Water Treatment Processes

1
Water Treatment Processes

• Water Treatment Plant
• Operation

2
Water Treatment Processes

• Section 1 Water Treatment Concerns
• Section 2 Well Considerations
• Section 3 Conventional Water System Processes
• Section 4 Disinfection By-Product Control
• Section 5 Corrosion Control
• Section 6 Demineralization Processes
• Section 7 Coagulation Process Control
• Section 8 Water Softening

3
Section 1Water Treatment Concerns

• Microbial Contamination Concerns
• Barriers to Contaminants Reaching the Public
• Where Contamination Comes From
• Bacterial Indicators and Pathogens
• Primary Standards
• Secondary Standards

4
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.

5
Multiple Barrier Approach
Source Selection and Protection
Treatment Methods and Efficiencies
Distribution Maintenance and Monitoring
6
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
7
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.

8
Some Facts About Bacteria

• 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.

9
Bacteria and PathogenicIndicators in Water
Treatment
Total Coliform Ferment Lactose _at_ 35OC
Include Species of Genera Citrobacter Enterobacter Klebsiella E. Coli
Fecal Coliform Grow at 44OC Produce Enzyme
E. Coli More Specific Indicator of Contamination
HPC lt 500 colonies/ml

• Photo CDC. E. coli 0157H7
• 11 of 140 cause gastrointestinal disease

10
Identifying Source of Contaminants
11
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.  

12
Primary Standards and their Maximum Contaminant
Levels (MCLs)
Contaminant MCL (mg/l) Arsenic
0.010 Asbestos 7 (MFL) Fluoride
4.0 Mercury 0.002 Nickel 0.1 Nitrate 10 Ni
trite 1 Total NitrateNitrite
10 Sodium 160
13
Disinfectants and Disinfection By-Products

• 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

14
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

15
Secondary StandardMaximum Contaminant Levels
Contaminant MCL (mg/l) Chloride 250 Sul
fate 250 TDS 500 Copper 1.0 Fluoride 2.0 Iro
n 0.30 Manganese 0.05 Silver 0.1 pH
(MRCL) 6.5 to 8.5 Color (MCRL) 15 cfu
16
Protecting Well by Grouting

• Prevent movement of water between aquifer
  formations
• Preserve quality of producing zones
• Preserve Yield
• Prevent water intrusion from surface
• Protect Casing against Corrosion!

Pressure Testing of Grout Seal _at_ 10 psi for 1
hr. Should be Performed.
17
Section 2Well Considerations

• Floridan Aquifer
• Well Contaminants
• Preventing Contamination at the Well Head

18
Floridian Aquifer Across Florida
19
Well Source Water ParametersQuality and
Quantity Dictates Depth of Well

• TDS
• Total Hardness
• Total Fe and Mn
• Chlorides Sulfates
• Total Alkalinity
• Nitrate

• pH
• Corrosivity
• CO2
• H2S
• Fluoride

20
Preventing Contamination at the Well Head
Observation Likely Pathway
1 Septic tanks, broken storm or san. pipes, ponds Through Surface Strata
2 Drainage up-hill Surface water runoff
3 Well subject to flooding Surface water transport of contaminants
4 Casing termination Must be 1 and above 100 yr flood plane
21
Preventing Contamination at the Well Head
(continued)
Observation Likely Pathway
5 Area around well is wet Corroded Casing Pipe
6 Possible Abandoned wells in area Surface water intrusion from contaminated source
7 Sanitary condition unacceptable Contaminated water intrusion
8 Cracking in Well Slab Contaminated water intrusion
22
Preventing Contamination at the Well Head
(continued)
Observation Likely Pathway
9 Evidence of Algae or Mold on Slab Birds and insects attracted by moist conditions
10 Poor Drainage Surface water intrusion from contaminated source
11 Seal water Draining into well head Contaminated water entering borehole
12 Well Seal damaged Contaminated water intrusion
23
Preventing Contamination at the Well Head
(continued)
Observation Likely Pathway
13 Fittings pointing upward Contaminated Water intrusion into casing
14 Well vent not properly installed Contaminated Water intrusion into casing
15 Check Valve absent or not working Contaminated water back-flowing into casing
16 Cavitation or water hammer Ck. Valve damage water back-flowing into casing
24
Preventing Contamination at the Well Head
(continued)
Observation Likely Pathway
17 Well Site Security Compromised Contaminated Water from undesirable activities
18 Livestock or wild animals close by Animal source of Contamination
19 Surface water evidence ID Indicator organisms, color, temp and TOC contributing
20 Several wells available One well is more likely to contribute than others
25
Preventing Contamination at the Well Head
(continued)
Observation Likely Pathway
21 Intermittent Well Operation Contaminated occurring from long-term biological activity
22 Wet or extreme weather events Contamination from run-off or from higher pumping levels.
26
Section 3Conventional Water System Processes

• TOC in Source Water
• Disinfection and Uses of Chlorine
• Aeration and Aerator Types
• Iron and Hydrogen Sulfide Control
• Filtration
• Sedimentation

27
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
28
Disinfection with Chlorine

• 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.

29
Reactions of Chlorine with Water Constituents

• Reducing Compound (inorganics)
• Production of Chloramines
• Production Chlororganics
• Combined Chlorine
• Breakpoint Chlorination
• Free Chlorine Residual

30
DISINFECTION BYPRODUCTS REMAIN
Fe Mn H2S
Add NH3
Dichloromine
0.2
0.6
0
Chloromine
0
Breakpoint Chlorination Curve
31
Other Chlorine Uses

• 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

32
Aeration

• 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

33
Cascade Tray Aerator

• 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

34
Forced Draft Aeration System

• Includes weatherproof blower in housing
• Counter air through aerator column
• Includes 24 mesh screened downturned inlet/outlet
• Discharges over 5 or more trays

35
Packed Tower Odor Removal System

• Uses Henrys Law constants for mass transfer
• Usually requires pilot testing
• Used to Remove VOCs below MCL
• Col to Packing gt71 ratio
• Air to water at pk gt251
• with max 801
• Susceptible to Fouling from CaCO3 gt 40 PPM

36
Iron Problems - Most Prevalent in Unconfined,
Surficial, and Biscayne Aquifers

• 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

37
Iron, Turbidity/TOC Relationships
38
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)

39
Treatment of Dissolved Iron
Type of Treatment Removal Considerations
Oxidation w/ Chlorine Max. 0.1 mg/l w/o filtration
Greensand Filter 0 10 mg/l w/ pH gt 6.8
Ion Exchange Softener 0 10 mg/l
Phosphate Addition 0 2 mg/l
40
Fe Aeration Plot of pH vs. Time for Iron
Removal at 90Efficiency(min 30
minutesdetention)
41
Filtration Requirements forIron and Manganese

• Requires bé DEP at gt 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

42
Hydrogen Sulfide Removal Techniques (DEP)
 
 
43
Hydrogen Sulfide Removal Dynamics
Soluble
Gas
44
Clarification

• 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

45
Causes of Poor Clarifier Performance

• 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)

46
Filtration

• 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.

47
Filter Applications
Nanofiltration
48
Media Configurations forGravity Filters

• Single media (sand)
• Dual Media (sand and anthracite)
• Mixed or multi-media (sand, anthracite and
  garnet)

49
Characteristics of Various Filters
Filter Media Sz (mm) Spec Grav Depth (in) Flow Flow gpm/sf
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
50
Calculating Filter Flow Rate

• 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 20 gpm
  / sft
• 150 sf
• 
  

51
Causes of PoorFilter Performance

• 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

52
Common Filter Operation Deficiencies
Filters are started dirty (i.e., without backwashing Increases in plant flow rate made with no consideration of filtered water quality Filter to waste capability is not being used or not monitored if 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
53
Filter Integrity Testing

• 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 lt 2)
• Observe clearwell for evidence of media
• Check for uneven flow splitting to filters

54
Backwash Parameters

• 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

55
Sand Filter 40 Multimedia 25 Deep Bed
50
15 to 20 gpm/sft Min. Expansion 25
56
Determining Backwash Expansion in Plant
Can be made with tin can lid
57
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

58
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

59
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.

60
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

61
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
62
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 lt 0.2 mg/L
• HPC Data
• No Dead Ends

63
Formation of DBP in a Water System
64
Disinfectant and DBP Production in a Typical
Water System
65
DBP Reduction Techniques in a Water Distribution
System

• Reducing detention time in storage tanks,
• Ensuring turnover in distribution system
• Flushing dead-end lines.

66
Typical Distribution System Water Age (Days) in
Pipelines
Population Miles of WM Water Age
gt 750,000 gt 1,000 1 7 days
lt 100,000 lt 400 gt 16 days
lt 25,000 lt 100 12 24 days
AWWA Water Age for Ave and Dead End Conditions
67
There are Two Types of Flushing Used by Water
Distribution Systems
Unidirectional Flushing gt 2.5 fps velocity that
removes solid deposits and biofilm from pipelines
Conventional Flushing lt 2.5 fps velocity that
reduces water age, raises disinfectant residual
removes coloration

68
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)

69
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

70
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

71
Corrosion and Chemical Activity

• Most all forms of corrosion are chemical
  reactions (erosion is the exception) that require
  three things
• 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.

72
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.

73
Factors Affecting Corrosion

• Waters pHs
• Water alkalinity
• Solids content
• Temperature
• Materials Used for pipes and other fittings.

74
Cathodic Action Resulting inTuberculation in
Water Pipelines
Inside Pipe Wall
1.5
75
Effects of pH on the Rate of Corrosion of Iron in
Water
76
Relationships between Alkalinity, pH
A Water can be Corrosive or Depositing based upon
its pH and Alkalinity.
77
Affects of Raising or Lowering Alkalinity and
CO2 by Chemical Addition
78
Determining pH of Water
pH log 2.2 x 106 X (Alkalinity in mg/l as CaCO3) (CO2 in mg/l) pH log 2.2 x 106 X (Alkalinity in mg/l as CaCO3) (CO2 in mg/l)
Measured Alkalinity 60 mg/l as CaCO3 Measured CO2 7.4 mg/l
pH log 2.2 x 106 X 60/7.4 7.25 pH log 2.2 x 106 X 60/7.4 7.25
Approximate pH between 7.0 to 8.0
79
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 lt LI 0 gt Scale Forming

80
Recommended Treatment for Corrosive and Scaling
Water based on LI
81
Troubleshooting Customer Complaints caused by
Corrosion

• Water Characteristic Likely Cause
• Red/reddish-brown Water Distribution Pipe
  Corrosion
• Blueish Stains on fixtures Copper Line
  Corrosion
• Black Water Sulfide Corrosion of Iron
• Foul Tastes and Odors By-Products of
  Bacteria
• Loss of Pressure Tuberculation
• Lack of Hot Water Scaling
• Reduced Life of Plumbing Pitting from
  Corrosion
• Tastes Like Garden Hose Backflow From Hose

82
Sequestering Action ofPoly and Ortho Phosphates
83
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 (gt5 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

84
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

85
Section 6Demineralization Processes

• Basic Demineralization Systems
• RO Operating Considerations
• Pretreatment Fouling and Scaling Issues
• Ion Exchange Considerations
• Sodium/Calcium Exchange

86
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

87
Reverse Osmosis (RO)Treatment Considerations

• Used to Remove Highly Concentrated Salts (TDS)
• Operating pressure lt 400 psi
• Salt Rejection Rates of lt 95
• Turbidity lt1 NTU
• Flux Range 15 32 GFD (gallons Flux per day per
  sq. ft. membrane surface)

88
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

89
Operating ConsiderationsIon Exchange Softening

• Iron and Manganese
• Corrosiveness of Brine Solution
• Pump Strainer
• Fouling of Resin

90
Optimal Water Characteristics for Ion Exchange

• pH 6.5 9.0
• NO3 lt 5 mg/l
• SO4 lt 50 mg/l
• TDS lt 500 mg/l
• Turbidity lt 0.3 NTU

Selectivity Considerations
S04-2 gt NO3-2 gt CO3-2 gt NO2-2 gt CL-1
91
Sodium Exchange MCL
Considerations

• Sodium provides 100 exchange for Ca and Mg
• NaZeolite Ca --gt CaZeolite Na
  and NaZeolite Mg --gt 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

92
Section 7Coagulation 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

93
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
94
The Periodic Chartalso Provide the Atomic Weight
of an Element
Atomic Number
8 O
Oxygen 15.99
Symbol
Includes Isotopes Use 16
Name
Atomic Weight
95
Solids and Colloidal Material
Suspended Solids Suspended in the Water and can be Removed by Conventional Filtration
Colloids Finely Charged Particles that do not Dissolved
Turbidity The Cloudy Appearance of Water caused by Suspended Matter and Colloids
Zeta Potential Electrical Charge of a suspended particle
96
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.

97
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

98
Polymers and Ionic Charges

• Cationic
• Anionic -
• Nonionic

Used with Metal Coagulants in water treatment
Bridging Action of Cationic Polymer with
Colloidal Particles
99
Factors Affecting the Coagulation Process

• pH (pH Range Al, 5 7 Fe, 5 8)
• Alkalinity of water (gt 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)

100
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

101
Section 8Hardness 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

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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 waters
  Calcium and Magnesium Content
• Water is considered hard when it has a hardness
  concentration of gt 100 mg/l expressed as calcium
  carbonate equivalent
• Water that hardness lt 100 mg/l expressed as CaCO3
  is considered soft
• Hardness can either be removed by water treatment
  or sequestered using phosphates

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Methods of Removing Hardness
Treatment Method Hardness Levels Retained
Lime Softening (Chemical Precipitation) Solubility Level of about 35 mg/l (CaCO3)
RO (Nanofiltration) (Membrane Filtration) 85 90 removal
Ion Exchange (Chemical Exchange) Basically Zero Water must be blended
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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 waters content of carbonate,
  bicarbonate, hydroxide, and occasionally borate,
  silicate, and phosphate.
• In natural waters, Alkalinity Bicarbonate
  Hardness Total Carbonate Hardness

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Relationships among pH, Alkalinity and Indicators
100
0
Bicarbonate and Carbonate
Bicarbonate
Carbonate and Hydroxide
CO2
T Alkalinity
T0
P Alkalinity
P0
CaCO3
Mg(OH)2
9.4
10.6
100
pH
10.2
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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

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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

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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.

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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