Excess Biofilm Control by Distributor-Speed Modulation

The concept of slowing the distributor speed to flush excess biofilm from rock media was discovered by English investigators in the late 1940s. In the 1980s, German investigators quantified the hydraulic effect of average flow and distributor speed in terms of instantaneous or flushing intensity ( SK ), in mm pass of an arm. Studies and analysis conducted in recent years have found that the use of slowed distributor speed was effective in improving performance, but that optimum speed was much higher than that required to flush the media. This information evolved into distributor control drive arrangements that would automatically provide the optimum speed as a function of flow and loading. This concept has been retrofitted at several wastewater-treatment plants, and the Central Valley, Utah, design and initial results are presented. A number of sizing formulations are provided that have evolved from these experiences.