Adhesion Processes in the Purification of Water

In the filtration of aqueous suspensions through grainy layers, the adhesion of the suspended particles to the grains of filtering material or to earlier-deposited particles prevails over the hydro-dynamic forces in the flow, which tend to detach the adhering particles. 

The results obtained by Mints [343] confirm the presence of adhering suspended particles on the surface of the sand. The process of filtration is characterized by the filtration index jS, which represents the retaining power of the sand. Since the filtration process is largely determined by the adhesion of the suspended matter, the value of P characterizes the adhesion of the suspension to the grains of sand  

For the filtration of an Fe(OH)3 suspension an analogous curve is obtained. The results of these investigations enable us to compare the effectiveness of the adhesion of various filtering materials. For this purpose we must calculate the Re number for a given charge and velocity of filtration  

K the characteristics of the filter charge vary layer by layer, the quantity a is variable and has to be calculated for the various layers of charge. The adhesion efficiency factor is in this case cal- 

The Mackrle paper [25] took no account of such processes as the autohesion of contaminant particles to each other and their adhesion to a layer of earlier-adhering particles, nor the detachment of adhering particles by the flow of water. These deficiencies are to some extent eliminated in the papers of Mints [345, 346], who in calculating the efficiencies of grainy filters treated the adhesion processes with due allowance for the balance of forces associated with the adhesion or detachment of the adhering particles  

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