Direct Filtration





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:








Direct filtration can be accomplished through different types of media.






Filter Process Objectives


The objectives of any filter process are to:









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: