Immobilizing polycyclic aromatic hydrocarbon degrading bacteria with gel microspheres for bioaugmentation remediation of soil in a surfactant-enhanced slurry bioreactor

Microbial immobilization technology (MIT) is considered a feasible way to overcome unfavorable environmental conditions when a bioaugmentation method is used to remediate contaminated soil. In the present study, the feasibility of using immobilized PAH-degrading bacteria for the bioaugmentation remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soil is explored in a surfactant-enhanced slurry bioreactor for the first time. The results showed that the immobilized Pseudomonas sp. DH-6 microspheres, which were prepared with 80 g/L polyvinyl alcohol (PVA), 10 g/L sodium alginate (SA), and 8 g/L activated carbon (AC), had good spherical shape and mechanical strength, and exhibited excellent performance for the removal of PAHs. The immobilized DH-6 was proven to significantly surpass the free DH-6 strain for removing of PAHs when encountering harsh environmental conditions, such as caustic pH and elevated concentrations of salts. The stability experiments showed that the immobilized DH-6 had excellent storage and recycling stability, and the removal efficiencies of PAHs could reach over 95 % after 90 days of storage or 5 times of use. This study also verified the effectiveness of immobilized DH-6 microspheres for the bioaugmentation remediation of PAH-contaminated field soil in a surfactant-enhanced slurry bioreactor. The results showed that 78.2 % of PAHs were removed within 21 days, which was significantly higher than that of the control group (39.9 %). This study reveals that the PVA/SA/AC gel microspheres with suitable immobilized strain could be engineered to achieve effective and time-saving bioaugmentation remediation of contaminated soil in slurry bioreactors.