Recalcitrance as a catalyst for new developments

Humic substances are very recalcitrant in anaerobic environments as substrates, mostly due to their non-hydrolyzable high molecular weight structure, which is incompatible for cell uptake. The recalcitrant nature can be applied towards immobilizing pollutants into non-toxic humic substances. Certain anaerobic bioconversions such as demethylation of lignin and reduction of nitro- or azo groups can active pollutants for humification processes upon subsequent exposure to air. Although humic substances provide no carbon or engery for microorganisms, the evidence presented here indicates that they are very active as terminal electron acceptors and redox mediators promoting the anaerobic degradation and biotransformation of priority pollutants.