Thermal regeneration of adsorbents, and photocatalytic destruction of hazardous organic compounds

A treatment strategy was examined where organic pollutants in aqueous phase were first removed by fixed-bed adsorption, followed by off-line regeneration of adsorbent and clean up of regeneration fluid by catalysis. The regeneration of adsorbents was conducted by the following methods: (1) photocatalysis at elevated temperature; and (2) saturated steam. The destruction of the desorbed organics was examined in both, aqueous and steam phases.; The thermal regeneration study was conducted using saturated steam at 160{dollar}spcirc{dollar}C. The process was examined for at least 6 cycles of adsorption/regeneration with the following 5 compound: tetrachloroethylene (PCE), carbon tetrachloride (CCl{dollar}sb4{dollar}), p-dichlorobenzene (DCB), o-chlorobiphenyl (o-PCB), and methyl ethyl ketone (MEK). The adsorbent evaluated was Ambersorb 563, a carbonaceous synthetic adsorbent, obtained from Rohm & Haas Co. (Philadelphia, PA). It was observed that the adsorption capacity of the adsorbent for PCE, p-DCB, CC{dollar}sb4{dollar}, and MEK was completely recovered with the steam regeneration process. In the case of o-PCB, there was about 20% loss in adsorbent capacity after the first cycle, however, the adsorption capacity for cycles 2 through 6 was almost the same.; For photocatalytic regeneration, the adsorbents were impregnated with the photocatalyst and regenerated in presence of UV-light and hot water (about 90{dollar}spcirc{dollar}C) using different reactor options. The laboratory study was conducted using tetrachloroethylene as the model compound. A field study was also conducted at Tyndall AFB for treatment of groundwater contaminated with BTEX (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene) compounds. It was observed that the photocatalytic regeneration process was not effective to completely recover the capacity of the adsorbent. The predominant mechanism of the regeneration process was observed to be thermal desorption.; Photocatalysis using 1%Pt-TiO{dollar}sb2{dollar} photocatalyst was employed for degradation of desorbed organics in the aqueous phase. The BTEX compounds in the aqueous phase were removed to below detection levels. The PCE, o-PCB, and p-DCB compounds in the aqueous phase were completely mineralized, where as only about 53% destruction of CCl{dollar}sb4{dollar} was observed. No significant destruction of organics was observed in steam phase at 160{dollar}spcirc{dollar}C with the following catalysts: Ambersorb 563, TiO{dollar}sb2{dollar} and Pt-TiO{dollar}sb2{dollar} supported on Ambersorb 563, CoO supported on silica gel, and TiO{dollar}sb2{dollar}, and Pt-TiO{dollar}sb2{dollar} photocatalysts supported on silica gel.; The regeneration study showed that saturated steam at 160{dollar}spcirc{dollar}C was effective to recover the capacity of spent adsorbents. The steam regeneration results were described by plug-flow pore and surface diffusion model assuming that the interparticle mass transfer occurs in liquid phase, and external transfer in the gas phase. It was observed that the model can describe the experimental data for PCE and CCl{dollar}sb4{dollar} fairly well.