Changes on dissolved oxygen in phenolic wastewaters during the oxidation by Fenton reagent

When dihydroxylated benzenes are oxidized, during the initial minutes there is an elevated consumption of dissolved oxygen (DO), achieving a minimum value. Next, DO increases following second order kinetics, whose reaction rates depend on the nature of the compounds. In this stage, occurs the catalyst regeneration that releases oxygen, being possible to establish a relation-ship between the rate of OD formation, kDO (L 2 /mg 2 min) and the iron regeneration. The OD release is greater during the oxidation of hydroquinone (kDO=0.32) than catechol (kDO=0.24), because the ortho-substituted benzenes may form organometallic complexes that act as chelator agents. For resorcinol the OD formation is very slow (kDO=0.04) because may form supramolecular structures with ferric ions impeding its regeneration. By the turbidity of the water, it has quantified the amount of iron involved in the formation of metal-complexes. At the maximum turbidity, in the case of hydroquinone all dissolved iron is as Fe 2+ . However, for catechol, 4% of catalyst is as Fe 3+ and for resorcinol, 53%.