Water Treatment Processes Water Treatment Plant Operation Florida

Water Treatment Processes Water Treatment Plant Operation Florida Rural Water Association Water Treatment Plant Operation

Water Treatment Processes n n n n 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 Florida Rural Water Association Water Treatment Plant Operation 2

Section 1: Water Treatment Concerns Microbial Contamination Concerns n Barriers to Contaminants Reaching the Public n Where Contamination Comes From n Bacterial Indicators and Pathogens n Primary Standards n Secondary Standards n 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 p. H, Lead, and Copper Nearby Agriculture Nitrates, Pesticides and Coliform Nearby Mining Metals and p. H 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 n n n 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 bacteria. Bacteria are inconceivably small and measured in microns. One micron is equal to 1/1, 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 Include Species of Genera Fecal Coliform E. Coli HPC Ferment Lactose @ 35 OC Citrobacter Enterobacter Klebsiella E. Coli Grow at 44 OC Produce Enzyme More Specific Indicator of Contamination Photo: CDC. E. coli 0157: H 7 11 of 140 cause gastrointestinal disease < 500 Florida Rural Water Association 9 Water Treatment Plant Operation colonies/ml

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 MCL (mg/l) Arsenic 0. 010 Asbestos 7 (MFL) Fluoride 4. 0 Mercury 0. 002 Nickel 0. 1 Nitrate 10 Nitrite 1 Total Nitrate+Nitrite 10 Sodium 160 Florida Rural Water Association Water Treatment Plant Operation 12

Disinfectants and Disinfection By-Products n n n 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. n EPA recommends MCL limits n Some states such as Florida have set regulatory limits on these contaminants n Florida Rural Water Association Water Treatment Plant Operation 14

Secondary Standard Maximum Contaminant Levels Contaminant Chloride Sulfate 250 TDS Copper Fluoride Iron Manganese Silver p. H (MRCL) Color (MCRL) MCL (mg/l) 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 n n n 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 n Well Contaminants n Preventing Contamination at the Well Head n Florida Rural Water Association Water Treatment Plant Operation 17

Floridian Aquifer Across Florida Rural Water Association Water Treatment Plant Operation 18

Well Source Water Parameters Quality and Quantity Dictates Depth of Well n n n TDS Total Hardness Total Fe and Mn Chlorides & Sulfates Total Alkalinity Nitrate n n n p. H Corrosivity CO 2 H 2 S Fluoride Florida Rural Water Association Water Treatment Plant Operation 19

Preventing Contamination at the Well Head # Observation 1 Septic tanks, broken Through Surface Strata storm or san. pipes, ponds Drainage up-hill Surface water runoff 2 3 4 Well subject to flooding Casing termination Likely Pathway Surface water transport of contaminants Must be 1’ and above 100 yr 20 flood plane

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 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 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 n Disinfection and Uses of Chlorine n Aeration and Aerator Types n Iron and Hydrogen Sulfide Control n Filtration n Sedimentation n 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 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 n n 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) n Production of Chloramines n Production Chlororganics n Combined Chlorine n Breakpoint Chlorination n Free Chlorine Residual n Florida Rural Water Association Water Treatment Plant Operation 29

DISINFECTION BYPRODUCTS REMAIN Fe Mn 0. 6 H 2 S Add NH 3 Dichloromine 0. 2 Chloromine 0 0 Breakpoint Chlorination Curve Florida Rural Water Association Water Treatment Plant Operation 30

Other Chlorine Uses n n 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 n Aeration is generally used in small systems to remove naturally occurring dissolved gasses from the water such as CO 2 and H 2 S. 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 n n 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 n n 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 n n n 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 Ca. CO 3 > 40 PPM Florida Rural Water Association Water Treatment Plant Operation 35

Iron Problems - Most Prevalent in Unconfined, Surficial, and Biscayne Aquifers n n n Iron dissolved by reaction with CO 2 Iron from well sources will be in a dissolved state When exposed to O 2 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 n Precipitates will form in the distribution system n Iron particles will stain clothes and fixtures (Red Water Complaints) n 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/ p. H > 6. 8 0 – 10 mg/l 0 – 2 mg/l Florida Rural Water Association Water Treatment Plant Operation 39

Fe Aeration ++ Plot of p. H 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 n Turbidity must be no more than 2 NTUs above Source Water n Oxidized particles must generally be removed n Anthracite filters are frequently employed with higher iron content n 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 n n 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 n n 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 n n 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 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 n n n Single media (sand) Dual Media (sand anthracite) Mixed or multi-media (sand, anthracite and garnet) Florida Rural Water Association Water Treatment Plant Operation 48

Characteristics of Various Filter Media Sz (mm) Spec Grav Depth 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 n n n 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 Increases in plant flow Filter to waste (i. e. , without rate made with no capability is not being backwashing 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 Significant build up of resulting in media loss, mudballs in filter media underdrain or support gravel damage Individual filtered water quality is different and quality is not monitored Performance following backwash is not monitored or recorded. Calibration procedures are not practiced There are no records available which document performance Florida Rural Water Association Water Treatment Plant Operation 52

Filter Integrity Testing n n n 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 Typically at about 24 hour intervals n Rate: 15 gpm/sft – 20 gpm/sft n Expand at min. 25% n Backwashing Duration: 5 - 10 min. n Filter to waste for 3 - 5 min. n Water used for backwashing: 2% - 4% per filter of total water produced n 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 n n 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 n Factors Affecting By-Product Formation n Locating THM and HAA 5 Areas n Formation of THMs and HAA 5 s n Controlling Disinfection By-Products n Importance of Water Age n Flushing Methods and Benefits n 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. n 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. n NOM consists of various chemical compounds containing carbon, originating from decayed natural vegetative matter found in water. Florida Rural Water Association 59 n Water Treatment Plant Operation

Factors Affecting Disinfection By -Production Turbidity and the type of NOM present n Concentration of Chlorine added n p. H of water n Bromide Ion Concentration n Temperature n Contact Time n Florida Rural Water Association Water Treatment Plant Operation 60

Locating TTHM Areas n High Water Age n Storage Tanks do not fluctuate n No / Few Customer Areas n Stagnant Areas n Dead Ends n Bad Pipe n Regrowth Areas Pipe Tuberculation with Bacterial Growth producing Organic Precursors Florida Rural Water Association Water Treatment Plant Operation 61

Locating HAA 5 Areas n Low Demand Areas n Toward Middle System Areas w/ Stagnant / Low Water Age n Areas with No / Little Regrowth – Eliminate Biodegradation Locations – Free Chlorine Residuals < 0. 2 mg/L – HPC Data n 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, n Ensuring turnover in distribution system n n 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 2. Other flushing points at least twice annually (DEP requires quarterly flushing) 3. At intervals necessary to maintain consistent water quality throughout the distribution system 4. Often enough to maintain adequate disinfection residuals throughout the distribution system 5. Whenever Customer complaints of bad taste, odor, clarity or turbidity are received (DEP requirement) 1. 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 Methods n Factors Affecting Corrosion n Corrosion Tuberculation Example n p. H and Alkalinity Relationships n Langerlier Index n Troubleshooting Corrosion Complaints n Basics of Sequestering n 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 n n n 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 p. Hs n Water alkalinity n Solids content n Temperature n Materials Used for pipes and other fittings. n 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 p. H on the Rate of Corrosion of Iron in Water Florida Rural Water Association Water Treatment Plant Operation 75

Relationships between Alkalinity, p. H A Water can be Corrosive or Depositing based upon it’s p. H and Alkalinity. Florida Rural Water Association Water Treatment Plant Operation 76

Affects of Raising or Lowering Alkalinity and CO 2 by Chemical Addition Florida Rural Water Association Water Treatment Plant Operation 77

Determining p. H of Water (Alkalinity in mg/l as Ca. CO 3 ) p. H = log {2. 2 x 10 X } 6 (CO 2 in mg/l) Measured Alkalinity 60 mg/l as Ca. CO 3 Measured CO 2 = 7. 4 mg/l p. H = log {2. 2 x 106 X 60/7. 4 } = 7. 25 Approximate p. H between 7. 0 to 8. 0 Florida Rural Water Association Water Treatment Plant Operation 78

Use of the Langerlier Index for Determining Water Stability n n Every water has a particular p. H value where the water will neither deposit scale nor cause corrosion. A stable condition is termed saturation. Saturation (p. Hs), varies depending on calcium hardness, alkalinity, TDS, and temperature. The Langerlier Index = p. H – p. Hs 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 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 n n 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 n n n 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 n RO Operating Considerations n Pretreatment; Fouling and Scaling Issues n Ion Exchange Considerations n Sodium/Calcium Exchange n Florida Rural Water Association Water Treatment Plant Operation 85

Ion Exchange, Membrane Filtration and Electrodialysis n n 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 n n n 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 p. H 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 n Corrosiveness of Brine Solution n Pump Strainer n Fouling of Resin n Florida Rural Water Association Water Treatment Plant Operation 89

Optimal Water Characteristics for Ion Exchange p. H NO 3 SO 4 TDS Turbidity 6. 5 – 9. 0 < 5 mg/l < 500 mg/l < 0. 3 NTU Selectivity Considerations S 04 -2 > NO 3 -2 > CO 3 -2 > NO 2 -2 > CL-1 Florida Rural Water Association Water Treatment Plant Operation 90

Sodium Exchange MCL Considerations n Sodium provides 100% exchange for Ca++ and Mg++ Na. Zeolite + Ca++ --> Ca. Zeolite + Na+ and Na. Zeolite + Mg++ --> Mg. Zeolite + Na+ n n n 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 + Na. OCl 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 n Elemental Weights and Chemical Formulas n Particle Chemistry and Colloidal Particles n The Floc Building Process n Optimizing the Coagulation Process n Use of a Jar Test n 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 Use 16 O Atomic Number Symbol Oxygen Name 15. 99 Atomic Weight 94

Solids and Colloidal Material Suspended Solids Colloids Turbidity Zeta Potential Suspended in the Water and can be Removed by Conventional Filtration Finely Charged Particles that do not Dissolved The Cloudy Appearance of Water caused by Suspended Matter and Colloids Electrical Charge of a suspended particle 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. n These inorganic salts will react with the alkalinity in the water to form insoluble flocs which will trap the suspended matter in them. n Florida Rural Water Association Water Treatment Plant Operation 96

Removal of Colloidal Particles by Coagulation & Flocculation Floc Building Process : n n n 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 n n n 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 n n n n p. H (p. H 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 n n n Alum initially reacts with low alkalinity With Ferric Chloride requires chemical to reach optimal p. H before reacting Adding too much coagulant increases turbidity Florida Rural Water Association Water Treatment Plant Operation 100

Section 8: Hardness and Water Softening n n n n Hardness Removal by Softening Treatment Methods Used to Remove Hardness Alkalinity Definitions Alkalinity/Acidity Relationships p. H and Lime Treatment Removal of Color and Organics Importance of Recarbonation Florida Rural Water Association Water Treatment Plant Operation 101

Water Hardness n n n 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 Ca. CO 3 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 (Ca. CO 3) 85 – 90% removal Basically Zero Water must be blended Florida Rural Water Association Water Treatment Plant Operation 103

Alkalinity Definitions n n The capacity of water to neutralize acids. The measure of how much acid must be added to a liquid to lower the p. H 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 p. H, Alkalinity and Indicators 0% 100% Bicarbonate and Carbonate Bicarbonate CO 2 Carbonate and Hydroxide T Alkalinity T=0 P Alkalinity P=0 p. H Ca. CO 3 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 p. H Values n n n Below 4. 5 only CO 2 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 n n n Because water has unused lime (calcium hydroxide) and magnesium hydroxide in solution at high p. H (p. H 11), these must be converted to a stable forms. CO 2 is added to reduce Ca(OH)2 to Ca. CO 3 which precipitates at about p. H 10; additional CO 2 is added to convert Mg(OH)2 to soluble Mg(HCO 3)2 which occurs at a p. H 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 n n n 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