MICROBIAL DECONTAMINATION OF POLLUTED SOIL IN A SLURRY PROCESS

Oil-contaminated soil (2.3-17 g/kg), even soil with high clay and silt content, was remediated microbiologically in a slurry reactor. The pr esence of soil, however, Limits the degradation rate of oil. In contra st with results from experiments using oil dispersed in water, the rel ative composition of the oil components in a soil slurry after degrada tion was about the same as that of the original oil. Thus the composit ion of the degraded oil is the same as that of the original oil, which is indicative for a physical, rather than a (bio)chemical, limitation on the oil degradation rate. About 70% of the contaminant was readily available and was degraded in less than eight days. The dual injected turbulent suspension (DITS) reactor is able to combine remediation of part of the contaminated (polydisperse) soil with separation of the s oil into a heavily and a lightly polluted fraction. In continuous oper ation, lowering the overall soil residence time from 200 to 100 h did not significantly increase the oil concentration in the effluent soil. Therefore a soil residence time of less than 100 h is feasible. With a residence time of 100 h, overall oil degradation rates at the steady state were more than 70 times faster than in a comparable land farm. After treatment in a DITS reactor, the remaining oil in the contaminat ed soil fraction is slowly released from the soil. From a batch experi ment it was found that another 10 weeks were needed to reach the Dutch reference level of 50 mg/kg. This can be done in a process with a low energy input, such as a landfarm.