Soil Remediation – A Review

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Volume 2, Issue 1, 2015

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Available online at www.ijiere.com

International Journal of Innovative and Emerging

Research in Engineering

e-ISSN: 2394 - 3343 p-ISSN: 2394 - 5394

SOIL REMEDIATION – A REVIEW

Bansari Ribadiya

a

_{, Mehali Mehta}

b

a_{Student, M.E Environmental Engineering, Sarvajanik College of Engineering & Technology, Surat, India- 395001} b_{Assistant Professor, Department of Civil Engineering, Sarvajanik College of Engineering and Technology, Surat,}

India-395001

ABSTRACT:

A variety of techniques for soil remediation have been compiled and summarized. The paper is intended to provide an overview of remediation methods currently utilized for soil remediation. Remediation methods, categorized as biological, chemical, or physical, are covered for contaminated soils and environmental waters. It is recognized that no single specific technology may be considered as a treatment for all contaminated site problems. This paper reviews soil remediation technologies, such as isolation and containment, solidification/ stabilization technologies, soil washing and flushing technologies, electrokinetics and phytoremediation. Selection of the most appropriate soil remediation method depends on site characteristics, concentration, types of pollutants to be removed and the final use of a contaminated medium.

Keywords:Site remediation; Soil remediation; Soil vapour extraction; Natural attenuation; Electro Kinetic

I. INTRODUCTION

Soil is the basic environmental elements constituting ecosystem, and the important material basis of human being surviving and developing. The environmental safety of soil becomes severe in India with the boost of industrialization and urbanization. Soil contamination is caused by the presence of manmade chemical alterations in naked ground. This type of contamination typically results from the rupture of underground storage tanks, application of pesticides, percolation of contaminated surface water, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals.

The biggest concern associated with soil contamination is the harm it can cause to human health. There are significant health risks involved with direct contact with contaminated soil, the vapors from the contaminants and even secondary contamination of water supplies.

There are a number of different methods currently employed in the process of dealing with soil contamination. Often, the selection of the most effective strategy will depend on the nature of the contamination, how the method will impact surrounding wildlife or humans living in the general vicinity, and the degree of success that can be anticipated from the soil remediation effort. It is not unusual for a given tract of land to undergo more than one cleanup operation in order to deal with the presence of multiple contaminants.

Among the processes used in soil remediation, excavation and dredging are among the most common. This process involves extracting soil that is contaminated and deemed to be unrecoverable using current technology, and transporting it to a landfill set aside for this purpose. Often, purified soil is used to fill in the area where the extraction took place.

II. CAUSESOFSOILCONTAMINATION

With the rise of concrete buildings and roads, one part of the Earth that we rarely see is the soil. It has many different names, such as dirt, mud and ground. However, it is definitely very important to us. The plants that feed us grow in soil and keeping it healthy is essential to maintaining a beautiful planet. However, like all other forms of nature, soil also suffers from pollution. The pollution of soil is a common thing these days, and it happens due to the presence of manmade elements.

The main reason why the soil becomes contaminated is due to the presence of manmade waste. The waste produced from nature itself such as dead plants, carcasses of animals and rotten fruits and vegetables only adds to the fertility of the soil. However, our waste products are full of chemicals that are not originally found in nature and lead to soil pollution.

A. Industrial Activity: Industrial activity has been the biggest contributor to the problem in the last century,

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2 off in a manner that can be considered safe. As a result, the industrial waste lingers in the soil surface for a long time and makes it unsuitable for use.

B. Agricultural Activities: Chemical utilization has gone up tremendously since technology provided us with

modern pesticides and fertilizers. They are full of chemicals that are not produced in nature and cannot be broken down by it. As a result, they seep into the ground after they mix with water and slowly reduce the fertility of the soil. Other chemicals damage the composition of the soil and make it easier to erode by water and air. Plants absorb many of these pesticides and when they decompose, they cause soil pollution since they become a part of the land.

C. Waste Disposal: Finally, a growing cause for concern is how we dispose of our waste. While industrial waste is

sure to cause contamination, there is another way in which we are adding to the pollution. Every human produces a certain amount of personal waste products by way or urine and feces.

While much of it moves into the sewer the system, there is also a large amount that is dumped directly into landfills in the form of diapers. Even the sewer system ends at the landfill, where the biological waste pollutes the soil and water. This is because our bodies are full of toxins and chemicals which are now seeping into the land and causing pollution of soil.

D. Accidental Oil Spills: Oil leaks can happen during storage and transport of chemicals. This can be seen at most

of the fuel stations. The chemicals present in the fuel deteriorate the quality of soil and make them unsuitable for cultivation. These chemicals can enter into the groundwater through soil and make the water undrinkable.

III.EFFECTS OF SOIL CONTAMINATION

A. Effect on Health of Humans: Considering how soil is the reason we are able to sustain ourselves, the

contamination of it has major consequences on our health. Crops and plants grown on polluted soil absorb much of the pollution and then pass these on to us. This could explain the sudden surge in small and terminal illnesses. Long term exposure to such soil can affect the genetic make-up of the body, causing congenital illnesses and chronic health problems that cannot be cured easily. In fact, it can sicken the livestock to a considerable extent and cause food poisoning over a long period of time. The soil pollution can even lead to widespread famines if the plants are unable to grow in it.

B. Effect on Growth of Plants: The ecological balance of any system gets affected due to the widespread

contamination of the soil. Most plants are unable to adapt when the chemistry of the soil changes so radically in a short period of time. Fungi and bacteria found in the soil that bind it together begin to decline, which creates an additional problem of soil erosion.

The fertility slowly diminishes, making land unsuitable for agriculture and any local vegetation to survive. The soil pollution causes large tracts of land to become hazardous to health. Unlike deserts, which are suitable for its native vegetation, such land cannot support most forms of life.

C. Decreased Soil Fertility: The toxic chemicals present in the soil can decrease soil fertility and therefore decrease

in the soil yield. The contaminated soil is then used to produce fruits and vegetables which lacks quality nutrients and may contain some poisonous substance to cause serious health problems in people consuming them.

D. Toxic Dust: The emission of toxic and foul gases from landfills pollutes the environment and causes serious

effects on health of some people. The unpleasant smell causes inconvenience to other people.

E. Changes in Soil Structure: The death of many soil organisms (e.g. earthworms) in the soil can lead to alteration

in soil structure. Apart from that, it could also force other predators to move to other places in search of food. A number of ways have been suggested to curb the current rate of pollution. Such attempts at cleaning up the environment require plenty of time and resources to be pitched in. Industries have been given regulations for the disposal of hazardous waste, which aims at minimizing the area that becomes polluted. Organic methods of farming are being supported, which do not use chemical laden pesticides and fertilizers. Use of plants that can remove the pollutants from the soil is being encouraged. However, the road ahead is quite long and the prevention of soil pollution will take many more years.

VI. CLASSES OF SOIL REMEDIATION

Two distinct classes of soil remediation can be defined: 1. in-situ

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3 In-situ cleanups - meaning that no excavation of the contaminated soil occurs - are often preferred because they are generally less expensive. However, they generally take a longer time to effect treatment to the desired limits and there is less certainty about the uniformity of treatment because of the inherent variability in soil and aquifer characteristics and difficulty in monitoring progress. On the other hand, excavating a contaminated area (ex-situ approach) and treating the material on the same site (ex-(ex-situ, on-site) or transporting it to a remote site for cleaning (ex-situ, off-site) can often be more complicated and expensive. Nevertheless, ex-situ remediation has the added bonus of taking the bulk of contaminants away before they can spread further. It also allows homogenization of the contaminated soil before treatment and ensures monitoring so that soils are cleaned to the desired limits within a relatively short time. Some technologies can have both in-situ and ex-situ applications. While the principle of the technique remains the same, the technological set-up differs.

VII. CATEGORIES OF REMEDIATION TECHNOLOGIES

In general, remediation tehnologies can be grouped into categories based on their treatment mechanism: biological, physical, chemical, electrical, and thermal. These are further subdivided into in situ and ex situ processes (as indicated above). Physical, chemical and electrical mechanisms have been abridged into one group, called physico-chemical, because these mechanisms normally occur together and overlap in the treatment process. “Thermal” has been listed separately because the driving force for the decontamination is heat.

The various techniques usually work well when applied to a specific type of soil pollution, though no readily available treatments were implemented that could clean all types of pollutants. Due to the complex nature of many polluted soils and the fact that pollution, in many situations, is due to the presence of a “cocktail” of different types of contaminants, it is frequently necessary to apply several remediation techniques (treatment train) to reduce the concentrations of pollutants to acceptable levels.

A. Biological Treatments

Biological treatment is a process whereby contaminants in soil, sediments, sludge or groundwater are transformed or degraded into innocuous substances such as carbon dioxide, water, fatty acids and biomass, through the action of microbial metabolism.

Biological processes are typically implemented at low cost. Contaminants can be destroyed and often little to no residual treatment is required. However, the process requires more time and it is difficult, in general, to determine whether contaminants have been completely destroyed. Additionally, microbes may often be sensitive to toxins or highly concentrated contaminants in the soil.

B. Physico-Chemical Treatments

Physico-chemical treatments use the physical and/or chemical and/or electrical properties of the contaminants or of the contaminated medium to destroy (i.e., chemically convert), separate, or contain the contamination. In the physical processes the phase transfer of pollutants is induced. In the chemical processes the chemical structure (and then the behaviour) of the pollutants is changed by means of chemical reactions to produce less toxic or better separable compounds from the solid matrix.

These treatments are typically cost effective and can be completed in short time periods (in comparison with biological treatment). Equipment is readily available and is generally not engineering or energy-intensive.

Certain in-situ physico-chemical treatment technologies are sensitive to certain soil parameters. For example, the presence of clay or humic materials in soil causes variations in horizontal and vertical hydraulic parameters, which, in turn, cause variations in physicao-chemical process performance.

C. Thermal Treatments

Thermal treatments, where the driving force of the process is heat, generally offer quick cleanup times but are typically the most costly treatment group. This difference, however, is less in ex-situ applications than in in-situ applications. Cost is driven by energy and equipment costs and is both capital and Operation & Maintenance (O & M) intensive. Thermal processes use heat to increase the volatility, to burn, decompose, destroy or melt the contaminants.

Cleaning soil with thermal methods may take only a few months or several years. The time it takes depends on three major factors that vary from site to site: type and amounts of chemicals present; size and depth of the polluted area; type of soil and conditions present.

VIII. ELECTRO KINETIC REMEDIATION

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Figure 1 Electro kinetic remediation [6]

Basic electrokinetics remediation site contains an external direct current source, a positively charged electrode (or anode) and a negatively charged electrode (or a cathode) placed into the ground. Placements of electrodes are based on size and shape of known contaminant plumes. The removal of contaminants and prevention of plume migration are big influences in determining the arrangement of electrodes. Each electrode is encased in a reservoir well in which an electrolytic solution can be injected [5]. The electrolytic solutions serve both as a conducting media (or pore fluid) and as a means to extract contaminants and introduce chemicals or biological entities [4]. Another use of the electrolytic solution is for control and/or depolarization of electrode reactions. Immersed in a solution the electrodes can result in oxidation at the anode site and the reduction at the cathodic site. The oxidation and formation of an acidic front are by products of the process and cause varying degree of influence to the system. By pumping, processing and testing the electrolytic solution at each electrode site you can extend the life and efficiency of the system.

Electrokinetic remediation is applied to many contaminants that can be dissolved within groundwater. Heavy metals are one of the main contaminants that are removed by the electrokinetics process. Some metals like cadmium (II) can be removed with high consequences on energy expenditure. Chromium (III) can be removed but with low efficiency because of the ease of hydrolysis allowing it to sorb to other substances. Chromium (IV) is also a candidate for electrokinetics removal although chromium (IV) migration is retarded in the presence of sulfur because it will break down into chromium (III). Other heavy metal species that are tested and reported to be treatable include; mercury, zinc,iron, lead, copper, and magnesium.

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