Lexikon

soil itself is very complex. Soil is not just a collection of fine mineral particles. Soil also contains air, water, dead organic matter (litter), and various types of living organisms: microorganisms, plants and soil living animals.
The formation of a soil is influenced by climate, topography, parent material, time and the organisms present. The two most important components of soils are the inorganic and organic colloidal (particle size under cc. 1 micron) particles, the clay fraction and the humus molecules.

Soil particles pack loosely, forming a soil structure filled with pore spaces. These pores contain soil solution (liquid) and air (gas).Accordingly, soils are often treated as a three physical phase system. Most soils have a density between 1 and 2 g/cm³.

Water from precipitate moves downward into the soil, it causes both mechanical and chemical translocations of material. The complete chemical removal of substances from the soil profile is known as leaching. Leached substances often end up in the groundwater zone and then travel by groundwater flow into water bodies like rivers, lakes, and oceans. Eluviation refers to the movement of fine mineral particles (like clay) or dissolved substances out of an upper layer in a soil profile. The deposition of fine mineral particles or dissolved substances in a lower soil layer is called illuviation.

Soil Classification Systems have been developed to provide scientific and technological information about the nature of a soil found in a particular location. In general, environments that share comparable soil-forming factors produce similar types of soils. This phenomenon makes classification possible. Numerous classification systems are in use worldwide. United States and Canada use different system than Europe. In Hungary the dynamic classification system is used, which is based on the equilibrium developmental state of the soil.

soil acidification is a process whereby soil becomes acid (pH < 7) because acid parent material is present or in regions with high rainfall, where soil leaching occurs. Acidification can be accelerated by human activities such as the use of fertilisers, deposition of industrial and vehicular pollutants.

soil aggregate consisting of two or more soil particles bound together by various forces.

process whereby primary soil particles (sand, silt, clay) are bound together, usually by natural forces, inorganic compounds and organic substances derived from root exudates and microbial activity (mucoidal products). Soil aggregates are arranged to form soil peds, units of soil structure, classified by size, shape (platy, prismatic, columnar, angular, subangular, blocky, granular…) and grade (single-grain, massive, weak, moderate, strong). From an agronomical point of view, the most important soil aggregates are in range 3–1 mm.

soil bioremediation based on aerobic oxidation means that the soil remediation is based on aerobic biodegradation. The microbiological biodegradation occurs in this case on a high redoxpotential of +0,8-+0,6 Volt. The degrading microorganisms utilise the pollutant as enbergy sources. The source of oxigen is the atmospheric air, soil air, or dissolved oxigen in soil moisture or ground water. If the oxigen-concentration is low, the technologist can increase it by aeration of the soil or the groundwater as well as by adding peroxide substances or other oxigene release compounds ORC to serve as oxigene source for the activation of the aerobic soil microbes.

small size laboratory microcosm prepared from a soil core, an undisturbed part of the soil with original microstructure. SCM is mainly for studying the microscale spatial gradients and processes in the soil.

damage to the land's productive capacity because of poor agricultural practices such as

• the excessive use of pesticides or fertilizers,
• soil compaction from heavy equipment, or
• erosion of topsoil,
• salination,
• nutrient depletion,
• humus degradation and
• pollution eventually of the soil, resulting in reduced ability to produce agricultural products.

soil flushing is a process whereby a solution of water, surfactants, or cosolvents is applied to the soil or injected into the subsurface to treat contaminated soil or groundwater. When treating soil, the injection is often designed to raise the water table into the contaminated soil zone. Injected water and treatment agents are recovered together with flushed contaminants.

soil fracturing is an enhancement technology designed to increase the efficiency of other in situ technologies in difficult soil conditions. The fracturing extends and enlarges existing fissures and introduces new fractures, primarily in the horizontal direction. When fracturing has been completed, the formation is then subjected to vapor extraction, either by applying a vacuum to all wells or by extracting from selected wells, while other wells are capped or used for passive air inlet or forced air injection. Technologies commonly used in soil fracturing include pneumatic fracturing (PF) and hydraulic fracturing. Fracturing is applicable to the complete range of contaminant groups with no particular target group. The echnology is used primarily to fracture silts, clays, shale, and bedrock.

Source: EURODEMO Project

soils support a number of inorganic and organic chemical reactions. Many of these reactions are dependent on some particular soil chemical properties. One of the most important chemical properties influencing reactions in a soil is pH. Soil pH is primarily controlled by the concentration of free hydrogen ions in the soil matrix. Soils with a relatively large concentration of hydrogen ions tend to be acidic. Alkaline soils have a relatively low concentration of hydrogen ions. Hydrogen ions are made available to the soil matrix by the dissociation of water, by the activity of plant roots, and by many chemical weathering reactions.

Soil fertility is directly influenced by pH through the solubility of many nutrients. At a pH lower than 5.5, many nutrients become very soluble and are readily leached from the soil profile. At high pH, nutrients become insoluble and plants cannot readily extract them. Maximum soil fertility occurs in the range 6.0 to 7.2.

Determination of soil pH is a complicate matter: we have to add water to be able to measure the pH, with this we dilute the soil (and the hydrogen ions to be measured) and we initiate the dissolution of normally particulate solid matter, which may modify the pH (for example, limestone). The whole procedure is time dependent.

soil remediation based on aerobic biodegradation is an oxidative process catalysed by microbes. Microbes, mainly bacteria utilise the contaminant as substrate for producing energy. Aerobic bacteria use athmospheric oxigen for the oxidation of the polluting organic compounds and produce inorganic products, such as CO₂, NO₃ and H₂O. This process is also called mineralisation.

When athmospheric oxigen is limited, the biodegradation is catalysed by facultative anaerobic microbes, which use NO₃ for their alternative respiration. In this case the oxidation/mineralisation products from the substrate the contaminant are alcohols or aldehydes.

anaerobic biodegradation of soil contaminants is based on the aternative respiration of soil microorganisms, using oxigen from NO₃^2-, SO₄^2-or CO₂, as hydrogen-acceptor instead of atmospheric oxigen. Paralel to the oxidation of the contaminant energy source in this case, nitrate, sulfate and carbonate are reduced into N₂ via nitrite NO₂⁻, nitric oxide NO, nitrous oxide N₂O, H₂S and CH₄ respectively.

There are some metals which can also be reduced and function as electronacceptor, such as ferric ion Fe³⁺reduction to Fe²⁺ or Fe⁰, manganic ion Mn⁴⁺ reduction to Mn²⁺, selenate SeO₄^2- reduction to selenite: SeO₃^2- and Se⁰, arsenate AsO₄^3- reduction to arsenite: AsO₃^3- or uranyl ion UO₂²⁺ reduction to uranium dioxide UO₂ for the electron transport chain.

The anaerobic biodegradation of xenobiotics needs a microorganism- and metabolism-specific redoxpotential. The soil remedial biotechnology is responsible for ensuring the proper redoxpotential in the soil to control the process and run biodegradation on the optimum.

To control the redoxpotential the technologist should ensure sufficient quantity of nitrate, sulfate or any other electronacceptors in the soil.

solidification/stabilisation (S/S) is a process which physically binds or encloses contaminants within a stabilised mass and is performed both ex situ and in situ. This technology reduces the mobility of hazardous substances and contaminants in the environment through both physical and chemical means.

Ex situ S/S requires excavation of the material to be treated, and the resultant material must be disposed.

In situ S/S uses auger/caisson systems and injector head systems to add binders to the contaminated soil or waste without excavation, and the resultant material is left in place.