Summary of Direct Filtration With Rapid Sand Filters

Coagulant Aid Filter Loading

Investigator and Dose (mg/L) (gpm/ft2)

Borchardt and O'Melia (1961)» None 0.2-2

Davis and Borchardt (1966) None 0.49

None 0.49

None 1.9

None/Fe 1.9 NA

Foess and Borchardt (1969) None 2

Kormanik and Cravens (1978) None —

" Lab culture of algae.

Filter

2

d50 = 0.40

NA

d50 = 0.75

d50 = 0.29

d50 = 0.75

d50 = 0.29

NA

d50 = 0.75

2

d50 = 0.71

0.92

Removal declines to 21-45% after 15 hr 50% algae removal 22% algae removal 34% algae removal 10% algae removal 2% algae removal 45% algae removal pH 2.5; 90% algae removal pH 8.9; 14% removal 62% SS removal 11-45% SS removal direct granular media filtration. Diatomaceous earth filtration is capable of producing a high-quality effluent when treating wastewater stabilization pond water, but the filter cycles are generally less than 3 hr. This results in excessive usage of backwash water and diatomaceous earth, which leads to very high costs and eliminates this method of filtration as an alternative for polishing wastewater stabilization pond effluents.

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