Local Water Contaminants

Transcription

1 Local Water Contaminants CWQA 2017 Annual General Meeting Waterloo, Ontario By: Mike Weatherill Purolite Canadian Technical Sales Specialist Presentation Overview Some Water Chemistry Basics Local Contaminant Overview The Water Softening Process Tannins / Organics in Water Disinfection Byproducts (DBPs) Organic Removal Solutions Other Contaminants 2 1

2 What is an ion? Definition: An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons Cations (+) & Anions (-): a cation is a positively charged molecule and an anion is a negatively charged molecule Common Cations in Water Sodium (Na + ) Calcium (Ca 2+ ) Magnesium (Mg 2+ ) Iron (Fe 2/3+ ) Hydrogen (H + ) Common Anions in Water Chloride (Cl - ) Sulfate (SO 4 2- ) Nitrate/Nitrite (NO 2- /NO 3- ) Bicarbonate (HCO 3- ) Hydroxide (OH - ) 3 Ionic Compounds and Electro-neutrality All cations and anions in water will combine to form a chemical complex (+) with (-). Also, the sum of all positive ions will always equal the sum of all the negative ions to form an equilibrium. Some Common Compounds H+ OH = H 2 O AKA: WATER Cl = NaCl AKA: SALT or BRINE Ca+ SO 4 = CaSO 4 AKA: GYPSUM or DRYWALL 4 2

3 Local Contaminant Overview Region: Ontario Common Local Impurities CONTAMINANT WHY REMOVE RESIN TREATMENT Hardness (Ca, Mg) Hardness will deposit scale on piping Water Softener and distribution systems. It is much worse when the water is heated i.e.: a home water heater, dishwasher, kettle Iron (Fe) Iron can leave red coloured deposits and can also bind to bacteria Water Softener with standard resin for low levels (<2ppm) or with a specialty resin for higher levels (2-20ppm) Arsenic (As) Arsenic is a proven carcinogen Specialty Iron Oxide Impregnated resin 6 3

4 Common Local Impurities cont. CONTAMINANT WHY REMOVE RESIN TREATMENT Organics (TOC) Notdirectly a health concern but will Various anion resin make the water unappealing to drink options available. due to the colour, taste and odor. Will also stain fabrics and fixtures Disinfection Byproducts Byproducts from chlorine disinfection are proven carcinogens (THM, HA) Remove the organics prior to chlorination 7 The Water Softening Process 4

5 The Water Softening Process Service Cycle Mg+ Regeneration Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Kinetics...seconds...minutes 9 A Closer Look At Brine Regeneration Equilibrium Shift Mg+ Mg+ Mg+ Mg+ 10% Brine Concentration (NaCl) with a 30min contact time 10 5

6 Tannins / Organics in Water What are Tannins? Tannins are natural organic materials that are dissolved in water Tannins add a brownish yellow colourto the water which can stain fabrics and fixture. They can also give the water a musty taste and odor 12 6

7 SOURCES OF ORGANICS Found primarily in surface waters (rivers, lakes) Vegetation (tannic and fulvic acids) Industrial waste Domestic waste Animal waste 13 Humic Acid Chemical Structure 14 7

8 Fluvic Acid Chemical Structure 15 How to Measure Organics in Water? There are many different types of organics so the measurement techniques can vary. The most popular techniques for measuring organics in water are as follows: TOC Total Organic Carbon (ppm); via lab analysis or inline instrumentation TANNINS Optics based measurement most commonly used in residential applications using a test kit 16 8

9 Disinfection Byproducts (DBPs) DISINFECTION BYPRODUCTS Naturally occurring organic matter such as humicand fulvicthat are present in water being disinfected can potentially result in the formation of a variety of toxic byproducts. These include trihalomethanes(thm) and haloacetic acids (HAA). Human studies have shown a direct link between exposure to THM and a higher risk of certain cancer types including: colon, rectal, pancreatic, kidney and brain cancers. Human studies have also suggest a link between THM exposure and some reproductive side-effects. 18 9

10 Health Canada MAC Guidelines The maximum acceptable concentration (MAC) for trihalomethanesin drinking water is mg/l (100 ppb) * US EPA THM MAC = 80ppb HAA MAC = 60ppb *From: Guidelines for Canadian Drinking Water Quality Guideline Technical Document - Trihalomethanes 19 Trihalomethanes (THM) Chemicals The most common THMs in water are a group of four chemicals that are formed when chlorine is used for disinfection of water with organics: chloroform (CHCl 3 ), bromoform(chbr 3 ) bromodichloromethane(chbrcl 2 ) dichlorobromomethane (BDCM) 20 10

11 WHO Guidelines for THM Table 2: WHO Guideline Values for Trihalomethanes in Drinking Water (WHO, 1996) WHO Guideline Value Chloroform 200 μg/l Bromodichloromethane 60 μg/l Dibromochloromethane 100 μg/l Bromoform 100 μg/l *From: World Health Organization (1993). Guidelines for drinking-water quality, 2nd edition, Volume 1: Recommendations. World Health Organization, Geneva 21 Cancer Potency Factors for THM Table 4: USEPA Cancer Potency Factors Compound Chloroform Cancer Potency Factor insufficient data Bromodichloromethane mg/kg/day Dibromochloromethane mg/kg/day Bromoform mg/kg/day *From: World Health Organization (1993). Guidelines for drinking-water quality, 2nd edition, Volume 1: Recommendations. World Health Organization, Geneva 22 11

12 The Solution The solution for the prevention of the formation of THM in drinking water is to remove the organics prior to chlorination. Utilities should make every effort to maintain concentrations as low as reasonably achievable without compromising the effectiveness of disinfection * *From: Guidelines for Canadian Drinking Water Quality Guideline Technical Document - Trihalomethanes 23 Organic Removal Options 12

13 Organic Removal Options Conventional coagulation and filtration most often used for large scale municipal applications Activated Carbon effective up to certain levels of TOC UV full TOC destruction requires a 254 NM UV system Nano-filtration high pressure membrane technology Ion Exchange Resin low cost, high capacity and can treat high levels of organics. Brine regenerated system operated similarly to a water softener. 25 Ion Exchange Resin for Organic Removal 26 13

14 Organic Removal Resin Selection Resin selection for organic removal is based on two main factors: 1. Inlet TOC levels in PPM 2. N factor calculation The N factor is the ratio of total organics to total inorganic anions in the water: N factor Resin choice < 1 Gel type SBA 1 to 2 Type I styrene Macroporous SBA 2 to 3 Type II Macroporous SBA 3 to 4 Acrylic gel SBA 4 to 8 Acrylic Macroporus SBA 8+ Specialty Resin 27 Other Resin Selection Factors Styrenic Resin Hydrophobic it does not like water 20-90% organic removal Difficult to completely regenerate (~70% elution during regeneration) More prone to organic fouling over time Acrylic Resin Hydrophilic it likes water 50-90% organic removal Much easier to regenerate (~95% elution during regeneration) Resistant to organic fouling = longer lifespan 28 14

15 Styrene vs Acrylic SBA 29 Gel vs. Macroporous Gel clear Macroporous opaque Surface area = 4 m 2 /gm Appears solid Moderate cross-linking Depends on diffusion Surface area = 1000 m 2 /gm Continuous solid and void Higher cross-linking Kinetics based on surface 30 15

16 Resin Structure Gel vs Macroporous 31 Macroporous Pores 32 16

17 Tannin Removal System Sizing TOC < 5 PPM; use a flow rate of 3 USGPM/ft 3 of resin, treating approximately 20,000-gallons/ft 3 per cycle. TOC 5-20 PPM, use a flow rate of 2 USGPM/ft 3 of resin, treating approximately 15,000-gallons/ft 3 -per cycle. TOC > 20 PPM, use a flow rate of 1 USGPM/ft 3 of resin, treating approximately 10,000-gallons/ft 3 per cycle 33 Other Parameters < 10 grains of hardness is okay, > 10 grains you must soften first Remove all suspended solids before the resin With low TDS/high organic waters the ph can be depressed by up to 2 units High alkalinity waters can lead to fishy amine odor especially with hot water Resin lifespan is much shorter with higher levels of organics 34 17

18 Lessons Learned The effectiveness of a removal is very flowrate dependent Not all water sources are the same so the resin selection will vary based on the source Macrcoporousacrylic based resin work the best for most locations in Canada Some people have a higher sensitivity to odors from anion resin Specialty resin available for very high levels of organics (ie: an area with cedar bogs or coal ash deposits) 35 Organic Fouling 18

19 Organic Fouling Organics can accumulate on anion resin over time Tannins tend to migrate to the inner resin matrix and are hard to elute during regeneration All resin will become irreversibly fouled over time so should be replaced every 3-7 years. Cleanup measures The additional of soda ash to the brine tank has proven an effective clean up measure for organically fouled resin. By increasing the ph of the brine the organics become more soluble and thus are eluted more effectively. Other: Industrial organic traps add 1% caustic soda (NaOH) to the brine but this isn t suggested for drinking water applications. 37 Symptoms of Fouling Clumping / Loss of Resin in backwash Higher pressure drop and flow restrictions Possible channeling which leads to early breakthrough Reduced service throughput Poor effluent water quality More frequent regenerations 38 19

20 Organic Fouling Picture 39 IX Resin for Other Contaminants CONTAMINANT Bromide Nitrate Hexavalent Chromium Perchlorate Arsenic Uranium Manganese RESIN OPTION Regenerable selective resin for reducing bromide and the subsequent potential formation of bromomethanes and bromate. Nitrate selective, Type II SBA, Type I SBA Type I brine regenerable SBA Single-use resin requiring ph adjustment Specialty selective resins Single use Iron oxide-infused adsorbent resin Brine regenerable type II SBA Fouling resistant Shallow Shell core SAC, brine regenerable cation resin. Fouling resistant Shallow Shell core SAC, brine regenerable; handles up to 20 ppm 40 20

21 Why Purolite? Highest Quality Products Throughout all Purolite plants, production is carefully controlled to ensure that our products meet the most stringent criteria. Reliable Service Purolite employs the largest technical sales organization in the industry. Innovative Solutions We strive to make the impossible possible Three key characteristics: Our entrepreneurial spirit Our dedication to serving our customers Our desire to be the leader in resin technology 41 21

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