Coliform Organism Removals by Diatomite Filtration

Abstract

This study investigated the removal of coliform organisms by diatomite filtration, along with the factors that influence coliform removal such as raw water coliform level, filter aid permeability, flow rate, and body feed concentrations. In addition, the use of coated filter aids was investigated, as well as the use of small iron dosages to the raw water, to improve the removal process.

Removal of particulate matter on coated filter media

“…Diatomite coated with coagulants have been reported to produce removal of bacteria, color, and turbidity significantly better than the removal obtained with like grades of uncoated diatomite (4). However, more recent studies indicate that the removals of bacterial suspensions by coated and uncoated diatomite are not significantly different (28).…”

“…It was explained that the earlier filtration tests, in which bacteria removals were improved, the raw water had turbid material in addition to bacteria and the bacteria were probably associated with the turbidity which was removed more effectively by the coated media. In the latter tests, the suspensions of bacteria were prepared with a turbidity-free water and removals using coated diatomite were not significantly dif ferent than those with uncoated diatomite (28).…”

Removal of particulate matter on coated filter media

“…This is possible if the suspended particles are larger in diameter than a few microns since the smaller grades of diatomite have an approximate mean particle size of less than 5 microns. However, there are reports of bacteria, turbidity, and color compounds passing through the finer grades as well as coarser grades of diatomite in quantity (4,28,51), This observation indicates a need to increase the effect of other possible mechanisms of removal, as previously discussed, in an effort to improve the removal of colloidal and subcolloidal particles by diatomite filtration.…”