Lexikon

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acidification of soil
adaptation of soil microflora

adaptation is the evolutionary process whereby a population becomes better suited to its habitat. This process takes place over many generations, and is one of the basic phenomena of biology.

The term adaptation may also refer to a feature which is especially important for an organism's survival.Such adaptations are produced in a variable population by the better suited forms reproducing more successfully, that is, by natural selection.

Microorganism, due to their short generation time may succesfully be adapted to new environmental conditions, such as temperature, salinity, nutrient supply, toxic contaminants, etc.

The genom of the microorganisms is very versatile: their adaptive genes, which can be swithched on, when necessary, the frequent mutations and the horizontal gene-transfer between the members of the population and the whole microbial community makes the soil microbes flexible and possible to adapt to the utilisation of new substrates (also soil contaminants) and to become resistant to toxic chemical substances. In the soil biofilms, where microorganism are living strongly realted to each-other, special forms of horizontal gene transfer may exist, and the genes necessary fir survival can be dispersed in the community with the help of mobile genetical elements, such as plasmids, jumping genes, phages, etc.

The adaptive behaviour of the soil microorganisms makes possible to eliminate soil contaminants and prevent Earth from continuously increasing contaminant-concentrations in soils.

aeration of soil

aeration of soil means the amount of air-filled pores in the soil, expressed as the volume difference between total porosity and actual soil moisture. Optimum soil aeration is 30% but strongly depends on the structure and packing state of soil particles; 15–20% is normally satisfactory for the growth of grasses and cereals; below 10% is not good for plant growth.

Aerobic and facultative anaerobic microorganisms in the soil may intesively use oxigene and produce CO2 when biodegradable organic soil-contaminants are present in high concentration. If oxygen have been consumed, the redoxpotential decreases in soil, and slower facultative anaerobs start to dominate: the biodegradation of contaminants slows down.

A biodegradation based soil remediation technology can be intensified by soil aeration, increasing the redoxpotential in the soil and activating aerobic degrading microorganisms. This process is called bioventing.

air injection into soil
air soiling potential
air- permeability of soil
application of microbial inoculant for soil remediation
biodegradation in soil

Decomposers of organic matter are found in the soils. These groups of living organismsm perform different functions:

• Microflora: certain types of bacteria and fungi are the major or primary decomposers; they are capable of digesting complex organic matter and transforming it into simpler substances that can be utilised by other organisms;

• Microfauna: certain types of protozoa and nematodes feed on or assimilate microbial tissues and excrete mineral nutrients;

• Mesofauna: includes a large number of organisms, ranging from small arthropods like mites (Acari) and springtails (Collembola) to potworms (Enchytraeidae). They break up plant detritus, ingest soil and organic matter or feed on primary decomposers thereby having a large influence on regulating the composition and activity of soil communities;

• Macrofauna: including ants, termites, millipedes and earthworms, contribute to organic matter decomposition by breaking up plant detritus and moving it down into the soil system thereby improving the availability of resources to microflora (through their nest building and foraging activities).

biodegradation of organic pollutants in soil
biological soil tretament in slurry phase reactor
chemical immobilisation/stabilisation in soil
chemical oxidation in soil

chemical oxidation typically involves reduction/oxidation redox reactions that chemically convert hazardous contaminants to nonhazardous or less toxic compounds that are more stable, less mobile, or inert. Redox reactions involve the transfer of electrons from one compound to another.

Specifically, one reactant is oxidized loses electrons and one is reduced gains electrons.

The oxidizing agents most commonly used for treatment of hazardous contaminants in soil are ozone, hydrogen peroxide, hypochlorites, chlorine, chlorine dioxide, potassium permanganate, and Fentons reagent hydrogen peroxide and iron.

Cyanide oxidation and dechlorination are examples of chemical treatment. This method may be applied in situ or ex situ, to soils, sludges, sediments, and other solids, and may also be applied for the in situ treatment of groundwater.

Source: US-EPA, ClU-In: http://www.clu-in.org/techfocus/default.focus/sec/In_Situ_Oxidation/cat/Overview/

chemical reduction in soil
chemical soil treatment in slurry phase reactor
chlorine-respiration based soil remediation
classification of soil remediation technologies
D-value: site specific remedial target value of the Hungarian soil regulation

it is a risk based target concentration for contaminated sites and contaminates soils. The Hungarian low requires the calculation of this target concentration in the remedial plan. The D-value is land-use specific.

different forms of organic pollutants in soil
economical evaluation of soil remediation
electrokinetic soil remediation

electrokinetics relies upon application of a low-intensity direct current through the soil between ceramic electrodes that are divided into a cathode array and an anode array. This mobilizes charged species, causing ions and water to move toward the electrodes. Metal ions, ammonium ions, and positively charged organic compounds move toward the cathode. Anions such as chloride, cyanide, fluoride, nitrate, and negatively charged organic compounds move toward the anode.

Removal of contaminants at the electrode may be accomplished by several means, among which are: electroplating at the electrode; precipitation or co-precipitation at the electrode; pumping of water near the electrode; or complexing with ion exchange resins.

Source: US-EPA, Clu-In: http://www.clu-in.org/techfocus/default.focus/sec/Electrokinetics%3A_Electric_Current_Technologies/cat/Overview/

enhanced composting for POP-contaminated soil
ex situ bioremediation of soil and sediment in slurry reactor
ex situ soil bioremediation in reactors
ex situ soil remediation
ex situ soil treatment
ex-situ thermal soil treatment

ex situ thermal treatment of soil contaminants generally involves the destruction or removal of contaminants through exposure to high temperature in treatment cells, combustion chambers, or other means used to contain the contaminated media during the remediation process. The main advantage of ex situ treatments is that they generally require shorter time periods, and there is more certainty about the uniformity of treatment because of the ability to screen, homogenize, and continuously mix the contaminated media; however, ex situ processes require excavation of soils, which increases costs and engineering for equipment, permitting, and materials handling worker safety issues.

Thermal processes use heat to separate, destroy, or immobilize contaminants. Thermal desorption and hot gas decontamination are separation technologies. Pyrolysis and conventional incineration destroy the contaminants. Vitrification destroys or separates organics and immobilizes some inorganics.

Incineration is a heat-based technology that has been used for many years to burn and destroy contaminated materials. Because it is considered to be a conventional rather than an innovative technology, its treatment here is limited to information listed under "Additional Resources."

EX SITU THERMAL DESORPTION involves the application of heat to excavated wastes to volatilize organic contaminants and water. Typically, a carrier gas or vacuum system transports the volatilized water and organics to a treatment system, such as a thermal oxidation or recovery unit. Based on the operating temperature of the desorber, thermal desorption processes can be categorized as either high-temperature thermal desorption (320 to 560ºC or 600 to 1,000ºF) or low-temperature thermal desorption (90 to 320ºC or 200 to 600ºF).

HOT GAS DECONTAMINATION involves raising the temperature of contaminated solid material or equipment to 260ºC (500ºF) for a specified period of time. The gas effluent from the material is treated in an afterburner system to destroy all volatilized contaminants. This method will permit reuse or disposal of scrap as nonhazardous material.

PLASMA HIGH-TEMPERATURE RECOVERY uses a thermal treatment process applied to solids and soils that purges contaminants as metal fumes and organic vapors. The vapors can be burned as fuel, and the metals can be recovered and recycled.

PYROLYSIS is defined as chemical decomposition induced in organic materials by heat in the absence of oxygen. Pyrolysis typically occurs under pressure and at operating temperatures above 430ºC (800ºF). The pyrolysis gases require further treatment. The target contaminant groups for pyrolysis are SVOCs and pesticides. The process is applicable for the separation of organics from refinery wastes, coal tar wastes, wood-treating wastes, creosote-contaminated soils, hydrocarbon-contaminated soils, mixed (radioactive and hazardous) wastes, synthetic rubber processing wastes, and paint waste.

THERMAL OFF-GAS TREATMENT is one of several approaches that can be used to cleanse the off-gases generated from primary treatment technologies, such as air stripping and soil vapor extraction. In addition to the established thermal treatments, organic contaminants in gaseous form can be destroyed using innovative or emerging technologies, such as alkali bed reactors.

VITRIFICATION technology uses an electric current to melt contaminated soil at elevated temperatures (1,600 to 2,000ºC or 2,900 to 3,650ºF). Upon cooling, the vitrification product is a chemically stable, leach-resistant, glass and crystalline material similar to obsidian or basalt rock. The high temperature component of the process destroys or removes organic materials. Radionuclides and most heavy metals are retained within the vitrified product. Vitrification can be conducted in situ or ex situ.

Source: US-EPA, Clu-In:

http://www.clu-in.org/techfocus/default.focus/sec/Thermal_Treatment%3A_Ex_Situ/cat/Overview/

extraction from soil by organic solvents

solvent extraction uses an organic solvent as an extractant to separate organic and metal contaminants from soil. The organic solvent is mixed with contaminated soil in an extraction unit. The extracted solution then is passed through a separator, where the contaminants and extractant are separated from the soil. Organically bound metals may be extracted along with the target organic contaminants.

extraction from soil by solvents

solvent extraction from soil uses an organic solvent as an extractant to separate organic and metal contaminants from soil. The organic solvent is mixed with contaminated soil in an extraction unit. The extracted solution then is passed through a separator, where the contaminants and extractant are separated from the soil. Organically bound metals may be extracted along with the target organic contaminants.

extraction of LDNAPL from soil
fate of inorganic pollutants in soil
fate of organic pollutants in soil
fracturing rocky soil before treatment

fracturing is a way to crack rock or very dense soil, like clay, below ground. It is not necessarily a cleanup method in itself. Rather, fracturing is used to break up the ground to help other cleanup methods work better. The cracks, which are called fractures, create paths through which harmful chemicals can be removed or destroyed.

Hydraulic fracturing uses a liquid?usually water. The water is pumped under pressure into holes drilled in the ground. The force of the water causes the soil (or sometimes rock) to crack. It also causes existing fractures to grow larger. To fracture soil at greater depths, sand is pumped underground with the water. The sand helps prop the fractures open and keep them from closing under the weight of the soil.

Pneumatic fracturing uses air, to fracture soil. It also can help remove chemicals that evaporate or change to gases quickly when exposed to air. When air is forced into the soil, the chemicals evaporate and the gases are captured and treated above ground.

Air can be forced into the ground at different depths within a hole. When air is forced near the ground surface, the surface around the holes may rise as much as an inch, but will settle back close to its original level. In both pneumatic and hydraulic fracturing, equipment placed underground directs the pressure to the particular zone of soil that needs to be fractured.

Blast-enhanced fracturing uses explosives, such as dynamite, to fracture rock. The explosives are placed in holes and detonated. The main purpose is to create more pathways for polluted groundwater to reach wells drilled for pump and treat cleanup.

Source: US-EPA, Clu-In: http://www.clu-in.org/techfocus/default.focus/sec/Fracturing/cat/Overview/

gasoil

gasoil is an intermediate distillate product from petroleum, used for diesel fuel, heating fuel and sometimes as feedstock for other industries, e.g. plastic industry.

Global soil orders

In the United States 12 soil orders are defined. In 1975, Soil Taxonomy was published by the United States Department of Agriculture's Soil Survey Staff. This system for classifying soils has undergone numerous changes since that time, and the 2nd edition was published in 1999. Soil Taxonomy remains one of the most widely used soil classification systems in the world.

At the highest level, Soil Taxonomy places soils in one of 12 categories known as orders: the 12 soil orders are listed below in the sequence in which they key out in Soil Taxonomy:

  • Gelisols - soils with permafrost within 2 m of the surface
  • Histosols - organic soils
  • Spodosols - acid forest soils with a subsurface accumulation of metal-humus complexes
  • Andisols - soils formed in volcanic ash
  • Oxisols - intensely weathered soils of tropical and subtropical environments
  • Vertisols - clayey soils with high shrink/swell capacity
  • Aridisols - CaCO3-containing soils of arid environments with subsurface horizon development
  • Ultisols - strongly leached soils with a subsurface zone of clay accumulation and <35% base saturation
  • Mollisols - grassland soils with high base status
  • Alfisols - moderately leached soils with a subsurface zone of clay accumulation and >35% base saturation
  • Inceptisols - soils with weakly developed subsurface horizons
  • Entisols - soils with little or no morphological development.

The World Reference Base (WRB) ensures the uniform classification of soils all around the world.

WRB was originally an initiative of FAO and UNESCO, supported by UNEP and the International Society of Soil Science which dates back to 1980. The intention of the project was to work towards the establishment of a framework through which ongoing soil classification could be harmonized. The final objective was to reach international agreement on the major soil groups to be recognized at a global scale as well as on the criteria and methodology to be applied for defining and separating them.

Such an agreement was meant to facilitate the exchange of information and experience, to provide a common scientific language, to strengthen the applications of soil science and to enhance the communication with other disciplines. Several meetings of the ISSS subgroup were held starting in 1982 in New Delhi. In 1992, in Montpellier, France, it was decided that there was no justification to develop a completely new classification system very different from the Revised Legend published by FAO in 1988. Therefore the FAO Revised Legend was to be adopted as the Framework for WRB’s future work and that it would be the task of the working group to further develop its definitions and linkages to the existing FAO units, in order to give them more depth and validity.

Source of description:

http://www.fao.org/nr/land/soils/soil/en/

http://soils.cals.uidaho.edu/soilorders/

grain size fractionation as soil remediation technology
in situ soil flushing

soil flushing means the in situ washing of the unsaturated soil zone.

For in situ soil flushing, large volumes of water, at times supplemented with surfactants, cosolvents, or treatment compounds, are applied to the soil or injected into the groundwater to raise the water table into the contaminated soil zone. Injected water and treatment agents are isolated within the underlying aquifer and recovered together with flushed contaminants.

Source: US-EPA, Clu-In: http://www.clu-in.org/techfocus/default.focus/sec/In_Situ_Flushing/cat/Overview/

in situ soil treatment
in situ thermal soil treatments

many different methods and combinations of techniques can be used to apply heat to polluted soil and/or groundwater in situ. The heat can destroy or volatilize organic chemicals. As the chemicals change into gases, their mobility increases, and the gases can be extracted via collection wells for capture and cleanup in an ex situ treatment unit. Thermal methods can be particularly useful for dense or light nonaqueous phase liquids (DNAPLs or LNAPLs). Heat can be introduced to the subsurface by electrical resistance heating, radio frequency heating, dynamic underground stripping, thermal conduction, or injection of hot water, hot air, or steam.

The main advantage of in situ thermal methods is that they allow soil to be treated without being excavated and transported, resulting in significant cost savings; however, in situ treatment generally requires longer time periods than ex situ treatment, and there is less certainty about the uniformity of treatment because of the variability in soil and aquifer characteristics and because the efficacy of the process is more difficult to verify.

ELECTRICAL RESISTANCE HEATING uses arrays of electrodes installed around a central neutral electrode to create a concentrated flow of current toward the central point. Resistance to flow in the soils generates heat greater than 100ºC, producing steam and readily mobile contaminants that are recovered via vacuum extraction and processed at the surface. Electrical resistance heating is an extremely rapid form of remediation with case studies of effective treatment of soil and groundwater in less than 40 days. Three-phase heating and six-phase soil heating are varieties of this technology.

INJECTION OF HOT AIR can volatilize organic contaminants (e.g., fuel hydrocarbons) in soils or sediments. With deeper subsurface applications, hot air is introduced at high pressure through wells or soil fractures. In surface soils, hot air is usually applied in combination with soil mixing or tilling, either in situ or ex situ.

INJECTION OF HOT WATER via injection wells heats the soil and ground water and enhances contaminant release. Hot water injection also displaces fluids (including LNAPL and DNAPL free product) and decreases contaminant viscosity in the subsurface to accelerate remediation through enhanced recovery.

INJECTION OF STEAM heats the soil and groundwater and enhances the release of contaminants from the soil matrix by decreasing viscosity and accelerating volatilization. Steam injection may also destroy some contaminants. As steam is injected through a series of wells within and around a source area, the steam zone grows radially around each injection well. The steam front drives the contamination to a system of ground-water pumping wells in the saturated zone and soil vapor extraction wells in the vadose zone.

RADIO FREQUENCY HEATING is an in situ process that uses electromagnetic energy to heat soil and enhance soil vapor extraction. The technique heats a discrete volume of soil using rows of vertical electrodes embedded in soil or other media. Heated soil volumes are bounded by two rows of ground electrodes with energy applied to a third row midway between the ground rows. The three rows act as a buried triplate capacitor. When energy is applied to the electrode array, heating begins at the top center and proceeds vertically downward and laterally outward through the soil volume. The technique can heat soils to over 300ºC.

THERMAL CONDUCTION (also referred to as electrical conductive heating or in situ thermal desorption) supplies heat to the soil through steel wells or with a blanket that covers the ground surface. As the polluted area is heated, the contaminants are destroyed or evaporated. Steel wells are used when the polluted soil is deep. The blanket is used where the polluted soil is shallow. Typically, a carrier gas or vacuum system transports the volatilized water and organics to a treatment system.

VITRIFICATION uses an electric current to melt contaminated soil at elevated temperatures (1,600 to 2,000ºC or 2,900 to 3,650ºF). Upon cooling, the vitrification product is a chemically stable, leach-resistant, glass and crystalline material similar to obsidian or basalt rock. The high temperature component of the process destroys or removes organic materials. Radionuclides and heavy metals are retained within the vitrified product. Vitrification can be conducted in situ or ex situ.

Source: US-EPA, Clu-In: http://www.clu-in.org/techfocus/default.focus/sec/Thermal_Treatment%3A_In_Situ/cat/Overview/

injection into soil
inorganic pollutants, chemical forms in soil
interstitial water in soil and rock

subterranean water in the pores of rocks, soils, and bottom sediments of oceans, seas, and lakes.

Two types of interstitial water are distinguished, according to the size of the enclosing interstices: macrocapillary and microcapillary. In interconnected macrocapillary pores, interstitial water moves easily by force of gravity; this is called free, or gravitational, water. Interstitial water in microcapillary pores, is influenced by the surface forces of mineral particles; it has the properties of bound water, which is separated by pressing out, centrifuging, or drawing out under a vacuum.

In the late 1960’s the term “interstitial water” came to be used primarily for water enclosed in microcapillaries; in marine geology this water is also called silt water. The water is present in all rocks and bottom sediments, but it is especially characteristic of clay rocks and sediments. Geological reserves of this water are significantly greater than reserves of free water. The interstitial water of the microcapillary pores is the medium in which the processes determining the mass exchange between hydrous and solid phases of rocks and sediments occur most intensively. For this reason, interstitial water is important in the history of subsurface water, the diagenesis of sediments, and the catagenesis of rocks. It affects the strength and behavior of rocks when engineering structures are erected.

microbial and plant immobilistion, stabilisation in soil
microbial stabilisation in soil
moisture-forms in soil
multi-phase extraction of contaminated soil

multi-phase extraction uses a vacuum system to remove various combinations of contaminated groundwater, separate-phase petroleum product, and vapors from the subsurface. The system lowers the water table around the well, exposing more of the formation. Contaminants in the newly exposed vadose zone are then accessible to vapor extraction. Once above ground, the extracted vapors or liquid-phase organics and ground water are separated and treated.

Source: US-EPA, Clu-In:http://www.clu-in.org/techfocus/default.focus/sec/Multi-Phase_Extraction/cat/Overview/

Natural Attenuation as basis of soil remediation
natural attenuation of organic pollutants in soil
oil-sorbing capacity of the soil
on site soil remediation