Abstract
Pulp bleaching wastewater (PBW) was treated with ozone to evaluate the effects of ozone treatment on the dissolved organic carbon (DOC) and the molecular size distribution. It was found that the DOC in PBW was decreased substantially by ozone oxidation. It was also found that the substantial part of DOC cannot be removed by using UV irradiation or UV/H2O2 as a pretreatment step. The macromolecules were degraded to smaller fragments during ozone treatment, and 92.3% of macromolecules (M.W.3, 000-10, 000) was found to be converted to smaller fragments or mineralized during ozone treatment. In addition, the rate of DOC removal separately by biological treatment of fluidized aerobic reactor or by ozone treatment, was 30%. Removal rate by biological treatment after ozone treatment was increased up to 47%. Consequently, in total, 76% of DOC was removed. An obvious explanation for this is that monomol ecularization of polymolecular is carried out by ozone oxidation, and bio-degradation of DOC is promoted due to the increase of smaller fragment ratio.
