Direct Filtration — Past, Present, Future

by Gary S. Logsdon, (M.ASCE), Research Sanitary Engr.; Water Supply Research Div., Municipal Environment Research Lab., U.S. E.P.A., Cincinnati, Ohio,

Serial Information: Civil Engineering—ASCE, 1978, Vol. 48, Issue 7, Pg. 68-73

Document Type: Feature article


The Safe Drinking Water Act of 1974 for the first time established national drinking water standards on turbidity and other drinking water characteristics. Up until that time, the accepted standard for turbidity was 5 NTU. Now, cities will be required to meet the tougher 1 NTU standard — unless granted a variance. The upshot of this is that many communities around the U.S. that previously have not treated their water (merely chlorinated it) could be required to install treatment plants in order to meet the new turbidity standard. Rather than constructing a full-blown conventional water-treatment plant, it would be less costly to install a so-called direct-filtration plant. In a conventional plant, coagulation and settling precedes sand filtration. In direct filtration, on the other hand, the settling step is eliminated, saving the cost of the settling basins, which can account for 20 to 30% of the capital cost of the plant. When applied to suitable raw waters, direct filtration has worked well.

Subject Headings: Drinking water | Turbidity | Water treatment plants | Filtration | Safety | Standards and codes | Chlorine | Coagulation

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