The Use of Magnesium Hydroxide
Slurry as a Safe and Cost Effective
Solution for H2S Odor and Corrosion in
Sanitary Sewer Systems
Aileen Gibson
Chris Knapp
Steve Leykauf
Wastewater Treatment History
• In 1977, the Clean Water Act Increased
Requirements for Secondary Treatment
• Categorical Pre-treatment Reduced Heavy Metals
• Shift from Phosphate to Sulfur Based Detergents
• More Centralized Treatment
• Low Flow Plumbing Fixtures
Corrosion Effect
DISSOLVED SULFIDE VS. TOTAL METALS
M
et
a
s
e
d
i
f
l
Su
ls
10
15
10
5
Corrosion Threshold
0
1980
1985
1990
0
1995
DISSOLVED SULFIDE
CONCENTRATION (mg/l)
TOTAL METALS
CONCENTRATION (mg/l)
20
Effects on Municipalities
• Hydrogen Sulfide (H2S) Formation Has Increased
• Accelerated Biogenic Corrosion
• Increased Sewer and Plant Odors
• Grease Buildup (Fats, Oil and Grease – FOG)
• Treatment Plant Upsets
• Higher Cost of Treatment
Facts
• U.S. Wastewater Infrastructure is Failing
Faster than it is Being Replaced
• Sanitary Sewer Overflows (SSO’s) are Very
Costly Fiscally and Politically
• Odor and FOG are Significant Problems
Which Also Carry High Fiscal and Political
Expense
Corrosion Chemistry
• When Dissolved
Oxygen Falls Below 0.1
mg/l, Wastewater Turns
Septic and Anaerobic
• These Bacteria
(SRB) Reduce Sulfate
to Sulfide Producing
the Rotten Egg Smell
Called Sewer Gas
H22S Gas H22S Gas
D.O.<0.1 mg/l
Corrosion Chemistry
H22S
H22S
H22S
H22S Gas
H22S Gas H22S Gas
SO42-
HS-
H
H22S
S
• Hydrogen Sulfide
Gas is the Principal
Source of Odor and
Corrosion
• Evolution of H2S is a
Function of Dissolved
Sulfide Concentration,
Water Temperature,
Turbulence and pH
At pH 7 Roughly 50% of
the Dissolved Sulfide
Can Exist As Hydrogen
Sulfide
H22S
H22S
H22S
H22S Gas
H22S Gas H22S Gas
1200
5.00
H2S(g)
4.00
H2S(aq)
HS-
1000
800
3.00
600
2.00
400
1.00
200
0.00
0
3
4
5
6
7
pH
8
9
10
H 2 S(g) in air (ppm)
H2 S (aq) and HS - in solution (mg/L)
6.00
SO42-
HS-
H
H22S
S
Corrosion Chemistry
Thiobacillus
• In the Headspace H2S
Gas is Biologically
Converted to Strong
Sulfuric Acid by
Thiobacillus Bacteria
• This Results in
Corrosion of Sewage
System Infrastructure
Acid Attacks
Concrete
H22S + O2 = H2SO4
SO42-
HS-
H2S
Magnesium Hydroxide Slurry
Properties
Properties
Mg(OH)2 Purity, % (dry basis)
Median particle size, microns
Dry solids, %
Viscosity, cps
pH
* THIOGUARD® Magnesium Hydroxide Slurry
Typical*
98.8
3
61.0
200
10.0
How Does Magnesium Hydroxide
Slurry Work?
1200
H2 S (aq) and HS - in solution (mg/L)
6.00
5.00
H2S(g)
4.00
H2S(aq)
HS-
1000
H 2 S(g) in air (ppm)
• Mg(OH)2 Raises the
Wastewater pH to 8.08.5
Resulting In:
™ Reduced Efficiency
of SRB and Less
Sulfide Production
™ Reduced or
Elimination of H2S
Gas Production
™ Reduced Corrosion
Rate of Sewer Pipes
800
3.00
600
2.00
400
1.00
200
0.00
0
3
4
5
6
7
pH
8
9
10
Magnesium Hydroxide Slurry
Benefits
• Prevents Formation of H2S Odor & Corrosion in
Municipal Collection Systems
• Extends Life of Sewer System
• Reduces FOG
• Mg(OH)2 Dosage Is Not Dependent On Sulfide
Concentration
FOG (Fats, Oils & Grease)
Before Mg(OH)2….
After Mg(OH)2
Magnesium Hydroxide Slurry
Additional Benefits
• Due to pH Buffering Ability of Mg(OH)2, Less
Feed Points Are Required
• No Sludge Is Formed As With Iron Salts
• Non-Hazardous and Non-Corrosive
• Improves Downstream Wastewater Treatment
Operations
Total System Treatment
Benefits
Mg(OH)2
Slurry
Primary
Treatment
Collection
System
Biological
Treatment
Secondary
Clarifier
Disinfection
Effluent
Digestion Conditioning
Dewatering
Biosolids
Case Study: Canton, OH
• Using Mg(OH)2 at Stark County (Canton, OH)
– High H2S at Plum Street Manhole in Waynesburg, OH
– Inject 2 Miles Upstream in Magnolia Wetwell
Injected Tg
H2S Reduction
Lowered
Feed Rate
Case Study: Summit County, OH
Begin Tg Feed
Intentionally Terminate Tg Feed
Case Study: Akron, OH
Started feeding
Thioguard at 2:15pm
4-18-06
Start Seeing Effects
of Thioguard
Addition
Case Study: Lagrange, IN
350
Injected Tg
300
Hourly Average
Hourly Maximum
H2S PPM at LS #6
250
Terminated Tg
200
150
100
50
0
5/14/07 0:00
5/16/07 0:00
5/18/07 0:00
5/20/07 0:00
5/22/07 0:00
5/24/07 0:00
5/26/07 0:00
Case Study: Steuben Lakes, IN
80
THIOGUARD
Feed Starts
70
60
Start Seeing
THIOGUARD
Effects Here
H2S PPM
50
Hourly Maximum
40
Hourly Average
30
20
10
0
2/27/2007
2/28/2007
2/28/2007
3/1/2007
3/1/2007
3/2/2007
3/2/2007
3/3/2007
3/3/2007
3/4/2007
3/4/2007
3/5/2007
Mg(OH)2 Slurry Handling
• Slurry Requires Periodic Agitation to Keep
Solids in Suspension
• Maintain Minimum Line Velocity Through
Feed Lines
• Recommend Peristaltic or Progressive Cavity
Pumps for Metering
• With 0oC Freezing Point, Need Freeze
Protection On Equipment
Mg(OH)2 Slurry Equipment
• Bulk Storage and Feed System
– 2500-Gallon Tank
With Heat Pads
– Peristaltic Feed
With VFD
– Control Panel
With Power and
Control Signal
Connections
Mg(OH)2 Slurry Equipment
• Tote Storage and Feed
System
•
•
•
•
•
Agitator
275-Gallon Day Tank
Control Panel
Flow Meter
Air-Driven Transfer
Pump
• Progressive Cavity Feed
Pump
Compared To Other Treatment Options
Magnesium Hydroxide Slurry Is…
• Less Expensive, Particularly At High Sulfide
Concentrations
• More Effective For Odor and Corrosion Control
• Non-Hazardous and Non-Corrosive
• Can be Used System-Wide
• Solves More Problems
Thank You.
Any Questions?