Percolation assisting additives

Numerical models are used to predict the performance and assist in the design of final cover systems. The availability of models used to conduct water balance analyses of ET cover systems is currently limited, and the results can be inconsistent. For example, models such as Hydrologic Evaluation of Landfill Performance (HELP) and Unsaturated Soil Water and Heat Flow (UNSAT-H) do not address all of the factors related to ET cover system performance. These models, for instance, do not consider percolation through preferential pathways may underestimate or overestimate percolation and have different levels of detail regarding weather, soil, and vegetation. In addition, HELP does not account for physical processes, such as matric potential, that generally govern unsaturated flow in ET covers.39 42 47... 

Finally, microfilters are described as part of the microchannel system in order to assist sample preparation. Channels with diameters less than 30 /rm can easily be blocked by particulates in the sample, or crystals formed in solutions held in a micro-reservoir. While prefiltration outside of the microchannel system can separate most particles out of the sample solution prior to addition to the biosensor system, volumes required for macrofiltration are much larger than the volume finally applied to the biosensor. In addition, crystal or aggregate formation inside the channel cannot be avoided. Thus, the use of microfilters inside the microchannel system will be an important element in miniaturized biosensors. Filters have been described for trapping cells from blood [53], percolation filters for filtering solvents containing particulate materials ranging from dust to cells [54], and nanofilters that can separate particles as small as 44 nm [55]. 

FIGURE 2.9 Normal, assisted, and resisted percolation with and without additives, normal, no additive assisted, with NaC resisted, with NaSl. 

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