Hydrogen peroxide decomposition and quinoline degradation in the presence of aquifer material

Hydrogen peroxide is used as a source of oxygen for enhanced bioremediation of contaminated subsurface environments and as an oxidant in engineered systems. While a number of aspects of hydrogen peroxide chemistry are well understood, the importance and relationship between hydrogen peroxide decomposition and contaminant degradation in the presence of subsurface materials is not clear. We report on batch and column studies examining this relationship using quinoline and a sandy aquifer material. The rate of hydrogen peroxide decomposition followed a simple first order relationship, but the loss of quinoline was much more complex than anticipated. The stoichiometric efficiency (i.e. the amount of quinoline degraded for a given loss in hydrogen peroxide) increased dramatically with decreasing concentration of aquifer material. Surface scavenging of reactive intermediates is believed to cause this unexpected behavior. This hypothesis was supported by increased quinoline removal after treatment to remove or inactivate catalytic sites. A model is proposed capable of predicting the extent of quinoline degradation as a function of the aquifer material solids concentration. The findings show that batch and column data for this system and perhaps others involving reactive intermediates must be interpreted with caution. Our results suggest that phosphate addition to retard hydrogen peroxide decomposition could increase contaminant degradation, previously attributed to only biological processes. It may also be possible to enhance chemical degradation in the subsurface and in engineered systems by addition of amendments to modify the surfaces and control reaction pathways.