Water Treatment Processes
Water Treatment Plant
Operation
Water Treatment Processes
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Section 1:
Section 2:
Section 3:
Processes
Section 4:
Section 5:
Section 6:
Section 7:
Section 8:
Water Treatment Concerns
Well Considerations
Conventional Water System
Disinfection By-Product Control
Corrosion Control
Demineralization Processes
Coagulation Process Control
Water Softening
Florida Rural Water Association
Water Treatment Plant Operation
2
Section 1:
Water Treatment Concerns
Microbial Contamination Concerns
 Barriers to Contaminants Reaching the
Public
 Where Contamination Comes From
 Bacterial Indicators and Pathogens
 Primary Standards
 Secondary Standards

Florida Rural Water Association
Water Treatment Plant Operation
3
Microbial Contamination is Primary
Concern of Water Operators
Coliform bacteria
Common in the environment and are generally not harmful but their
presence in drinking water indicates that the water may be contaminated
and can cause disease.
Fecal Coliform and E coli
Bacteria whose presence indicates that the water may be contaminated
with human or animal wastes. Microbes in these wastes can cause
short-term effects, such as diarrhea, cramps, nausea, headaches, or
other symptoms.
Turbidity
Has no health effects. However, turbidity can interfere with disinfection
and provide a medium for organisms that include bacteria, viruses, and
parasites that can cause symptoms such as nausea, cramps, diarrhea,
and associated headaches.
Florida Rural Water Association
Water Treatment Plant Operation
4
Multiple Barrier Approach
Source:
Selection and
Protection
Treatment:
Methods and
Efficiencies
Florida Rural Water Association
Water Treatment Plant Operation
Distribution:
Maintenance
and Monitoring
5
Where Contamination Comes
From
Condition
Test For:
Reoccurring Gastro-illness*
Coliform in Drinking Water
Pipeline Failure
pH, Lead, and Copper
Nearby Agriculture
Nitrates, Pesticides and Coliform
Nearby Mining
Metals and pH
Nearby Landfill
VOCs, TDS, Chlorides, & Sulfate
Nearby Fueling
VOCs
Bad Taste/Odors
Hydrogen Sulfide and Iron
Stains Clothes/Plumbing
Hydrogen Sulfide and Iron
Scaly Residue
Hardness
* Multiple Sources, ie. runoff, septic tanks, CAFOs
Florida Rural Water Association
Water Treatment Plant Operation
6
Microbial Contaminants found in
Surface Water or UDI Sources
Cryptosporidium and Giardia
Parasites that enters lakes and rivers through
sewage and animal waste. These typically
cause mild gastrointestinal diseases.
However, the disease can be severe or fatal
for people with severely weakened immune
systems. EPA and CDC have prepared
advice for those with severely compromised
immune systems who are concerned about
these organisms.
Florida Rural Water Association
Water Treatment Plant Operation
7
Some Facts About Bacteria
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Bacteria are widely distributed on earth
They have been found 4 miles above earth and 3
miles below sea sediments.
One gram of fertile soil contains up to 100,000,000
bacteria.
Bacteria are inconceivably small and measured in
microns. One micron is equal to 1/1,000,000 of a
meter.
During the rapid growth phase bacteria undergo
fission (cell division) about every 20 to 30 minutes.
One bacterial cell after 36 hrs of uncontrolled
growth, could fill approximately 200 dump trucks.
Florida Rural Water Association
Water Treatment Plant Operation
8
Bacteria and Pathogenic
Indicators in Water Treatment
Total
Coliform
Ferment
Lactose @ 35OC
Include
Species
of
Genera
Fecal
Coliform
Citrobacter
Enterobacter
Klebsiella
E. Coli
Grow at 44OC
Produce Enzyme
More Specific
Indicator of
Contamination
< 500
colonies/ml
E. Coli
HPC
Photo: CDC. E. coli 0157:H7
11 of 140 cause gastrointestinal disease
Identifying Source of
Contaminants
Florida Rural Water Association
Water Treatment Plant Operation
10
Primary or Inorganic
Contaminants
Mineral-Based Compounds
These include metals, nitrates, and asbestos.
These contaminants are naturally-occurring in
some water, but can also get into water
through farming, chemical manufacturing,
and other human activities. Potential health
effects include learning disorders,
kidney and liver damage. EPA has set
legal limits on 15 inorganic contaminants.
Florida Rural Water Association
Water Treatment Plant Operation
11
Primary Standards and their
Maximum Contaminant Levels (MCLs)
Contaminant
Arsenic
Asbestos
Fluoride
Mercury
Nickel
Nitrate
Nitrite
Total Nitrate+Nitrite
Sodium
MCL (mg/l)
0.010
7 (MFL)
4.0
0.002
0.1
10
1
10
160
Florida Rural Water Association
Water Treatment Plant Operation
12
Disinfectants and Disinfection
By-Products
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Disinfectants are water additives that are
used to control microbes
Disinfection By-products are created when
chlorine is added in the presence of naturally
occurring low levels of organic materials
found in drinking water
Both are regulated because of health
concerns
Florida Rural Water Association
Water Treatment Plant Operation
13
Secondary Standards and
Concerns
These compounds cause aesthetic
concerns such as taste, odor and color.
 EPA recommends MCL limits
 Some states such as Florida have set
regulatory limits on these contaminants

Florida Rural Water Association
Water Treatment Plant Operation
14
Secondary Standard
Maximum Contaminant Levels
Contaminant
Chloride
Sulfate
TDS
Copper
Fluoride
Iron
Manganese
Silver
pH (MRCL)
Color (MCRL)
MCL (mg/l)
250
250
500
1.0
2.0
0.30
0.05
0.1
6.5 to 8.5
15 cfu
Florida Rural Water Association
Water Treatment Plant Operation
15
Protecting Well by Grouting
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Pressure Testing of Grout Seal @
~10 psi for 1 hr. Should be
Performed.
Prevent movement of
water between aquifer
formations
Preserve quality of
producing zones
Preserve Yield
Prevent water intrusion
from surface
Protect Casing against
Corrosion!
Florida Rural Water Association
Water Treatment Plant Operation
16
Section 2
Well Considerations
Floridan Aquifer
 Well Contaminants
 Preventing Contamination at the Well
Head

Florida Rural Water Association
Water Treatment Plant Operation
17
Floridian Aquifer Across Florida
Florida Rural Water Association
Water Treatment Plant Operation
18
Well Source Water Parameters
Quality and Quantity Dictates Depth of Well
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TDS
Total Hardness
Total Fe and Mn
Chlorides & Sulfates
Total Alkalinity
Nitrate
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pH
Corrosivity
CO2
H2S
Fluoride
Florida Rural Water Association
Water Treatment Plant Operation
19
Preventing Contamination at
the Well Head
#
Observation
Likely Pathway
1
Septic tanks,
broken storm or
san. pipes, ponds
Drainage up-hill
Through Surface Strata
Well subject to
flooding
Casing termination
Surface water transport of
contaminants
Must be 1’ and above 100
20
yr flood plane
2
3
4
Surface water runoff
Preventing Contamination at
the Well Head (continued)
#
Observation
Likely Pathway
5
Area around well is
wet
Possible Abandoned
wells in area
Sanitary condition
unacceptable
Cracking in Well
Slab
Corroded Casing Pipe
6
7
8
Surface water intrusion
from contaminated source
Contaminated water
intrusion
Contaminated water
intrusion
Florida Rural Water Association
Water Treatment Plant Operation
21
Preventing Contamination at
the Well Head (continued)
#
Observation
9
Evidence of Algae
or Mold on Slab
Poor Drainage
10
11
12
Likely Pathway
Birds and insects attracted
by moist conditions
Surface water intrusion
from contaminated source
Seal water Draining Contaminated water
into well head
entering borehole
Well Seal damaged Contaminated water
intrusion
Florida Rural Water Association
Water Treatment Plant Operation
22
Preventing Contamination at
the Well Head (continued)
#
Observation
Likely Pathway
13
Fittings pointing
upward
Well vent not
properly installed
Check Valve absent
or not working
Cavitation or water
hammer
Contaminated Water
intrusion into casing
Contaminated Water
intrusion into casing
Contaminated water backflowing into casing
Ck. Valve damage & water
back-flowing into casing
14
15
16
Florida Rural Water Association
Water Treatment Plant Operation
23
Preventing Contamination at
the Well Head (continued)
#
Observation
Likely Pathway
17
Well Site Security
Compromised
Livestock or wild
animals close by
Surface water
evidence ID
Several wells
available
Contaminated Water from
undesirable activities
Animal source of
Contamination
Indicator organisms, color,
temp and TOC contributing
One well is more likely to
contribute than others
18
19
20
Florida Rural Water Association
Water Treatment Plant Operation
24
Preventing Contamination at
the Well Head (continued)
#
Observation
Likely Pathway
21
Intermittent Well
Operation
22
Wet or extreme
weather events
Contaminated occurring
from long-term biological
activity
Contamination from run-off
or from higher pumping
levels.
Florida Rural Water Association
Water Treatment Plant Operation
25
Section 3:
Conventional Water System Processes
TOC in Source Water
 Disinfection and Uses of Chlorine
 Aeration and Aerator Types
 Iron and Hydrogen Sulfide Control
 Filtration
 Sedimentation

Florida Rural Water Association
Water Treatment Plant Operation
26
Organic Carbon (TOC) in
Natural Waters mg/l
Mean Surface Water 3.5
Sea Water
Ground Water
Surface Water
Swamp
Wastewater
Wastewater Effluent
.1 .2
.5 1.0
2 5 10 20 50 100 200 500 1000
Florida Rural Water Association
Water Treatment Plant Operation
27
Disinfection with Chlorine
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The primary methods of disinfection is the use of
chlorine gas, chloramines, ozone, ultraviolet light,
chlorine dioxide, and hypochlorite.
Generally Chlorine will be used by small systems and
may be applied as a gas, solid or liquid.
The most common chlorine application is sodium
hypochlorite or bleach.
Primary Disinfectants are used to inactivate microbes
and Secondary Disinfectants are used to provide for a
residual chlorine concentration that prevents microbial
regrowth.
Florida Rural Water Association
Water Treatment Plant Operation
28
Reactions of Chlorine with
Water Constituents
Reducing Compound (inorganics)
 Production of Chloramines
 Production Chlororganics
 Combined Chlorine
 Breakpoint Chlorination
 Free Chlorine Residual

Florida Rural Water Association
Water Treatment Plant Operation
29
DISINFECTION
BYPRODUCTS
REMAIN
Fe
Mn
H2 S
0.6
Add
NH3
Dichloromine
0.2
Chloromine
0
0
Breakpoint Chlorination Curve
Florida Rural Water Association
Water Treatment Plant Operation
30
Other Chlorine Uses
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Chlorine is often used as an oxidant to remove
inorganic impurities such as iron and hydrogen sulfide
When used in this manner particulate matter is formed
that often must be removed.
Chlorine is also used to prevent the growth of algae on
tank walls and other surfaces exposed to sunlight and
to prevent bacteria from growing inside filters and
tanks
Chlorine has been used to remove color, taste and odors
but will produce disinfection by-products which are
regulated
Florida Rural Water Association
Water Treatment Plant Operation
31
Aeration
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Aeration is generally used in small systems to
remove naturally occurring dissolved gasses
from the water such as CO2 and H2S.
Aeration may also be used to oxidize iron
which then drops out as precipitate and must
be filtered.
Special aerators called Packed Towers are
sometimes used to remove VOCs
Florida Rural Water Association
Water Treatment Plant Operation
32
Cascade Tray Aerator
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Even distribution of
water over top tray
Loading Rates of 1 to 5
GPM for each sft. of
Tray area.
Trays ½” openings
perforated bottoms
Protection from insects
with 24 mesh screen
Florida Rural Water Association
Water Treatment Plant Operation
33
Forced Draft Aeration
System
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Includes weatherproof
blower in housing
Counter air through
aerator column
Includes 24 mesh
screened downturned
inlet/outlet
Discharges over 5 or
more trays
Florida Rural Water Association
Water Treatment Plant Operation
34
Packed Tower Odor
Removal System
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Uses Henry’s Law constants
for mass transfer
Usually requires pilot
testing
Used to Remove VOCs
below MCL
Col to Packing >7:1 ratio
Air to water at pk >25:1
with max 80:1
Susceptible to Fouling from
CaCO3 > 40 PPM
Florida Rural Water Association
Water Treatment Plant Operation
35
Iron Problems - Most Prevalent in Unconfined,
Surficial, and Biscayne Aquifers
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Iron dissolved by reaction
with CO2
Iron from well sources
will be in a dissolved state
When exposed to O2
precipitants form
Visible as red and brown
color
Will stain fixtures and
clothes
Imparts taste and odor
Florida Rural Water Association
Water Treatment Plant Operation
36
Iron, Turbidity/TOC
Relationships
Florida Rural Water Association
Water Treatment Plant Operation
37
Dissolved Iron Problems
Soluble iron passing into the water
distribution system will encourage the
growth of iron bacteria
 Precipitates will form in the distribution
system
 Iron particles will stain clothes and
fixtures (Red Water Complaints)

Florida Rural Water Association
Water Treatment Plant Operation
38
Treatment of Dissolved Iron
Type of Treatment
Removal Considerations
Oxidation w/ Chlorine
Greensand Filter
Ion Exchange Softener
Phosphate Addition
Max. 0.1 mg/l w/o filtration
0 – 10 mg/l w/ pH > 6.8
0 – 10 mg/l
0 – 2 mg/l
Florida Rural Water Association
Water Treatment Plant Operation
39
Fe
++
Aeration
Plot of
pH vs. Time for
Iron Removal at
90%
Efficiency
(min 30 minutes
detention) Florida Rural Water Association
Water Treatment Plant Operation
40
Filtration Requirements for
Iron and Manganese
Requires bé DEP at > 1.0 mg/l Fe
 Turbidity must be no more than 2 NTUs
above Source Water
 Oxidized particles must generally be
removed
 Anthracite filters are frequently
employed with higher iron content

Florida Rural Water Association
Water Treatment Plant Operation
41
Hydrogen Sulfide Removal
Techniques (DEP)
Sulfide
(mg/l)
Recommended
Treatment Process
Achievable Range
of Removal
< 0.3
Direct Chlorination
100%
> 0.3
100%
0.3 to 0.6
Direct Chlorination
(requires filtration)
Conventional Aeration
0.6 to 3.0
Forced Draft Aeration
90%
> 3.0
Packed Tower Aeration
> 90%
Florida Rural Water Association
Water Treatment Plant Operation
50%
42
Hydrogen Sulfide Removal
Dynamics
Gas
Soluble
Florida Rural Water Association
Water Treatment Plant Operation
43
Clarification
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Clarifiers are often used in water treatment to
allow particles to settle prior to filtration.
Special clarifiers called “Upflow Clarifiers” are
used in surface water treatment plants that
used coagulants and in softening plants that
use lime. These types of clarifiers perform
several treatment processes in one tank
Florida Rural Water Association
Water Treatment Plant Operation
44
Causes of Poor Clarifier
Performance
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If Surface water plant flocculators are
not adjusted for rate of flow
Sludge removal is not routine
There is no test to control sludge
quantities
Settled water turbidities are not measured
or are not measured routinely (e.g.,
minimum of once per shift)
Florida Rural Water Association
Water Treatment Plant Operation
45
Filtration
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Filters are primarily used to remove particulate matter
and turbidity from the water.
The primary types of filters used in water treatment are
Rapid Sand or gravity and Pressure Filters
Special Membrane Filters are used for Particulate and
Microbial removal.
Special Filters employ Resins and Media such as
greensand and are used to remove select contaminants
such as iron and manganese. Activated carbon filters are
used to remove organic compounds.
Florida Rural Water Association
Water Treatment Plant Operation
46
Nanofiltration
Filter Applications
Florida Rural Water Association
Water Treatment Plant Operation
47
Media Configurations for
Gravity Filters
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Single media (sand)
Dual Media (sand
and anthracite)
Mixed or multimedia (sand,
anthracite and
garnet)
Florida Rural Water Association
Water Treatment Plant Operation
48
Characteristics of Various Filters
Filter
Media
Sz
(mm)
Spec
Grav
Depth
Flow Flow
gpm/sf
(in)
Slow Sand
Fine Sand
0.2
2.6
36 – 48
Gravity
.05 - .03
Rapid Sand
Course Sand
0.35 – 1.0
2.6
24 – 36
Gravity
2– 4
Dual Media
Anthracite
Sand
0.9 – 1.2
0,4 – 0,55
1.4 – 1.6
2.6
18 – 24
6 – 10
Gravity
4– 5
Mixed Media
Anthracite
Sand, Garnet
0.9 – 1.2
0,4 – 0,55
0.2
1.4 – 1.6
2.6
4.2
16.5
9
4.5
Gravity
5
Diatom. Earth
Diatomaceous
0.005 to
0,125
1/16 to 1/8
Pressure
or
Vacuum
0.5 – 5
Pressure
All Media
Application
Pressure
2– 4
49
Calculating Filter Flow Rate
1.
2.
Determine Surface Area of Filter
Measure Filter Rise with stopwatch and tape
measure (often meters are out of calibration)
Example: 150 sft surface area, 10.7” rise in 20
seconds
(10.7 in / 12 in/ft) x 150 sft x 7.48 gal/cft = 1000 gal.
(20 seconds / 60 min ) = 0.333 min
Flow Rate = 1000 gal / 0.333 min
150 sf
=
Florida Rural Water Association
Water Treatment Plant Operation
20 gpm / sft
50
Causes of Poor
Filter Performance

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Filter Problems: operational, mechanical
equipment failure, media failure
Turbidity Errors: calibration, air bubbles,
debris
Chemical Feed Failures: coagulant, coagulant
aid, filter aid
Poor Water Quality: increased turbidity, algae
Operating Plant intermittently exceeding peak
loading capacity
Florida Rural Water Association
Water Treatment Plant Operation
51
Common Filter Operation
Deficiencies
Filters are started dirty
(i.e., without
backwashing
Increases in plant flow
Filter to waste
rate made with no
capability is not being
consideration of filtered used or not monitored if
water quality
utilized
Filters removed from
service without
reducing plant flow,
resulting in overload
Operations staff
backwash the filters
without regard for filter
effluent turbidity
Backwash rate too low
for longer period or
stopped early to
conserve water
No testing of filters
resulting in media loss,
underdrain or support
gravel damage
Significant build up of
mudballs in filter media
Individual filtered water
quality is different and
quality is not monitored
Performance following
backwash is not
monitored or recorded.
There are no records
available which
document performance
Calibration procedures
are not practiced
Florida Rural Water Association
Water Treatment Plant Operation
52
Filter Integrity Testing
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Evaluates filter media, support gravel and
underdrains
Check for filter depth, surface cracking,
mudball and segregation
Media is checked by excavation
Steel rod is used to probe support gravel
location and uniformity (should vary < 2”)
Observe clearwell for evidence of media
Check for uneven flow splitting to filters
Florida Rural Water Association
Water Treatment Plant Operation
53
Backwash Parameters
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Typically at about 24 hour intervals
Rate: 15 gpm/sft – 20 gpm/sft
Expand at min. 25%
Backwashing Duration: 5 - 10 min.
Filter to waste for 3 - 5 min.
Water used for backwashing: 2% - 4% per filter of
total water produced
Florida Rural Water Association
Water Treatment Plant Operation
54
Sand Filter ~40%
Multimedia ~25%
Deep Bed
~50%
15 to 20
gpm/sft
Min.
Expansion
25%
Florida Rural Water Association
Water Treatment Plant Operation
55
Determining Backwash
Expansion in Plant
Can be made with tin can lid
Florida Rural Water Association
Water Treatment Plant Operation
56
Visual Identification of Filter
Problems




Mudballs – Formed by chemical deposits of
solids during backwashing (leads to coating
of media surfaces)
Surface Cracking – Caused by compressible
matter around media at surface
Media Boils – Caused by too rapid of
backwash and displaces gravel support below
Air Binding – Caused by excessive headloss
(infrequent backwashing) allowing air to
enter media from below
Florida Rural Water Association
Water Treatment Plant Operation
57
Section 4
Disinfection By-Product Control
Disinfection By-Product Formation
 Factors Affecting By-Product Formation
 Locating THM and HAA5 Areas
 Formation of THMs and HAA5s
 Controlling Disinfection By-Products
 Importance of Water Age
 Flushing Methods and Benefits

Florida Rural Water Association
Water Treatment Plant Operation
58
Disinfection By-Product (DBP)
Formation



Disinfection Byproducts (DBP) are produced by
the reaction of free chlorine with organic material
found in natural waters.
The amount of organic materials in a natural water
called NOM can be approximated by the amount
of Total Organic Carbon (TOC) present in the
water source.
NOM consists of various chemical compounds
containing carbon, originating from decayed
natural vegetative matter found in water.
Florida Rural Water Association
Water Treatment Plant Operation
59
Factors Affecting Disinfection
By-Product Production
Turbidity and the type of NOM present
 Concentration of Chlorine added
 pH of water
 Bromide Ion Concentration
 Temperature
 Contact Time

Florida Rural Water Association
Water Treatment Plant Operation
60
Locating TTHM Areas

High Water Age

Storage Tanks do not fluctuate

No / Few Customer Areas

Stagnant Areas

Dead Ends

Bad Pipe

Regrowth Areas
Pipe Tuberculation
with Bacterial
Growth producing
Organic Precursors
Florida Rural Water Association
Water Treatment Plant Operation
61
Locating HAA5 Areas

Low Demand Areas

Toward Middle System Areas w/ Stagnant / Low
Water Age

Areas with No / Little Regrowth
– Eliminate Biodegradation Locations
– Free Chlorine Residuals < 0.2 mg/L
– HPC Data

No Dead Ends
Florida Rural Water Association
Water Treatment Plant Operation
62
Formation of DBP in a Water
System
63
Disinfectant and DBP Production in a
Typical Water System
64
DBP Reduction Techniques in a Water
Distribution System
Reducing detention time in storage
tanks,
 Ensuring turnover in distribution system


Flushing dead-end lines.
Florida Rural Water Association
Water Treatment Plant Operation
65
Typical Distribution System
Water Age (Days) in Pipelines
Population
Miles of WM
Water Age
> 750,000
> 1,000
1 – 7 days
< 100,000
<
400
> 16 days
< 25,000
<
100
12 – 24 days
AWWA: Water Age for Ave and Dead End Conditions
Florida Rural Water Association
Water Treatment Plant Operation
66
There are Two Types of Flushing
Used by Water Distribution Systems
Conventional Flushing
& Unidirectional Flushing
< 2.5 fps velocity that reduces
water age, raises disinfectant
residual removes coloration
> 2.5 fps velocity that removes
solid deposits and biofilm from
pipelines
67
How Often to Flush
• Dead-end mains at least monthly
• Other flushing points at least twice annually
(DEP requires quarterly flushing)
• At intervals necessary to maintain consistent
water quality throughout the distribution
system
• Often enough to maintain adequate disinfection
residuals throughout the distribution system
• Whenever Customer complaints of bad taste,
odor, clarity or turbidity are received (DEP
requirement)
Florida Rural Water Association
Water Treatment Plant Operation
68
Flushing Benefits Summarized
• Restores disinfectant residual
• Maintains or improves water quality
a. Reduces bacterial growth
b. Reduces customer complaints
• Restores flow and pressure in the distribution system
a. Reduces sediment
b. Reduces corrosion and tuberculation in mains
• Reduces DBP problems and lowers disinfection costs
• Reduces pipeline maintenance costs
• Increases life expectancy of the distribution system
• Typically results in a fire hydrant maintenance program
Florida Rural Water Association
Water Treatment Plant Operation
69
Section 5
Corrosion Control
Corrosion Control Methods
 Factors Affecting Corrosion
 Corrosion Tuberculation Example
 pH and Alkalinity Relationships
 Langerlier Index
 Troubleshooting Corrosion Complaints
 Basics of Sequestering

Florida Rural Water Association
Water Treatment Plant Operation
70
Corrosion and Chemical
Activity
Most all forms of corrosion are chemical
reactions (erosion is the exception)
that require three things:
1.
2.
3.
A carrier such as Water that allows the movement of
positively charged ions (from Anode+ to Cathode-)
A condition (water metal contact) that allows metals
to disassociate (ionize) and allows electrons to flow
An imbalance that favors the transport of metals or
ions to achieve a chemical balance in a water solution.
Florida Rural Water Association
Water Treatment Plant Operation
71
Corrosion Control Methods



Corrosion Control is employed in water treatment
to protect pipeline materials, appurtenances and
fittings from leaching problematic (iron) and/or
dangerous inorganic chemicals (lead and copper).
Three types of treatment are generally used: 1.)
Chemical Adjustment, Water Treatment and
Sequestering
Protection Measures in water system include the
use of sacrificial metals and electronic cathodic
protection.
Florida Rural Water Association
Water Treatment Plant Operation
72
Factors Affecting Corrosion
Water’s pHs
 Water alkalinity
 Solids content
 Temperature
 Materials Used for pipes and other
fittings.

Florida Rural Water Association
Water Treatment Plant Operation
73
Cathodic Action Resulting in
Tuberculation in Water Pipelines
Inside
Pipe Wall
1.5”
74
Effects of pH on the Rate of Corrosion of
Iron in Water
Florida Rural Water Association
Water Treatment Plant Operation
75
Relationships between
Alkalinity, pH
A Water can be
Corrosive or
Depositing
based upon it’s
pH and
Alkalinity.
Florida Rural Water Association
Water Treatment Plant Operation
76
Affects of Raising or Lowering
Alkalinity and CO2 by Chemical Addition
Florida Rural Water Association
Water Treatment Plant Operation
77
Determining pH of Water
(Alkalinity
in
mg/l
as
pH = log {2.2 x 10 X
CaCO3)}
6
(CO2 in mg/l)
Measured Alkalinity
60 mg/l as CaCO3
pH = log
Measured CO2
= 7.4 mg/l
6
{2.2
x
10
X 60/7.4 } = 7.25
Approximate pH between 7.0 to 8.0
Florida Rural Water Association
Water Treatment Plant Operation
78
Use of the Langerlier Index for
Determining Water Stability




Every water has a particular pH value where
the water will neither deposit scale nor cause
corrosion.
A stable condition is termed saturation.
Saturation (pHs), varies depending on
calcium hardness, alkalinity, TDS, and
temperature.
The Langerlier Index = pH – pHs
Corrosive < LI = 0 > Scale Forming
Florida Rural Water Association
Water Treatment Plant Operation
79
Recommended Treatment for Corrosive
and Scaling Water based on LI
Saturation Index
-5
-4
-3
-2
-1
-0.5
0
0.5
Description
General Recommendation
Severe Corrosion
Treatment Recommended
Severe Corrosion
Treatment Recommended
Moderate Corrosion
Treatment Recommended
Moderate Corrosion
Treatment May Be Needed
Mild Corrosion
Treatment May Be Needed
None- Mild Corrosion
Probably No Treatment
Near Balanced
No Treatment
Some Faint Coating
Probably No Treatment
1
2
3
Mild Scale Coating
Treatment May Be Needed
Mild to Moderate Coatings
Treatment May Be Needed
Moderate Scale Forming
Treatment Advisable
4
Severe Scale Forming
Treatment Advisable
Florida Rural Water Association
Water Treatment Plant Operation
80
Troubleshooting Customer
Complaints caused by Corrosion
Water Characteristic
Red/reddish-brown Water
Blueish Stains on fixtures
Black Water
Foul Tastes and Odors
Loss of Pressure
Lack of Hot Water
Reduced Life of Plumbing
Tastes Like Garden Hose
Likely Cause
Distribution Pipe Corrosion
Copper Line Corrosion
Sulfide Corrosion of Iron
By-Products of Bacteria
Tuberculation
Scaling
Pitting from Corrosion
Backflow From Hose
Florida Rural Water Association
Water Treatment Plant Operation
81
Sequestering Action of
Poly and Ortho Phosphates
Florida Rural Water Association
Water Treatment Plant Operation
82
Polyphosphates for Sequestering Soluble
Iron and Manganese after Treatment




The Polyphosphate, Hexametaphosphate is
commonly used for Sequestering Soluble Iron
and Manganese
Sequestering is used when soluble Iron and
Manganese exists after treatment; The Agent is
added after sedimentation
Large doses (>5 mg/l) will soften rust deposits
in pipelines which are transported into homes
Proper dose is to keep soluble iron and/or
manganese tied up for 4 days
Florida Rural Water Association
Water Treatment Plant Operation
83
Use of Orthophosphates for
Sequestering



Orthophosphate is used to sequester iron ions
at pipe surfaces
The Sequestering forms a protective coating
that prevents further iron migration
Ortho/Poly Blends provide both sequestering
of soluble iron and iron movement from
pipelines under corrosive conditions
Florida Rural Water Association
Water Treatment Plant Operation
84
Section 6:
Demineralization Processes
Basic Demineralization Systems
 RO Operating Considerations
 Pretreatment; Fouling and Scaling
Issues
 Ion Exchange Considerations
 Sodium/Calcium Exchange

Florida Rural Water Association
Water Treatment Plant Operation
85
Ion Exchange, Membrane
Filtration and Electrodialysis


Several special treatment processes are used to
remove selected mineral contaminants from the
water. These include Ion Exchange, Membrane
Filtration and Electrodialysis.
These systems remove selected salts such as
sodium, hardness consisting of Calcium and
Magnesium and removal of selected contaminants
such as Nitrate or Arsenic
Florida Rural Water Association
Water Treatment Plant Operation
86
Reverse Osmosis (RO)
Treatment Considerations





Used to Remove Highly Concentrated
Salts (TDS)
Operating pressure < 400 psi
Salt Rejection Rates of < 95%
Turbidity <1 NTU
Flux Range 15 – 32 GFD (gallons Flux
per day per sq. ft. membrane surface)
Florida Rural Water Association
Water Treatment Plant Operation
87
Pretreatment Requirements for
Reverse Osmosis Systems
Suspended Particulates
Colloidal materials
Microbiological Matter
Chlorine
Carbonates
Sulfate
Silica
Iron
Hydrogen Sulfide
Blockage Filtration
Fouling
Coagulation/Filtration
Fouling
Chlorine
Failure
GAC or Dechlorination
Scaling
pH adjust or Softening
Scaling
Inhibitor or Cation Rem.
Scaling
Softening
Scale/Foul Greensand (no aeration)
Scale/Foul Degasification
Florida Rural Water Association
Water Treatment Plant Operation
88
Operating Considerations
Ion Exchange Softening
Iron and Manganese
 Corrosiveness of Brine Solution
 Pump Strainer
 Fouling of Resin

Florida Rural Water Association
Water Treatment Plant Operation
89
Optimal Water Characteristics
for Ion Exchange
pH
NO3
SO4
TDS
Turbidity
6.5 – 9.0
< 5 mg/l
< 50 mg/l
< 500 mg/l
< 0.3 NTU
Selectivity Considerations
S04-2 > NO3-2 > CO3-2 > NO2-2 > CL-1
Florida Rural Water Association
Water Treatment Plant Operation
90
Sodium Exchange
MCL Considerations

Sodium provides 100% exchange for Ca++ and Mg++
NaZeolite + Ca++ --> CaZeolite + Na+
and
NaZeolite + Mg++ --> MgZeolite + Na+



For every grain (17.1 grains = 1 mg/l) of hardness removed from
water, about 8.6 mg/1 of sodium is added.
Sodium MCL = 160 mg/l - Initial Na water concentration + NaOCl
5 grains needed for corrosion control (86 mg/l) thus:
source water hardness limit ~ 350 mg/l hardness (~20 grains)
ie. 100% x 5 grains, or 15 grains removed x 8 = 134 mg/l Na
20 grains
Provides 134 mg/l Na and 5 grains or 86 mg/l Hardness
Florida Rural Water Association
Water Treatment Plant Operation
91
Section 7
Coagulation Processes Control
Metal Charges and Electron Attraction
 Elemental Weights and Chemical
Formulas
 Particle Chemistry and Colloidal Particles
 The Floc Building Process
 Optimizing the Coagulation Process
 Use of a Jar Test

Florida Rural Water Association
Water Treatment Plant Operation
92
Periodic Table of the Elements
Valances are shown at the top of the Periodic Table, F
is one electron short and Mg has two extra electrons
93
The Periodic Chart
also Provide the Atomic Weight of an
Element
8
Includes
Isotopes
Atomic Number
O
Symbol
Oxygen
Name
Use 16
15.99
Atomic Weight
94
Solids and Colloidal Material
Suspended
Solids
Colloids
Suspended in the Water and can be
Removed by Conventional Filtration
Finely Charged Particles that do not
Dissolved
Turbidity
The Cloudy Appearance of Water
caused by Suspended Matter and
Colloids
Electrical Charge of a suspended
particle
Zeta Potential
Florida Rural Water Association
Water Treatment Plant Operation
95
Primary Coagulants
Primary coagulants are lime, aluminum
sulfate (alum), ferrous sulfate, ferric
sulfate and ferric chloride.
 These inorganic salts will react with the
alkalinity in the water to form insoluble
flocs which will trap the suspended
matter in them.

Florida Rural Water Association
Water Treatment Plant Operation
96
Removal of Colloidal Particles
by Coagulation & Flocculation
Floc Building Process :





Neutralization of repulsive charges
Precipitation with sticky flocs
Bridging of suspended matter
Providing “agglomeration sites” for larger
floc
Weighting down of floc particles
Florida Rural Water Association
Water Treatment Plant Operation
97
Polymers and Ionic Charges



Bridging Action of Cationic
Polymer with Colloidal
Particles
Cationic +
*Anionic Nonionic
* Used with Metal
Coagulants in water
treatment
Florida Rural Water Association
Water Treatment Plant Operation
98
Factors Affecting the
Coagulation Process







pH (pH Range: Al, 5 – 7 ; Fe, 5 – 8)
Alkalinity of water (> 30 PPM residual)
Concentration of Salts (affect efficiency)
Turbidity (constituents and concentration)
Type of Coagulant used (Al and Fe salts)
Temperature (colder requires more mixing)
Adequacy of mixing (dispersion of chemical)
Florida Rural Water Association
Water Treatment Plant Operation
99
Jar Test Plot for Low Alkalinity
or Low Turbidity Water



Alum initially reacts
with low alkalinity
With Ferric Chloride
requires chemical to
reach optimal pH
before reacting
Adding too much
coagulant increases
turbidity
Florida Rural Water Association
Water Treatment Plant Operation
100
Section 8:
Hardness and Water Softening







Hardness Removal by Softening
Treatment Methods Used to Remove
Hardness
Alkalinity Definitions
Alkalinity/Acidity Relationships
pH and Lime Treatment
Removal of Color and Organics
Importance of Recarbonation
Florida Rural Water Association
Water Treatment Plant Operation
101
Water Hardness





Hardness in Water causes scaling, causes fibers
in clothes to become brittle and increases the
amount of soap that must be used for washing
Hardness in water is caused by the water’s
Calcium and Magnesium Content
Water is considered hard when it has a hardness
concentration of > 100 mg/l expressed as
calcium carbonate equivalent
Water that hardness < 100 mg/l expressed as
CaCO3 is considered soft
Hardness can either be removed by water
treatment or sequestered using phosphates
Florida Rural Water Association
Water Treatment Plant Operation
102
Methods of Removing
Hardness
Treatment Method
Hardness Levels
Retained
Lime Softening
(Chemical Precipitation)
RO (Nanofiltration)
(Membrane Filtration)
Ion Exchange
(Chemical Exchange)
Solubility Level of
about 35 mg/l (CaCO3)
85 – 90% removal
Basically Zero
Water must be blended
Florida Rural Water Association
Water Treatment Plant Operation
103
Alkalinity Definitions




The capacity of water to neutralize acids.
The measure of how much acid must be added to a
liquid to lower the pH to 4.5
It is caused by the water’s content of carbonate,
bicarbonate, hydroxide, and occasionally borate,
silicate, and phosphate.
In natural waters, Alkalinity = Bicarbonate
Hardness = Total Carbonate Hardness
Florida Rural Water Association
Water Treatment Plant Operation
104
Relationships among pH,
Alkalinity and Indicators
0%
100%
Bicarbonate and
Carbonate
Bicarbonate
CO2
Carbonate and
Hydroxide
T Alkalinity
T=0
P Alkalinity
P=0
pH
CaCO3
9.4
100% 10.2
Florida Rural Water Association
Water Treatment Plant Operation
Mg(OH)2
10.6
105
Types of Alkalinity that can be
Present at pH Values






Below 4.5 only CO2 present, no Alkalinity
Between 4.5 to 8.3 only Bicarbonate present
Between 8.3 to 10.2 Bicarbonate &
Carbonate.
Between 10.2 to 11.3 Carbonate & Hydroxide
At 9.4 Calcium Carbonate becomes insoluble
and precipitates
At 10.6 Magnesium Hydroxide becomes
insoluble and precipitates
Florida Rural Water Association
Water Treatment Plant Operation
106
Removal of Organics
by Lime Softening Precipitation
Calcium Carbonate
10% to 30% of
Color, TOC & DBP
Magnesium Hydroxide 30% to 60% of
TOC & DBP and
80% of Color
Addition of Alum/Ferric +5% to +15% of
Color, TOC & DBP
Sequential Treatment Additional Removal
Color, TOC and DBP
Florida Rural Water Association
Water Treatment Plant Operation
107
Recarbonation in Lime
Softening



Because water has unused lime (calcium
hydroxide) and magnesium hydroxide in
solution at high pH (pH 11), these must be
converted to a stable forms.
CO2 is added to reduce Ca(OH)2 to CaCO3
which precipitates at about pH 10; additional
CO2 is added to convert Mg(OH)2 to soluble
Mg(HCO3)2 which occurs at a pH of 8.4.
Reaction must be completed before filtration
so that calcium carbonate will not precipitate
in the filters or carry into distribution system.
Florida Rural Water Association
Water Treatment Plant Operation
108
Water Treatment Summary



Effective Water Treatment Requires the
application of accepted principles
Most Process Problems in Water Treatment
are the result of failure to recognize the
symptoms that result from improper
application or adherence to these factors
Most treatment plant problems can be
resolved by application of the techniques
presented
Florida Rural Water Association
Water Treatment Plant Operation
109