Recalcitrance as a catalyst for new developments

Humic substances are very recalcitrant in anaerobic environments as substra tes, mostly due to their non-hydrolyzable high molecular weight structure, which is incompatible for cell uptake. The recalcitrant nature can be appli ed towards immobilizing pollutants into non-toxic humic substances. Certain anaerobic bioconversions such as demethylation of lignin and reduction of nitro- or azo groups can activate pollutants for humification processes upo n subsequent exposure to air. Although humic substances provide no carbon o r energy for microorganisms, the evidence presented here indicates that the y are very active as terminal electron acceptors and redox mediators promot ing the anaerobic degradation and biotransformation of priority pollutants.