soils and fill materials containing rhizomes. Research over many years has characterised the biology and reproductive strategy of Japanese knotweed and has determined that small fragments of rhizomes as small as 10mm can develop into new plants .

Established control techniques are based on the repeated application of translocated and persistent herbicides over a three year program, or on frequent and repeated cutting to weaken the plant .

In another approach, treatments such as heating, freezing or incineration of the whole soil mass have been considered but rejected as uneconomical and impractical. Such treatments would have to be applied to the whole soil mass rather than to the Japanese knotweed alone, since the knotweed rhizomes are mixed with the soil.

Herbicide treatment can be effective but the treatment is of limited value because of the time taken for effective control and the need to protect watercourses as well as the public and adjacent vegetation from the hazardous herbicides which are used. If cutting is used to control the plant, the cutting must be undertaken on a one to two week cycle throughout the growing season over a period of many years . Each of the above methods require monitoring for an additional year to ensure and demonstrate that the weed has been eradicated. There is no current treatment that can eradicate Japanese knotweed within a few months to meet the time scales required when land is selected for a new development . The only effective and rapid method of eradication is the removal of the soil together with the rhizomes from site. This is an expensive process and merely transfers the problem of regeneration from the existing site to a landfill site. Developers must either remove all infested soil from the site to a landfill or bury it on site in a deep excavation. Mechanical disturbance alone without treatment can also transport rhizome fragments to begin new infestations, thereby exacerbating the problem.

Conventional mechanical screening has been attempted to remove rhizome fragments but this has found to be unsatisfactory, since the fragment sizes which need to be removed are so small that little or none of the soil can be reused. Also, the collected contaminated soil has to be dumped in landfill sites, where it can regenerate.

It is therefore an object of this invention to provide a soil treatment which is able to alleviate any risk that the vegetation being removed can regrow and in such a manner that the treated soil can be re-used on the site, thereby eliminating disposal costs and the risk of contaminating landfill sites . It is desirable that the treatment should only take a few weeks or months to complete, leaving the site available for redevelopment without delay.

In accordance with this invention there is provided a method of treating soil to eradicate viable underground vegetation parts which are able to regenerate into new vegetation, the method comprising excavating the ground of soil to be treated and mechanically processing the excavated soil to reduce the size of particles contained therein.

Underground parts of plants below a certain size are unable to regenerate and thus the risk of regeneration can be avoided by mechanically processing the soil to reduce the size of the underground parts to a point at which they are no longer viable . It will be appreciated that by the term soil we mean any kind of ground covering material, such as sand, clay, earth, aggregate or rubble in which plants are able to grow.

Mechanical processing apparatus suitable for use in the method are well known for other purposes and are widely available. One such known apparatus is a grinding apparatus which is used for reducing the particle size of concrete, rocks and other hard materials . We have realised that such grinding apparatus can be used to effectively treat soil to reduce the particle size of any viable underground plant parts contained therein.

Another type of known mechanical processing apparatus is a shredding apparatus which is used for shredding the stems, trunks and leaves of plants. We have realised that such shredding apparatus can also be used to effectively treat soil to reduce the size of any viable underground plant parts contained therein.

A disadvantage of grinding apparatus is that they will not work effectively where the soil being treated contains a high proportion of fine soil . A disadvantage of shredding apparatus is that they will not work effectively where the soil contains a high proportion of stones and rubble .

Thus, the soil to be treated is preferably separated by particle size exclusion into various classes of particle size prior to mechanical processing. Preferably the soil to be treated is separated by particle size exclusion into a first grade having particle sizes below a value in the range 25-30mm and into a second grade having particle sizes above said value.

In this manner, the first grade of particles can be treated by shredding and the second grade of particles can be treated- by grinding .

Prior to grinding the second grade of particles, any underground plant parts can be removed by hand or by other separation means such as by air blast separation. The separated plant parts can then be shredded and the remaining material ground. Alternatively, instead of grinding the second grade of particles, any underground plant parts can be removed by hand or by other separation means such as by air blast separation. The separated plant parts can then be shredded and the remaining coarse material used as aggregate provided no viable rhizome parts remain. In this manner, the need to grind coarse aggregates is avoided, thereby saving time and unnecessary expenditure .

The first grade of particles may contain wet materials, such as cohesive clay soils, containing rhizomes. Such materials are difficult to shred. Thus, prior to shredding the first grade of particles, the particles may be further separated by particle size exclusion into a third grade having particle sizes below a value in the range 5-10mm and into a fourth grade having particle sizes above said value. The particle size exclusion process brakes down any clumps of wet material containing rhizomes and as such, the third grade of particles will not contain any viable rhizome parts and can be replaced. The fourth grade of particles contains rhizomes parts and can be treated by shredding. A method in accordance with this invention is able to be performed on a large area within weeks rather than years, such that infested land can be redeveloped without delay. The treated soil can be re-used on site or at another site rather than having to dump it in landfill sites, thereby conserving landfill space and avoiding the need to provide replacement materials on site to fill previously contaminated areas .

The method in accordance with this invention avoids the use of herbicides with the consequent reduction in environmental risks . The method requires relatively low inputs of energy, unlike the previous methods involving freezing and incineration which have been considered . The method can be performed at any time of year and is not dependent on the plant being in active growth, unlike herbicide treatment methods.

The method utilises equipment which is widely available and is portable, so it can be brought to site to achieve treatment and then moved to another site. The method can be performed using small or large equipment, so that through-puts and costs can be matched to the scale of the site.

Embodiments of this invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

Figure 1 is a flow diagram illustrating a first method of soil treatment in accordance with this invention;

Figure 2 is a flow diagram illustrating a second method of soil treatment in accordance with this invention; and Figure 3 is a flow diagram illustrating a third method of soil treatment in accordance with this invention.

Referring to Figure 1 of the drawings, in order to treat a site contaminated with Japanese knotweed, the above- ground parts of the plant are cut down at step 10 and are disposed of by shredding or by burning.

The soil is then excavated at step 11 to a depth below the level to which the rhizomes of the Japanese knotweed are known to extend. The soil is also excavated to an area beyond the extent of the above-ground vegetation, since rhizomes of Japanese knotweed can extend a considerable lateral distance underground.

The excavated soil is then graded at step 12 into two classes, respectively having particle sizes X above and below a predetermined value Y. The value of Y may be adjustable and preferably lies in the range 25-50mm.

The soil may be graded by placing it on a conveyor comprising a plurality of rows of upstanding toothed wheels which are interleaved with the wheels of adjacent rows. The rows of wheels are driven and material is carried along the conveyor from one end to the other. Particulate matter having a particle size X below a certain size falls through the gaps between the interleaved wheels, the teeth on the wheels serving to break down softer larger particles. The speed at which the wheels are driven can be varied to vary the value of Y.

Particulate matter having a particle size X below Y is fed into a commercially available shredding apparatus at step 13 , where any rhizome particles in the soil are fragmented or damaged to a point where they are incapable of regeneration.

In an alternative embodiment, the graded particulate matter containing particles below a certain size may be buried in a deep excavation or landfill site, owing to the fact that any rhizome particles within this size class will be small and therefore less able to regenerate in deeper depths of soil .

Particulate matter having a particle size X above Y are ground at step 14. The treated soil output from the shredding and grinding steps 13 , 14 can then be replaced into the excavated area or if desired transported to a landfill site. In any event, it will be appreciated that no viable rhizome particles remain and thus the problem of regeneration of the Japanese knotweed is avoided.

Referring to Figure 2 of the drawings, in order to avoid having to grind all of the particulate matter having a particle size X above Y, following the grading at step 12, particulate matter having a particle size X above Y is initially treated at step 16 such that any large rhizome pieces are removed by hand or by liquid separation, air blast separation or any other suitable separation method. The large pieces can then be shredded at step 17. The remaining particles can then be ground at step 14 in the conventional manner. However, depending on the efficiency of the step 16, the grinding step 14 may be omitted and the remaining particles may be replaced into the excavated area or transported to a landfill site.

Referring to Figure 3 of the drawings, in a further embodiment, following the grading at step 12, particulate matter having a particle size X less than Y is further graded at step 18 into two classes, respectively having particle sizes X above and below a predetermined value Z in the range 5-10mm. The soil may be graded by placing it on a vibrating mesh screen, with the value of Z being determined by the mesh size.

Particulate matter having a particle size X above Z is fed into the shredding apparatus at step 13, where any rhizome particles in the soil are fragmented or damaged to a point where they are incapable of regeneration.

Any rhizome particles contained within the particulate matter having a particle size X below Z are unable to regenerate. Thus, the particulate matter having a particle size

X below Z can safely be replaced into the excavated area or if desired transported to a landfill site.

A method in accordance with this invention is able to rapidly treat areas invested with Japanese knotweed without the risk of regrowth. The treated soil can be re-used and thus transportation costs are avoided. The method uses grading, grinding and shredding apparatus which are widely commercially available in portable form so that the process can be performed on site.

Claims

1. A method of treating soil to eradicate viable underground vegetation parts which are able to regenerate into new vegetation, the method comprising excavating the ground of soil to be treated and mechanically processing the excavated soil to reduce the size of particles contained therein.

2. A method as claimed in claim 1, in which the soil to be treated is separated by particle size exclusion into two classes respectively having a relatively small and a relatively large particle size prior to mechanically processing the material .

3. A method as claimed in claim 2, in which the soil to be treated is separated by particle size exclusion into two classes respectively having particle sizes below a value in the range 25-30mm and particle sizes above said value.

4. A method as claimed in claims 2 or 3 , in which the separated particles having a having a relatively small particle size are mechanically processed by shredding.

5. A method as claimed in claims 2 or 3 , in which the separated particles having a having a relatively small particle size are further separated by particle size exclusion into two classes respectively having a relatively small and a relatively large particle size prior to mechanically processing the material .

6. A method as claimed in claim 5, in which the separated particles having a having a relatively small particle size are further separated by particle size exclusion into two classes respectively having particle sizes below a value in the range 5-10mm and particle sizes above said value.

7. A method as claimed in claims 5 or 6 , in which the further separated particles having a having a relatively small particle size are mechanically processed by shredding.

8. A method as claimed in any preceding claim, in which the separated particles having a having a relatively large particle size are mechanically processed by grinding.

9. A method as claimed in any of claims 2 to 7, in which any underground plant parts contained within the separated particles are removed by hand or by other separation means .

10. A method as claimed in claim 9, in which the separated plant parts are shredded.

11. A method as claimed in claims 9 or 10, in which the material remaining following separation of the underground plant parts is ground.

12. A method as claimed in any preceding claim, comprising returning the mechanically processed excavated ground soil to the ground.