While Avoiding Taste and Odor Mark Carlson Introduction Statement - - PowerPoint PPT Presentation

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
• xidant
• 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

1 2 3 4 5 6 7 8 2 4 6 8 10 12 14 16

Chlorine Residual (mg/L as Cl2/mgNH4-N) Chlorine Dose (mgCl2/mgNH4-N) NCl3 HOCl NH2Cl NHCl2

Chlorine –Sulfide Reactions

• 1. H2S + Cl2 2HCl + S0

S0 (ppt) HSn

• 2. S0

Note: These are reversible!

Increasing Oxidation

Polysulfide’s Presents a Taste and Odor Concern

• Some have characteristic hydrogen sulfide
• dor
• Can have a metallic taste or bitter mouth feel

Travel Time Complications

Well 16

Increased Travel Time

“Bleach” “Sewer” “Sulfurous” “Bad”

Careful Control of Chlorine Residual is Critical

1 2 3 4 5 6 0.2 0.4 0.6 0.8 1

Threshold Odor Number Chlorine Residual (mg/L)

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%

Beyond Careful Chlorine Control

• Treatment

– Catalytic Granular Activated Carbon – Membrane Degasser – Chloramines

• NonTreatment

– Selective Aquifer Depths

Gas In Gas Out Water Out Water In

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 H2S (mg/L) 0.16 Below Detection Mn (mg/L) 0.12 0.06 Fe (mg/L) 0.07 Below Detection NH4 (mg/L) 0.81 0.11 Threshold Odor Number 5 4

Granular Activated Carbon

Parameters Tested

• Sulfide

Concentration

• Threshold Odor

Number

 Chlorinous  Sulfurous  Metallic

(polysulfides)

Odor Detected 0 = no odor 1 = 100% 2 = 50% 3 = 24% 4 = 12% 5 = 2%

• 1. Catalytic GAC

0.00 1.00 2.00 3.00 4.00 5.00

Raw GAC

Threshold Odor Number Odor Detected 0 = no odor 1 = 100% 2 = 50% 3 = 24% 4 = 12% 5 = 2%

Strong Sulfur Odor

Two Tests of Membrane Degasser

• 3. Membrane Degasser After

Filters

• 2. Membrane Degasser Before

Filters

• 2. Membrane Degasser Before Filters

Nature of Taste and Odor Threshold Odor Number

1 2 3 4 5 6 Threshold Odor Number Treated with Membrane Degasser Odor Scale 0 = no odor 1 = 100% 2= 50% 3 = 24% 4 = 12% 5 = 2%

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Chlorinate d Raw Membrane pH 7.0 Membrane pH 7.5

Intensity of Odor

1 and 3 day average Sulfurous Chlorinous Metallic Odor Scale 0 = None 1 = noticeable 2 = moderately strong 3= objectionable

• 2. Membrane Degasser After Filters

1 2 3 4 5 6 Raw Filtered Membrane Threshold Odor Number

Day 1

Post Filter Comparison

TON on Chlorination TON Day 3 Odor Detected 0 = no odor 1 = 100% 2 = 50% 3 = 24% 4 = 12% 5 = 2%

Threshold Odor Number

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 Filtered Membrane Intensity of Odor

1 and 3 day average

PostFilter Comparison

Sulfurous Chlorinous Metallic Odor Scale 0 = None 1 = noticeable 2 = moderately strong 3= objectionable

Nature of Taste and Odor

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 H2S (mg/L) Below Detection Below Detection Mn (mg/L) 0.30 <0.05 Fe (mg/L) 0.13 <0.3 NH4 (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

22

• 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

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 Cl2 to NH3 Ratio) Use Permanganate for Iron & Manganese and dose chlorine at 4:1 Cl2 to NH3 Ratio to maintain a residual

24

Taste and Odor Testing

Sample checked for tastes and odors

25

Scale

 0 – no odor  1 – noticeable  2-moderately strong  3-objectionable

Results

• Chlorine Filters: a dose of 8.4 mg/L Cl2

needed

• Permanganate Filter: a dose of 0.7 mg/L

KMnO4 for oxidation and Cl2 dose of 2.9 mg/L for residual maintenance

Chlorine Tastes and Odors

0.75 0.50 0.29 0.25 0.29 0.00 0.29 0.42

0.00 0.20 0.40 0.60 0.80 1.00 1 3

Intensity of Chlorine Taste and Odor (0 to 3 scale)

Days After Chlorination

3.0 mg/L chloramine target 0.4 mg/L free chlorine target 0.8 mg/L free chlorine target

Remember a ranking of 1 = noticeable

Metallic Taste and Odor Results

0.35 0.15 0.38 0.18 0.25 0.27 0.23

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1 3

Intensity of Metallic Taste and Odor (0 to 3 scale) Days after Chlorination

3.0 mg/L chloramine target 0.4 mg/L free chlorinetarget 0.8 mg/L free chlorine target

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 Cl2 4 to 5 mg/L Cl2 Permanganate for Fe & Mn Chlorine for residual 0.7 mg/L KMnO4 2.7 mg/L Cl2 0.6 to 0.7 mg/L KMnO4 1.8 mg/L Cl2

32

Chlorination pH impacts reaction

From: Goodson, James, The Oxidation of Sulfides by Chlorine in Dilute Aqueous Solutions, PhD Dissertation, University of Florida, 1950 Extent of Reaction Rate 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

Chlorine Sulfide Reactions

H2S + Cl2  2HCl + S0

• 1. Chlorine reacts with hydrogen sulfide to form sulfur
• 2. Chlorine reacts with ammonia to form combined chlorine

Cl2 + NH4

+  NH2Cl (monochloramine)

NHCl2 (dichloramine) NCl3 (trichloramine)  

Chlorine Ammonia Reactions

Chlorine reacts with ammonia to form combined chlorine Cl2 + NH4

+  NH2Cl (monochloramine)

NHCl2 (dichloramine) NCl3 (trichloramine)  

Polysulfide Chemistry is Complicated

• An intermediate
• xidation 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

• 2. Dissolved Manganese is

attracted to surface of sorbent

• 1. Sorbent Surface “Charged”

with oxidant such as chlorine Mn+2

Cl2 Cl2

Iron and Manganese using a Sorbent Media

• 3. Dissolved Manganese is

sorbs to surface of sorbent Mn+2

Cl2 Cl2

• 4. Manganese oxidized - surface
• f sorbent acts as catalyst

Meridian Chlorine Dose Response

0.5 1 1.5 2 2.5 2 4 6 8 10 12 14 16

Residual Concentration (mg Cl2/mg NH4) Chlorine Dose (mg Cl2/mg NH4)

Chloramines Free Chlorine

0.73 mg/L NH4

Impact of Blending Chlorine and Chloramines

0.00 0.20 0.40 0.60 0.80 0% 20% 40% 60% 80% 100% 120%

Intensity of Taste and Odor (0 to 3 Scale) Blend Ratio - Percent of Chlorinated Water Added to Chloraminated Water

Chlorine Metallic/Bitter

Chlorine Ammonia Reactions

1 2 3 4 5 6 7 8 2 4 6 8 10 12 14 16

Chlorine Residual (mg Cl2/mgNH4-N)

Chlorine Dose (mgCl2/mgNH4-N)

Free Chlorine Combined Chlorine

NCl3 HOCl NH2Cl NHCl2