| A comparison of column flushing for phenanthrene-contaminated sandy soils was made by using an anionic surfactant, sodium dodecyl sulfate (SDS), a nonionic surfactant, Triton X-100 (TX100), and their mixed surfactants (SDS-TX100). The tested concentrations of surfactants were 1000, 1750, 2500 and 3250 mg·L-1 while the mass ratios of SDS to TX100 (S∶T) in the mixed surfactants were 1∶1, 1∶2 and 1∶4. It was shown that the elution curves (phenanthrene concentration in elutant versus porous volume number) by SDS were zigzag fluctuating rather than regular patterns while those by TX100 and SDS-TX100 were regular ones in which the phenanthrene concentrations in elutant increased, achieved maximum and then decreased with the porous volume numbers of eluting solutions. Moreover, the maximum phenanthrene concentrations increased and the total porous volume numbers decreased with surfactant concentration increasing. Given the surfactant and total porous volume number, the removal efficiencies of phenanthrene were positively related to surfactant concentrations. The removal efficiencies by TX100 and SDS-TX100 depended on concentration and ratio of surfactant and were much larger than those by SDS. Given 1000, 1750 and 2500 mg·L-1 of the surfactant concentrations respectively, the removal efficiencies by TX100 and SDS-TX100 were more than 95% but the total porous volume numbers by SDS-TX100 were less than those by TX100. Given 3250 mg·L-1 of the surfactant concentration, the total removal efficiencies by five surfactants (i. e. SDS, TX100, S∶T=1∶1, S∶T=1∶2 and S∶T=1∶4) achieved their maximum values as 70.8%, 99.9%, 99.9%, 98.7% and 99.2%, respectively, but the needed porous volume numbers by TX100 were the least among those by all surfactants. The results illustrates that the factors such as type, concentration and ratio of surfactant play important roles in surfactant-enhanced flushing remediation for soils contaminated by organics. |
