Remediation of phenolics-polluted sites by natural catalysts

Aim of this work is the investigation of natural processes occurring in polluted soils that transform phenolics into water-insoluble polymers. Thus, pollutant mineralization is replaced by immobilization into the soil. The processes are mediated by the catalytic action of widespread soil components such as enzymes (phenoloxidases, peroxidases) and clay minerals (containing Fe and Mn oxides). The initial, catalytic step of the polymerization reaction is phenol partial oxidation. Kinetic studies carried out in aerated slurry reactors on soil samples taken from a NAPL-contaminated site in Rositz (Germany) have shown that, at least for di-phenols, polymerization proceeds at a much higher rate than biodegradation. Furthermore, polymerization takes place at phenol concentration levels that are usually toxic for microorganisms (beyond 0.2 g/L). Natural, endogenous catalysts are less effective for other classes of phenols, e.g. cresols. Therefore, the use of plant tissues in the removal of recalcitrant phenols has been studied, as well. Such augmentation technique to the natural catalytic activity of soil results in the polymerization of recalcitrant phenols. It is economically admissible, however, only for phenols of zero or marginal reactivity with bare soil.