The effect of ozonation and filtration on AOC (assimilable organic carbon) value of water from eutrophic lake

The effects of applying ozone into the source water of Cheng-Ching Lake Water Works (CCLWW) on the analysis of AOC (assimilable organic carbon) were compared in the laboratory and pilot-scale tests. CCLWW takes its raw water from an eutrophic lake. A pilot plant, established in CCLWW in southern Taiwan, was performed to improve the quality of water obtained by the former treatment processes. The direct application of ozone to the source water of CCLWW is called the pre-O3 process. The post-O3 process involves the treatment of effluent with ozone through a sand filter, following other treatments, including pre-O3, coagulation and sedimentation. In a laboratory test, a 0.45 μm membrane filter was used to replace the facility of filtration for a sand filter. AOCTotal comprises AOCP17 and AOCNOX, which were determined using the P. fluorescens strain P17 and the Spirillum species strain NOX, respectively. During over 2 years' sampling in eutrophic lake, it revealed that AOCP17 contributed substantially to AOCTotal. However, the filtrate from the source water obtained by filtering through a 0.45 μm membrane filter had an AOC Total much lower than that of the source water, especially for the considerable decrease of AOCP17. Also, the AOC value in source water is increased with algae number but not with NPDOC (non-purgeable dissolved organic carbon). This result indicated that algae numbers existing in the eutrophic lake might affect the analysis of AOC. Following the pre-O3 process at the pilot-scale plant, the AOCP17 was markedly lower than that of the source water, and AOCNOX was slightly higher than that of the source water. However, when post-O3 was added to the effluent from a sand filter at the pilot-scale plant, AOCNOX exceeded that before post-O3, while AOCP17 differed slightly from that before post-O3. Apparently, this difference may be due to the algae number existing in the water samples. These results were verified by applying ozone to the source water, and to filtrate obtained by filtering through a 0.45 μm membrane filter in a lab-scale test, respectively. Copyright © 2006 International Ozone Association.