Removal of Nematodes by Rapid Sand Filtration

The results of a study on rapid sand filtration indicated that, with a low percent nematode motility, the removal of nematodes increased with decrease in sand size. As the percent motility increased, the removal of nematodes decreased. Also, as the percent motility increased, the percent removal of nematodes by all sand sizes studied approached one another. An evaluation of motile nematodes in the influent and effluent showed that most motile nematodes could eventually pass through the sand bed even though some of them could be temporarily retained in the sand during the early stages of the filtration process. From a balance of nematodes entering and leaving the system, it also appeared that motile nematodes could dislodge the nematodes which were initially retained in the sand bed. Thus, these two phenomena resulted in an over-all decrease in removal of nematodes. The effect of increased motility, which tended to decrease nematode removal, was more significant then the expected benefits of using chemical pretreatment.