A column study of persulfate chemical oxidative regeneration of toluene gas saturated activated carbon

Abstract

Soil vapor extraction (SVE) is a remediation technology for removing volatile organic contaminants (e.g., toluene) from the subsurface. Charcoal activated carbon (AC) adsorption is a commonly applied method of containing the chemical vapors exhausted as SVE offgas. This study aimed to investigate the potential for the thermal activated persulfate (TAP) process to regenerate toluene gas saturated AC. The experimental AC adsorption column setup consisted of AC and wet TAP regeneration units. When influent toluene gas saturated the AC and achieved breakthrough from the adsorption column, regeneration of the saturated AC was achieved by flushing with 50 or 100 mM persulfate solution at 50 or 80 °C. The TAP regenerated AC retained >90% of its adsorption efficiency when regenerated with 100 mM sodium persulfate (SPS) solution flushed at 50 and 80 °C. The removal of sorbed toluene during the TAP process relied on mass transfer (i.e., sorbed toluene dissolved into the SPS solution). The flushed toluene was rapidly destroyed in the SPS solution by oxidative degradation. These results suggested that, sufficient oxidation of toluene occurs with thermal assistance at a Δ[SPS]/AC dosage of approximately >50 (g/g) at 50 °C or above. These parameters successfully regenerated AC saturated toluene in the TAP process. An economic evaluation based on the amount of SPS and electricity required indicated that, the cost is far less than conventional rotary kiln and microwave heat AC regenerations. This TAP oxidative AC regeneration could be a cost effective alternative to other types of carbon bed regeneration, and will likely provide cost benefit when used to treat toluene offgas from on-site SVE, because it both removes toluene from the AC, and destroys it in the regeneration solution.