Treatment of Groundwater for Iron and Manganese While Avoiding Taste and Odor Mark Carlson
Introduction • Statement of Problem • Background Chemistry • Two case studies
Statement of Problem • Removal of iron or manganese requires an oxidant • Chlorine is cheap, reliable and also disinfects • However, side reactions do occur
Side Reactions Chlorine + Ammonia =Chloramines Chlorine + Hydrogen Sulfide = Sulfur and Polysulfides
Chlorine Ammonia Reactions 8 Chlorine Residual (mg/L as 7 6 Cl 2 /mgNH 4 -N) NHCl 2 5 HOCl 4 3 2 NH 2 Cl 1 NCl 3 0 0 2 4 6 8 10 12 14 16 Chlorine Dose (mgCl 2 /mgNH 4 -N )
Chlorine – Sulfide Reactions 1. H 2 S + Cl 2 2HCl + S 0 S 0 (ppt) 2. S 0 - HS n Note: These are reversible!
Increasing Oxidation
Polysulfide’s Presents a Taste and Odor Concern • Some have characteristic hydrogen sulfide odor • Can have a metallic taste or bitter mouth feel
Travel Time Complications Well 16 Increased Travel Time “Bleach” “Bad” “Sewer” “Sulfurous”
Careful Control of Chlorine Residual is Critical 6 Odor Detected 5 0 = no odor Threshold Odor Number Maintaining Residual > 0.3 and 1 = 100% 4 <0.7 mg/L Minimized Odors in these waters 2 = 50% 3 3 = 24% 4 = 12% 2 5 = 2% 1 0 0 0.2 0.4 0.6 0.8 1 Chlorine Residual (mg/L)
Beyond Careful Chlorine Control Water In • Treatment Gas Out – Catalytic Granular Activated Carbon – Membrane Degasser – Chloramines • NonTreatment – Selective Aquifer Depths Gas In Water Out
Case Studies Well 21 Well 16 Meridian, ID Nampa, ID
Nampa Water Quality Parameter Raw Well Water Filtered pH 9.2 9.0 to 9.2 H 2 S (mg/L) 0.16 Below Detection Mn (mg/L) 0.12 0.06 Fe (mg/L) 0.07 Below Detection NH 4 (mg/L) 0.81 0.11 Threshold Odor Number 5 4
Granular Activated Carbon
Parameters Tested • Sulfide Concentration • Threshold Odor Number Odor Detected 0 = no odor 1 = 100% Chlorinous 2 = 50% Sulfurous 3 = 24% 4 = 12% Metallic 5 = 2% (polysulfides)
1. Catalytic GAC 5.00 Strong Sulfur Odor Threshold Odor Number Odor 4.00 Detected 0 = no odor 3.00 1 = 100% 2 = 50% 2.00 3 = 24% 4 = 12% 1.00 0 5 = 2% 0.00 Raw GAC
Two Tests of Membrane Degasser 2. Membrane Degasser Before Filters 3. Membrane Degasser After Filters
2. Membrane Degasser Before Filters Nature of Taste and Odor Odor Scale 1.4 Sulfurous 0 = None Threshold Odor Number 1 = noticeable 1.2 Chlorinous Intensity of Odor 1 and 3 day average 2 = moderately Odor Scale 6 Metallic Threshold Odor Number 1.0 strong 0 = no odor 5 3= objectionable 1 = 100% 0.8 4 2= 50% 3 0.6 3 = 24% 2 4 = 12% 1 0.4 5 = 2% 0 0.2 0.0 Membrane Membrane Chlorinate d Raw pH 7.0 pH 7.5 Treated with Membrane Degasser
2. Membrane Degasser After Filters Post Filter Comparison Threshold Odor Number 6 Nature of Taste and Odor Threshold Odor Number PostFilter Comparison TON on Chlorination 5 0.90 TON Day 3 Odor Scale Sulfurous 0.80 0 = None Day 1 4 Odor 1 = noticeable Chlorinous Detected 0.70 Intensity of Odor 2 = moderately strong 0 = no odor 3 1 and 3 day average 0.60 3= objectionable Metallic 1 = 100% 2 = 50% 0.50 2 3 = 24% 0.40 4 = 12% 1 0.30 5 = 2% 0 0.20 Raw Filtered Membrane 0.10 0.00 Filtered Membrane
Well 16, Meridian - Approach • Test Different Aquifer Depths • Adjust Treatment to Minimize Tastes and Odors
Meridian Water Quality and Goals Parameter Raw Well Water Goal H 2 S (mg/L) Below Detection Below Detection Mn (mg/L) 0.30 <0.05 Fe (mg/L) 0.13 <0.3 NH 4 (mg/L) 0.73 No goal pH 7.6 No goal Minimize tastes and odors
At each depth Below Ground Surface Water Chlorinated and Tested for Taste and Odors • On collection water sample checked for ammonia • Chlorine Dosed at 10x the ammonia concentration Scale 0 – no odor 1 – noticeable 2-moderately strong 3-objectionable 22
Metallic Taste Present at All Depths 23
Pilot Test Approach Chlorine vs. Permanganate Use Permanganate for Iron & Dose chlorine at just enough to Manganese and dose chlorine at provide 0.5 mg/L residual (~10:1 4:1 Cl 2 to NH 3 Ratio to maintain Cl 2 to NH 3 Ratio) a residual 24
Taste and Odor Testing Scale 0 – no odor 1 – noticeable 2-moderately strong 3-objectionable Sample checked for tastes and odors 25
Results • Chlorine Filters: a dose of 8.4 mg/L Cl 2 needed • Permanganate Filter: a dose of 0.7 mg/L KMnO 4 for oxidation and Cl 2 dose of 2.9 mg/L for residual maintenance
Chlorine Tastes and Odors 1.00 Intensity of Chlorine Taste and Odor 3.0 mg/L chloramine target 0.80 0.4 mg/L free chlorine target 0.75 0.8 mg/L free chlorine target 0.60 (0 to 3 scale) 0.50 0.42 0.40 0.29 0.29 0.29 0.25 0.20 0 0.00 0.00 0 1 3 Days After Chlorination Remember a ranking of 1 = noticeable
Metallic Taste and Odor Results 1.0 Intensity of Metallic Taste and 0.9 3.0 mg/L chloramine target 0.8 Odor (0 to 3 scale) 0.4 mg/L free chlorinetarget 0.7 0.8 mg/L free chlorine target 0.6 0.5 0.38 0.4 0.35 0.3 0.27 0.25 0.23 0.18 0.2 0.15 0.1 0 0 0.0 0 1 3 Days after Chlorination Remember a ranking of 1 = noticeable
Conclusions • Chlorine Dose and Residual Control Good First Step • Catalytic GAC is Gold Standard for Hydrogen Sulfide Removal • Membrane Degasser Has Promise – pH dependant • Chloramine Residuals Minimized Metallic Taste and Reduced Dose 29
END Comments and Questions
Extra Stuff
Chemical Doses Projections with Bottom of Chemical Treatment Existing Well Water Well Packed off Chlorine only 7.5 mg/L Cl 2 4 to 5 mg/L Cl 2 Permanganate for Fe & Mn 0.7 mg/L KMnO 4 0.6 to 0.7 mg/L KMnO 4 Chlorine for residual 2.7 mg/L Cl 2 1.8 mg/L Cl 2 32
Chlorination pH impacts reaction Extent of Reaction • Extent of oxidation peaks between pH 6.5 and pH 7.2 • Sharply slows outside this range • Rate of reaction slows as pH increases • pH above 7.2 – partial oxidation and slower rate Rate of Reaction From: Goodson, James, The Oxidation of Sulfides by Chlorine in Dilute Aqueous Solutions, PhD Dissertation, University of Florida, 1950
Chlorine Sulfide Reactions 1. Chlorine reacts with hydrogen sulfide to form sulfur H 2 S + Cl 2 2HCl + S 0 2. Chlorine reacts with ammonia to form combined chlorine + NH 2 Cl (monochloramine) Cl 2 + NH 4 NHCl 2 (dichloramine) NCl 3 (trichloramine)
Chlorine Ammonia Reactions Chlorine reacts with ammonia to form combined chlorine + NH 2 Cl (monochloramine) Cl 2 + NH 4 NHCl 2 (dichloramine) NCl 3 (trichloramine)
Polysulfide Chemistry is Complicated • An intermediate oxidation product • Some peak between pH 7 and 8 • Others increase with pH • Chemical analysis difficult to analyze • Can be volatile
Iron and Manganese using a Sorbent Media 1. Sorbent Surface “Charged” with oxidant such as chlorine 2. Dissolved Manganese is Cl 2 attracted to surface of sorbent Cl 2 Mn +2
Iron and Manganese using a Sorbent Media 3. Dissolved Manganese is sorbs to surface of sorbent Cl 2 4. Manganese oxidized - surface of sorbent acts as catalyst Cl 2 Mn +2
Meridian Chlorine Dose Response 2.5 Residual Concentration (mg Cl 2 /mg NH 4 ) Chloramines Free Chlorine 2 1.5 1 0.5 0 0 2 4 6 8 10 12 14 16 Chlorine Dose (mg Cl 2 /mg NH 4 ) 0.73 mg/L NH 4
Impact of Blending Chlorine and Chloramines 0.80 Intensity of Taste and Odor (0 to 3 0.60 Chlorine 0.40 Scale) Metallic/Bitter 0.20 0.00 0% 20% 40% 60% 80% 100% 120% Blend Ratio - Percent of Chlorinated Water Added to Chloraminated Water
Chlorine Ammonia Reactions 8 Free Chlorine Chlorine Residual (mg Cl 2 /mgNH 4 -N) 7 Combined Chlorine 6 NHCl 2 5 HOCl 4 3 2 1 NH 2 Cl NCl 3 0 0 2 4 6 8 10 12 14 16 Chlorine Dose (mgCl 2 /mgNH 4 -N)
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