Microbiological approaches for the treatment of spent catalysts

Homogeneous and heterogeneous catalysts are widely used for diverse industrial processes in order to produce clean fuels and many other valuable products, being spent hydroprocessing catalysts the major solid wastes of the refinery industries and the main contribution to the generation of spent catalysts. Because of its hazardous nature, the treatment and metal recovery from this kind of residues has gained increasing importance, due to the depletion of natural resources and environmental pollution. Although there are techniques already available for these purposes, they generate large volumes of potentially risky wastes and produce the emission of harmful gases. Thus, biotechnological techniques may represent a promissory alternative for the biotreatment and recovery of metals contained in spent catalysts. To this end, diverse microorganisms, comprising bacteria, archaea and fungi, have been analyzed to characterize their metal removal abilities from spent catalysts. A broad scenario about the advances regarding to the management and traditional treatment of spent catalysts is presented, followed by a detailed overview of the microbiological biotreatment approaches reported to date.