|
H2O2 |
Iron Salts |
| Description |
Hydrogen peroxide (H2O2) is a liquid product supplied as a 35% or 50% solution. It is available in containers of 50 or 300 gallons, or in bulk shipments of 500 - 20,000 gallons. Solid peroxide products (sodium percarbonate and calcium peroxide) are also available. |
Iron salts are supplied as liquid solutions containing 5-12% ferrous or ferric iron as either a chloride or sulfate salt. They are supplied in containers of 55 or 300 gallons, or in bulk shipments of 4,000 - 20,000 gallons. |
| Control Mechanism(s) |
Oxidizes H2S Retards septicity (adds dissolved oxygen) Promotes bio-oxidation of organic odors |
Ferrous salts precipitate H2S
Ferric salts may both oxidize and precipitate H2S
|
| Chemical Reaction(s) |
Neutral - Acid pH: H2S + H2O2 --> S + 2 H2O
Alkali: S2- + 2 O2 ----> SO42-
Prevention: 2 H2O2 ----> O2 + 2 H2O
|
Ferrous Salts: H2S + FeCl2 ----> FeS + 2HCl
Ferric Salts: 3 H2S + 2 FeCl3 ----> S + 2 FeS + 6 HCl |
| Dose Ratios (lbs Fe per lb-H2S) |
|
Neutral - Acid |
Alkali |
Prevention |
| Theoretical |
1.0 |
4.0 |
4.0 |
| Practical |
1.2 - 1.5 |
4.5 - 5.0 |
2 - 8 |
|
|
Ferrous Salts |
Ferric Salts |
| Theoretical |
1.7 |
1.1 |
| Practical |
2 - 8 |
1.3 - 8 |
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Applications |
Gravity mains (< 3-4 hours retention)Force mains (< 1-2 hours retention)
Terminus of long retention force mainsTreatment plant headworksSolids processingSeptage and leachate
Odor scrubbersPonds and lagoons |
Gravity mains
Force mains
Anaerobic digesters
Solids processing units
Solids transfer lines
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Advantages |
High selectivity toward H2SAdds dissolved oxygen to retard downstream septicity
Produces no harmful by-productsExtensive history of useIn-line nitrification and BOD reduction possible
Simple feed systemsRelative low feed rates (small storage tanks) |
Extensive history of use
Simple feed systems
Effective for long-duration control
Can improve clarification processes
Assists in phosphate removal and struvite control
Not impacted by oxygen uptake rates
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|
Disadvantages |
High dosages are needed for control > 2 hoursOrganic odors require bio-mediated oxidation
Reaction may take several minutes (without catalysis)Oxidizer classification may restrict dosing sites
|
Removes dissolved oxygen from the water
Precipitate settles out in low-velocity sewers (< 2 fps)
Iron films form on pipe walls and instrument sensors
Ineffective for (non-sulfide) organic odors
Hard to achieve low sulfide limits (pH dependent)
Does not destroy sulfide (H2S may volatilize if the pH is lowered)
Product purity may impact biosolids re-use (heavy metal contamination)
Messy to handle
CERCLA rating may restrict dosing sites (persistent environmental hazard)
High dosages may cause solids carry-over from clarifiers
Solids production (> 3 lbs/lb - Sulfide) increases processing and disposal costs
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Special Notes |
Hydrogen peroxide is one of the more rapidly growing alternatives due to its cost-effectiveness and environmental compatibility. |
Iron salts may be used synergistically with oxidants such as H2O2. |
