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Hydrogen Peroxide as a Replacement for Sodium Hypochlorite
Hydrogen peroxide may be used in both mist scrubbers and packed tower scrubbers as a replacement for sodium hypochlorite (bleach). Like bleach, the process involves two concurrent mechanisms: 1) absorption of the odors (H2S) into the alkaline scrubbing solution; and 2) oxidation of the absorbed sulfide in solution.
H2S + NaOH → NaSH + H2O
4H2O2 + H2S → H2SO4 + 4H2O
Typical dose ratios are 5 parts H2O2 per part H2S or, when used in place of bleach, one gallon 50% H2O2 for every 10 gallons of 15% sodium hypochlorite (NaOCl). This generally translates into a break-even cost scenario. Sufficient caustic soda (NaOH) is added to maintain a pH of 10.0 - 10.5 in the scrubbing solution.
There is also in practice a process which uses H2O2 in series with bleach to scrub composting odors. This process relies on a series of three packed tower scrubbers: the first is a pH neutral water wash (to remove ammonia and amine odors); the second uses a conventional caustic/bleach solution in which the bleach is purposely overdosed (to oxidize the complex organic sulfur odors); and the third uses a caustic/H2O2 solution (to remove the unreacted chlorine vapors carried over from the second stage).
H2O2 + HOCl → HCl + H2O + O2
Typical dose ratios are 0.5 parts H2O2 per part hypochlorite (OCl-), with sufficient caustic soda (NaOH) added to maintain a pH of 8.5 in the scrubbing solution.