AU639730B2 - Soil washing - Google Patents

Description

AUSTRALIA6 PATENTrS ACT 15 7 3 Qn COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: '..Go'mplete Specification Lodged: Accepted: Lapsed: Published: -Priority: Related Art: Name of Applicant: Ad&Aress of Applicant Actual Inventors: Address for Service: TO BE COMPLETED) BY APPLICANT Suitew 90 onmercial Road, Melbourne,-VTktoria- 3400,-Autral- £cu U NOEL MURPHY PETER NICHOLLS, Patent Attorney, of Ellesmere, 5 Ardmillan Road, Moonee Ponds, Victoria 3039, Australia.

Complete Specification for the invention entitled: "SOIL WASHING".

The following statement is a full description of this invention, including the best method of performing it known to me:- This invention relates to the removal or separation, from soil and/or soil particles, of hydrocarbon contaminants and other substances including those generally regarded as pollutants or as being objectionable on environmental or other grounds. For the purposes of this specification all of these substances will for convenience be called "pollutants".

In a preferred form the invention is concerned with restoring to, or substantially to, its former state, sand or soil on a site which has become contaminated such as by hydrocarbons e.g. oil spillage, or on a beach or river frontage which has been polluted by oil carried by sea or river water.

We have found that washing with water can afford a simple, cost- 0* effective and environmentally attractive method of restoring the ground substantially to its condition before the advent of the pollutive agencies.

9* However in the past it has often been considered necessary to transport contaminated soil from the site to a suitable washing plant and to refill the hole with cean or substantially clean soil such as provided by the plant.

This kind of operation often requires a large number of heavy-duty road vehicles, with consequent noise, exhaust emission and dust, and risk of road damage and impairment of the neighbourhood.

An object of the invention is to provide for soil washing in a simple and cost-effective manner.

Another object is to provide for soil washing on site, thereby avoiding the need for concomitant large-scale transport operations.

The above and other objects and advantages will become apparent hereinafter.

A sordFinFg to thc present invention a mthod rmoving ze -epaaif g pollutants from soil add te teps of rapily agitaing -a According to the present invention a method of providing in situ environmentally suitable backfill material for hydrocarbon-polluted land, includes the steps of pouring water onto said land, forming with said water a slurry of particles including soil particles with hydrocarbon adhering thereto, rapidly agitating the slurry, conducting a flow of said slurry to a treatment pond system for gravitational separation of materials of differing densities, allowing hydrocarbon matter now freed from said soil particles to separate therefrom, allowing said soil particles to settle in the system, and removing said soil particles from the system as said backfill material.

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4':9 2A Oilg 1 t cy suspensi of saidsei-n-waterto -disldge -pollutants-and-pourigh U, into a treatment pond system to allow soil, freed from at least som s former contamination, to settle, and to allow hydrocarbo nd other lower-density pollutants to rise to the surface, rem g a fraction of said lower-density pollutants and water fr e top of the pond, draining the residue in the pond and reco erig, from said drained residue, soil from which pollutants have been separated.

But in order that the invention may be better understood reference will now be made to the accompanying drawings which are to be considered as part of this specification and read herewith. In the drawings: Figure 1 is a schematic diagram of a practical embodiment of the Sinvention, and Figure 2 is a map showing a site or tract of land with areas of heavy, moderate and trace soil contamination and a typical manner of locating plant for the application, to the site, of the method shown in Figure 1.

Referring to the drawings in more detail, a supply 14 of e.g.

S. recirculated ground water may be fed to the working area of a cutter suction dredge 15 of a kind known per se the action of which is to produce a slurry of water, soil and contaminants in which at least some of the contaminants have been dislodged from the soil by the agitating action of the dredge. The slurry is delivered by conduit 16 to pond system 17 into which, at 21, water may be supplied, as required, from the mains. Soil 18 freed from at least some of its former pollutants, is allowed to settle in the pond, is recovered at suitable intervals, and may be returned to the site astpart of the back fill, as at 19.

Hydrocarbon and other low-density contaminants rise to the surface of the ponds.

-3- Oil and water from the top of the pond system may pass over a weir or the like into a separator of a kind known per se capable of removing sufficient oil and other contaminants to render the residual water acceptable, in reasonable quantities, as drainage.

Preferably the soil is given sufficient time in the pond system to enable substantially all of the soil substantially all "fractions" or particle-sizes of soil) to settle.

The action of dredge 15 may itself provide sufficient agitation to dislodge most or at least sufficient contaminants to render the soil suitable for backfilling. Water supply 14 may make up for any lack of ground water in the o excavated site. The water may be introduced from a local supply e.g. mains 0.* 0* water, river water or sea water.

00 Before dredging, it may be necessary to use an excavator to remove debris or rubble. Contaminated material thus excavated may be screened to S* separate the larger pieces for separate cleaning. The rest can be delivered to the dredge for treatment in the normal manner.

Should unacceptably high levels of hydrocarbon or other gases be indicated, suitable de-gassing means can be provided in advance of the excavation.

Advantageously pond system 17 comprises a bank of ponds six) side-by-side shown 1 to 6, the level of liquid in each pond being limited by an overflow weir. Contaminated water flowing over the weir is collected in an open channel common to all ponds, whereby the water is led to a separator 7 such as an "API separator" or e.g. some other type wherein is established a slow gravity flow of suitable depth in a channel the dimensions of which can be so related to the volumetric rate of flow that the residence time of water in the channel is at -4least the time taken for a typical oil globule or particle to rise from the bottom to the surface of the water therein.

A rotary drum or like surface skimmer 20 can be provided to remove oil from the downstream end of the channel, and sludge can be continuously or intermittently pumped from the bottom of the channel into sludge tank 13 for disposal subject to such treatment as may be necessary or desirable. Sludge containing low to medium concentrations of contaminants may be given a pond treatment as hereinbefore described e.g. with biological agents and/or surfactants, so as to render it suitable as backfill. However under other circumstances e.g.

if the kind or concentration of contaminants in the sludge render it beyond redemption, it can be disposed of at some site or in some manner approved for that purpose.

Oil from the separator may be subjected to a final separation step at 11 thence passed to storage tank 12 from which it can be disposed of in any suitable and appropriate manner.

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'At least the greater part of water from the middle levels at the "dean" end of the separator may be recycled to the dredging area to replenish a "pool" in which the dredge operates. However a part of such separator water might also be collected in waste-water holding tanks 8, 9, 10 for disposal e.g. by release into the local sewerage system in accordance with prevailing regulations.

Additional washing of soil in the ponds may be effected by introducing via the bottom of the ponds a supply of uncontaminated water e.g. from the local mains supply, or treated water. Detergents or surfactants may be added to all or selected ponds to enhance the treatment process. Biological agents could also be introduced at this stage.

Claims (3)

1. A method of providing in situ environmentally suitable backfill material for hydrocarbon-polluted land, includes the steps of pouring water onto said land, forming with said water a slurry of particles including soil particles with hydrocarbon adhering thereto, rapidly agitating the slurry, conducting a flow of said slurry to a treatment pond system for gravitational separation of materials of differing densities, allowing hydrocarbon matter now freed from said soil particles to separate therefrom, allowing said soil particles to settle in the system, and removing said soil particles from the system as said backfill material.

2. A method as claimed in claim 1 further including the step of removing, from the residue in the pond system, water that is substantially free of hydrocarbon, and returning it to said land as part of the water supplied thereto for forming said slurry.

3. A method of providing in situ an environmentally suitable land o backfill, substantially as herein described with reference to the accompanying s drawings. DATED this 7th day of May, 1993. BRIG/9TWATER TECHNOLOGY PTY LTD their Ptent Attorney: PETER ICHOLLS N-x^ r I -4 -4 0 C PUNP