Considerations in Selecting the Optimal Activation Technique for Sodium Persulfate Oxidation

Several key laboratory and field considerations should be carefully evaluated when choosing the most appropriate activation technique for optimal use of sodium persulfate. Among the most critical considerations include 1) VOC destruction efficiency; 2) life of the oxidant; 3) possibility of chemical daylighting; 4) corrosion issues; and 5) soil permeability.

Based on analytical results from multiple bench scale treatability tests, both hydrogen peroxide activation (catalyzed and stabilized peroxide) and high pH activation have shown excellent VOC destruction rates over 95%.  Many petroleum hydrocarbons and chlorinated compounds have been efficiently destroyed, including BTEX, MTBE, TBA, vinyl chloride, TCE, PCE, and 1,1-DCA.   

The measurement of residual oxidant levels should be performed in the laboratory at several time intervals to evaluate consumption of persulfate during treatability testing. Persulfate SOD/TOD values below 5 g/kg have been determined to be the most efficient and favorable for use in the field. 

Chemical daylighting is a common safety issue when injecting catalyzed hydrogen peroxide (CHP, a Fenton’s reaction catalyzed by ferrous iron). Sodium citrate can be effectively used as a stabilizer that slows the rapid decomposition of peroxide that occurs during CHP.  A significant benefit of using citrate with peroxide is the minimization of the occurrence and severity of chemical daylighting. This is an important safety consideration when injecting near occupied buildings.

Use of sodium hydroxide (high pH) and catalyzed hydrogen peroxide (low pH) requires careful safety considerations when injecting these chemicals near existing USTs and other sensitive subsurface utilities. The pH levels typically remain at corrosive levels (> 10 pH or < 4 pH) for a period of 10 to 40 days following injection.     

Injection of chemical oxidants at sites with tight soils (silts and clays) often requires enhancement of the soil permeability by use of pressure pulse technology or pneumatic fracturing.