Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation, Ozonation and Ozone/Hydrogen Peroxide Process

Abstract

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-CODCr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-CODCr dramatically increased. Until dissolved ozone was detected, 0.3 mgO3/mgTOC0 (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional CODCr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-CODCr, TOC and ATU-BOD5 were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of CODCr and UV254 had good linear relationship until the removal amounts of CODCr and UV254 were 30 mg/L and 0.11 cm−1, respectively. Therefore UV254 would be useful for an indicator for CODCr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/CODCr.