Disinfection, Chlorination and Oxidation. Daniel B. Stephens & Associates, Inc.

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1 Disinfection, Chlorination and Oxidation

2 Chlorination/Disinfection Glossary Bacteria: living single-celled microscopic organisms having characteristics of both plants and animals; often useful but may also cause disease Chloramines: chemical compounds formed from the reaction of chlorine with ammonia (NH 3 ); also called combined chlorine Chlorination: application of chlorine to water, generally for the purpose of disinfection, but also for other purposes such as odor control

3 Chlorination/Disinfection Glossary Coliform bacteria: bacteria used as an indicator of pollution; divided into two groups - total coliform (TC) and fecal coliform (E. coli. - found in the intestinal track of warm-blooded animals); fecal coliform is an indication of pollution. Chlorine demand: the difference between the amount of Cl 2 added to water (Cl 2 dose) and the amount of Cl 2 remaining after a period of contact time (Cl 2 residual) Cl 2 demand (mg/l) = Cl 2 dose (mg/l) Cl 2 residual (mg/l)

4 Chlorination/Disinfection Glossary Disinfection: the addition of chlorine, ozone, UV light, etc. to water in order to kill or inactivate disease causing organisms; effectiveness measured using the coliform test Free available Cl 2 : portion of total Cl 2 residual not combined with ammonia; free Cl 2 includes hypochlorous acid (HOCL) and hypochlorite ion (OCl - )

5 Chlorination/Disinfection Glossary Pathogens: disease causing organisms such as bacteria, viruses, protozoa; examples are typhoid, cholera, dysentery, poliomyelitis, giardiosis, and cryptosporidiosis Sterilization: process that makes free from all living organisms

6 s 1890s Scientists demonstrate that microorganisms can cause disease. First application of chlorine disinfectants to water facilities in England. First application of chlorine disinfectants to U.S. municipal water facilities in Jersey City and Chicago. First U.S. drinking water bacterial standard. Chlorination first used in the U.S. and Canada Early 1960s 1970s 1972 Over 1,000 U.S. cities employ chlorine disinfection. U.S. drinking water bacterial standard becomes more stringent. More than 19,000 municipal water systems operate throughout the U.S. Chlorine dioxide begins to gain acceptance as a drinking water disinfectant. Passage of the U.S. Clean Water Act for restoring and maintaining surface water quality Passage of the U.S. Safe Drinking Water Act; the US Environmental Protection Agency is given authority to set water quality standards which states must enforce. Amendments to the U.S. Safe Drinking Water Act extend existing law to recognize: source water protection, operator training, funding for water system improvements, and public information. Disinfection By-Product Rule

7 Introduction to Chlorine Disease-causing organisms can be found in surface water and in some groundwater. The addition of a chemical disinfectant may be necessary if the drinking water is to meet the coliform MCL, preventing any waterborne diseases. Cl 2, due to it relatively low cost, availability & ease of use and one other important reason, is the most commonly used disinfectant/oxidant for this purpose.

8 Introduction to Chlorine (Cl 2 ) Chlorine is available in 3 forms: Chlorine gas Calcium or sodium hypochlorite solution Calcium or sodium Hypochlorite powder (HTH)

9 100% available 5 % % available 65 % - 70 % available 9

10 Chlorine Strength, Storage, and Aging Sodium Hypochlorite Concentrations vs Specific Gravity (USA BlueBook Operator s Companion, 9 th ed. page 169) Trade % Sp Gr Trade % Sp Gr

11 Chlorine Strength, Storage, and Aging 11

12 Properties of Cl 2 Cl 2 gas Amber-yellow in color Containing 99.5% pure Cl 2 Has a penetrating and distinctive odor Slightly heavier than water 2½ heavier than air Has very high coefficient of expansion; i.e., a temperature change from 50 F to 85 F will cause a volume increase from 84% to 89% No Cl 2 cylinder should be filled over 85% capacity (see above characteristic) One liter of liquid Cl 2 can evaporate to produce 450 liters Cl 2 gas Cl 2 is non-flammable & non-explosive but it will support combustion 12

13 Mechanism of Disinfection Four mechanisms have been proposed to explain the action of disinfectants: Damage to the cell wall: Damage or destruction of the cell wall will result in cell disintegration and death. Some agents, such as penicillin, inhibit the synthesis of the bacteria cell wall. Alteration of cell permeability: Agents such as phenolic compounds and detergents alter the permeability of the cytoplasmic membrane. These substances destroy the selective permeability of the membrane and allow vital nutrients, such as N and P, to escape.

14 Mechanism of Disinfection (cont.) Four mechanisms (cont.): Alteration of the colloidal nature of the protoplasm: Heat, radiation, and highly acidic or alkaline agents alter the colloidal nature of the protoplasm. Heat will coagulate the cell protein and acids or bases will denature proteins, producing a lethal effect. Inhibition of enzyme activity: Oxidizing agents such as chlorine can alter the chemical arrangements of enzymes and deactivate the enzymes.

16 The Reaction of Chlorine with Water Cl 2 + H 2 O HOCl + HCl Hypochlorous acid, HOCl is one of two free available chlorine residual forms. Due to the ease with which it penetrates into and kills bacteria, it is the most effective form of free residual for disinfection. However some of the HOCl dissociates to form an acid.

17 The Reaction of Chlorine with Water HOCl H + + OCl - Hypochlorite ion is the second type of free available Cl 2 residual and is a relatively poor disinfectant, primarily because of its inability to penetrate into the bacteria. In addition to the hypochlorite ion, hypochlorous acid also releases a hydrogen ion, an acid that can lower the ph if insufficient alkalinity is present.

18 Effectiveness The effectiveness of Cl 2 is based on 5 important factors ph Temperature Concentration Contact time Demand

19 Effectiveness ph strongly influences the ratio of HOCl to OCl - Low ph values favor the formation of HOCl, the more effective free residual. High ph values favor the formation of OCl -, the less effective free residual. As ph increases from 7 to 10, the OCl - begins to predominate and the time required for free residual to effectively disinfect increases.

20 Effectiveness Temperature The higher the temperature, the more effective chlorination. Lower temperatures slightly favor the formation of HOCl Lower temperatures allow Cl 2 residuals to persist somewhat longer. Chemical and biological reaction rates increase as the temperature increases, making Cl 2 more effective at higher temperatures.

21 Effectiveness Concentration of Cl 2 Time dependent for different organisms. Providing conditions remain constant, as the contact time is increased, less concentration is needed to accomplish the same level of disinfection. As dosage concentration is increased, contact time can be decreased.

22 Effectiveness Contact Time The destruction or inactivation of an organism is directly related to the contact time.

23 Effectiveness Demand: The inorganic and organic material in raw and finished water take part in the reactions with Cl 2 Reaction with ammonia (NH 3 ) is one of the most common. NH 3 can result from decaying vegetation or from domestic and industrial waste. Cl 2 reacts with NH 3 to form chloramines, or combined chlorine residual. Uses the chlorine that would otherwise be available for disinfection. Other demand-causing reactions include Fe, Mn, S compounds, turbidity, TOC/DOC, biofilm.

24 Formation of Chloramines NH3 + chlorine NH 2 Cl + H 2 O ammonia monochloramine (ph > 7.5) NH 2 Cl + chlorine NHCl 2 + H 2 O dichloramine (ph < 7.5) NHCl 2 + chlorine NCl 3 + H 2 O trichloramine (ph < 7.4)

25 Formation of Chloramines The formation of chloramine compounds depends on the ph of the water and the presence of ammonia. Chloramines are a combined available chlorine which is a less active oxidizing agent than free available chlorine, but it has a longer lasting residual. 25 times the amount of combined available chlorine is needed to be as effective as free available chlorine.

26 Breakpoint Chlorination

27 Chlorine Demand The consumption of chlorine used for disinfection What is added What is used What remains Dosage Demand = Residual Organics Microorganisms Ammonia-Nitrogen Nitrate Iron Silt

28 Reaction with Iron (Fe) Iron is an undesirable element in water often found in groundwater, is easily oxidized and precipitated by chlorine, causes red stains (red water), and can plug well screens; aeration may be an effective treatment. The chemistry: 2Fe(HCO 3 ) 2 + Cl 2 + Ca(HCO 3 ) 2 2Fe(OH) 3 + CaCl 2 + 6CO 2 Ferric hydroxide precipitates almost immediately to form a fluffy, rust-color sludge. Calcium bicarbonate represents the alkalinity. Each mg/l of iron removed requires 0.64 mg/l of Cl 2.

29 Reaction with Manganese (Mn) Manganese is an undesirable constituent often found in groundwater supplies. Causes brown or black water, stains on fixtures Normally in the form of a soluble salt, manganous sulfate (MnSO 4 ) Cl 2 forms the precipitate manganese dioxide (MnO 2 ) Reaction time is relatively slow, about 2 hours DO NOT want this to occur in distribution system

30 Reaction with Manganese (Mn) Each mg/l of Mn removed requires 1.3 mg/l of free available Cl 2. Combined available Cl 2 is not effective. MnSO 4 + Cl 2 + 4NaOH MnO 2 + 2NaCl + Na 2 SO 4 + 2H 2 O

31 Reaction with Hydrogen Sulfide (H 2 S) H 2 S is found in groundwater supplies and rarely in surface waters At 0.05 mg/l, H 2 S can give water an unpleasant taste. At 0.5 mg/l, H 2 S gives off an odor of rotten eggs. At > mg/l, H 2 S can be fatal in minutes if inhaled. At concentrations > 4.3% by volume in the air, H 2 S is flammable.

32 Reaction with Hydrogen Sulfide (H 2 S) When Cl 2 is used to remove H 2 S, one of two reactions can occur, depending on Cl 2 dosage and ph values: 2.2mg/L ph 6.4 will convert 1mg/L of H2S to sulfur, forming a fine colloidal particle that causes a milky-blue turbidity. Cl 2 + H 2 S 2HCl + S The second reaction is operationally preferred. 8.9 mg/l of Cl ph 6.4 will convert 1 mg/l of H 2 S to sulfuric acid. 4Cl 2 + H 2 S + 4H 2 O 8HCl + H 2 SO 4

33 Zone 1 Zone 2 Zone 3 Zone 4

34 Taste and Odor Thresholds Compound Free HOCl Monochloramine Dichloramine Nitrogen trichloride Taste/Odor Threshold 20 mg/l 5 mg/l 0.8 mg/l 0.02 mg/l

35 Operational Considerations There may be times when chlorine taste and odor complaints become a problem in the distribution system. This problem is generally related to high combined residuals and inadequate free residual. The solution to this problem may be to increase the chlorine dose rate to get past the breakpoint.

36 Operational Considerations As a rule of thumb, the free residual should be at least 85% of the total residual in order to prevent chlorine taste and odor problems and insure an adequate free residual for effective disinfection. A sudden increase in combined chlorine may signify the presence of organic contaminants such as dirt and debris. The sudden presence of organic material may result from a line break, loss of pressure or unprotected cross connection such as lawn irrigation, etc.

37 Chlorine Residual Testing DPD Colorimetric

38 Chlorine Residual Testing Determine reagent blank Free residual testing contact time 60 seconds 3 minutes Total residual testing contact time 3 6 minutes Regulatory minimum 0.2 mg/l at EP (SW) Looking for residual 0.2 mg/l after 24 hours (SW) DO NOT exceed the MRDL maximum residual disinfectant level 4 mg/l for chlorine, chloramines CWS, NTNCWS 0.8 mg/l for chlorine dioxide TNCWS

39 Chlorine Operation and Maintenance

40 85 % 40

41 Daily feed rates are not to be exceeded - freezing will occur. Fusible Plug is designed to melt at 158 F to 165 F 150 lb. cylinder 1 ton cylinder 41

Chlorine/Sulfur Dioxide Leak Indicator Bottles Chlorine and sulfur dioxide gas leaks can be easily & safely identified with aqueous ammonia vapor.

43 Chlorine/Sulfur Dioxide Leak Indicator Bottles Chlorine and sulfur dioxide gas leaks can be easily & safely identified with aqueous ammonia vapor. Chlorine and sulfur dioxide safely react with ammonia to form a visible white cloud that identifies the source of the chemical leak. Ammonia may cause problems with metal alloys. Anyone testing for chlorine leaks with ammonia water (ammonia hydroxide solutions) on brass or copper alloys must take care that only the ammonia vapor and not the liquid solution comes into contact with the alloy.

47 47

48 Troubleshooting Gas Chlorinators Symptom Low Feed Rate and Low Vacuum Low Feed Rate and High Vacuum Feed Rate Jumps Feed Rate Won t Zero Chlorine Gas at Vent Probable Cause Clogged Injector/Ejector Clogged Gas Feed Line Closed Cylinder Valve Empty Cylinder Clogged Flow Controller/Needle Valve Dirty Flow Indicator/Rotameter Dirty Pressure Regulating Valve No Vacuum No Supply Water Vacuum Leak 48

49 Emergency Kit A For 100 lb. and 150 lb. Chlorine Cylinders

51 Emergency Kit B For Chlorine 1-Ton Containers

53 One Ton Cylinder

54 Powder Chlorine (Calcium Hypochlorite) Calcium Hypochlorite Ca(OCl) 2 Dry loose granular material Also comes in tablet form White or yellow-white in color Contains 65% - 70% available Cl 2 by weight Other 35% - 30% are binding compounds of lime Supports combustion

55 Liquid Chlorine (Sodium Hypochlorite Solution) Sodium Hypochlorite (NaOCl) Clear to greenish-yellow liquid solution 9% - 15% available Cl 2 No fire hazards are connected to NaOCl quite corrosive Reactive with other chemicals

56 Sodium hypochlorite generating unit, 0.8% available produced Clor-Tec

57 MIOX System

58 PERISTALTIC TYPE CHEMICAL FEED PUMP

61 Diaphragm Chemical Feed Pump Type Coupling nut 4-function valve Return line & pressure relief Pump head Suction Fitting Injection check valve Discharge tubing Spacer E.P.U Suction tubing Metering pump housing Speed knob (% of max. strokes/min.) Stroke knob (% max. of solution Discharge. Pump must be running To make adjustments. Ceramic weight Power cord Foot valve 61

62 LMI Calculating Required Output Set-up & Installation Desired mg/l X GPM (Max Flow of Well Pump) % Concentration of Chemical (Use % as a decimal) = Required Pump Output in GPH X.006 (Conversion to GPH) Calculating output % Required Pump Output Maximum Output of Pump = % Output Required from Pump Calculating % Speed & % Stoke % Output Required from Pump = % Speed & % Stroke (Square Root)

63 Wastewater Dechlorination Physical or chemical removal of all residual chlorine prior to effluent discharge, accomplished using: Long detention times Aeration Sunlight Activated carbon Sulfur-based chemicals: Sulfur dioxide - SO 2 Sodium sulfite - Na 2 SO 3 Sodium bisulfite - NaHSO 3 Sodium thiosulfate - Na 2 S 2 O 3

64 Sulfur Chemical Dechlorination Sulfur dioxide - SO 2 : Most common, frequently used Reacts on 1:1 basis 1mg/L SO 2 removes 1 mg/l chlorine residual Uses same type of equipment as gas chlorination; if using chlorine gas rotameter to measure SO 2 flow multiply reading by 0.95 to get pounds per day of SO 2 used (due to slight difference in density of the 2 gases)

65 Sulfur Dioxide Properties Colorless gas, pungent odor Chemical in any form is NOT flammable or explosive Gas can be cooled and compressed to a colorless liquid Under pressure, liquid and gas will stay in equilibrium Container pressure function of temperature Dry gas is not corrosive; in presence of moisture gas forms sulfuric acid H 2 SO 4 not a ph factor unless alkalinity is very low Excessive dosage can reduce DO (and increase BOD) and decrease ph

Disinfection, Chlorination and Oxidation. Daniel B. Stephens & Associates, Inc.

Disinfection, Chlorination and Oxidation Chlorination/Disinfection Glossary Bacteria: living single-celled microscopic organisms having characteristics of both plants and animals; often useful but may