瑞典专利SE1350284A1 Use of acidogenic leachate, procedure and plant for soil washing

专利PDF首页>>瑞典专利

专利附录

专利说明

权利要求

类似技术

同族专利

引用文献

法律状态

优先权

专利摘要:
z4(z4) ABSTRACT The inVention relates to soil Washing using acidogenic leachate. A plant and a method for soilWashing using acidogenic leachate are described. Preferably the plant is arranged to betransported to the site Where the contaniinated soil is located so that the soil Washing can be performed on site.
公开号:SE1350284A1
申请号:SE1350284
申请日:2013-03-08
公开日:2014-09-09
发明作者:Anders Kihl；Anders Lagerkvist
申请人:Ragn Sells Ab；
IPC主号:

专利说明:

1(z4) Use of Acidogenic Leachate, Method and Plant for Soil Washing Technical FieldThe present invention relates to a use of acidogenic leachate according to claim l. It also relates to a method of soil Washing and a plant for soil Washing.
Background and Related Art Traditionally arsenic, copper and chromium have been used as impregnating agents for Wood.These are all toxic and discarded impregnated Wood is considered hazardous Waste. Otherimpregnating agents include creosote, Which Will leak polyaromatic hydrocarbons PAH intothe environment. The manufacturing, use, or disposal, of impregnated Wood is a source ofcontamination of the soil, Which in some cases renders large areas unsafe for use for a long time.
In Sweden alone there are approximately 80 000 contaminated areas and arsenic is one of themost common problematic element in these areas. To enable the use of these areascontaminated soil has to be removed and usually treated before landfilling. Then virginmaterials must be excavated for remediation of the contaminated site and hence high costsand stress on the environment. Soil Washing is generally performed by sieving the soil toobtain the smallest particles, since the vast maj ority of the hazardous material is bound to thesmallest particles. These particles are then separated and removed. The remaining portion ofthe soil contains only a small fraction of the initial pollution, making the area safe for useagain. This procedure results in three fractions of soil: one fraction is heavily contaminatedand must be removed. A larger fraction is less heavily contaminated but must still beremoved. The remaining fraction is substantially free of contaminants and may safely be putback on the same site. Hence, With this soil Washing method a large fraction of the soil must be removed.
This is a quite expensive procedure, and also not effective for soil that consists predominantlyof small particles, Which Will be contaminated to an equal degree. In this case there Will be nofraction of the soil that is free of contaminants. This is the case, for example, near river banks.
For example in the Scandinavian countries, a large part of the industries have traditionally z(z4) been located near rivers, leaving polluted areas where the prior art method of soil washing is not very useful.
There are also experiments with soil washing by means of chemical agents. This soil can beput back on the same site if the treatment method is suff1ciently effective to removecontaminants from the soil. For example, complex forrning chemicals such as EDTA may beadded to a liquid, which will then extract certain heavy metals from the soil. See Bossart, K.;Müller, R.; Schwermetallextraktion aus kontaminierten Böden mittels biologisch abbaubarer Chelatbildner; Diploma thesis, ETH Zürich, 2002. The liquids used are quite expensive to produce, which is an obstacle to large-scale use.
There is therefore a need for a method for soil washing that enables the washing of any type of soil, including soil that consists predominantly of fine particles.
Summary of the Invention An aspect of the invention therefore relates to the use of acidogenic leachate to wash soil. Inthis document the term acidogenic leachate will be used for leachate that is produced bydecomposing organic waste under anaerobic conditions, as will be discussed below. Suchacidogenic leachate is effective for removing contaminants such as metal cations and PAHfrom contaminated soil. The acidogenic leachate can be obtained, for example, by allowingorganic material to react with a liquid under anaerobic conditions. The liquid may be water or a leachate, or another suitable liquid.
For reasons to be discussed in the following, a liquid to be used for soil washing should havea low pH value and a low redox potential and also one or more components that will formcomplexes binding metal ions. An acidogenic leachate of the type used in the inventionfulf1lls all these criteria.
A low pH combined with low redox potential will increase the As(III)/As(V) ratio leading togreater arsenic release from soil as shown in Bowell R.J. (1994): Sorption of arsenic by iron oxides and oxyhydroxides in soils, Applied Geochemistry, vol. 9, pp. 279-286 Acidogenic solutions of the type used according to the invention can be produced by adding an acid such as sulfuric acid and a complex forrning substance such as EDTA to water. This 3(z4) method is costly and norrnally results in a solution that is not economically feasible for soil washing.
According to the invention therefore, preferably acidogenic leachate is used. Acidogenicleachate is typically the result of an anaerobic decomposition of organic waste with the aid ofmicroorganism, such as lactic acid bacteria, or bacteria producing forrnic acid, acetic acid orpropionic acid, and leading to an accumulation of organic acids and alcohol in solution. Suchbacteria may be naturally present in the organic waste or added to it to facilitate theacidogenic reaction. Such anaerobic decomposition occurs spontaneously when organicmaterials are exposed to water in the absence of oxygen and other oxidizing agents and isoften referred to as incomplete anaerobic decomposition, since the decomposition is halted atthe acidogenic state rather than continuing to produce methane, carbon dioxide and water. Theresulting solution is virtually cost free and extremely well suitable for soil washing. Theorganic waste used to produce the acidogenic leachate may be different types of ordinaryhousehold waste, such as food waste, or any other type of organic material, including sewage sludge, manure, or industrial waste such as wood waste or forest residues.
The function of the acidogenic leachate is threefold: Arsenic occurs naturally in an equilibrium between AsV and Asm. Acidogenic leachateprovides an environment with low redox potential, which results in reduction of AsV to Asmin the contaminated soil. Hence, the fraction of Asm in the soil increases in comparison toAsV. Asm is more unstable and so luble in water than AsV which results in higher mobility andextraction of As from the solid phase in the presence of acidogenic leachate. Moreover, thelow pH of acidogenic leachate results in desorption of As from positively charged solid surfaces.
AsV is typically bound to other ions, such as Fe ions, whereas Asm is generally much moresoluble in water. Reducing AsV to Asm is advantageous because Asm more readily than AsVforms complexes with complex forrning organic components in the leachate. The complexes thus formed may be separated from the soil in subsequent steps.
The acidogenic leachate also provides an acidic environment that helps reduce the valence of the arsenic ions, which makes it more soluble and helps the forrning of complexes. 4(z4) The acidogenic leachate also comprises a large portion of organic complex forrningcompounds, which will bind the ions that are to be washed out. The leachate is also effectivefor binding other types of contaminants which forrn strong complexes with large organicmolecules such as fulvic acid. Other such contaminants include PAH, dioxins and other metalions, such as mercury. Hence, a liquid to be used for soil washing should have a low pH valueand a low redox potential and also one or more components that will forrn complexes binding metal ions.
The invention also relates to plant for soil washing comprising a washing container forexposing contaminated soil to acidogenic leachate to produce washed soil and contaminatedleachate, liquid providing means arranged to provide acidogenic leachate to the washingcontainer and first separating means arranged to separate the contaminated acidogenic leachate from the washed soil.
The invention also relates to a method for soil washing comprising the following steps: 0 Exposing contaminated soil to acidogenic leachate for a first period of time to producewashed soil, whereby fatty acids in the acidogenic leachate forrn complexes withcontaminants in the soil, resulting in a contaminated leachate, and 0 Separating the soil from the contaminated leachate to produce washed soil.
Preferably the method further comprises the step of rinsing the washed soil to remove anycontaminated leachate kept within the soil. This may be done using a rinsing liquid and/orvacuum filtering to produce clean soil. If rinsing liquid is used the result of this step is rinsed soil and contaminated rinsing liquid.
In embodiments of the invention the plant ﬁarther comprises a rinsing container forperforming the rinsing step, and second separating means arranged to separate the rinsed soilfrom the contaminated rinsing liquid. The rinsing container may be the same container as thewashing container or may be a separate container. If the rinsing container is a secondcontainer, the first separating means preferably includes first transporting means for transporting washed soil from the washing container to the rinsing container. It would also be 5(z4) possible to transport the washed soil, and the rinsed soil using external means, such as an excavator.
The first and/or second separation means may include a tap for releasing the contaminatedleachate and/or the contaminated rinsing liquid, respectively. Altematively, or in addition, thefirst and/or second separation means includes a mechanism, such as a transport line or a feedscrew, for lifting the washed and/or rinsed soil from the washing and/or rinsing container to anext container. Sedimentation steps may also be used in the separation, by allowing thewashed soil, or the rinsed soil, as the case may be, to settle at the bottom of the container before removing the contaminated leachate or rinsing liquid, respectively.
The plant may further comprise a soil container for receiving rinsed soil from the rinsing container.
The plant outlined above can be made so that it comprises only parts that are mobile betweensites where there is contaminated soil to be washed. For example, one or more of the washing,rinsing and soil containers may be adapted for transporting by one or more trucks dependingon their size and weight. Or standard containers for transporting may be used, and possiblymodified, for example, by the inclusion of liquid outlets. The method and plant discussedabove are therefore particularly suitable for soil washing on site, that is, without moving thesoil to another place to be washed. Also, since all the soil can be rendered free ofcontaminants, no soil has to be removed from the site after washing. In this case the methodmay further comprise the step of transporting one or more of the containers to the site wherethe contaminated soil is located, wherein the method is performed near the location of the contaminated soil.
The acidogenic leachate may have been produced on site or somewhere else, by decomposingorganic material in an anaerobic environment and adding water or another suitable liquid, foruse in the method. With the chemical treatment according to the invention, a compact plantfor soil washing can be achieved. Preferably the soil can be washed on site, without the needfor long transports. Preferable embodiments of the washing method and plant allow the plant to be mobile between different sites where soil washing is needed. 6(z4) Preferably the method comprises the additional step of purifying the contaminated leachateand if applicable rinsing liquid that has been used for washing the soil. This can be achievedby completing the anaerobic degradation chain to methane generation, where most of theorganic compounds in solution will degrade to water, carbon dioxide and methane. By doingso pH will rise to about neutral conditions and organic complex forrners will be consumed.This in combination with the formation of uncharged complexes of hydroxides and sulfideswill lead to a separation and concentration of metals and arsenic in a small Volume sludge phase while most of the organics will end up in gas phase.
As mentioned above, the term acidogenic leachate in this document means the leachateproduced in the acidogenic phase of the decomposition of organic waste, which occurs after the aerobic phase and before the methanogenic phase like in the landfill.
Under acidogenic degradation conditions, organic material is mainly degraded to thefollowing end products: Volatile fatty acids, alcohols, carbon dioxide and hydrogen gas. Thesedegradation products are to a large extent soluble in water causing high loads of organicmaterial in the formed leachates. The fatty acids will, by a lowering of leachate pH and by their capability of forrning metal complexes, increase the mobility of many metals.
Brief Description of the Drawings The inVention will be described in more detail in the following, with reference to thedrawings, in which Figure l discloses a prior art plant for soil washing which may be used for implementing theinVention.
Figure 2 discloses a plant for soil washing which may be used for implementing the inVentionaccording to a first, simplified embodiment.
Figure 3 is a ﬂow chart outlining a first possible method for soil washing using the plant ofFigure l or Figure 2.
Figure 4 discloses a second embodiment of a plant for soil washing which may be used forimplementing the inVention.
Figure 5 is a ﬂow chart outlining a first possible method for soil washing using the plant ofFigure 3.
Figure 6 shows a third embodiment of a plant for soil washing which may be used for implementing the inVention. 7(z4) Figure 7 illustrates an overall process according to embodiments of the invention.
Detailed Description of Embodiments The leachate to be used in the process according to embodiments of the invention may beobtained by a process in Which organic Waste is allowed to decompose in an oxygen-freeenvironment With hydrolyzing and ferrnenting microorganisms, such as lactic acid bacteria.Such lactic acid bacteria may be naturally present in the organic Waste or actively added to it.When Water is added, a solution With a loW pH is obtained. This solution, or leachate, is anacidogenic leachate comprising volatile fatty acids VFA, and fulvic acid. These VFAs andfulvic acid are macromolecules that bind various types of contaminants by forrning strongcomplexes. As explained above, the properties of this acidogenic leachate make it particularly suitable for Washing contaminated soil.
The essential requirement for Washing the soil is that the contaminated soil be exposed to theacidogenic leachate for a suitable period of time for the contaminants to be extracted from thecontaminated soil. The result is Washed soil and acidogenic leachate comprising complexesholding the contaminants. Preferably, thereafter, the Washed soil is rinsed by a rinsing liquid,Which may be pure Water. Other liquids are perceivable, for example ethanol or anotheralcohol, but Water is probably the most cost-efficient. It may also be feasible to use a liquidthat can help restore the pH value after treatment With the acidogenic leachate. For example,the rinsing liquid may comprise calcide to help increase the pH value. The result of the rinsingprocess is clean soil and contaminated Water holding the remainder of the complexes holding the contaminants.
The clean soil may be spread in the environment again. The contaminated leachate and rinsingliquid is preferably purif1ed. The preferred Way of purifying the leachate is to use ananaerobic bioreactor Where the organic content is degraded by microorganisms, resulting inbiogas (methane and carbon dioxide). When the complex-forming agents in the contaminatedleachate are broken down the solubility of the elements of concem, that is, arsenic, zinc, lead,copper, chromium, cadmium etc Will decrease and they Will precipitate from the Water. Thisprocess therefore contributes to cleaning the Water. The precipitation may be enhanced byadding sulphur to the leachate before the bioreactor. The addition of sulphur Will cause manyelements of concem to precipitate as sulphides in the bioreactor. The same process is observed at municipal solid Waste landf1lls Where complexation of metals With S in form of s(z4) sulfides occurs under methanogenic phase, under anaerobic conditions and With a low redox.This makes metals less soluble in water and hence it results in reduced leaching of metals.The bioreactor may therefore be seen as a landfill where organic waste is landfilled and wherebiogas is extracted. Organic contaminants in the contaminated leachate such as PAH will stayin the bioreactor when the complexing agents are degraded. Some organic contaminants maybe degraded in the bioreactor. Both the leachate and the rinsing water will probably needtreatment, depending on the amount of contaminants such as PAH. Known methods ofremoVing PAH from water include filtering, for example with actiVated carbon, ordegradation of PAH with ozone. Such methods exist in the prior art and are not part of the inVention.
One possible embodiment of a plant for soil washing is illustrated in Figure 2, which shows asoil washing plant containing a large open first container ll holding an amount of soil 13. Atthe bottom of the container there is a tap 15 for letting out liquid. Undemeath the tap there is asecond container l7. In use, the soil 13 to be washed is placed in the first container ll andacidogenic leachate is added to the first container ll so that all the soil is exposed to theleachate. The leachate is held in a large sack 19 or other suitable container. When theleachate has reacted with the soil for a suitable time for binding as much as possible of thearsenic, and/or other contaminants found in the soil to the complex forrning mo lecules, theleachate can be removed from the first container ll through the tap l5. Thereafter, a rinsing liquid is added to rinse the soil in the first container.
To make the reactions more efficient it will be feasible to cause the soil and leachate to form asuspension. In that case a mixer may be used to stir the suspension to reduce treatment time. If a suspension is made a sedimentation step may be included to allow the so lids to settle.
The method is illustrated in the ﬂow chart of Figure 3, described here with reference to Figure2.
In step S21 soil that is to be washed is placed in the first container ll.
In step S22 acidogenic leachate is added to the first container ll and the reactor is closed.Preferably the reactor should be tightly closed to secure anaerobic conditions and to trap themethane that is formed in the reaction between the contaminated soil and the leachate.
It would of course be possible to reverse the order of steps S2l and S22, or to introduce leachate and soil at the same time. 9(z4) After a suitable reaction time, in step S23, the acidogenic leachate, now holding thecontaminants, as described above, is released through the tap 15 into the second container 17.The reaction time depends on the nature and quality of the leachate, and the amounts andtypes of contaminants.
In step S24, a rinsing liquid, for example, pure water is added to the soil and released throughthe tap 15 into the second container 17, possibly after a period of time. Step S24, and ifdesired steps S23 and S24, may be repeated as needed.
When the soil is clean, it can be removed from the first container 11, for example, by tipping the container, and retumed to the site from where it was taken, or to another place.
The second container 17 now holds a contaminated ﬂuid which is a mixture of acidogenicleachate and the water used to rinse the soil. This contaminated ﬂuid may be treated insubsequent steps, by any known method suitable for the contaminations present. This isnorrnally achieved by adding one or more agents that are suitable for binding the respectivecontaminants to the contaminated ﬂuid. In the case of arsenic and some other metals, asuitable agent is sulphur. The result of adding sulfur to the liquid under anaerobic conditions,with the assistance of bacteria using substrates such as carbon dioxide, methyl and theacetatotrophic substrate, is that the arsenic reacts with the sulfur to form arsenic sulfide, AsS,whereas the hydrocarbons are split to form methane, which may be used as a source ofenergy, and carbon dioxide. In the embodiments shown in Figures 1 and 3, this is typically done in the liquid co llecting container.
Preferably, in a preceding step S21, the leachate can be produced on site as well, in a reactortank, large bag, or the like, suitable for producing acidogenic leachate as outlined above. This may be the container 19 used to add the leachate to the first container 1.
A second embodiment of a plant for soil washing is shown in Figure 4. A method for use withthis embodiment is outlined in Figure 5.
The plant of Figure 4 includes a first container 21 in which soil is mixed with acidogenicleachate to be washed. The first container 21 preferably has a lid (not shown) for closing ittight while the soil and leachate are reacting and a tap 25 at or near the bottom for releasingliquid into a second container 27 arranged to hold contaminated liquid. A third container 31 isarranged to receive the washed soil from the first container 21. In the third container 31 the washed soil is cleansed with water or another suitable rinsing liquid. The third container 31 1o(z4) also has a tap 33 for releasing contaminated rinsing liquid into the second container 27 or into a different container (not shown).
There is also a fourth container 35 for receiving the clean soil from the third container 31.First transport means 37 are arranged for transporting the washed soil from the first container21 to the third container 31 and second transport means 39 are arranged for transporting theclean soil from the third container to 31 the fourth container 35. The first 37 and second 39transporting means may be, for example, transport lines or feed screws arranged to lift the soilfrom the one container to a point above the next container and release it into the nextcontainer. It would also be possible to use a machine, such as an excavator, for moving thesoil, provided it could be done in such a way as to leave a major part of the leachate in the first container.
In the first and third container the soil might be stirred to increase the contact between the soiland the acidogenic leachate, or rinsing liquid, respectively. This may be achieved by first andsecond stiiring means 22, 32 in the first 21 and third 31 container, respectively, or in some other way. If feed screws are arranged in the containers, the contents of the container could be stirred by running the feed screws backwards.
A similar type of transporting means as the first and second transporting means 37, 39 may bearranged for transporting the clean soil from the fourth container 35, although this is notshown. Altematively, the fourth container 35 may be arranged to be tilted to release the cleansoil. As mentioned before, each of the containers 21, 27, 31, 35 is preferably arranged to bemobile, so that the fourth container 35 may be moved to the place where the clean soil should be applied and emptied there.
Figure 5 is a ﬂow chart illustrating a method that may be used with the plant of Figure 4.
In step S41 a suitable amount of acidogenic leachate is introduced into the first container 21and in step S42 a suitable amount of soil to be washed is introduced into the first container 21.This order could be reversed; either soil or leachate may be introduced first, or both at the same time.
After a suitable amount of time, sufficient for the contaminating particles to react with the leachate, the cleaned soil is transported in step S43 to the third container 31 by means of the 11(z4) first transporting means 37. In the third container 3l the washed soil is cleansed in step S44using another type of rinsing liquid, preferably pure water, which may be introduced into thethird container before, after or at the same time as the washed soil. The soil is kept in thefourth container 35 for a suitable amount of time. The clean soil is then, in step S45,transported from the third container 3l to the fourth container 35, or altematively directly to the ground where it is to be placed.
The contaminated leachate from the first container 21 and the contaminated rinsing liquidfrom the third container 3l are released into the second container 27 for ﬁarther treatment. Thecontaminated liquid in the second container 27 may be treated in substantially the same wayas discussed in connection with Figure 2. The contaminated liquid in all embodiments willprobably comprise a fraction of the finest soil particles. In this case the liquid may be kept inthe second container 27 for a long enough time to allow the soil particles to settle at thebottom, so that the contaminated leachate and the sludge resulting from the sedimentation canbe managed separately. The leachate should be transported to a water treatment plant and the sludge, which will also be probably contaminated, should be transported to a landfill.
As with the method shown in Figure 3, there may preferably be a preceding step in which theacidogenic leachate is produced on site. The content of the first and third containers are preferably stirred to increase the exposure of the soil to the respective liquid in each container.
As an altemative to releasing the leachate and rinsing liquid through a tap 25, 33 at the bottomof the first and third containers, respectively, the entire content of the respective container,including soil and liquid may be tipped into a sieve above another container, so that the soil will be kept in the sieve and the contaminated liquid will be collected in the other container.
In a preferred embodiment the plant used for soil washing according to the invention ismobile. This can be achieved with both the embodiment shown in Figure l and the embodiment shown in Figure 3.
Preferably, the soil washing process is followed by a process of purifying the contaminated leachate and/or rinsing liquid, as discussed above in connection with figure 3. 1z(z4) Figure 6 is an overview of another embodiment of a soil washing plant according to theinvention. As the skilled person will realize, elements of this embodiment can be combinedwith elements of previous embodiments. For example, in this embodiment pipelines are usedfor transporting liquid and soil between all containers, whereas in previous embodiments,various types of lifting arrangements have been used for the soil and the liquids have beenreleased from the containers through taps in the containers. It would be possible to use pipelines and pumps between some containers and lifting mechanisms between others.
Figure 6 shows a pile of soil 61 that is to be washed. The soil has been excavated, norrnallyfrom somewhere nearby. The soil 61 is provided to a reception tank 63, for example by meansof an excavator, wheel loader, or the like (not shown). A leachate tank is 65 arranged to holdthe acidogenic leachate to be used for soil washing. The leachate may be produced in the tank,or may be produced elsewhere and provided to the tank. In the former case, organic waste andwater are provided to the leachate tank 65 and allowed to reach for a period of time to providethe acidogenic leachate. From the leachate tank a leachate pipeline 67 is arranged to provideleachate to a reception tank 65. To control the ﬂow of leachate a valve 68 and optionally a pump 69 are provided in the leachate pipeline 67.
A mixing container 71, corresponding in function to the first container of Figure 3, is arrangedto receive a mixture of soil and leachate from the reception tank 63 through a mixture pipeline73. A pump 74 is arranged in the mixture pipeline 73 for pumping the mixture from thereception tank 63 to the mixing container 71. In the mixing container 71 more leachate isprovided from the leachate tank 65 through a branch of the leachate pipeline 67. As will beunderstood, the reception tank is optional but may, when present, serve to facilitate the mixingof soil and leachate. It would be possible to provide soil and leachate from the pile 61 and theleachate tank 65 directly to the mixing tank 71. In the mixing tank 71 the mixture of soil andleachate is preferably stirred continuously or at intervals, to maximize the exposure of the soilto the leachate. Special mixing means 72 may be provided in the mixing tank 71, or themixing may be performed by means of the excavator or some other means. The mixture iskept in the mixing tank 71 for a suitable amount of time, which may be in the range of one or a few hours.
From the mixing tank 71 the mixture is fed to one or more sedimentation tanks 73 through a pipeline 75 having a pump 76. In the sedimentation tank or tanks 73 the washed soil is 13(z4) allowed to sink to the bottom and the leachate is released into a leachate treatment tank 77through a pipeline 78. An outlet for the leachate can be arranged in the container based on thelevel of sludge in the sedimentation tank. If possible, leachate can be released by free fall,otherwise it may be removed actively, for example, by means of a pump. The remaining soilin the sedimentation tank 73 will still be soaked with contaminated leachate, which must beremoved from the soil. From the sedimentation tank 73 the soil is therefore transportedthrough a soil pipeline 80 by means of a pump 8l to a rinsing tank 83. In the rinsing tank arinsing liquid is added, to replace the leachate in the crevices in the soil. As discussed above,the rinsing liquid may be water, alcohol, or another suitable liquid. It may be feasible to makethe liquid slightly alcalic to restore the pH value of the soil after being exposed to acidogenicleachate. This can be achieved, for example, by adding calcium to water. In the same way asin the mixing tank, it is advantageous to stir the content in the rinsing tank, in order to makethe rinsing process more efficient. This may be achieved by special mixing means 84 or by some other suitable means.
From the rinsing tank 83 the rinsed soil is transported to a final tank 85 through a pipeline 87comprising a pump 88. In the final tank 85 is preferably a sedimentation tank where the soil isallowed to settle and excess rinsing ﬂuid is removed. The rinsing ﬂuid is typically transportedto a water treatment plant (not shown). It may be exposed to treatment such as f1ltering orsedimentation on the way there and/or in the treatment plant itself. The remaining soil in the final tank 85 may be transported to a landfill or to be reused somewhere.
An altemative to rinsing the washed soil in the rinsing tank 83 would be vacuum f1ltering ofthe soil. This would extract the water from the pores and crevices in the soil resulting in a more compact soil.
The mixing tank 7l and the sedimentation tanks 73 together with the pipeline between themare used for the same purpose as the first container in Figures 2 and 4. The rinsing tank isused for the same purpose as the third container in Figure 4. As the skilled person will realize, elements of the different plants may be combined as long as all the functions are performed.
The leachate treatment tank may be used in the same way as the second container 27 of Figure 2or3. 14(z4) Another option for leachate treatment would be to recirculate it to a landf1ll. In manycountries, including Sweden, depositing liquid in this way is currently prohibited. But ifperrnitted, the landf1ll would in this case function as a type of reactor. The landf1ll norrnallycontains sufficient levels of sulfur for to initiate the same reactions as described abovewithout any addition of sulfur: arsenic and other heavy metal ions would precipitate in theform of sulf1des and be appropriately stored in the landf1ll without any need for furthertransportation. If not, obviously, sulfur may be added. The bacteria needed to promote thisreaction are already present in the landf1ll and feed on the content of the leachate. This would therefore be a cost-efficient way of handling the leachate.
Figure 7 illustrates the overall process of soil washing according to an embodiment of theinvention. To begin with, contaminated soil is stored in a deposit in step S61 and acidogenicleachate is stored in a leachate tank in step S65. The leachate may be produced in the leachatetank 65 by mixing organic waste and water and allowing it to react for a period of time.Instead of water, another ﬂuid, such as leachate from a landf1ll area may be used forproducing the leachate in this and all other embodiments. Soil and leachate are provided to amixing container 7l and mixed to a suspension in a step S7l. As discussed above the mixing container 7l is preferably closed to provide anaerobic conditions.
The same types of reactions as described above will occur in the mixing container 7l. After asuitable amount of time, allowing as much of the contaminating ions as possible to react withthe complex forrners in the leachate, the soil is separated from the leachate in step S73. Asshown above, this may be achieved in different ways, including sedimentation of the soil in asedimentation tank 73, lifting of the soil out of the mixing tank as shown in Figure 3, andsieving of the soil. After the separation step S73 the soil is rinsed in a rinsing step S83 and theleachate is managed in step S77. Norrnally rinsing step S83 is performed by means of arinsing liquid as discussed above, but it can also be done by extracting the contaminatedleachate by means of vacuum f1ltering, or by a combination of these two methods. As shownin figure 2, the soil may be kept in the mixing tank 7l for this, but the process can be runmore eff1ciently by moving the soil to a separate rinsing tank 83 allowing the washing of newsoil in the mixing tank 7l. In step S85 the soil is separated from the rinsing liquid. Again thismay be done in different ways, as discussed for step S73. The rinsed soil may be deposited ina landfill or may be placed on the ground as fresh soil. The rinsing liquid after step S85 is transported to a water treatment plant. 15(z4) In step S77 the contaminated leachate is treated, preferably in a closed container 77, by theaddition of sulfide and/or other suitable reactants to the leachate. As explained above, this willlead to precipitation of the heavy metal ions. In this reaction, gases such as carbon dioxideand methane will also be released. Typically the leachate also contains dissolved soilparticles. After a sedimentation step the leachate can be transported to the water treatment plant and the sedimented sludge can be transported to the landfill.
The acidogenic leachate can be produced from a number of different sources of organicmaterial, including food waste, bread, vegetables, fuel fraction, paper mill sludge, or manuresuch as horse manure. Mixtures of organic material have also been used, including a mixtureof paper mill sludge and food waste, and a mixture of horse manure and fuel fraction. Inexperiments acidogenic leachate has been found to be several times more effective in washing off ions such as arsenic, copper and zinc, compared to soil washing with distilled water.
In the following, results from some such experiments will be presented. It should be notedthat these data are based on a limited number of experiments. They should not be interpretedas limiting the scope of the invention in any way, but merely serve to illustrate some Workingexamples of the inventive idea. In each case a liquid-to-solid ratio (L/ S) of 2 was used for soilwashing, that is, an amount of soil was mixed with twice the amount of leachate and allowed to react for a period of time.
Table la below shows the amounts of ions of Al, As, Ca, Cu Fe, K, Mg, Na, P, S and Znwashed out of As polluted soil by leachate produced from mixed food waste, bread,vegetables, respectively. Acidogenic leachate has also been found to wash out mercury from soil, although this is not reﬂected in table l. 16(z4) Mixed food Bread Vegetab1es Disti11 WaterWaste A1 23.2 110.24 28.16 No dataAs 148.6 271.16 192.73 25.42Ca 3831.7 989.29 839.04 No dataCu 8.9 29.54 12.33 0.22 Fe 6.6 166.75 25.97 No dataK 1495.2 446.06 923.28 No dataMg 580.4 178.32 140.94 No dataNa 1443.1 1000.48 121.64 No dataP 48.9 182.7 68.1 No dataS 528.1 97.77 146.29 No dataZn 169.7 642.26 339.44 0.77 Table I amounts of ions washed out by dzﬁferent types of 1eachate, and dístílled water in mgper kg ofsoíl.
As can be seen, a11 the different types of acidogenic 1eachate turned out to be more effectivethan water, the actua1resu1ts Varying for different types of ions. In these experiments thereaction time for producing the acidogenic 1eachate was near1y two months starting fromorganic waste. The amount of water added to the substrate was approximately twice theamount of dry substance in the organic waste. The time a11owed for soi1 washing was 24 hours.
The time needed for producing the acidogenic 1eachate natura11y depends on Various factors,inc1uding0 the type of waste used, in particu1ar how easi1y degradab1e it is 0 the amount of water added to the waste the temperature the amount of acid-forming bacteria the types of acid-forming bacteria For examp1e food waste wi11 be more easi1y degradab1e than paper mi11 s1udge, fue1 fraction somewhere between the two. 17(z4) The time needed for soil washing, that is, the time that the soil should be exposed to theacidogenic leachate also depends on a number of factors, including0 the nature of the acidogenic leachate, for example the concentration of Variousreactants,0 the ratio between the amounts of leachate and soil, respectively,0 the temperature0 the geometry of the soil/leachate interface. This may be improved by stirring themixture of soil and leachate.In optimal conditions the exposure time between the soil and the leachate can be reduced to an hour or less.
In the following some data from an experiment including Various types of leachate, water witha commercially available complex forrning substance (EDTA) and distilled water will bediscussed: The different types of leachate were produced using food waste, fuel fraction, paper mill sludge and horse manure, respectively.
The main characteristics of the different types of organic waste used are shown in Table 2: Waste pH EC TS (%) VS (%) COD (g/l)FOOd Waste 4.16 1.94 23.2iO.16 85.66iO.86 950i170.8Fuel fraCtiOn 6.84 1.83 74.24i2.55 77.15i3.33 200i27.8Paper mill sludge 7.55 0.83 32.46i1.68 66.42iO.99 40i5.5Horse manure 8.12 0.91 27.26i1.18 47.52i1.18 203i23.6 Table 2 characteristics of the diﬁferent types of organic waste used for producing leachate,including standard deviation for TS, VS, COD, indicated by i EC electrical conductivity expressed as mS/ cm. In this context, this is an indicator of thetotal salinity and the amount of dissolved matter in a sample.
TS Total solid, indicating the dry content of the materials VS Volatile so lids, the bumable fractions in the materials, roughly indicating the organic content in the materials 1s(z4) COD Chemical Oxygen Demand is the total measurement of all chemicals in the Water that can be oxidized, Which indicates the level of organic matter content of the Wastes.
The food Waste had already been through slow acidogenesis for one month in a refrigerator When the experiment Was set up, Which explains its loW initial pH Value.
Each of the types of Waste Was also analyzed for trace elements. Fuel fraction contained a certain amount of Zn, Pb and Cr While the other types of Waste did not.
The experiment covered five different compositions of Waste, A, B, C, D and E, as outlined in table 3: Food waste Fuel fraction Paper mill sludge Horse manure Tap waterA 0.39 kg 3.33 kgB 0.97 kg 4.11 kgc 0.54 kg 3.33 kgD 0.16 kg 0.87 kg 6.75 kgE 0.49 g 0.09 kg 4.50 kg Table 3 the diﬁferent types of waste used t0 obtain the diﬁferent leachates.
Table 4 illustrates the main characteristics of acidogenic leachate produced based on the combinations shown in Table 3, and also based on diluted food Waste: Waste origins pH EC (mS/cm) Fatty acid (M) COD (g/l) Food waste 3.59 2.34 0.12 213.33i10.4 Diluted food waste 4.57 1.33 0.02 50.5i7.47 Fuel fraction 5.82 5.3 0.01 14.25i1.77 Paper mill sludge 5.35 6.13 0.04 25.25i3.18 Paper mill sludge 5.48 5.71 0.04 43.33i17.02+ food waste Horse manure 6.66 3.98 0.005 44.5i6.38+ fuel fraction Table 4 Characteristics of leachate After acidogenesis for 3 months for food Waste and 2 months for the rest, all the pH dropped,but not significantly. COD values declined in all the Wastes, especially in food Waste, fuel fraction and the combination of horse manure+ fuel fraction. 19(z4) Table 5 illustrates eluate properties of the leachates based on A, B, C, D, E presented in Table 3 as Well as diluted food Waste leachate and Water With EDTA and distilled Water after Hg soil Washing.
Waste origins pH EC (ms/cm) COD (g/l) Food waste 4.9 6.26 20015Diluted food waste (20% conc.) Fuel fraction 6.91 5.35 12.83i4.04Paper mill sludge 5.94 7.87 22.17i0.76Paper mill sludge + food waste 5.81 7.68 25:53Horse manure + fuel fraction 7.15 5.27 19.38i4.42Water with EDTA 6.53 2.17 ---Distill water 7.32 1.6 --- T able 5 Eluate properties after Hg washíng Table 6 illustrates eluate properties of the leachates based on A, B, C, D, E presented in Table 3 as Well as diluted food Waste leachate and Water With EDTA and distilled Water after Hg soil Washing Waste origins pH EC (ms/cm) COD (g/l)Food waste 6.43 8.44 87.5i23.8Diluted food waste (20% conc.) 6.99 2.67 25.75i4.6Fuel fraction 7.63 5.88 13.17i3.47Paper mill sludge 6.11 7.92 19.75i2.6Paper mill sludge + food waste 6.18 7.67 25.5i4.24Horse manure + fuel fraction 7.7 5.23 11.88i4.42Water with EDTA 7.49 2.23 --- Distill water 8.51 1.2 --- T able 6 Eluate properties after As washíng As can be seen from tables 5 and 6, after soil Washing COD values decreased and pH values increased. Both changes Were n1ore pronounced for the Washing of As contaniinated soil than for Hg contaniinated soil. zo(z4) Table 7 illustrates the amount of Washed-out elements after As soil Washing for different types of leachate, and for distilled Water.
Bread Vegetables Mixed food Distill waterwasteAl 55.24 13.69 11.6 0.08As 135.87 93.77 74.5 12.74Ca 495.71 422.80 1920.0 51.14Cd 0.83 0.44 0.3 0.05Cr 7.26 2.43 1.2 0.06Cu 14.80 6.23 4.5 0.11Fe 83.55 15.89 3.3 0.18K 223.51 457.94 749.2 8.48Mg 89.35 71.91 290.8 6.27Mn 42.77 31.03 31.1 0.72Na 501.32 59.44 723.1 17.84Zn 321.82 173.74 85.0 0.39P 91.55 34.45 24.5 0.33S 48.99 74.18 264.6 35.91 Table 7 Element concentration in the eluate in mg/l aﬁer As soil washing using leachate based 0n diﬂerent types of organic waste As in tables la and lb, all the leachates Were significantly n1ore effective than distilled Water. It should be noted that the differences between the different types of leachate may be due to different properties of the different types of organic Waste; however, it could also be due to other factors, such as different Waste/Water ratios or to different leachate strength.

权利要求:
Claims (19)
[1] 1. l. Use of an acidogenic leachate for soil Washing, said acidogenic leachate being obtainable by decomposition of organic Waste under anaerobic conditions.
[2] 2. Use of an acidogenic leachate according to claim l, Wherein the acidogenic leachate isobtainable by a process of decomposing organic matter in the presence of acid-producing bacteria, such as bacteria producing forrnic acid, acetic acid, propionic acidand lactic acid, and adding Water to the decomposed organic matter to obtain the acidogenic leachate.
[3] 3. Use of an acidogenic leachate according to claim 2, Wherein the process further comprises the separating the acidogenic leachate from residual solid matter.
[4] 4. Use of an acidogenic leachate according to claim 2 or 3, Wherein the organic matter is bread or vegetables
[5] 5. A plant for soil Washing comprising a Washing container (2; ll; 2l;7l) for exposingcontaminated soil to acidogenic leachate to produce Washed soil and contaminatedleachate, liquid providing means (19; 65) arranged to provide acidogenic leachate tothe Washing container (2; ll; 2l;7l) and ﬁrst separating means (l5; 37; 73, 78, 80) arranged to separate the contaminated acidogenic leachate from the Washed soil.
[6] 6. A plant according to claim 5, further comprising a rinsing container (l l; 3l; 83) forexposing the Washed soil to a rinsing liquid to remove contaminated acidogenicleachate from the Washed soil to produce rinsed soil and contaminated rinsing liquid,and second separating means (l5; 39; 85) arranged to separate the rinsed soil from the contaminated rinsing liquid.
[7] 7. A plant according to claim 6, Wherein the rinsing container is the same container as the Washing container. zz(z4)
[8] 8. A plant according to any one of the claims 5 - 7, Wherein the first and/or secondseparation means includes a tap (15) for releasing the contaminated leachate and/or the contaminated rinsing liquid.
[9] 9. A plant according to any one of the claims 5 - 7, Wherein the first and/or secondseparation means includes a mechanism, such as a transport line or a feed screWs, forlifting the Washed and/or rinsed soil from the Washing and/or rinsing container to a next container.
[10] 10. A plant according to claim 6, Wherein the rinsing container (1 1; 31; 83) is a secondcontainer separate from the Washing container (2; 11; 2l;7l), the first separatingmeans including first transporting means (37; 75, 76, 80, 81) for transporting Washed soil from the Washing container (2; 11; 21;71) to the rinsing container (1 1; 31; 83).
[11] 11. ll. A plant according to claim 6, ﬁarther comprising a soil container (35, 85) for receiving rinsed soil from the rinsing container (1 1; 31; 83).
[12] 12. A plant according to any one of the claims 5 - 11, Wherein at least the Washingcontainer (2; 11; 21;71) and/or the rinsing container (1 1; 31; 83) is arranged to be transportable to enable soil Washing in different locations.
[13] 13. A method for soil Washing comprising the following steps: a. Exposing contaminated soil to an acidogenic leachate for a first period of timeto produce a suspension of leachate and Washed soil, Whereby fatty acidmolecules in the acidogenic leachate form complexes With contaminants in thesoil, resulting in a contaminated leachate b. Separating the soil from the contaminated leachate to produce Washed soil.
[14] 14. The method of claim 10, Wherein the first period is in the interVal of 1 to 48 h,preferably 2 to 24 h.
[15] 15. A method according to claim 13, ﬁarther comprising the step ofc. rinsing the Washed soil using a rinsing liquid and/or Vacuum f1ltering to produce clean soil. z3(z4)
[16] 16. A method according to c1aim 13 or 14, further comprising the step ofd. purifying the contaminated 1eachate by precipitating contaminants such asmetal cations the in contaminated 1eachate, e.g. by adding a Substance such as a su1fate to the contaminated 1eachate.
[17] 17. A method according to any one of the c1aims 13 - 15, ﬁarther comprising the step,preceding method step a, of producing the acidogenic 1eachate by decomposing organic materia1 in an anaerobic environment
[18] 18. A method according to any one of the c1aims 13 - 16, ﬁarther comprising the step oftransporting the Washing and/or rinsing container to the site Where the contaminatedsoi1 is 1ocated, Wherein the method is performed near the 1ocation of the contaminated soi1.
[19] 19. A method of producing an acidogenic 1eachate comprising the steps of e. Letting organic materia1 decompose in acidogenic conditions, preferab1yanaerobic conditions, preferab1y in the presence of acid producing bacteriasuch as bacteria producing 1actic acid, forrnic acid, acetic acid or propionicacid, f Adding Water or another suitab1e liquid to the decomposing organic materia1, to obtain the acidogenic 1eachate.

类似技术:

公开号 | 公开日 | 专利标题

CN101648207B|2011-04-06|Chemical oxidation remediation method for organism-contaminated soil and remediation device

Pagnanelli et al.2009|Mechanisms of heavy-metal removal by activated sludge

US5833855A|1998-11-10|Situ bioremediation of contaminated groundwater

Xiaoli et al.2007|Characteristics and mobility of heavy metals in an MSW landfill: Implications in risk assessment and reclamation

Mattei et al.2016|Reclamation of river dredged sediments polluted by PAHs by co-composting with green waste

Tichy et al.1998|Bioleaching of metals from soils or sediments

Xu et al.2011|Arsenic release from arsenic-bearing Fe–Mn binary oxide: Effects of Eh condition

HUE035667T2|2018-05-28|Combined chemical oxidation/assisted bioremediation of contaminants

Bolton et al.1991|Elemental composition and speciation of some landfill leachates with particular reference to cadmium

Virkutyte et al.2005|Copper and trace element fractionation in electrokinetically treated methanogenic anaerobic granular sludge

CN107321782A|2017-11-07|A kind of method that EDTA complexings ferrous ion activation calper calcium peroxide removes soil petrochina hydrocarbon

CN102329023A|2012-01-25|Processing method of garbage leachate

Zeng et al.2020|Mutual interactions between reduced Fe-bearing clay minerals and humic acids under dark, oxygenated conditions: hydroxyl radical generation and humic acid transformation

Smyntek et al.2018|Assessment of sulphate and iron reduction rates during reactor start-up for passive anaerobic co-treatment of acid mine drainage and sewage

SE1350284A1|2014-09-09|Use of acidogenic leachate, procedure and plant for soil washing

de Carluccio et al.2020|Multi-barrier treatment of mature landfill leachate: effect of Fenton oxidation and air stripping on activated sludge process and cost analysis

Peters et al.1997|Selenium associations in estuarine sediments: redox effects

Li et al.2019|Rapid control of black and odorous substances from heavily-polluted sediment by oxidation: Efficiency and effects

JP2007253075A|2007-10-04|Soil purifying method

Long et al.2009|Releasing behavior of copper in recirculated bioreactor landfill

Möller et al.2004|Precipitation of heavy metals from landfill leachates by microbially‐produced sulphide

CN109304363B|2021-03-30|Chemical remediation agent suitable for petroleum-polluted soil and use method thereof

Håkansson et al.2008|Sulphate reducing bacteria to precipitate mercury after electrokinetic soil remediation

Bourechech et al.2018|Treatment of leachate from municipal solid waste of Mostaganem district in Algeria: Decision support for advising a process treatment

JP2004066193A|2004-03-04|Contaminated soil cleaning method

同族专利:

公开号 | 公开日

EP2964403A2|2016-01-13|

CN105026062A|2015-11-04|

SE537085C2|2014-12-30|

WO2014135380A3|2014-12-04|

WO2014135380A2|2014-09-12|

CL2015002423A1|2016-06-24|

引用文献:

公开号 | 申请日 | 公开日 | 申请人 | 专利标题

US5494649A|1991-10-03|1996-02-27|Cognis, Inc.|Process for removing heavy metals from paint chips|

US5160636A|1992-01-17|1992-11-03|Chemical Waste Management, Inc.|Process for the treatment of mixed wastes|

US5563066A|1993-10-26|1996-10-08|Buchanan; Alan B.|Method and apparatus for remediating contaminated soil containing organic compounds|

US5605417A|1994-07-18|1997-02-25|The Dragun Corporation|Method and apparatus for improving degradation of an unsecured landfill|

US6020185A|1997-05-23|2000-02-01|Geovation Consultants, Inc.|Method and composition for the anaerobic biodegradation of toxic compounds|

JP2000107743A|1998-10-06|2000-04-18|Kurita Water Ind Ltd|Method for decomposition of organic chlorine compound in soil and/or ground water|

US6403364B1|2000-01-28|2002-06-11|Geovation Consultants Inc.|Method for the enhanced anaerobic bioremediation of contaminants in aqueous sediments and other difficult environments|

US6562235B1|2000-08-08|2003-05-13|Groundwater Services, Inc.|Enhanced anaerobic treatment zones in groundwater|

AU2002332868A1|2001-09-06|2003-03-24|Gannett Fleming, Inc.|In-situ process for detoxifying hexavalent chromium in soil and groundwater|

JP2008246273A|2006-09-20|2008-10-16|Tekken Constr Co Ltd|Washing treatment system for soil contaminated with dioxins and the like|

CN101244424B|2007-02-15|2011-02-16|沈阳大学|Experimental device for washing heavy metal pollution|

CN100534651C|2007-04-29|2009-09-02|哈尔滨工业大学|Agent for phytoremediation of soil polluted by heavy metals using the waste active Sludge as the original material and the method of the phytoremediation of soil polluted by heavy metals|

JP2010172880A|2009-02-02|2010-08-12|Univ Of Miyazaki|Method for clarifying heavy metal-contaminated soil by metal bondable material recovered by fixed metal ion affinity adsorption|

CN201848424U|2010-11-11|2011-06-01|南京市环境保护科学研究院|Contaminated soil leaching remediation equipment|

CN102009064B|2010-11-11|2012-10-10|天津大学|Process and system for recovering and removing residual solvent from soil|

CN102225420B|2011-03-31|2012-07-25|浙江工商大学|Method for remedying soil polluted by difficultly degradable chlorinated organics|

CN102319726B|2011-06-15|2013-10-30|姜桂荣|Method for comprehensively utilizing low-concentration heavy metal-containing soil improvement and repairing damaged soil by plants after detoxification of contaminated field|

CN102633618A|2012-04-06|2012-08-15|广东省生态环境与土壤研究所|Hydroxy acid titanium complexes promoting detoxification of halogenated organic matter-polluted soil by means of dehalogenation, as well as preparation and application thereof|CN105880272B|2016-02-22|2017-03-08|华中农业大学|Heavy-metal contaminated soil drip washing repair system|

CN108723071B|2018-05-22|2021-01-05|河北省冀信环保科技有限公司|Chromium-containing soil harmless treatment device and treatment method|

法律状态:

优先权:

申请号 | 申请日 | 专利标题

SE1350284A|SE537085C2|2013-03-08|2013-03-08|Use of acidogenic leachate, procedure and plant for soil washing|SE1350284A| SE537085C2|2013-03-08|2013-03-08|Use of acidogenic leachate, procedure and plant for soil washing|

EP14709891.7A| EP2964403A2|2013-03-08|2014-02-20|Use of acidogenic leachate, method and plant for soil washing|

PCT/EP2014/053357| WO2014135380A2|2013-03-08|2014-02-20|Use of acidogenic leachate, method and plant for soil washing|

CN201480011768.7A| CN105026062A|2013-03-08|2014-02-20|Use of acidogenic leachate, method and plant for soil washing|

CL2015002423A| CL2015002423A1|2013-03-08|2015-08-28|Use of acidic leachate, method and floor washing plant.|

[返回顶部]