Effect of preozonation on characteristics of algae cells and algae-derived organic matter (AOM) with respect to their removal by coagulation

Abstract

The presence of algae cells and algae-derived organic matter (AOM) including extracellular organic matter (EOM) and intracellular organic matter (IOM) has a significant impact on drinking water treatment. Jar tests were conducted with or without preozonation to assess the effect of preozonation on the characteristics of AOM and algae cells with respect to their removal by the following coagulation process. Algae cells and AOM were analyzed by photomicrography, particle size distribution, UV absorbance scanning, HPSEC-UV and batch ultrafiltration (UF). Micrographs and particle size distribution of algae cells with or without ozonation showed that ozonation could oxidize chlorophyll in algae cells, damage algae cells to varying degrees and increase the settling property of algae cells. UV absorbance scanning showed there were more protein-like substances in AOM. Molecular weight (MW) distribution revealed that IOM and EOM had almost the same species of organic matter: the major species of IOM was organic matter with high MW and EOM was organic matter with lower MW. Overall, preozonation can enhance the coagulation process by greatly increasing the removal efficiency of algae cells and particles. At the same time, preozonation is not very effective on enhancing AOM removal, for it is limited in improving the removal rate of EOM, and it can cause the release of IOM.