Chemical treatment of cork-processing wastewaters for potential reuse

The chemical treatment of cork-processing wastewater by ozonation, alone and in combination with hydrogen peroxide and UV radiation was investigated. A reduction of the chemical oxygen demand (COD) ranging from 42% to 76% was obtained during ozonation after 3 h of reaction, depending on the experimental conditions. The additional presence of hydrogen peroxide and UV radiation enhanced the efficiency of the ozonation treatment due to the contribution of the OH radicals formed in the decomposition of ozone. Thus, final reductions of the COD higher than 90% and a complete elimination of phenolic compounds and absorbance at 254 nm were achieved in both Advanced Oxidation Processes (AOPs), O-3/H2O2 and O-3/UV. Therefore the effluent resulting from the ozonation treatments can be reused in the cork-processing industry. In a second step, the chemical treatment was conducted by means of UV radiation alone and by the action of hydroxyl radicals, which were generated by the following AOPs: UV/H2O2, Fenton's reagent, and photo-Fenton system. The single photochemical process resulted in 9% of the organic matter present being removed, while the AOPs significantly enhanced this reduction with values in the range 20-75%. Kinetic studies for both groups of treatments were performed, and apparent kinetic rate constants were evaluated. In the ozone-based experiments, the rate constants ranged from 1846 to 10922 dM(3) mol(-1) O-3 h(-1), depending on the operating conditions. In the oxidation experiments using oxidants other than ozone, the rate constants varied between 0.06 and 1.19 h(-1). (C) 2004 Society of Chemical Industry.