Soil Washing as a Remediation Technique for Land Contamination
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Added on 2023/06/05
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This report discusses soil washing as a remediation technique for land contamination. It covers the process, appropriate conditions, chemicals it can clean, and its advantages and disadvantages. The report also includes six steps involved in soil washing and various methods used for it.
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LAND CONTAMINATION AND REMEDIATION
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Table of Contents INTRODUCTION...........................................................................................................................1 Soil washing.................................................................................................................................1 Remediation process....................................................................................................................1 Chemicals which are cleaned using soil washing........................................................................2 Appropriate Conditions and media for soil washing...................................................................2 Advantages and disadvantage of soil washing............................................................................2 CONCLUSION................................................................................................................................3 REFERENCES................................................................................................................................5
INTRODUCTION Remediation is a process which involves cleanup of environmental sites which are contaminated. It is concerned with cleaning up contaminants in soils and groundwater. The remediation techniques are an important aspect in cleaning the contaminants in soils (Feng and et.al., 2020). Soil washing is an ex- situ remediation technique that is adopted with the purpose of removing hazardous contaminants from soil by washing it with a liquid. The present report describes soil washing as a remediation technique, the chemicals it can be used for and its advantages and disadvantages. Soil washing Soil washing is a remedial technique which is an ex- situ technology for removal of contaminants from soil through use of two types of processes. These are physical separation and chemical leaching (Zhai and et.al., 2018). Soil washing can be undertaken in one of the following two ways which removes contaminants through: By dissolving them or making their suspension in the wash solution By concentrating them into a smaller soil volume with the help of various methods such as particle size separation, attrition scrubbing, gravity separation. Remediation process The particle size separation method of soil washing is based on the concept that organic and inorganic contaminants possess a tendency to bind to silt or clay, chemically or physically. Through the physical processes of compaction and adhesion, enable the silt and clay particles to attachtothesand andgravelparticles.Thewashingprocessesworkby separatingand concentrating the contaminants into a smaller soil volume this smaller volume can be further treated or disposed of, as per the condition. Through the method of Gravity Separation, high or low specific gravity particles can be effectively removed. These include compounds containing heavy metals such as radium oxide and lead. Through the method of Attrition Scrubbing, adherent contaminant films can be removed from coarser particles. Sequential washing is another method that is used for soil washing technology (Gluhar, Kaurin and Lestan, 2020). This is suitable for removal of complex mixture of contaminants in the soil such as mixture of metals, SVOCs and non -volatile organics. 1
Generally, the following six steps are used in soil washing technique: Pretreatment is done which involves removing oversized particles form the soil. In the next step, the coarse and fine grained soil particles are separated in a scrubbing unit. After separation, coarse grain treatment is undertaken.As coarse grain particles are likely to be less polluted, these are generally treated using surface attrition. The next step is Fine – grained treatment. The fine soil particles which are of < 0.05 mm are found to be highly contaminated. This requires use of a suitable washing solution for treating them which contains a mixture of water and chemicals (Rui and et.al., 2019). Spent washing solution treatment is the next step. Lastly, residual management is undertaken in which the treated soil and residuals if considered polluted undergo further treatment. Chemicals which are cleaned using soil washing There are various chemicals which are cleaned up using soil washing technology. These include SVOCs (Semi Volatile organic compounds), heavy metals and fuels. SVOCs are substances that are primarily composed of carbon and hydrogen atoms. These have boiling points higher than 200 degrees Celsius. Common SVOCs include PAHs and PCBs. The various heavy metals are arsenic, copper, lead, mercury etc. However, this technology finds its use on only selected VOCs and pesticides (Bai and et.al., 2019). In addition to this the soil washing technology also cleans a variety of inorganic and organic contaminants. Appropriate Conditions and media for soil washing One of the key factors that determines the appropriate condition for soil washing is the distribution of grain size at the site. The appropriate conditions for using soil washing as a remediation technique are lower levels of silt, clay and organic matter. This technique is not suitable for those soils which contain contaminants which adsorb strongly to the soil particles. Another appropriate condition for soil washing is that the site should be large. This is because the technique would not be cost effective unless there is 5000 tons of contaminated soil on the site (Muñoz-Morales and et.al., 2017). Advantages and disadvantage of soil washing Advantages 2
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Following are the advantages of soil washing as a remediation technique: It is a cost effective technique which helps in reducing the amount of soil which needs further treatment. With this technique, 90 percent volume of the originally contaminated soil can be reduced. Another advantage of soil washing is that this technique is performed on site due to which after washing it becomes possible to use large amount of soil which is not contaminated. Soil washing technique not only saves time and money but also provides the opportunity of closely monitoring and controlling the soil that is being treated. The process can be run at a very high rate of 100 cubic yards per day (Fabbricino and et.al., 2018). A wide range of contaminants can be removed using soil washing technique. These can be both organic and inorganic contaminants. This remediation technique requires fewer permits which makes it relatively easy method to be employed for removal of contaminants. Disadvantages The various disadvantages of soil washing technique are as follows: Sometimes the waste mixtures are complex. As a result of this it becomes difficult to make appropriate washing fluids. There are situations when the humic content in the soil is high. Such soils with high humic content may require pretreatment. The aqueous stream may require to be treated during demobilization (Zhai and et.al., 2018). The treated residuals may sometimes contain certain levels of washing solvent which may be hazardous. For addressing this issue, additional treatment steps may be required. The organics that clay sized particles absorb may be difficult to be removed. 3
CONCLUSION From the report it can be concluded that Soil washing is a remediation technique which is cost and time effective and is suitable for treatment of soil contaminants on large sites. It involves use of physical and chemical separation for removing soil contaminants. SVOCs (Semi Volatile organic compounds), heavy metals and fuels are the various chemicals which are cleaned using soil washing technique. Distribution of grain size at the site plays a key role in determining the appropriateness of soil washing technique. 4
REFERENCES Journals and Books Bai, X. and et.al., 2019. Remediation of phenanthrene contaminated soil by coupling soil washing with Tween 80, oxidation using the UV/S2O82− process and recycling of the surfactant.Chemical Engineering Journal.369. pp.1014-1023. Fabbricino, M. and et.al., 2018. Soil washing optimization, recycling of the solution, and ecotoxicityassessmentfortheremediationofPb-contaminatedsitesusing EDDS.Sustainability.10(3). p.636. Feng, W. and et.al., 2020. Soil washing remediation of heavy metal from contaminated soil with EDTMP and PAA: Properties, optimization, and risk assessment.Journal of Hazardous Materials.381. p.120997. Gluhar, S., Kaurin, A. and Lestan, D., 2020. Soil washing with biodegradable chelating agents andEDTA:technologicalfeasibility,remediationefficiencyandenvironmental sustainability.Chemosphere.257. p.127226. Muñoz-Morales,M.andet.al.,2017.Remediationofsoilspollutedwithlindaneusing surfactant-aidedsoilwashingandelectrochemicaloxidation.Journalofhazardous materials.339. pp.232-238. Rui, D. and et.al., 2019. Remediation of Cd-and Pb-contaminated clay soils through combined freeze-thaw and soil washing.Journal of hazardous materials.369. pp.87-95. Zhai, X. and et.al., 2018. Remediation of multiple heavy metal-contaminated soil through the combinationofsoilwashingandinsituimmobilization.ScienceoftheTotal Environment.635. pp.92-99. 5