Direct Filtration

 

 

PURPOSE

 

The purposes of the direct filtration process include: compliance with treatment technique regulatory requirements; targeting impurities; and producing safe and aesthetically pleasing drinking water.

 

 

 

 

Compliance with Treatment Technique Regulatory Requirements

 

The USEPA (U.S. Environmental Protection Agency) Surface Water Treatment Rule requires continuous filtration and disinfection as treatment techniques for all surface waters, including groundwater sources designated by the VDH as groundwater under the direct influence of surface water (GUDI).

 

 

 

 

 

 

Turbidity and the Direct Filtration Process

 

When source water is generally within the turbidity range of 1 to 2 NTU, it may be a candidate for direct filtration.

 

 

 

Compliance with Turbidity Requirements

 

 

 

 

 

Produce Safe and Aesthetically Pleasing Drinking Water

 

The three criteria for the second purpose of direct filtration, which is to provide safe and aesthetically pleasing water, include:

 

 

 

 

Free of Disease-Causing Organisms

 

 

 

 

 

Free of Toxic Substances

 

 

 

 

 

No Disagreeable Taste, Odor, and Appearance

 

 

 

 

Target Impurities

 

Targeting impurities is the third, and final, purpose of the direct filtration process. The key constituents in the source water that are targeted by an ďabbreviatedĒ (filtration) process include:

 

 

 

 

 

 

General Characteristics of Appropriate Source Waters

 

Direct filtration is used for source waters with the following general water quality characteristics.

 

 

 

 

 

Pilot Testing of Source Waters

 

To verify that a source water can be treated with direct filtration, pilot testing should be performed prior to the design of the facility. This demonstrates the ability of the process to perform in accordance with all drinking water regulations.

 

The abbreviated direct filtration process does not include the following processes that are components of the conventional filtration process:

 

 

 

 

 

GENERAL OVERVIEW OF DIRECT FILTRATION

 

Direct filtration can be accomplished through different types of media.

 

 

 

 

 

Filter Process Objectives

 

The objectives of any filter process are to:

 

 

 

 

 

 

Coagulation

 

The optimum dose for direct filtration is the lowest dose that achieves filtrate quality and production goals. The purpose of adding a coagulant aid is to increase floc strength and density.

 

The most commonly used chemicals to achieve coagulation in this type of process are:

 

 

 

 

 

Media Bed Configurations

 

Any one of the following filter bed configurations might be found in a direct filtration plant: