ABSTRACT
Ever since then, conventional treatments have undergone substantial improvements and filters, as well, have been modified so as to achieve a better operation from a mechanical and hydraulic standpoint. Still, direct filtration with a separate coagulation-flocculation step is based on interception-occlusion principles which exploit the gravitational and inertial transport forces, whereas in contact flocculation, Brownian motion plays an important role in addition to the forces. Direct filtration can also be employed for the removal of dissolved substances. It is quite common to employ filters to remove iron and manganese after oxidation. Filters also find a widespread application in the removal of substances rendered insoluble by appropriate chemical reactions (phosphates, tannin, humic and fulvic acids, etc.). The actual practice of direct filtration is, therefore, based on experimental observations, assuming that the optimal filtering cycle is obtained when the maximum permissible pressure drop matches the maximum permissible effluent quality.
