Bioremediation technologies are today well established techniques for the clean up of chemically contaminated soils. In this work we have focused on the ex-situ treatments, with particular reference to slurry-phase bioreactors (SPB) and solid—phase bioreactors (SoPB). Several SPB studies have shown that rates of contaminant biodegradation decrease significantly as the contaminant bioavailability becomes the rate limiting step. In this case, the long—time degradation phase can be more cost effectively carried out in a SoPB rather than in a SPB. Moreover, the SPB breaks up the larger soil particles and homogenizes soil, nutrients and biomass. This avoids in the following SoPB non-uniform contaminant removal and low rates and extent of degradation due to the lack of homogenization. In this frame the main aim of this work has been to investigate at a laboratory and pilot-scale the influence of various operating parameters on the combined slurry and solid-phase bioremediation technique for a contaminated soil. For what concerns SPB, it has been found that, under certain constraints, a low hydraulic retention time allows for a better utilization of the reactor volume. The soil drawn from the SPB can be fed effectively to the SoPB for completing the soil clean up, where an important improvement of the performances has been found using a surfactant as a soil additive.
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