City of Atlanta
Department of Watershed Management
Bureau of Drinking Water
Introduction to
Drinking Water Treatment
The Bureau of
Drinking Water
oversees all
aspects of the
water system,
including raw water
supply, treatment,
distribution and
water quality
compliance.
GLOSSARY OF TERMS
potable
mgd (million gallons per day)
intake
terbidity - particles and pollutants
NTU - measured unit of turbitity, how dirty the water is based on light reflectivity levels
coagulation
flocculation
floc - combined weight of dirt and alum
sedimentation
seasonal turnover - the switch of cool/warm water from top/bottom of reservoir spring/fall
distribution
system control - centralized logistics board, schematic diagram that shows how each stage is
functioning
fluid mechanics
watershed
History of Atlanta’s Sewer System
The City of Atlanta and the
surrounding region have grown
tremendously in the last 100
years. While growth is
essential to maintaining our
economic vitality, it can have
negative effects on the
environment.
In its earliest days, Atlanta
used open watercourses to
capture stormwater and
divert it into nearby brooks
and creeks.
Chattahoochee River, Atlanta’s Water Source
In 1891, the Chattahoochee River was selected as the
source for Atlanta’s water by Mayor William Hemphill.
Today the Chattahoochee River is valued more as a source of drinking water and recreation than as a transportation artery.
Facilities – Water Treatment Plants
←
Chattahoochee Water
Treatment Plant
→
Chattahoochee River Intake
Facilities – Water Treatment Plants
Hemphill Water Treatment Plant
Facilities – Water Treatment Plants
Chattahoochee River Intake
Chattahoochee WTP
Hemphill WTP
The City currently has a raw
water permit of 180 million
gallons per day (mgd) from the
GA Dept. of Natural Resources,
EPD.
The CWTP is manually
operated, staffed 24/7 and has a
maximum capacity of 64.9 mgd.
The HWTP is manually
operated, staffed 24/7, and has
a maximum capacity of 136.5
mgd.
Water from the
Chattahoochee River Intake
enters and flows by gravity to
the Chattahoochee Raw Water
Pumping Station.
Water is screened and
chemicals are applied to it
before it leaves the intake.
The water is sent from the
intake to the Chattahoochee
WTP by the Raw Water Pumping
Facility.
The pump station consists of
five high-service pumps that
send water to the Hemphill
Reservoirs and four low-service
pumps that send water to the
CWTP.
CWTP receives raw water
directly from the Chattahoochee
Raw Pumping Station.
The current treatment
process at the plant consists of
flocculation, sedimentation,
filtration, disinfection and
storage.
Raw water from the
Chattahoochee Raw Pumping
Station flows into the plant
where chemicals are added to
promote flocculation.
CWTP has four finished water
pumps that send water to the
distribution system.
The HWTP is one of three
water treatment plants that
provides potable water for the
City of Atlanta and parts of
Fulton County. (The AtlantaFulton County Plant also
supplies water to Atlanta.)
The HWTP supplies water to
retail, residential, commercial,
and industrial customers within
the City and portions of Fulton
County.
Two reservoirs are located at
HWTP (No. 1 – cap. 180 mg) and
(No. 2 – cap. 345 mg).
As of 1987, seventeen filters
have been installed, bringing
the filter rate to 136.5 mgd total.
Atlanta’s Raw Water Reservoir
at the Hemphill Complex
Water Cycle and Treatment Process
From the river to your home, from your home
to the river.
↓
CONVENTIONAL WATER TREATMENT
PROCESS
→
Intake
Coagulation and Flocculation
Sedimentation
Filtration
Disinfection
Storage
Coagulation and Flocculation
Coagulation and flocculation may be broadly described as
chemical and physical processes that mix coagulating
chemicals and flocculation aids with water.
The chemistry of coagulation / flocculation
consists of three processes:
Flash Mix
Coagulation
Flocculation
Coagulation and Flocculation
Flash Mix
In the flash mixer, coagulant chemicals are added to the water and the water is
mixed quickly. Flash mixing typically lasts a minute or less.
Coagulation and Flocculation
Coagulation
After flash mixing, coagulation occurs.
particles suspended in water.
Coagulation removes dirt and other
Alum and other chemicals are added to water to form particles called “floc” which
attract the dirt particles. The combined weight of the dirt and the alum (floc)
become heavy enough to sink to the bottom during sedimentation.
Coagulation and Flocculation
Flocculation
During flocculation, a process of gentle mixing brings the fine particles formed by
coagulation into contact with each other. This process typically lasts for about
thirty to forty-five minutes.
Sedimentation
Sedimentation is a physical process used to settle out suspended
solids in water under the influence of gravity.
Suspended particles settle and carry down most of the microorganisms. Clear
water is then moved to filtration.
Filtration
The water passes through filters, some made of layers of sand,
gravel, and charcoal that help remove even smaller particles.
Filter Washing
Filter Washing
Post Chemical Treatment
Chlorine is added to kill water borne bacteria or
microorganisms that are found in untreated water.
Calcium Hydroxide (Lime) is added to increase pH in water.
Phosphoric Acid (Phos) is added to the water to properly
coat the pipes for corrosion control.
Hydrofluosilicic Acid (Fluoride) is added to the water to
prevent tooth decay.
Clean Water –
After Disinfection
Storage
Hemphill Water Treatment Plant finished water is stored in three
underground clear well tanks. Clear wells #1 and #3 hold 10MG each.
The #2 Clear well is our largest storage tank which holds 15MG.
Pumping to Distribution System
Finished water is then pumped through various sized pipes to homes and
businesses throughout the City of Atlanta and parts of other counties.