Removal of PAHs at high concentrations in a soil washing solution containing TX-100 via simultaneous sorption and biodegradation processes by immobilized degrading bacteria in PVA-SA hydrogel beads

Soil washing process enhanced by surfactants is a promising technique in removing organic pollutants from soil. In this work, a simultaneous sorption and biodegradation technique was used to remove 16 PAHs from a soil washing solution (SWS) obtained by rinsing a heavily contaminated soil from a coking plant with Triton X-100 (TX-100). This was done by immobilizing a pyrene-degrading bacterial strain in polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads. Removal performance of free bacteria, blank PVA-SA beads and beads with immobilized degrading bacteria at a low, medium and high initial concentration was evaluated. The recycling and removal performance of the used beads were also examined. Our findings showed that hydrogel beads with immobilized bacteria at a medium concentration can remove around 77% ∑16PAHs from SWS in 96 h. The beads can be recycled and reused to treat a new SWS; 32-55% ∑16PAHs was removed in 24 h. The bead provided protection for bacteria against the co-existing substances such as TX-100. The bacteria-immobilized beads are more efficient and sustainable than free bacteria and blank beads due to simultaneous sorption and biodegradation processes, thus providing a solid reference for possible industrial application of bacteria immobilization technique to deal with SWSs with complex composition.