Examples of Iron and Manganese Treatment

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Examples of Iron and Manganese Treatment
CEE 483 February 25, 2009 Russell Porter, P.E.
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Objectives

• Brief Summary of Fe and Mn Treatment Theory
• Two Design Examples
• Existing Fe and Mn Plant Retrofit to Fe/Mn/As
  Treatment
• Existing Ion Exchange Plant Retrofit to Fe/Mn
  Treatment

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Fe and Mn Treatment Theory

• Fe/Mn Treatment by several methods
• Lime softening
• Conventional treatment (coagulation,
  flocculation, settling, filtration)
• Membranes
• Fe and Mn removal by oxidation/filtration

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Fe and Mn Oxidation/Filtration Theory

• First Step - Oxidation
• Natural form in groundwater-soluble
• Fe2
• Mn2
• Oxidized form insoluble
• Fe3 - Fe2O3 or Fe(OH)3 Rust
• Mn4 - MnO2 Black Precipitate

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Fe and Mn Oxidation/Filtration Theory

• Oxidation of Fe - Rapid
• 2Fe2 1/2O2 5H2O ? 2Fe(OH)3 4H
• Oxidation of Mn - Slow
• Mn2 1/2O2 H2O ? MnO2 2H
• Catalyzed Oxidation of Mn - Rapid
• Mn2 1/2O2 H2O ? MnO2 2H
• MnO2 is Mn Oxidation Catalyst.

MnO2
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Fe and Mn Oxidation/Filtration Theory

• Several Oxidants are Used.
• Ozone
• Chlorine
• Cl2 gas
• Hypochlorite
• KMnO4
• Air (Oxygen)

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Fe and Mn Oxidation/Filtration Theory

• Second Step - Filtration
• Theoretically Similar to Other Types of
  Filtration
• Special Media - MnO2 Surface 2 Types

Solid MnO2 Mineral (Mn Ore)
Core Glauconite, Dolomite, Silica
Manufactured MnO2 Surface
Manufactured Media Greensand, Birm
Mined and Processed Media - Pyrolusite
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Fe and Mn Oxidation/Filtration Theory

• Second Step - Filtration
• Theoretically Similar to Other Types of
  Filtration
• Special Media - MnO2 Surface

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CASE STUDY 1 BACKGROUND

• Existing Iron and Manganese Treatment Facility
• Served by Three Wells
• 1,100 gpm
• Startup in 1997
• Planned Expansion to 1,650 gpm

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RAW WATER QUALITY
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EXISTING PLANT
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DESIGN PARAMETERS FOR EXISTING PLANT
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EXISTING PLANT
Ozone Venturi Inductor
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EXISTING PLANT
Ozone Contact Tanks
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EXISTING PLANT
Filter Units
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TASTE AND ODOR ISSUES
Large Number of Customer Complaints Survey Data
- Unsatisfactory Taste and Smell over 50 of the
Time Description of Tastes Dirty Sour Descriptio
n of Odors Earthy Algae-like Chlorinous
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TASTE AND ODOR ISSUES
Staff noted musty backwash odor. Biofilm noted
in ozone contact tanks and filters. Lab analysis
confirmed presence. Iron Bacteria (Gallionella
ferruginea) Sulfur Bacteria (Thiodendron
mucosum) Protozoa Larval Crustaceans Nematodes
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BIOFILM GROWTH
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INITIAL INVESTIGATION

• Initial investigation focused on ozone
  performance.
• Ozone Nameplate Capacity 0.65 mg/L
• Post Injector Ozone Concentration 0.1 mg/L
• Post Ozone Contactor Concentration 0 mg/L
• Hypothesis Insufficient ozone dose in ozone
  contact tanks allowed biogrowth to occur.

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BENCH-SCALE OZONE INVESTIGATION
Bench-scale Testing Goal What dose of ozone
would produce a measurable concentration after
ozone contact tanks (6.5 minutes)? Bench-scale
test used a comparison between ozone behavior in
distilled and raw water to determine ozone
demand. Bench-scale test compared ozone doses of
0.9 mg/L, 1.6 mg/L, and 1.9 mg/L.
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RESULTS OF BENCH SCALE TESTS
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BENCH-SCALE OZONE INVESTIGATION
Bench-scale test indicated that there is an
immediate demand of 0.6-0.7 mg/L. Bench-scale
test indicated that dosing at approximately 1.1
mg/L would provide a trace of ozone after 6.5
minutes.
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FULL-SCALE OZONE INVESTIGATION
Additional Ozone Equipment Rented Ozone Dose
1.1 mg/L (0.65 mg/L Pre-test) Post Injector
Ozone Concentration 0.4 mg/L (0.1 mg/L) Post
Ozone Contactor Concentration 0.1 mg/L (0 mg/L)
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RESULTS OF FULL SCALE TEST
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FULL-SCALE OZONE INVESTIGATION
Increased Ozone Improved Water Quality Fewer
Customer Complaints Not Totally Eliminated No
Biofilm Present Staff Noted Backwash Musty Odor
Diminished
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ADDITIONAL FULL-SCALE INVESTIGATION
Ambient air injected at venturi instead of
ozone.
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ADDITIONAL FULL-SCALE INVESTIGATION
Results of Ambient Air Injection Test Customer
complaints decreased compared with
ozone. Biofilm present but no musty odor. Iron
and manganese removal same as with ozone.
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OTHER PILOT WORK
Plant expansion provided opportunity for review
of other technology. Hypochlorite oxidation and
pyrolusite filtration chosen based on preliminary
cost analysis. City was interested in
discontinuing ozone due to maintenance burden.
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PYROLUSITE TREATMENT SCHEMATIC
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PILOT STUDY PARAMETERS
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PERFORMANCE OF PYROLUSITE
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COMPARISON OF TREATMENT TECHNOLOGIES
Hypochlorite and pyrolusite provided best Mn
removal. Significant Cost Advantage with
Hypochlorite and Pyrolusite.
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ARSENIC REMOVAL
DOH decreased MCL from 50 µg/L to 10 µg/L in
January 2006. Raw Water Arsenic -11-15 µg/L
Requires Treatment As BATs for Small
Systems Adsorption (generally Fe Oxide Media) Ion
Exchange Oxidation/Filtration Oxidation/Filtratio
n is an As BAT.
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ARSENIC REMOVAL OXIDATION/FILTRATION
First Step Oxidation of Arsenite (As III) to
Arsenate (As V) OCl- H3AsO3 ? Cl-
H3AsO4 Second Step Filtration Arsenate must
complex to form a solid to be filtered out.
Arsenate has an affinity for ferric
oxides. Ability to remove As by Ox./Filt. is
dependent upon iron content of water. Iron can
be added as FeCl3.
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ARSENIC REMOVAL
Arsenic removal tested as part of
chlorination/pyrolusite filtration pilot. FeCl3
added to determine optimal dose. Field test kit
(Industrial Test Systems) and commercial lab
samples were used to measure As.
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ARSENIC REMOVAL PILOT WORK
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TREATMENT PLANT DESIGN CRITERIA
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New Filters
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New Filters
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New Onsite Hypochlorite System
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TREATMENT PLANT PERFORMANCE
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TREATMENT PLANT PERFORMANCE
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ARSENIC REMOVAL

• Initial start-up testing indicated that 2-3 mg/L
  as Fe would remove As below MCL to the 6-8 µg/L
  range.
• First compliance sample - lt2 µg/L
• Future optimization testing will investigate
  improved As during filter runs.

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CONCLUSIONS

• Initial taste and odor issues possibly caused by
  ozone interactions with organic material and
  accumulated biofilm.
• Ambient air and ozone showed no difference in Mn
  removal for the Birm system.
• Chlorine oxidation and pyrolusite filtration
  performed better at Mn and Fe removal than ozone
  and Birm.
• Chlorine oxidation and pyrolusite filtration
  appear to have greatly improved taste and odor
  issues. Chlorine injection prior to filtration
  limits biofilm.
• FeCl3 addition to chlorine oxidation/pyrolusite
  filtration can remove As below MCL.

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Case Study No. 2
Klickitat - Unincorporated Community Served By
Klickitat PUD 450 Residents
Klickitat River Source until 1990 Two Groundwater
Wells/Softener since 1990
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Well Raw Water Quality
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Water Quality Issues

• Iron and Manganese
• Low pH
• Hardness
• Hydrogen Sulfide

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Initial Situation

• Treatment since 1990
• Ion Exchange Softener
• Bulk 12.5 Sodium Hypochlorite
• 250 gpm Capacity
• High Number of Customer Complaints
• Rusty, chlorinous, bitter, metallic, cloudy,
  salty, septic
• 69 of customer surveyed bought bottled water.
• Corrosion of WTP Equipment
• Frequent Wastewater Plant Disruptions

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Decision Factors

• Pending Failure
• EPA Grant
• Test Well 3000 Ft. Away
• Fe/Mn Present
• H2S Present
• Higher pH
• Lower Hardness
• WWTF Discharge Issues
• Operations Maintenance

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Plant Corrosion
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Plant Corrosion
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Project Parameters

• Iron/Manganese Targeted
• Pilot Study
• Treat Existing Wells
• pH Not Treated
• Future Options for Test Well and Other Treatment
  Left Open

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Modifications

• Remove Softener System
• Install Iron Oxidation/Filtration
• Bulk Hypochlorite
• Pyrolusite Filtration
• Repair Existing Building

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Pyrolusite Design Parameters
Parameter
Value
Total Capacity
250 gpm
Pressure
100 psi
Number of Filters
4
Filter Diameter
36 inches
Loading Rate
8.8 gpm/ft2
Backwash Rate
30 gpm/ft2
Chlorine Residual
0.6 mg/l
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Installation And Startup
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Comparison Of Processes
Parameter (MCL)
Raw
Softener
Fe/Mn Oxidation/Filtration
2.2 2.9 mg/l
lt0.05-1.1
.01-.05
Fe (0.3 mg/L)
Mn (0.05 mg/L)
lt0.015 0.06 mg/l
0.03
ND
pH
6.5 6.9
6.5 6.9
6.4 6.8
Hardness
50 350 mg/l as
1.0-6.0 mg/l as
270 mg/l as CaCO3
CaCO3
CaCO3
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Ventilated Hypochlorite Closet
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Existing Lixator Becomes A..
Site Plan
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New Backwash Settling Basin
Flow Control Outlet
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Improvement Results

• Finished Water Improvements
• No Fe/Mn or H2S
• Hardness Present
• Low pH
• Customer Satisfaction Initially High
• Customer Complaints Have Not Disappeared
  Altogether
• Metallic Taste
• Additional Work in Future Phases

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Questions ?