Effects of Joint-reaction Combined by Ozonation and Coagulation on Aquatic Organic Matters

Abstract

Variations of residual ozone concentration in pure water and Al2(SO4)3 solution were studied. The spectral characteristics, contents of organic compounds and disinfection by products (DBPs) yields in preozonated, preozonated coagulated (POC) and ozonated combined coagulated (OC) waters were detected by differential absorbance(DA), three dimensional fluorescence excitation-emission matrix spectroscopy (3D-EEM), GC and TOC. The purpose of the work was to investigate the effects of ozonation combined with coagulation on their oxidation extents of organic matter and the production of DBPs. Studies showed that there were remarkable differences between the two processes, POC and OC, which proved the existence of joint interaction of ozone and coagulant. The joint interaction involved the following aspects. 1 Decomposition rate of ozone was improved; and the free radical production was increased during OC compared with POC. Comparing to ozone alone, 15.2% and 23.9% more radical capture with ozone 2mg·L-1, Al3+ 1 mg·L-1, 3 mg·L-1 were detected. 2 The difference of OC and POC was found in that organic matter removal of OC was lower than that of POC. The pathways of OC and POC showed difference, which resulted in differences of reaction between organic matter and disinfectant, as well as yields of DBPs. OC removed UV254 and DOC more efficiently than single ozonation or single coagulation; but less efficiently than POC. DCAAFP (Dichloroacetic acid formation potential) and TCAAFP (Trichloroacetic acid formation potential) were 47 μg·L-1 and 20.5 μg·L-1 respectively after treatment by POC with O3 1mg·L-1and Al3+1mg·L-1, and chloroform formation potential (CFFP) was 97.8 μg·L-1, which were 51%, 64.6% and 41.5% respectively lower than those in the raw water. Under the same dose conditions, DCAAFP, TCAAFP and CFFP after OC were 48.4 μg·L-1, 21.4 μg·L-1 and 117.3 μg·L-1, respectively, which were 49.6%, 63% and 29.5% lower than those in raw water. The difference between the efficiencies of POC and OC would be enlarged with increase of coagulant dose under the same ozone dose. Considering its safety and efficiency, the ozone dosage, adding spot and coagulant species must be taken into account when combined treatment of preozonation and coagulation is used; further investigations are also needed.