Drinking Water Filtration at a Municipal Water Utility

FiltrationFiltrationat the Bloomington, ILat the Bloomington, ILWater Treatment PlantWater Treatment Plant

Old Plant FiltersOld Plant Filters1929, 1956, 19661929, 1956, 1966

Old Plant FiltersOld Plant Filters

• Filters #1-12: GAC-Capped Sand

• 435 square feet per filter (20’ x 21.75’)

• Operated at a flow rate of ~ 1 gpm/ft2

• Fixed surface wash nozzles

Old Plant Filters: Influent Trough Old Plant Filters: Influent Trough

Old Plant FiltersOld Plant FiltersAfter Pressure WashingAfter Pressure Washing

PVC Surface W

ash Piping

Old Plant Filters:Old Plant Filters:Fixed Surface Wash NozzlesFixed Surface Wash Nozzles

PVC Pipe and Nozzles

Old Plant Filters: Media RemovedOld Plant Filters: Media Removed

ManifoldLat

erals

Old Plant Filters: UnderdrainOld Plant Filters: Underdrain

Perforated Cast Iron Lateral Piping :

Uniform Distribution of Backwash Water

New Plant Filters - 1994New Plant Filters - 1994

New Plant Filters: GAC CapNew Plant Filters: GAC Cap

24” filter cap replaced with virgin GAC every two years

New Plant Filters: Influent TroughNew Plant Filters: Influent Trough

Wash Water Trough

Influent Channel and

Wash Water Gullet

New Plant Filters: Influent TroughNew Plant Filters: Influent Trough

• Filters #13-18

• Dual-cell filters

• 462 square feet per filter (10.75’ x 21.5’ x 2 cells)

• Operated at a flow rate of ~ 2 gpm/ft2

• Rotating surface wash

New Plant Filters:New Plant Filters:Rotating Surface WashRotating Surface Wash

Surf

ace

Was

h H

eade

r

New Plant FiltersNew Plant Filters

GAC Removed

Sand Layer Exposed

Granular Activated CarbonGranular Activated Carbonand Silica Sandand Silica Sand

BackwashBackwash

Sand Grab SampleSand Grab Sample

Filter Core SampleFilter Core Sample

Silica Sand Granular Activated Carbon

Top / Bottom of Sand LayerTop / Bottom of Sand Layer

top bottom

New / Old SandNew / Old Sand

New sand is finer; more uniform

New / Old SandNew / Old Sand

D10 (new) = 0.52 mm D10 (old) = 0.58 mm

Examination of Old SandExamination of Old SandStereo MicroscopeStereo Microscope

Examination of Old SandExamination of Old Sand

Examination of Old SandExamination of Old Sand

Examination of Old SandExamination of Old Sand

Examination of Old SandExamination of Old Sand

Elution of Old SandElution of Old Sand

Organisms Rinsed from Old SandOrganisms Rinsed from Old Sand

GAC Grab SampleGAC Grab Sample

Chain of CustodyChain of Custody

New / Old CarbonNew / Old Carbon

new old

black grey

New / Old CarbonNew / Old CarbonOld GAC has lost both ‘fines’ & larger particlesOld GAC has lost both ‘fines’ & larger particles

Examination of Old CarbonExamination of Old Carbon

Examination of Old CarbonExamination of Old Carbon

Examination of Old CarbonExamination of Old Carbon

Examination of Old CarbonExamination of Old CarbonStalked, Epiphytic Bacteria extend from GAC surfaceStalked, Epiphytic Bacteria extend from GAC surface

Examination of Old CarbonExamination of Old CarbonBacteria fluoresce under UV illuminationBacteria fluoresce under UV illumination

Examination of Old CarbonExamination of Old CarbonMicrobial Colonization of GAC SurfaceMicrobial Colonization of GAC Surface

Examination of Old CarbonExamination of Old Carbon

Examination of Old CarbonExamination of Old Carbon

Examination of Old CarbonExamination of Old Carbon

Replacing Lost SandReplacing Lost Sand

The Changing of the CarbonThe Changing of the Carbon

Disinfection after GAC/Sand ReplacementDisinfection after GAC/Sand Replacement