Sodium Hypochlorite

Sodium Hypochlorite Applications

Sodium Hypochlorite (NaOCl) is proven technology for short to medium duration hydrogen sulfide control in collection system gravity and forcemains, treatment plant headworks, recycle streams, wet scrubbers,  and small systems (HTH tablets).  Sodium hypochlorite has been used for over 30 years in hydrogen sulfide control applications and is a well understood technology. 

Sodium hypochlorite oxidizes hydrogen sulfide and organic odors.  If overdosed, sodium hypochlorite can inhibit biofilm growth thereby reducing hydrogen sulfide formation in collection system piping.  Sodium hypochlorite is fast reacting with hydrogen sulfide and organic odor compounds, making it a good choice for application in wet scrubbers and short duration sulfide control.  NaOCl also reacts with ammonia, forming chloramines that may provide some residual hydrogen sulfide control.                  

Sodium Hypochlorite Properties and Dosing

Sodium hypochlorite (NaOCl) may be considered a liquid form of chlorine, kept in solution by the incorporation of caustic (NaOH).  It is supplied as 12 - 15% solution in containers of 1 to 300 gallons, and in bulk quantities of 4,000 - 20,000 gallons. Depending on ambient temperature, it has a half-life (in storage) of 2 - 6 months.

Sodium hypochlorite oxidizes hydrogen sulfide according to the following equation:

H2S + 4 NaOCl H2SO4 + 4 NaCl

Theoretical dose ratios of NaOCl are dependent on whether ammonia is present or not. In the absence of ammonia, the dose ratio is 9.4 lbs NaOCl:lb H2S with practical dose rates anywhere from 10 to 15 depending on the application.  In the presence of ammonia (which is the case in municipal wastewater), the dose ratio is 2.3 lbs NaOCl:lb H2S with practical dose rates anywhere from 3.5 to 5 depending on the application. 

Sodium Hypochlorite Costs and Sources

Typical pricing for sodium hypochlorite solution is $.60 to $0.90 per gallon but may fluctuate dramatically based on the supply and demand dynamics of the NaOH and chlorine markets.  The cost per pound of sulfide treated is anywhere from $4.50 to $10.00 in the absence of ammonia and $1.60 to $3.50 in the presence of ammonia.       

Sodium Hypochlorite Drawbacks

Some drawbacks of sodium hypochlorite use are as follows: 

  • Consumed by the ammonia in wastewater application
  • Has a relatively short shelf life
  • Forms chlorinated by-products (VOC emissions)
  • Chlorine odors are emitted if overdosed
  • High doses are needed to suppress downstream odor generation
  • Potential exists for biotreatment inhibition from overdosing

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