Surfactant recovery and efficient separation of PAHs from surfactant solutions by low-cost waste activated sludge and...

The treatment and surfactant recovery of soil washing/flushing effluent containing high levels of surfactants and organic pollutants are critical for the surfactant-assisted remediation of soils and waste management due to their complexity and high-potential risks. Combination of waste activated sludge material (WASM) and a kinetic-based two-stage system design was introduced in this study as a novel strategy for the separation of phenanthrene and pyrene from Tween 80 solutions. The results showed that WASM can effectively sorb phenanthrene and pyrene with high affinities (K_d) of 2325.5 L·kg^-1 and 9911.2 L·kg^-1, respectively. This allowed a high-level recovery of Tween 80 of 90.47 ± 1.86%, with selectivity of up to 69.7. In addition, a two-stage design was constructed, and the results showed an improved reaction time (approximately 5% of equilibrium time in conventional single-stage process) and increased the separation levels of phenanthrene or pyrene from Tween 80 solutions. For instance, the minimal total operating time for the sorption of 99% pyrene from 1.0 g·L^-1 Tween 80 was only 23.0 min in the two-stage process compared to that of 480 min with a 71.9% removal level in the single-stage system. Results indicated that the combination of low-cost waste WASH and two-stage design was a high-efficiency and time-saving way to recover surfactants from soil washing effluents.