Removal of Solid Soil

Liquefiable Soil The first stage in the removal of this type of soil is believed to be liquefaction of the soil (Cox, 1986). Penetration of the soil by surfactant (and associated water molecules) from the cleaning bath with resulting liquefaction may be a key process in the removal of this type of soil (Cox, 1984). In cases where penetration of the solid soil by surfactants or other additives does not occur, an increase in the temperature of the cleaning process may result in its liquefaction. The liquefied soil is then removed by the roll-back mechanism described above (Cox, 1987). 

Particulate Soil Removal of particulate solid soil by aqueous baths is accomplished by the following mechanisms  

The tendency of the bath B to spread over the soil particle P or the substrate S is given by the spreading coefficients (Chapter 6), SB/p and SB/s, respectively, where 

Adsorption of surfactant and other bath components (e.g., inorganic ions) at the substrate-liquid and particle-liquid interfaces. This causes a decrease in the work required to remove the particle from the substrate, since the free energy change per unit area involved in this process is the work of adhesion Wa (Chapter 6, Section IB), given in this case by the expression 

Adsorption of surfactants at these interfaces can result in a decrease in jSB and jPB, with a consequent decrease in the work required to cause removal of the particle from the substrate. 

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Oily soils containing amphiphilic species, such as fatty acids or fatty alcohols, can also be removed from substrates as a result of the formation of liquid crystal or mesomorphic phases between the amphiphile and a detergent. The liquid crystals are then broken up by subsequent osmotic penetration by water [140-142], Removal of solid soils by mesophase formation can be accelerated by increasing the temperature. This has been reported for stearyl alcohol [143] and for lauric, palmitic, and stearic acids [128, 129] and is likely due at least in part to the increased penetration of the soils at higher temperatures [128,129,143],... 

Removal of solid soils by penetration without liquid crystal formation has been reported for tripalmitin, octadecane, and tristearin [143-145]. In these cases penetration of detergents occurred at crack and dislocation sites of soils. 

Protein and starch stains are removed by proteases and amylases, respectively. Fats and oils are generally difficult to remove at low wash temperatures by conventional detergents. By using lipases, it is possible to improve the removal of fats/oils of animal and vegetable origin even at temperatures where the fatty material is in a solid form. Particulate soils can be difficult to remove, especially if the particle size is small. Removal of particulate soil from cotton fabric can be improved by use of a cellulase which removes cellulose fibrils from the surface of the yam. 

Time - resolved spectra of a solid hydrocarbon layer on the surface of an internal reflection element, interacting with an aqueous solution of a nonionic surfactant, can be used to monitor the detergency process. Changes in the intensity and frequency of the CH2 stretching bands, and the appearance of defect bands due to gauche conformers indicate penetration of surfactant into the hydrocaibon layer. Perturbation of the hydrocarbon crystal structure, followed by displacement of solid hydrocaibon from the IRE surface, are important aspects of solid soil removal. Surfactant bath temperature influences detergency through its effects on both the phase behavior of the surfactant solution and its penetration rate into the hydrocaibon layer. 

Solid hydrocarbon soils can be rapidly removed from the surface of a ZnSe IRE by alkyl polyethylene oxide) surfactants. The removal mechanism involves penetration of a small amount of the surfactant into the hydrocarbon layer, which causes an increase in methylene chain defects in the soil, and displacement of solid soil from the substrate. Solubilization of a large fraction of the solid soil is not required. 

As might be expected, large differences in the removability of solid particulate soil are due to differences in the chemical nature of the particle surface. Thus, iron... 

Fundamental principles leading to the removal of oily soil from the solid substrate by the so-called roll-up mechanism, in which liquid oil is displaced from the surface by the washing solution in the form of dispersed tiny droplets [60], are essentially the same as those evoked in the attachment of air bubbles onto a mineral surface. 

Studies [24] have shown that linear alcohol ethoxylates made with short-chain alcohols are effective as hard-surface cleaners. A shorter-chain hydrophobe is thought to confer greater solvency on the surfactant, which assists in the removal of solid, greasy soils. An intermediate amount of ethylene oxide was also found to be generally best for hard-surface cleaning. 

Water-insoluble liquid soils are commonly known as oily soils. Naturally occurring oily soils include hydrocarbons, saturated or unsaturated fatty acids, esters of fatty acids, and alcohols. Natural oily soils found on textiles are mixtures of oily components. Frequently, oil soils contain dispersed solid particulate matter (e.g., used motor oil). The most important properties of oily soils are their viscosity [1,2], polarity [3,4], and solubility in detergent solutions or dry-cleaning solvents. The removal of oily soil by detergency is facilitated by a low viscosity at the wash temperature. The polarity of soil affects adhesion of the soil on fibers, interaction with... 

The removal of solid, particulate soils from a substrate in an aqueous cleaning bath involves the wetting of the substrate and soil by the cleaning bath followed by adsorption of surfactant and/or other components at the substrate-liquid and... 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

Solid Soil Type and Size. Different soHd soils differ greatly in ease of removal and redeposition behavior. These differences can be traced to particle size and soil—substrate bonding. The effect of particle size variation on detergency has been studied with soil removal and redeposition techniques. 

Figure 9-3 portrays a hypothetical model of how chemical weathering and transport processes interact to control soil thicknesses. The relationship between soil thickness and rate at which chemical weathering can generate loose solid material is indicated by the solid curve. The rate at which transport processes can potentially remove loose solid weathering products is indicated by horizontal dotted lines. The rate of generation by chemical weathering initially increases as more water has the opporhmity to interact with bedrock in the soil. As soil thick-... 

Only a small fraction of faecal contaminants contributed to the enviromnent through human and animal faeces reach new hosts to infect them. Many of the defecated microorganisms never reach the soil and/or water bodies, since faecal wastes are submitted to purification (water) and hygienization (solids) processes, which remove a fraction of the pathogens and indicators. An important fraction of those that reach either the soil or water are removed (adsorption to soil particles and suspended solids, followed by sedimentation) and/or inactivated by natural stressors (physical, chemical and biological) in soil and water bodies. 

Turbidity, due to solid particles in suspension, is a parameter generally neglected. However, under water scarcity, it is very important to be controlled because it may restrict the use of water for irrigation. Solid particles may clog the water distribution systems as drippers or sprinklers. They may also affect the soil permeability. This is why in different countries in the Mediterranean region special devices for the removal of sediments especially are used when marginal waters are only available for irrigation. 

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