Fouling porosity distribution

Figure 15.9 Analyzed porosity distributions in fouling layers during the time course of the dead-end microfiltration under AP = 61 kPa for 0.5% cross-linked S. cerevisiae suspension.

As a result, these membranes suffer two deficiencies low flux rate due to the low porosity (i.e., limited permeability) and high fouling rate due to the asymmetric pore-size distribution having small pores on the surface [113]. 

Filter aids may be applied to the filtration operation in two ways. The first way is to precoat the filter medium using a precoat filter aid. The precoat is to behave as the actual filter medium. The function of such an application is to prevent the filter medium from clogging or fouling as well as to facilitate the removal of the formed cake at the end of filtration. The second way is to pretreat the suspension using a filter aid powder with a coarser size distribution prior to the filtration process. Such material is called body aid or admix. The functions of body aid are to increase the porosity of filter cake and to decrease its compressibility, resulting in a decrease in the cake resistance and in turn an increase in the filtration rate. 

The filter medium is the core of the whole filtration process. A premium filter with a desired selectivity should have a defined pore size and a narrow pore size distribution. In addition, filters with high porosity, smooth surface, and liquid affinity should be beneficial toward a higher permeation rate and lower fouling, as the feed liquid is being passed from the filter surface into the porous pathway inside the filter. 

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