The Riemann zeta-function

The disclosed method and apparatus relate to the rejuvenation of a bed of granular filter medium which has accumulated particulate and lint contaminants during filtration flow of dirty liquid. The method first includes the step of agitating the filter bed to break-up contaminants which have become agglomerated. The agitating step includes flowing the filter granules and the contaminants in a liquid mixture slurry from the filter bed housing through a closed flow path and then back to the filter housing. The bed is then at least partially reformed, with the finer particulates and lint being in the upper portion of the bed and the larger particulates being in the lower portion of the bed. Then, the upper portion of the bed is expanded and backwashed to remove the finer particulate contaminants and lint. At the same time, the lower portion of the bed and the heavier contaminants flow in a liquid mixture through a cleaning element to remove those heavier contaminants. The apparatus includes a closed recirculation flow path extending from an upper portion of the filter housing to a lower portion of the filter housing to accomodate the agitating step. A second closed flow path extends from the bottom of the housing to the cleaning element and back to a point spaced from the bottom of the housing, so that only the lower portion of the bed, with little or no lint, passes through the cleaning element during the contaminant removal step.