Conventional versus advanced treatment for eutrophic source water

The Cheng Ching Lake Water Works in southern Taiwan draws its raw water from an eutrophic lake. There are taste and odor problems in the finished water because the conventional treatment processes currently used cannot completely remove the metabolites of algae or other microorganisms. Consumers also complain about the high levels of hardness in the water. To improve the organoleptic properties of the finished water by upgrading the treatment processes, a pilot-scale study was conducted. Three processes were compared side by side: a conventional process without prechlorination (process 1); a conventional process plus ozone, granular activated carbon, and pellet-softening (process 2); and an integrated membrane process (ultrafiltration plus nanofiltration) following a conventional process (process 3). Results showed that process 3 produced water with the best quality, whether dissolved organics, biostability, or organoleptic parameters were concerned. The second-best results occurred with process 2, which produced water with high biostability and aesthetic quality. The study also found that simply avoiding prechlorination significantly improved the biostability of the finished water when compared with that of conventional processes.