DBP Control: Chloramine Chemistry. Chris Griffin Hach Company

Transcription

1 DBP Control: Chloramine Chemistry Chris Griffin Hach Company 1

2 BEFORE WE BEGIN 2

3 Who currently Uses Chlorine only? Before we begin. Uses Chloramination at their water plant or in distribution? Uses Chloramination only in distribution? Controls only with bench testing? Controls automatically with on-line instrumentation? What do you want to learn and take away from this session? 3

4 Summary Goal : Provide a more in-depth understanding of the Disinfection Process using Chloramines. Hands-on monochloramine testing. Balance is Key: Experience proves that the chloramination process can be extremely effective, but only if the concentration of ammonia and chlorine in the system remains in proper balance. Understand the Reactions: For optimal control of the chloramination process, understanding of the reactions taking place and measurement of the proper parameters can simplify operation and ensure proper disinfection 4

5 Take Away Messages Monochloramine can help reduce DBPs Proper measurement is the key to effective control Know through analysis where you are on the Chlorine Breakthrough Curve Target a Cl 2 to NH 3 ratio of 4:1 to avoid dichloramine formation Minimize unreacted ammonia free ammonia >than but close to 0 When making process changes, change only one variable at a time 5

6 Outline Introduction to Chloramination Optimizing Monochloramine Production Hands-on Monochloramine Testing Additional Related Material Applying the Concepts Making Adjustments Special Situations Determining Ammonium Feed Rate Nitrification Problems and monitoring 6

7 INTRODUCTION TO CHLORAMINATION 7

8 Chlorination Introduction to chloramination DBP s Alternative disinfection methods Chloramination monitoring 8

9 Chlorination Chlorine is the most often used disinfectant used for water treatment Use began in the early 1800 s for industrial water Used as a disinfectant in drinking water since mid s 9

10 Chlorination How does chlorine react with water? 10

11 Chlorine Chemistry Chlorine is added to water as chlorine gas or as sodium or calcium hypochlorite. Chlorine Gas: Cl 2 H O 2 HOCl H Cl - Sodium Hypochlorite: NaOCl H O 2 Na HOCl OH - 11

12 Chlorine Chemistry The two chemical species formed by chlorine in water are hypochlorous acid and hypochlorite ion HO C l Hypochlorous Acid H - O C l Hypochlorite Ion 12

13 Chlorine Chemistry Hypochlorous acid is the stronger disinfectant Below ph 7.5 free chlorine exists predominantly in the HOCl form Above ph 7.5 free chlorine exists predominantly in the OCl - form HOCl OCl - ph

14 CHLORINATION CURVE 14

15 Chlorination Curve What happens when chlorine is added to water? A chlorination curve will help describe what happens during this process 15

16 Chlorination Curve What is a chlorination curve? A graph of the amount of chlorine measured in a solution versus the amount of chlorine added 16

17 Chlorine Measured Chlorination Curve Chlorine Added 17

18 Chlorination Curve Begin adding chlorine to water Chlorine will first react to exhaust chlorine demand in the system Chlorine added will not be recovered in a chlorine test 18

19 Chlorine Measured Chlorination Curve Chlorine Added 19

20 Chlorination Curve Continue adding chlorine to the system Once chlorine demand is exhausted, additional chlorine added will be recovered in a chlorine test 20

21 Chlorine Measured Chlorination Curve Chlorine Added 21

22 Chlorine Testing Chlorine monitoring points Monitor preoxidation (if performed) At time of chlorine application In distribution system for adequate residual Cl Cl Cl

23 ALTERNATIVE DISINFECTANTS 23

24 Alternative Disinfectants - Outline Introduction to alternative disinfectants Chloramination Chloramination chemistry Chloramination curve Testing for disinfectants 24

25 Alternative Disinfectants What s the problem with chlorine? Chlorine is very reactive with organic matter and can form halogenated DBPs. For some systems, this poses no problems. For some systems, chlorine is a major contributor to a DBP problem. Remove the organic matter or seek alternate disinfectant 25

26 Alternative Disinfectants Alternative to chlorine which: Adequately disinfects Maintains residual Removes taste and odor compounds Practical Minimizes reactions with natural organic matter that form DBPs 26

27 Alternative Disinfectants The main alternative disinfectants that drinking water plants use are chloramines and chlorine dioxide. Some newer plants are also switching to: Ozone No residual, bromate by-product oxidation of bromide UV Disinfection No residual, destroys organic material Ozone or UV less frequently used due to the cost of treatment 27

28 Chloramines Chloramines are formed when free chlorine reacts with free ammonia present in the water Monochloramine (NH 2 Cl) GOOD form Dichloramine (NHCl 2 ) Trichloramine (NCl 3 ) 28

29 Chloramination Benefits Reduces formation of halogenated DBPs Maintains residual More economical than alternatives 29

30 OPTIMIZING MONOCHLORAMINE PRODUCTION 30

31 Free Chlorination: Chloramination Chemistry Cl 2 + H 2 O HOCl + OCl - (strong disinfectant) Chloramination: NH 3 + HOCl H 2 O + NH 2 Cl NH 2 Cl + HOCl H 2 O + NHCl 2 NHCl 2 + HOCl H 2 O + NCl 3 Organic Amines: Desired form (Mono) Increasing disinfection efficiency, but taste and odor problems Org N + HOCl OrgN-Cl (~no disinfecting) 32

32 Chloramination Chemistry Monochloramine is most stable, desired Relatively weak oxidizer compared to chlorine Germicidal effectiveness times less Higher CT required so Chlorine added first then Ammonia Maintains long residual times Higher residual levels are required in distribution system (2.0 mg/l 4.0 mg/l) 33

33 CT values for chlorine vs. chloramine 34

34 Taste and Odor Threshold Subjective values in water Monochloramine 5.0 mg/l Dichloramine 0.8 mg/l Trichloramine 0.02 mg/l 35

35 Chlorine Measured Chloramination Curve Chlorine Added 36

36 Chloramination Curve Begin adding chlorine to a water containing ammonia Initial addition of chlorine reacts to exhaust any chlorine demand present in the water Natural organic material (NOM) 37

37 Chlorine Measured Chlorination Curve Chlorine Added 38

38 Chloramination Curve Continue to add chlorine to the water After chlorine demand is exhausted, chlorine reacts with ammonia to form monochloramine HOCl + NH 3 NH 2 Cl + H 2 O 39

39 Chlorine Measured Chloramination Curve Chloramination I 5:1 Cl2:N Ratio Chlorine Added 40

40 Weight Based Units Atom Atomic Weight Atom Molecular Weight Chlorine 35.5 Chlorine (Cl 2 ) 71 Nitrogen 14 Ammonia (NH 3 ) 17 Hydrogen 1 Monochloramine (NH 2 Cl) 51 Dichloramine (NHCl 2 ) 85 Trichloramine (NHCl 3 ) 129 How do we get to these desired ratios? Derived from balancing the chemical reaction HOCl + NH 3 NH 2 Cl + H 2 O 41

41 Weight Ratios for the Ideal World 1 mol Cl 2 X 71 lb Cl 2 X 1 mol NH 3 = 71 lb Cl 2 = 4.2 lb Cl 2 1 mol NH 3 1 mol Cl 2 17 lb NH 3 17 lb NH 3 1 lb NH 3 1 mol Cl 2 X 71 lb Cl 2 X 1 mol NH 3 X 1 mol N = 71 lb Cl 2 = 5.06 lb Cl 2 1 mol NH 3 1 mol Cl 2 1 mol N 14 lb N 14 lb N 1 lb N 1 molecule of Free Chlorine reacts with 1 molecule of Free Ammonia to form 1 molecule of Monochloramine NH 3 or NH 3 -N form on analysis 42

42 Chlorine Measured Chloramination Curve Chloramination I 5:1 Cl2:N Ratio Chlorine Added 43

43 Chlorine Measured Chloramination Curve Chloramination I 5:1 Cl2:N Ratio Chlorine Added 44

44 Chloramination Curve Continue to add chlorine to the water After complete formation of monochloramine, monochloramine reacts with additional chlorine to form dichloramine and nitrogen trichloride. HOCl + NH 2 Cl NHCl 2 + H 2 O 45

45 Chloramination Curve Continue to add chlorine to the water As dichloramine and nitrogen trichloride form, the addition of chlorine continues to oxidize these compounds to nitrogen gases 46

46 Chloramination Curve Continue to add chlorine to the water The point at which all dichloramine is converted to nitrogen gas is the breakpoint. 47

47 Chlorine Measured Chloramination Curve Chloramination I II 5:1 Cl2:N Ratio Breakpoint 9:1 Cl2:N Ratio Chlorine Added 48

48 Chlorine Measured Chloramination Curve Chloramination I II 5:1 Cl2:N Ratio Breakpoint 9:1 Cl2:N Ratio Chlorine Added 49

49 Chloramination Curve Continue to add chlorine to the water After the breakpoint, all chlorine added to the water remains as free chlorine Breakpoint chlorination Cl 2 + H 2 O HOCl + OCl - 50

50 Chlorine Measured Chloramination Curve Chloramination I II Free Chlorination III 5:1 Cl2:N Ratio Breakpoint 9:1 Cl2:N Ratio Chlorine Added 51

51 Chlorine Measured Chloramination Curve Chloramination I II Free Chlorination III 5:1 Cl2:N Ratio Breakpoint 9:1 Cl2:N Ratio Chlorine Added 52

52 Chloramination Goals Complete formation of monochloramine (Stay in Section I) Optimal ratio of 3 to 5 : 1 Cl 2 :N Avoid dichloramine formation Avoid taste and odor problems Minimize un-reacted ammonia Control biofilm and nitrification 53

53 Chloramination Goals Real world operating conditions can influence the process ph Temperature Chlorine demand Reaction time, competing reactions Chloramine decay 54

54 Chloramination Species Curve we have been looking at is total chlorine What other species are involved in chloramination and what happens to their concentrations? 55

55 Chlorine Measured Chloramination Species Chloramination I II Free Chlorination III Total Chlorine Chlorine Added 56

56 Free Ammonia Free ammonia reacts with chlorine to form monochloramine until ammonia has been consumed 57

57 Chlorine Measured Chloramination Species Chloramination I II Free Chlorination III Total Chlorine Free Ammonia Chlorine Added 58

58 Monochloramine Monochloramine is equivalent to total chlorine until Section II where it reacts with chlorine to form new compounds. No monochloramine remains at the breakpoint. 59

59 Chlorine Measured Chloramination Species Chloramination I II Free Chlorination III Total Chlorine Monochloramine Free Ammonia Chlorine Added 60

60 Free Chlorine Free chlorine does not exist until after the breakpoint. After the breakpoint, all chlorine added to the system exists as free chlorine. 61

61 Chlorine Measured Chloramination Species Chloramination I II Free Chlorination III Total Chlorine Monochloramine Free Chlorine Free Ammonia Chlorine Added 62

62 Combined Chlorine Test Problems Theory goes that Total Chlorine Test = Free Cl 2 + Monochloramine + Dichloramine Free Chlorine Test = Free Cl 2 Total Test Free Test = Combined Chlorine 63

63 Combined Chlorine Test Problems Problems Can t tell if you have the desired monochloramine species Free Cl 2 measurements in presence of high levels of chloramines are inaccurate Chloramines break through and increase the Free Cl 2 test value Use an analytical method that measures what you are looking for: Monochloramine and free ammonia 64

64 Chloramine interference with DPD Free Chlorine 65

65 CHLORAMINATION TESTING 66

66 Chloramination Monitoring Monitor chloramines by measuring directly Monochlor-F method Chemical method specific for monochloramine Few interferences Optimized for chloramination monitoring 67

67 Chloramination Monitoring Monitor ammonia using: Ion selective electrode (ISE) Monochloramine and free ammonia test Colorimetric method most Hach instruments either have it or can be upgraded to run it A sequential test that first measures monochloramine, then sample is chlorinated to measure increase in monochloramine concentration Amount of free ammonia is calculated based on the increase in monochloramine 68

68 Chloramination Monitoring Monitor chloramination process using: Total chlorine Free chlorine Monochloramine will give a false-positive result in a free chlorine test Be aware of where free chlorine exists in chloramination (know where you are on chloramination curve) Use FreeChlorF / Indophenol Method test in special cases 69

69 Chloramines Chloramination - Why so many tests? Combination of ammonia and monochloramine (and maybe total chlorine) lets you know exactly where your process is on the breakpoint curve Keeping process under control saves time and money Can also improve aesthetics and perceived quality of your product 70

70 Chlorine Measured Where Am I When Total Chlorine = 3mg/L? Chloramination I II Free Chlorination III Chlorine Added 71

71 Chlorine Measured I Am Here! Chloramination I NH 2 Cl = t-dpd f-nh 3 -N > 0 II NH 2 Cl < t-dpd f-nh 3 -N = 0 Free Chlorination III t-dpd > 0 NH 2 Cl = 0 f-nh 3 -N = 0 Chlorine Added 72

72 HANDS-ON LAB TESTING 73

73 74

74 APPLYING THE CONCEPTS 75

75 What to measure Applying the Concepts Where to measure What results are we targeting How to make changes based on the data 76

76 To run the process we need Measured Concentrations of: Free Chlorine Total Chlorine Monochloramine Free Ammonia Goal Target Levels of these same parameters Current feed rates of chemicals Molecular Weights and Formulas for Chemicals Added Concentration and specific gravity of each liquid Chemical Added 77

77 Measuring Bulk Chemicals Confirm your as delivered bulk concentration Monitor degradation of actual concentration over time Confirm or adjust pumping rates based on actual concentration Particularly important if adding on manual calculations for PPD Titration of ingredient or Specific Gravity Hypochlorite Testing Thiosulfite titration 5-15% as Cl 2 Aqua Ammonia Testing Sulfuric acid titration 5-35% as NH 3 78

78 79

79 Free Chlorine What to measure Make sure we added the correct amount Determine how much ammonia needs to be added to form monochloramine Free Ammonia If we applied too much ammonia Determine how much Cl 2 needs to be added to form monochloramine Monochloramine to ensure our ratio of Cl 2 to NH 3 was correct Total Chlorine To see if other chloramines were formed 80

80 Where to measure Regulated Parameters At locations required by local regulators End of disinfection zone Point of Entry to distribution Process Control Upstream of the chemical injection points Down stream of the chemical injection points 81

81 Injection Points Cl 2 Cl 2 Cl 2 NH 3 NH 3 82

82 Free Chlorine Cl 2 Cl 2 NH 3 Cl 2 NH 3 83

83 Total Chlorine Cl 2 Cl 2 NH 3 Cl 2 NH 3 84

84 Monochloramine Cl 2 Cl 2 NH 3 Cl 2 NH 3 85

85 Free Ammonia Cl 2 Cl 2 NH 3 Cl 2 NH 3 86

86 What are our goals? Free Chlorine to meet CT requirements Free Chlorine concentration to meet target Monochloramine level Add ammonia based on desired target ratio Maintain smallest target residual free ammonia Common to operate less than 0.10 mg/l NH 3 Best practice 0.05 mg/l NH 3 Know where you are on the curve! 87

87 MAKING ADJUSTMENTS 88

88 Making Adjustments Set your target residual monochloramine, ratio, free ammonia levels Run your tests Periodically test you bulk chemicals Measure your flow rate and calculate mgd Measure your current feed rates and calculate dosages and ratios Calculate desired monochloramine dose Determine additional chlorine dose Determine new chorine dosage feed rate Confirm ratio Cl 2 :NH 3 Determine ammonia dose Determine new ammonia dosage feed rate And start the process over again 89

89 Making Adjustments Condition Remedy Note Free Cl 2 > NH 2 Cl Target Reduce Cl 2 dosage Prior to NH 3 NH 2 Cl too High Reduce NH 3 dose, then Measure, adjust one at a time Reduce Cl 2 dosage NH 3 too High Increase Cl 2 dosage OR Adjust only one parameter Reduce NH 3 dose No Residual NH 3 Increase NH 3 dosage OR Adjust only one parameter Reduce Cl 2 dose Total Cl 2 > NH 2 Cl Reduce Cl 2 dosage OR You are in Section II Increase NH 3 dose 90

90 SPECIAL SITUATIONS 91

91 Special Situations Source Water with Natural Ammonia Use the salicylate method or ISE for Ammonia measurement Free ammonia method, Nessler method not recommended Make sure measurements are made in new GW Chlorination systems Preoxidation Cl 2 sufficient to move to Section III 92

92 Special Situations Need to increase Chloramine Residual Know where you are on the curve Add in specified ratios and stay in Section I Reduce Free Ammonia Levels to avoid nitrification Measure free ammonia and add chlorine only, Section I 93

93 Blended Consecutive Systems or Boosters Mix usually pushes Into Section II Strategy 1 Push through Breakpoint to Section III Cl 2 -F with FreeChlorF Reagent Risk of additional DBP Strategy 2 Measure Cl 2 -F with DPD Convert Chlorinated Source to Chloraminated Add ammonia at proper ratio Blend produced waters Strategy 3 Measure NH2Cl and Free ammonia on sources Add chlorine or ammonia or both with PLC logic Feed back control on water leaving station 94

94 DETERMINING AMMONIUM FEED RATE 95

95 Liquid Ammonium Sulfate Example Liquid Ammonium Sulfate (LAS) What is LAS? 38-40% aqueous solution of (NH 4 ) 2 SO 4 Specific Gravity of to or to #/gallon Roughly 10% as Ammonia NH 3 96

96 Liquid Ammonium Sulfate Example So, a 40% LAS solution weighs ~10 #/gallon and each gallon contains 0.84 # N 97

97 Liquid Ammonium Sulfate Example Coarse Control: Expected Chlorine Feed pump rate at 4 #/hr. How much LAS required for a 4.5:1 Ratio (Chlorine : Nitrogen)? 98

98 Liquid Ammonium Sulfate Example Fine Control: Frequent laboratory measurements On-line analysis Measure, feedback, adjust and measure again What change do I need to do make with these readings? 99

99 What Adjustments Are Needed? 100

100 101 Nitrification Ammonia is converted to Nitrate Ammonia to Nitrite by nitrosomonas Nitrite to Nitrate by nitrobacters Increasing risk warmer temperatures C Longer detention times in distribution Adverse acute health impacts (blockage of 0 2 transport)

101 Circular Problem of Nitrification 102

102 103 Nitrification What to watch for Loss of residual disinfection Increase in HPC (using R2A agar) Lowering of ph Decrease in alkalinity Reduced dissolved oxygen Increase in Nitrite Increase in Nitrate What to do Reduce favorable conditions for organisms Increase flushing Periodic free chlorine burn *Remember Notifications

103 104 Take Away Messages Monochloramine can help reduce DBPs Proper measurement is the key to effective control Know through analysis where you are on the Chlorine Breakthrough Curve Target a Cl 2 to N ratio of 3-5:1 to avoid dichloramine formation Minimize unreacted ammonia free ammonia >than but close to 0 When making process changes, change only one variable at a time

104 105 Summary Goal : Provide a more in-depth understanding of the Disinfection Process using Chloramines Balance is Key: Experience proves that the chloramination process can be extremely effective, but only if the concentration of ammonia and chlorine in the system remains in proper balance. Understand the Reactions: For optimal control of the chloramination process, understanding of the reactions taking place and measurement of the proper parameters can simplify operation and ensure proper disinfection

105 106 Questions? Chris Griffin Hach Company

106 107