HYDROGEN-PEROXIDE USE TO INCREASE OXIDANT CAPACITY FOR INSITU BIOREMEDIATION OF CONTAMINATED SOILS AND AQUIFERS - A REVIEW

Biotransformation of organic pollutants is often most effective and complete under oxic or oxidant-rich conditions. Dissolved oxygen availability is frequently limiting the biotransformation of these organic compounds in the subsurface due to the limited aqueous solubility of oxygen, the relatively slow rate of re-aeration of groundwater in the saturated zone, and the significant biological oxygen demand exerted during aerobic metabolism. Addition of hydrogen peroxide (H2O2) can augment the oxidant capacity of the aquifer. This paper reviews several reactions pertinent to remediating contaminated groundwaters via H2O2 addition. H2O2 is disproportionated by the action of microbial catalase and several inorganic catalysts such as iron oxide species to give 0.5 mol O2 per mole of H2O2 consumed. The resulting dissolved oxygen should then be available for microbial respiration. If disproportionation occurs too quickly evolution of oxygen gas can form bubbles that lower aquifer permeability. Another type of reaction is direct oxidation of organic compounds by H2O2 in the presence of enzymes (peroxidases) or metal oxide catalysts. Molecular oxygen is not evolved as a result of this type of H2O2-consuming reaction. Modifications in treatment strategy may also be necessary to minimize H2O2 toxicity as H2O2 is known to be toxic at a concentration within the cell of 0.1 mM.