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 Residual (mg/l as Cl 2 /mgnh 4 -N) Chlorine Ammonia Reactions 8 7 6 5 4 3 2 NHCl 2 HOCl 1 0 NH 2 Cl NCl 3 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 2. S 0 S 0 (ppt) 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 Bleach Increased Travel Time Sewer Bad Sulfurous
Threshold Odor Number Careful Control of Chlorine Residual is Critical 6 5 4 3 2 Maintaining Residual > 0.3 and <0.7 mg/l Minimized Odors in these waters Odor Detected 0 = no odor 1 = 100% 2 = 50% 3 = 24% 4 = 12% 5 = 2% 1 0 0 0.2 0.4 0.6 0.8 1 Chlorine Residual (mg/l)
Beyond Careful Chlorine Control Treatment Catalytic Granular Activated Carbon Membrane Degasser Chloramines NonTreatment Selective Aquifer Depths Gas Out Gas In Water In Water Out
Case Studies Well 16 Nampa, ID Well 21 Meridian, 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
Sulfide Concentration Threshold Odor Number Parameters Tested Odor Detected 0 = no odor 1 = 100% 2 = 50% 3 = 24% 4 = 12% 5 = 2% Chlorinous Sulfurous Metallic (polysulfides)
Threshold Odor Number 1. Catalytic GAC 5.00 Strong Sulfur Odor 4.00 3.00 2.00 1.00 0.00 Raw 0 GAC Odor Detected 0 = no odor 1 = 100% 2 = 50% 3 = 24% 4 = 12% 5 = 2%
Two Tests of Membrane Degasser 2. Membrane Degasser Before Filters 3. Membrane Degasser After Filters
Chlorinate d Raw Membrane ph 7.0 Membrane ph 7.5 Threshold Odor Number Intensity of Odor 1 and 3 day average 2. Membrane Degasser Before Filters Nature of Taste and Odor 6 5 4 3 2 1 0 Threshold Odor Number Odor Scale 0 = no odor 1 = 100% 2= 50% 3 = 24% 4 = 12% 5 = 2% 1.4 1.2 1.0 0.8 0.6 0.4 0.2 Sulfurous Chlorinous Metallic Odor Scale 0 = None 1 = noticeable 2 = moderately strong 3= objectionable 0.0 Treated with Membrane Degasser
Raw Filtered Membrane Threshold Odor Number Day 1 Intensity of Odor 1 and 3 day average 2. Membrane Degasser After Filters Post Filter Comparison Threshold Odor Number 6 5 4 3 2 1 0 TON on Chlorination TON Day 3 Odor Detected 0 = no odor 1 = 100% 2 = 50% 3 = 24% 4 = 12% 5 = 2% 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 Nature PostFilter of Comparison Taste and Odor Sulfurous Chlorinous Metallic Odor Scale 0 = None 1 = noticeable 2 = moderately strong 3= objectionable 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 On collection water sample checked for ammonia Chlorine Dosed at 10x the ammonia concentration and Odors 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 Dose chlorine at just enough to provide 0.5 mg/l residual (~10:1 Cl 2 to NH 3 Ratio) Use Permanganate for Iron & Manganese and dose chlorine at 4:1 Cl 2 to NH 3 Ratio to maintain a residual 24
Taste and Odor Testing Sample checked for tastes and odors Scale 0 no odor 1 noticeable 2-moderately strong 3-objectionable 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
Intensity of Chlorine Taste and Odor (0 to 3 scale) Chlorine Tastes and Odors 1.00 3.0 mg/l chloramine target 0.80 0.75 0.4 mg/l free chlorine target 0.60 0.50 0.8 mg/l free chlorine target 0.40 0.42 0.25 0.29 0.29 0.29 0.20 0.00 0 0.00 0 1 3 Days After Chlorination Remember a ranking of 1 = noticeable
Intensity of Metallic Taste and Odor (0 to 3 scale) Metallic Taste and Odor Results 1.0 0.9 3.0 mg/l chloramine target 0.8 0.7 0.6 0.4 mg/l free chlorinetarget 0.8 mg/l free chlorine target 0.5 0.4 0.35 0.38 0.3 0.2 0.25 0.27 0.15 0.18 0.23 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 Chemical Treatment Existing Well Water Projections with Bottom of Well Packed off Chlorine only 7.5 mg/l Cl 2 4 to 5 mg/l Cl 2 Permanganate for Fe & Mn Chlorine for residual 0.7 mg/l KMnO 4 2.7 mg/l Cl 2 0.6 to 0.7 mg/l KMnO 4 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 Cl 2 + NH 4 + NH 2 Cl (monochloramine) NHCl 2 (dichloramine) NCl 3 (trichloramine)
Chlorine Ammonia Reactions Chlorine reacts with ammonia to form combined chlorine Cl 2 + NH 4 + NH 2 Cl (monochloramine) 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 Cl 2 2. Dissolved Manganese is attracted to surface of sorbent Mn +2 Cl 2
Iron and Manganese using a Sorbent 3. Dissolved Manganese is sorbs to surface of sorbent Media Cl 2 4. Manganese oxidized - surface of sorbent acts as catalyst Mn +2 Cl 2
Meridian Chlorine Dose Response 2.5 Residual Concentration (mg Cl 2 /mg NH 4 ) 2 1.5 1 0.5 0 Chloramines Free Chlorine 0 2 4 6 8 10 12 14 16 Chlorine Dose (mg Cl 2 /mg NH 4 ) 0.73 mg/l NH 4
Intensity of Taste and Odor (0 to 3 Scale) Impact of Blending Chlorine and Chloramines 0.80 0.60 0.40 Chlorine Metallic/Bitter 0.20 0.00 0% 20% 40% 60% 80% 100% 120% Blend Ratio - Percent of Chlorinated Water Added to Chloraminated Water
Chlorine Residual (mg Cl 2 /mgnh 4 -N) Chlorine Ammonia Reactions 8 7 Free Chlorine Combined Chlorine 6 5 4 3 2 NHCl 2 HOCl 1 0 NH 2 Cl NCl 3 0 2 4 6 8 10 12 14 16 Chlorine Dose (mgcl 2 /mgnh 4 -N)