Soil media

The harmful effects of air pollutants on human beings have been the major reason for efforts to understand and control their sources. During the past two decades, research on acidic deposition on water-based ecosystems has helped to reemphasize the importance of air pollutants in other receptors, such as soil-based ecosystems (1). When discussing the impact of air pollutants on ecosystems, the matter of scale becomes important. We will discuss three examples of elements which interact with air, water, and soil media on different geographic scales. These are the carbon cycle on a global scale, the sulfur cycle on a regional scale, and the fluoride cycle on a local scale. 

Future needs in support of model validation and performance testing must continue to be in the area of coordinated, well-designed field data collection programs supplemented with directed research on specific topics. The FAT workshop produced a listing of the field data collection and research needs for the air, streams/lakes/estuaries, and runoff/unsaturated/saturated soil media categories, as follows ... 

The results indicate that persistence of organosilicone surfactants in the parent molecule form will be limited on typical soil media and in aqueous environments. Reduced recovery was considered to be a result of abiotic degradation and/or strong sorption processes. Losses were most significant on solid media exhibiting extreme pH values and were also enhanced in the presence of clay substrates. Studies on clays indicated that pH, potential for intercalation and surface charges are important factors in the removal process. 

For air, the major degradation process involves reactions with free radicals such as hydroxyl groups (Atkinson 1985). For other media, it is clear that chloroform can be mineralized through both abiotic and biotic processes. Information in the available literature (Bouer and McCarty 1983 Rhee and Speece 1992) documents the disappearance of chloroform in water and soil media under both aerobic and anaerobic conditions as well as identification of the end products. 

Several pollution control technologies at the refinery promote cross-media transport, the transfer of pollutants from one medium to another. Wastewater, for example, may contain hydrocarbons that volatilize into the air at the refinery, the wastewater treatment plant converted these waterborne hydrocarbons into 2400 tons/year of sludge, which were recycled to the coker. Cross-media transport from air to water is not significant for hydrocarbons or chemical that are only slightly soluble in water (Allen et al, 1989). Studies performed by the National Center for Intermedia Transport at the University of California, Los Angeles, for instance, showed that most hydrocarbons released into the air do not transfer rapidly into other media. Therefore, ignoring intermedia transfer when examining air quality impacts is a reasonable analytical approach. Water-soluble compounds, such as methanol and MTBE, can transfer from air into water and soil media under certain conditions (Cohen et al., 1991). 

Companies focusing on conventional technologies geared toward compliance with single medium specific pollution control standards without being able to consider impacts on air, water, or soil media. 

Following the extraction of humic substances from soil media it is necessary to purify the humic substances by separating them from the nonhumic substances. Used in this sense purification is the removal of materials such as carbohydrates, proteins, lipids, low-molecular-weight compounds, and so on which have been co-extracted with the humic substances. This whole process is called isolation and is dealt with in Chapter 13 by Hayes. 

Pignatello, J. J. (2000). The measurement and interpretation of sorption and desoiption rates for organic compounds in soil media. In Advances in Agronomy, ed. Sparks, D. L., Academic Press, San Diego, CA, 1-73. 

Depth to groundwater Recharge rate Aquifer media Soil media Topography... 

Currently a number of laboratories are devoting considerable effort in developing methodology to characterize the various bonds involved in adsorption, many of which are not readily reversible by simple equilibration with water (e.g., 17). Thus retention cannot be viewed as processes that merely retard transport of pesticides in water, but can bind the chemicals irreversibly to soil surfaces (the so-called bound residue ) and totally remove the chemicals from transport. Such process as chemisorption may not be easily distinguished with chemical transformation of the compound in the soil media (18). 

A - Aquifer Media S - Soil Media T - Topography (Slope)... 

Soil Media. Soil media refers to that uppermost portion of the vadose zone characterized by significant biological activity. For... 

Impact of Vadose Zone. The vadose zone is defined as that zone above the water table and below the soil media which is unsaturated. For purposes of this document, this strict definition can be applied to all water table aquifers. However, when evaluating a confined aquifer, the "impact" of the vadose zone is expanded to include both the vadose zone and anysaturated zones which overlie the aquifer. The significantly restrictive zone above the aquifer which forms the confining layer is used as the type of medium which has the most significant impact. 

Electrokinetic processing derives its name from one of the four major electrokinetic phenomena. These arise from the coupling between electrical and hydraulic flows and gradients in suspensions and porous (soil) media, which can be responsible for electroosmosis, streaming potential, electrophoresis, and migration or sedimentation... 

Arduino, R, Miller, G. R., Ogurinde, A. (2002). Live modeling of 1 -D wave propagation in layered soil media. Computer Applications inEngineering Education, 9(4), 248-258. doi 10.1002/cae. 10003... 

FIGURE 6.15 Gas evolution data (filled symbols) plotted as percent mineralization for the biodegradation of bleached paperboard packaging material in a respirometer. Soil media (70 wt% humidity) with sewage sludge inoculum was used. Also included is a plot of the data (open symbols) as suggested by Equation 6.2. Source Reproduced with permission from Andrady and Song (1999). 

Definition of soil conditions and dynamic behavior of soil media ... 

The test might be carried in water or soil, but the latter is discussed here. In both cases a suitable volume of activated sludge to obtain complete mineralization of the sample in about a month is used as an inoculum. About lOcm per liter is recommended for aqueous systems and we have used 5cm per 50 g with soil media successfully. The inoculum must be used the same day as collected and kept aerated until used. Also sufficient urea and potassium hydrogen phosphate (0.1 and 0.05 percent of weight of polymer substrate) are added to the medium to fortify it and to promote faster microbial growth. 

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