Free-Living Nematode Removal by Rapid Sand Filters

Flow rates of 2, 4, and 6 gpm per sq ft gave approximately 98% removal of nonmotile Diplogasteroides sp., one of the predominate species found in waste treatment plant effluents, whereas only 25% of the motile worms were removed. The motility of the worms was observed to be the most important single factor in the removal of worms by filtration. Smaller, less motile worms were removed more effectively than larger, more motile worms. Percentage worm removal with filter influents having high concentrations of nematodes, predominantly non-motile, was higher than with water having low concentrations of nematodes, predominantly motile. Examination of the sand showed worm retention throughout the entire depth but with the highest concentrations near the top of the sand.