Study on the synergistic effect of UV/Fenton oxidation and mass transfer enhancement with addition of activated carbon in the bubble column reactor

For the UV/Fenton treatment of waste gas, low solubility of volatile organic compounds (VOCs) was a significant factor of limiting gas–liquid mass transfer and thus restricted the removal efficiency. In this study, synergistic effect of UV/Fenton oxidation and mass transfer enhancement with addition of activated carbon (AC) was observed through a drastic improvement of n-octane removal in a bubble column reactor. Firstly, the effect of AC on mass transfer was investigated. Result revealed that the addition of AC could change bubble behavior and largely enhance the mass transfer efficiency (volumetric mass transfer coefficient (kLa) increased from 0.0057 to 0.14 s−1 as 0–0.1% AC was added) due to the particle shuttle effect. Then AC was introduced into the UV/Fenton reaction system, and the removal efficiency of n-octane had been remarkably improved (maintained above 50% in 60 min with addition of 0.04% AC, compared with below 10% in 20 min for the UV/Fenton alone). Moreover, we comprehensively detected the concentration of residual reactants, intermediates, final products and hydroxyl radicals in the gas and liquid phase. Results indicated that addition of AC could mildly and stably generate hydroxyl radicals (10−8 M), and the mass balance showed that the mineralization efficiency had increased from 42.4% to 57.9%. For theoretical calculations, the value of the cooperation factor raising from 0.5 to 11.7 in 40 min could offer direct evidence for confirming the synergistic effect. Finally, the reaction pathways of n-octane in UV/Fenton or AC-UV/Fenton were proposed. It can be induced that the latter ones were more likely to first break the CC bond and then oxidize into small molecules acids or CO2.