TREATMENT OF ALGAL-LADEN WATER - PILOT-PLANT EXPERIENCES

In recent years an increase in the eutrophication of reservoirs has ad ded to the problems of lowland surface-water treatment. A pilot plant was installed to test the effectiveness of various treatment regimes f or a river source which was subject to occasional algal blooms, and a eutrophic reservoir source which was heavily contaminated with cyanoba cteria (Oscilatoria sp.). The treatment processes adopted were dissolv ed-air flotation for chemical coagulation, sand and anthracite filtrat ion, comparative disinfection stages using ozone and chlorine followed by granular activated carbon filtration. The dissolved-air flotation plant was not particularly effective for the removal of algae, but the sand/anthracite filtration process was capable of removing 50% of the algae. The ozone disinfection stage was adequate for disinfection and also reduced algal numbers. Overall the chlorine/granular activated c arbon method did not perform as effectively as the ozone/granular acti vated carbon process; the latter process was +99% effective for algal control, with river and reservoir sources.