Thermal
Redox Tech injects superheated water, which flashes into low-quality steam upon entrance to the subsurface. Superheated water is one of the most efficient common carriers of heat (i.e., compared to steam and air). Redox Tech utilizes steam for two main purposes. One purpose is to reduce the viscosity of the free product, either LNAPL or DNAPL so that it can be recovered more efficiently. The low-quality steam also helps to displace the less viscous-free product.
The second purpose involves heating the subsurface environment to thermally catalyze sodium persulfate. A total organic carbon (TOC) test is completed with sodium persulfate at 60o C for the oxidant. By thermally activating the persulfate, we can complete an in situ TOC test and destroy a wide range of organic compounds in place.
It is a common misconception that thermal technologies are extremely expensive. For illustrative purposes, the fuel cost to heat one ton of soil by 10oC is provided below.
- One ton of saturated soil, 30% total porosity, requires approximately 15,000 BTUs to raise 10oC
- One gallon of diesel contains approximately 135,000 BTU
- Fuel costs are less than $1 per ton for thermal activation
As a rule-of-thumb estimate, the total cost to heat soil 10oC is roughly $5 to $10 per ton, depending upon such factors as soil type, depth, availability of water, etc. The cost of each additional 10oC increase is roughly $2 to $3 per ton. A spreadsheet is provided below, which allows one to estimate the heat required to heat soil and water in situ. Also, a list of sites where steam-activated persulfate has been applied is provided