Chloramination, The Science Methods of Application & Other Stuff Ron Hidu, PE
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Ammonia Source
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Naturally Occurring Anhydrous Ammonia Aqueous Ammonia Ammonium Sulfate
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Aqueous Ammonia – NH4OH • H2O ▀ ▀ ▀ ▀ ▀ ▀ ▀
Ammonium Hydroxide 19, 25, 40 %...typically 19% SG = 0.926 7.8 lbs/gal Boiling point = 86º F Odor threshold = 5 ppm Fed directly 19% concentration provides 15.6% N by wt.
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Ammonium Sulfate - (NH4)2SO4 ▀ ▀ ▀ ▀ ▀ ▀ ▀ ▀
50 lb bags Granular; little issue with dusting Solubility up to about 40% solution @ 77º F Easiest to mix as 12% solution (i.e. 1 lb chemical to 1 gal water) Molecular wt. = 132.14 Ammonium Sulfate is 21% N by wt. Also proprietary products NSF 60
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Cost Comparison ▀
Ammonium Sulfate ▀ ▀ ▀
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~ 65¢ / lb (in pallet quantities, 2000 lbs, 40 bags) 21% N by wt. Equates to $3.09 / lb N
19% Aqueous ▀ ▀ ▀ ▀
~ 16¢ / lb (6000 gal delivery; 7300 lbs N) ~ 40¢ / lb (400 gal delivery; 500 lbs N) 15.6% N by wt - 7.8 lbs / gal Equates to $2.56 / lb N (400 gal delivery)
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Cost Example ▀ ▀ ▀ ▀ ▀
1 MGD 1.5 mg/l Cl2 Usage would be 3.0 lbs/day N (see table) Ammonium Sulfate = $9.27 / day Aqueous Ammonia = $7.68 / day
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Plant Flow Rate 700 4.2 50# Bag (99.5%) For 12% Solution For 12% Solution
Ratio 4.2:1 CL2-N 49.75 414.58 49.71
Total Chlorine Residual mg/l as Cl2 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 3 lbs N 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5
lb/hr as N 0.0167 0.0250 0.0334 0.0417 0.0500 0.0584 0.0667 0.0751 0.0834 0.0917 0.1001 0.1084 0.1168 0.1251 0.1334 0.1418 0.1501 0.1585 0.1668 0.1751 0.1835 0.1918 0.2002 0.2085
/day
lbs. lbs. Water gal. Water
GPM
Mix 1 Bag Ammonium Sulfate to 50 gallons of water
lb/hr as (NH4)2 (SO4) 0.0786 0.1180 0.1573 0.1966 0.2359 0.2752 0.3145 0.3539 0.3932 0.4325 0.4718 0.5111 0.5504 0.5898 0.6291 0.6684 0.7077 0.7470 0.7863 0.8257 0.8650 0.9043 0.9436 0.9829
hrs/bag 632.7 421.8 316.3 253.1 210.9 180.8 158.2 140.6 126.5 115.0 105.4 97.3 90.4 84.4 79.1 74.4 70.3 66.6 63.3 60.3 57.5 55.0 52.7 50.6
Feed Rate gal/hr 0.08 0.12 0.16 0.20 0.24 0.28 0.31 0.35 0.39 0.43 0.47 0.51 0.55 0.59 0.63 0.67 0.71 0.75 0.79 0.83 0.86 0.90 0.94 0.98
Feed Rate ml/min 5.0 7.4 9.9 12.4 14.9 17.3 19.8 22.3 24.8 27.3 29.7 32.2 34.7 37.2 39.7 42.1 44.6 47.1 49.6 52.0 54.5 57.0 59.5 62.0
3 ½ days / bag in 50 gal of water COMMITMENT & INTEGRITY DRIVE RESULTS
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Materials of Construction ▀ ▀ ▀ ▀ ▀
Poly tanks SCH 80 PVC (not for Anhydrous…SS) PE, PP, PTFE tubing No copper, brass, etc. If using peristaltic pumps with Aqueous, careful with hose (use silicone, Tygon, Bioprene©… not nitrile, rubber)
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Chemical Addition ▀
NH3 then NaOCl NaOCl then NH3
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Reaction is rapid
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Doesn’t matter…Typically OCl- first since you usually have to meet a CT requirement.
Monochloramine kinetics optimized at pH 8.5 and takes < 1 min. Drive pH higher due to Pb solubility (9.8)
Often difficult to find a chem feed pump that will operate well at the low dosages used (Prominent Mikro line??) Like to have a static mixer or orifice plate COMMITMENT & INTEGRITY DRIVE RESULTS
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Monitoring ▀
Ahead of dosing point: ▀ ▀
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At entrance to system: ▀ ▀
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Free Chlorine pH Total chlorine pH
Within system: ▀ ▀ ▀
Total chlorine pH (keep high, no Di, no need to monitor for Mono using APA6000) Trace free chlorine but no free NH3
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Chloramine Species Species
Formula
Odor Threshold (mg/l)
Taste Threshold (mg/l)
Monochloramine
NH2Cl
0.48
0.65
Dichloramine
NHCl2
0.13
0.15
Trichloramine
NCl3
0.02
0.02
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Chemistry Cl2 + H20 NaOCl + H20
HOCl + HCl HOCl + NaOH
(hydrolysis)
Free chlorine species
hypochlorous acid
Unbuffered water… Cl2 reduces pH; NaOCl raises pH
HOCl
H+ + OCl- (dissociation)
Equilibrium based on pH & temp
hypochlorite ion
Then add N either naturally or by NH3 source:
HOCl + NH3 HOCl + NH2Cl HOCl + NHCl2
NH2Cl + H2O NHCl2 + H20 NCl3 + H20
Too much chlorine (too high Cl2:N ratio) drives toward Tri., too little leaves excess free nitrogen…range 3:1 to 5:1 (4.2 stoichiometric), but differs for individual water chemistry COMMITMENT & INTEGRITY DRIVE RESULTS
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40
9.8 pH
5
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Case Studies ▀
Bath – 2003 ▀ ▀
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~3 MGD, Microfloc Plant upgrade included setup to go to chloramines using Aqueous ammonia 2) 750 gal bulk tanks PVC & CPVC piping Deliveries twice/yr Considered Ammonium sulfate (4 ½ bags / week), but plant had no provisions for dry chemical delivery and handling. Staff used to handling bulk hypochlorite and chlorine dioxide
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Case Studies (continued) ▀
Bangor – 2003 – Mutual Aid Study ▀ ▀ ▀ ▀
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Bangor, Brewer, Hampden, Orono-Veazie, Old Town Blending chloraminated and non-chloraminated waters pH variations Segregating waters
Bangor – 2007 – Anhydrous to Aqueous Conversion ▀ ▀
Reuse of equipment Cl2 to NaOCl conversion
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Case Studies (continued) ▀
Millinocket – 2001 ▀
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0.5 MGD IDI Advent, prechlorinate for filter runs, high organics, high DBPs 600 gpm Ammonium sulfate
Bar Harbor – 2009 ▀ ▀ ▀
3 MGD unfiltered, gravity flow Chlorine gas Ammonium sulfate at remote location (transmission line contactor) COMMITMENT & INTEGRITY DRIVE RESULTS
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Case Studies (continued) ▀
Vinalhaven I – 2005 ▀ ▀ ▀ ▀
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60,000 gpd, unfiltered (100 gpm) Ammonium sulfate Remote addition point, long transmission line contactor In-system mixing
Vinalhaven II– 2010 ▀ 60,000 gpd, bags, UV, OCl- (60 gpm) ▀ Ammonium sulfate ▀ Short CT contact time ▀ NH3 addition in proximity to pump station. COMMITMENT & INTEGRITY DRIVE RESULTS
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Case Studies (continued) ▀
Great Salt Bay – 2009 ▀ ▀ ▀ ▀
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160,000 gpd, unfiltered (300 gpm) UV, OCL-,Chloramine Ammonium sulfate NH3 addition in separate building after short transmission line contact for CT pH adjustment to 9.8 using soda ash
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Case Studies (continued) ▀
Hampden – 2001 & 2010 ▀ ▀
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340,000 – 440,000 gpd, consecutive system Rechlorination, pH adjustment
LDA – 2010 ▀ ▀ ▀ ▀
120,000 to 2 MGD, conventional filtration (Leopold) UV, OCL-, chloramines Long transmission line Ammonium sulfate
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