Magnesium Hydroxide Slurry: A Safe, Cost Effective Solution for ...

The Use of Magnesium Hydroxide
Slurry as a Safe and Cost Effective
Solution for H 2
S 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

DISSOLVED SULFIDE
CONCENTRATION (mg/l)
Corrosion Effect
20
DISSOLVED SULFIDE VS. TOTAL METALS
15
10
10
5
Sulfides
Metals
Corrosion Threshold
0
0
1980 1985 1990 1995
TOTAL METALS
CONCENTRATION (mg/l)

Effects on Municipalities
• Hydrogen Sulfide (H 2 S) 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
H 2 S Gas H 2 S Gas
D.O.

Corrosion Chemistry
H 2 S
H 2 S
H 2 S Gas
H 2 S
H 2 S Gas H 2 S Gas
SO
2-
4 HS - H 2 S
• Hydrogen Sulfide
Gas is the Principal
Source of Odor and
Corrosion
• Evolution of H 2 S 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
H 2 S
H 2 S
H 2 S Gas
H 2 S
H 2 S Gas H 2 S Gas
6.00
1200
H 2 S (aq) and HS - in solution (mg/L)
5.00
4.00
3.00
2.00
1.00
H 2 S (g)
HS -
H 2 S (aq)
1000
800
600
400
200
H2S (g) in air (ppm)
SO
2-
4 HS - H 2 S
0.00
0
3 4 5 6 7 8 9 10
pH

Corrosion Chemistry
• In the Headspace H 2 S
Gas is Biologically
Converted to Strong
Sulfuric Acid by
Thiobacillus Bacteria
• This Results in
Corrosion of Sewage
System Infrastructure
Thiobacillus
Acid Attacks
Concrete
H 2 S + O 2 = H 2 SO 4
SO 4
2-
HS - H 2 S

Magnesium Hydroxide Slurry
Properties
Properties
Typical*
Mg(OH) 2 Purity, % (dry basis) 98.8
Median particle size, microns 3
Dry solids, % 61.0
Viscosity, cps 200
pH 10.0
* THIOGUARD ® Magnesium Hydroxide Slurry

How Does Magnesium Hydroxide
• Mg(OH) 2 Raises the
Wastewater pH to 8.0-
8.5
Resulting In:
Reduced Efficiency
of SRB and Less
Sulfide Production
Reduced or
Elimination of H 2 S
Gas Production
Reduced Corrosion
Rate of Sewer Pipes
Slurry Work
H 2 S (aq) and HS - in solution (mg/L)
6.00
5.00
4.00
3.00
2.00
1.00
H 2 S (g)
H 2 S (aq)
HS -
0.00
0
3 4 5 6 7 8 9 10
pH
1200
1000
800
600
400
200
H2S (g) in air (ppm)

Magnesium Hydroxide Slurry
Benefits
• Prevents Formation of H 2 S 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

Biological
Biological
Treatment
Treatment
Secondary
Secondary
Clarifier
Clarifier
Digestion
Digestion
Effluent
Effluent
Conditioning
Dewatering
Conditioning
Conditioning
Dewatering
Dewatering
Primary
Primary
Treatment
Treatment
Collection
Collection
System
System
Disinfection
Disinfection
Biological
Biological
Treatment
Treatment
Primary
Treatment
Conditioning
Dewatering
Biosolids
Conditioning
Conditioning
Dewatering
Dewatering
Biosolids
Biosolids
Digestion
Digestion
Secondary
Secondary
Clarifier
Clarifier
Collection
Collection
System
System
Effluent
Effluent
Disinfection
Disinfection
Total System Treatment
Benefits
Mg(OH) 2
Slurry

Case Study: Canton, OH
• Using Mg(OH) 2 at Stark County (Canton, OH)
–High H 2 S at Plum Street Manhole in Waynesburg, OH
– Inject 2 Miles Upstream in Magnolia Wetwell
Injected Tg
H 2 S 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
300
Injected Tg
Hourly Average
Hourly Maximum
250
H2S PPM at LS #6
200
150
Terminated Tg
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
70
THIOGUARD
Feed Starts
H2S PPM
60
50
40
Start Seeing
THIOGUARD
Effects Here
Hourly Maximum
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 0 o C 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