Potential application of catalytic properties of humus on the degradation of priority pollutants
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Abstract
This review provides the state of the art of the catalytic roles of humic substances on the (bio)transformation of priority pollutants. Both biological and abiotic mechanisms are implicated during the conversion of different contaminants in which humic substances play a role. Quinone moieties are the main functional groups involved in the catalytic properties of humus. A large diversity of microorganisms can utilize humic substances as terminal electron acceptors during the anaerobic biodegradation of organic compounds, including recalcitrant pollutants, such as toluene and benzene, which can be mineralized in a few weeks by humus reducing microorganisms. Quinones and humus can also serve as electron shuttles (redox mediators) during the reductive transformation of electron-withdrawing pollutants (e.g. nitroaromatics, azo dyes, polyhalogenated pollutants and oxidized metalloids). The transfer of electrons mediated by humic substances enhances the reductive transformation of several pollutants increasing up to 500-fold the rates of conversion. Reduced quinones and humus can also support the microbial reduction of different electron acceptors (e.g. nitrate, fumarate, arsenate, selenate and perchlorate) by acting as electron donors. The catalytic properties of humus could be applied for the bioremediation of contaminated aquifers and for the anaerobic treatment of industrial wastewaters containing distinct priority pollutants.
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