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

Transcription

1 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

2 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

3 DISSOLVED SULFIDE CONCENTRATION (mg/l) Corrosion Effect 20 DISSOLVED SULFIDE VS. TOTAL METALS Sulfides Metals Corrosion Threshold TOTAL METALS CONCENTRATION (mg/l)

4 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

5 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

6 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.<0.1 mg/l

7 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

8 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 H 2 S (aq) and HS - in solution (mg/l) H 2 S (g) H 2 S (aq) HS H2S (g) in air (ppm) SO 2-4 HS - H 2 S ph

9 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

10 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

11 How Does Magnesium Hydroxide Mg(OH) 2 Raises the Wastewater ph to 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) H 2 S (g) H 2 S (aq) HS ph H2S (g) in air (ppm)

12 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

13 FOG (Fats, Oils & Grease) Before Mg(OH) 2.

14 After Mg(OH) 2

15 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

16 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

17 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

18 Case Study: Summit County, OH Begin Tg Feed Intentionally Terminate Tg Feed

19 Case Study: Akron, OH Started feeding Thioguard at 2:15pm Start Seeing Effects of Thioguard Addition

20 Case Study: Lagrange, IN Injected Tg Hourly Average Hourly Maximum 250 H2S PPM at LS # Terminated Tg /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

21 Case Study: Steuben Lakes, IN THIOGUARD Feed Starts H2S PPM Start Seeing THIOGUARD Effects Here Hourly Maximum Hourly Average /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

22 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

23 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

24 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

25 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

26 Thank You. Any Questions?