CHLORAMINATION AND CHLORAMINE ANALYSIS SW AWWA 2014

Transcription

1 CHLORAMINATION AND CHLORAMINE ANALYSIS SW AWWA 2014

2 COMBINED CHLORINE - CHLORAMINATION Chlorine (HOCl and OCl - ) reacts with ammonia to form chloramines, commonly referred to as combined chlorine The predominate species are monochloramine and dichloramine. A small fraction is trichloramine or nitrogen trichloride 2

3 Total residual chlorine, primarily monochloramine Free residual chlorine Total Chlorine Residual Cl 2 :N < 5:1, typical BREAKPOINT CURVE Cl 2 :N > 5:1, typical Breakpoint Cl 2 :N > 9:1, typical Chlorine Added 3

4 BREAKPOINT CURVE CONSIDERATIONS Shape of the curve is dependent upon amount of ammonia and other chlorine demand substances in the water temperature ph contact time Most effective disinfection, least taste and odor occurs with free residual chlorine Free chlorine may lead to formation of DBP 4

5 CHLORAMINATION Chloramination: Purposeful use of chlorine and ammonia to form monochloramine. Minimizes formation of chlorinated organics Ammonia to chlorine Ratio is controlled to favor formation of monochloramine, typically 5:1 Cl 2 :N Total residual chlorine test: All free and combined chlorine species 5

6 CHLORAMINES Less effective disinfection than free chlorine. HOCl is 25X more effective biocide Chloramines require longer contact time and/or greater concentration than free chlorine. Possible taste and odor (dichloramine) More stable than free chlorine (long distribution systems) Generally do not produce DBP (NH 2 Cl may form DBP NDMA being studied) 6

7 CHLORAMINE FORMATION Monochloramine - NH 2 Cl NH 3 + HOCl NH 2 Cl + H 2 O Dichloramine - NHCl 2 NH2Cl + HOCl NHCl2 + H2O Tricholoramine (Nitrogen Trichloride) - NCl 3 NHCl 2 + HOCl NCl 3 + H 2 O Chloramines are not as effective disinfectants as free chlorine 7

8 DEFINITION OF UNREACTED AMMONIA Ammonia in solution as NH 3 Free ammonia gas dissolved in water or; NH 4 - The ammonium ion 8

9 What are chloramines? Where are chloramines used? Chlorine and Ammonia Chloramination Objectives The Dance of Chlorine and Ammonia Building the Chloramination Curve Preventing Nitrification Cl H Cl H H N N H H Cl

10 WHAT ARE CHLORAMINES? The word chloramines describes the group of three compounds formed by mixing chlorine and ammonia together Monochloramine ideal form for drinking water treatment Dichloramine Trichloramine N Cl H H

11 WHERE ARE CHLORAMINES USED? Chloramines are used in drinking water as an alternative to the more aggressive disinfection of chlorine Chlorine reacts quickly with organic materials present in source water, which can cause the formation of undesirable disinfection by products (DBPs) that are regulated by the EPA Monochloramine i. Is less reactive than chlorine ii. Is a weaker disinfectant than chlorine iii. Requires a longer contact time than chlorine iv. Does not form DBPs v. Is more stable and maintains a longer residual vi. Formation is a complex process

12 CHLORINE AND AMMONIA Chlorine When mixed with water, chlorine forms hypochlorous acid and hypochlorite CHLORINE (Cl 2 ) + WATER (H 2 O) HYPOCHLOROUS ACID (HOCl) + HYPOCHLORITE (OCl-) Cl Cl

13 CHLORINE AND AMMONIA Ammonia When hypochlorous acid is mixed with ammonia, chloramines are formed H N H H - MONOCHLORAMINE (NH 2 Cl) HYPOCHLOROUS ACID + AMMONIA - DICHLORAMINE (NHCl 2 ) (HOCl) (NH 3 ) - TRICHLORAMINE (NCl 3 )

14 CHLORAMINATION OBJECTIVES Blend Chlorine and Ammonia together in a 1:1 molar ratio The goal is to exclusively form monochloramine Inhibit and/or eliminate the formation of dichloramine and trichloramine Dichloramine and trichloramine are unstable, and create taste and odor problems Minimize the introduction of significant amounts of free ammonia in the distribution system Excess free ammonia will promote the growth of bacteria and biofilms, and can lead to nitrification in the distribution system

15 NOM NATURALLY ORGANIC MATTER 15

16 Total CL 1 min Total CL 10 min Total CL 60 min Total CL 360 min Total Chlorine (mg/l) > 6:1 > 14: Chlorine Added (mg/l) USED WITH PERMISSION, GOLDEN STATE WATER 16

17 Free Ammonia (mg/l) Breakpoint chlorination dose of 16.4 mg/l is needed for complete removal of free ammonia min 10 min 60 min 360 min Chlorine Added (mg/l) USED WITH PERMISSION, GOLDEN STATE WATER 17

18 NITRIFICATION IN THE DISTRIBUTION SYSTEM Circular Problem NH 2 Cl + NH 3 /NH 4+ + NO 2- + NO 3 - Disinf f-nh 3 Distribution System ph DO NO 2 - Alk ph DO NO 3 - Alk Sloughing of biofilm causes Turbidity Flow HPC Customer Complaints

19 NITRIFICATION Conversion of ammonia to nitrites and nitrates NH 3 + O 2 NO H + + 2e - Nitrosomonas Nitrosococcus, and Nitrosospira. Conversion of nitrite to nitrate NO 2- + H 2 O NO H + +2e - Nitrobacter Nitrospina, Nitrococcus, and Nitrospira 19

20 INDICATION OF NITRIFICATION Chloramine residual Free Ammonia Temperature Dissolved Oxygen ph and/or alkalinity HPC NO 2 /NO 3 20

21 CONTROL STRATEGIES FOR DISCUSSION ph Free ammonia Water age Chloramine residual Light TOC Tank Mixing 21

22 NITRIFICATION Nitrifying bacteria feed on ammonia producing Nitrites which exert a chlorine demand which decreases the residual which allows microbes to flourish to produce more nitrites which continues the spiral until your residual is gone! aka feeding the beast

23 THE DANCE OF CHLORINE AND AMMONIA Chlorine and Ammonia are not well suited to each other for reaction. HOCl is favored at lower ph NH 3 is favored at higher ph Compromise used is usually around ph One ammonia molecule and one chlorine molecule are required to form monochloramine: Easy in the laboratory, but what about: Ammonia in sourcewater Variable chlorine demand in sourcewater

24 REACTION - FREE CHLORINE: Cl 2 + H 2 O HCl + HOCl HOCl H + + OCl - HOCl + OCl - + DPD Red complex (530 nm) Read as soon as possible after 20 sec mix.

25 Reaction - Total Chlorine: HOCl + OCl - + Chloramines + KI + DPD HOCl + OCl - + I 2 + DPD Red complex Read at 530 nm. Read after 3 to 6 minutes.

26 MONOCHLORAMINE AND FREE AMMONIA Method is designed for one sample. Note that 2 different programs (curves) are used. Presume cells are matched. Plan your timing well, as there are 2 five minute reaction periods. Program 66 for Monochloramine Program 388 for Free Ammonia The chemistry makes monochloramine by chlorinating free ammonia The powder reagent only reacts with monochloramine (M vial) The liquid reagent is chlorine and reacts with any free ammonia, making additional monochloramine (FA vial) By zeroing out the monochloramine, the free ammonia can be determined by difference

27 MONOCHLORAMINE AND FREE AMMONIA How it works: The powder chemistry reacts with monochloramine and forms a proportional green color (the M vial). The liquid reagent contains chlorine which converts any free ammonia to additional monochloramine (the FA vial). The difference between the 2 measurements is equal to the free ammonia, if any. A great tool for any chloraminating system (DW and WW).

28 BREAKPOINT CHLORINATION CURVE I II III Ideal zone for DW disinfection

29 CHLORAMINATION MONITORING & CONTROL Parameters Monochloramine Ammonia Total Chlorine Free Chlorine Data from each of the parameters above can help determine where water is on the breakpoint curve H O Cl

30 CHLORAMINATION MONITORING & CONTROL If the plant does a test for total chlorine, and obtains a result of 3 mg/l Total chlorine = 3.0 mg/l Where on the breakpoint curve are they? What part of the curve makes a significant difference

31 Where is 3 mg/l Total Chlorine? I II III 3 mg/l

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33 CHLORAMINATION MONITORING & CONTROL Laboratory Tests Monochloramine and free ammonia with Monochlor-F reagent Colorimetric method One method sequentially determines monochloramine and free ammonia Can be run on spectrophotometers and some colorimeters Indophenol chemistry Free Chlorine/Total Chlorine DPD colorimetric method Chloramine can produce false positive results Autocat 9000 Autotitrator for chlorine Ammonia ISE (ion selective electrode) Colorimetric ammonia test

34 CHLORAMINATION MONITORING & CONTROL Based on data from other tests, the analyst/operator will be able to tell where they are on the breakpoint curve

35 Zone 1 Monochloramine = Total Cl 2 Free ammonia > 0 Zone II Monochloramine < Total Cl 2 Free Ammonia = 0 Zone III Total Cl 2 > 0 Free Ammonia = 0 Monochloramine = 0

36 CHLORAMINATION MONITORING & CONTROL Total Chlorine Free Chlorine Monochloramine ph Alkalinity Nitrate/Nitrite DO HPC ATP DBP Nitrifying Bacteria Temperature

37 CHLORAMINATION AND CHLORAMINE ANALYSIS HACH TRAINING ACADEMY DRINKING WATER COURSE