Purification of cork processing wastewaters by ozone, by activated sludge, and by their two sequential applications

Wastewaters generated in the cork processing industry were treated in continuous reactors by means of single treatments separately—a chemical ozonation and an activated sludge system—and then by both sequential processes—ozonation followed by aerobic degradation, and aerobic degradation followed by ozonation. The removals obtained in the ozonation A alone were 12–54%, 65–81%, and 55–89% for the COD, total phenolics, and absorbance at 254 nm, respectively, while the consumed ozone yield ranged from 40% to 61%, and the biodegradability (BOD5/COD) varied from an initial 0.60 to final values between 0.68 and 0.93. The optimum hydraulic retention time and ozone partial pressure were 3 h and 3 kPa, respectively. The stoichiometric ratio was 0.56 g of organic substrate degraded per g of ozone consumed, while the rate constants obtained for the ozone disappearance and for the organic matter degradation were 4490 L g COD^-1 h^-1 and 1970 L g O3^-1 h^-1 respectively. The presence of hydrogen peroxide or UV radiation in addition to ozone increased the values of organic matter removal as well as the stoichiometric ratio and the rate constants. The aerobic treatment by the activated sludge system yielded COD removals between 13% and 37% for hydraulic retention times between 24 and 96 h, and the Contois model gave values of qmax=0.14 g COD g VSS^-1 h^-1 and K1=22.6 g COD g VSS^-1 for the main kinetic parameters. The sequential processes increased the substrate removal efficiencies in comparison with the individual processes. These enhancements were greater in the aerobic degradation–ozonation sequence than in the ozonation–aerobic degradation sequence.