Development of a two-stage washing and biodegradation system to remediate octachlorinated dibenzo-p-dioxin-contaminated soils

A two-stage system for octachlorinated dibenzo-p-dioxin (OCDD)-contaminated soil remediation was developed. Soil washing using emulsified oil (EO) was applied in the first stage for OCDD extraction followed by the second stage of bioremediation using P. mendocina NSYSU for remaining OCDD biodegradation. The major tasks included (1) determination of optimal soil washing conditions for OCDD extraction by EO, (2) evaluation of feasibility of OCDD biodegradation by P. mendocina NSYSU under aerobic cometabolic conditions using EO as the primary substrate, and (3) assessment of the effectiveness of OCDD removal using the two-stage system. During the soil washing stage, EO with two different oil-to-water ratios (1:50 and 1:200) and pore volumes were tested with initial soil OCDD concentration of 21,000 µg/kg. Results indicate that EO could effectively improve the solubility and desorption of OCDD in soils. Up to 74% of OCDD removal could be obtained after washing with 60 PVs of EO and dilution factor of 50. After the soil washing process, enriched P. mendocina NSYSU solution was added into the reactor to enhance the aerobic biodegradation of remaining OCDD in soils. P. mendocina NSYSU could use adsorbed EO globules as substrates and caused significant OCDD degradation via the aerobic cometabolic mechanism. Approximately 82% of the remaining OCDD could be removed after 50 days of operation, and P. mendocina NSYSU played important roles in OCDD biodegradation. Up to 87% of OCDD was removed through the EO washing and biodegradation process. The two-stage system is a potential technology to remediate dioxin-contaminated soils.