Removal of freshwater diatoms (Synedra acus and Stephanodiscus sp.) by preozonation and addition of polyamine coagulant-aid

Pilot studies were conducted for the removal of two freshwater diatoms (Synedra acus and Stephanodiscus sp.). Poly aluminum chloride (PAC), one of the coagulants commonly used in conventional potable water treatment, was found to be not effective in removing diatoms, especially for Synedra. In this work, preozonation and polyamine coagulant-aid in the presence of PAC were compared with each other and combined to investigate their performances on removing diatoms. It was found that the preozonation and polyamine coagulant-aid increased the removal rate significantly for both diatoms, better performance than PAC alone. When polyamine coagulant-aid and preozonation were combined with PAC, approximately 90% of Synedra and 100% of Stephanodiscus were eliminated. It can be concluded that the combination of preozonation and polyamine coagulant-aid in the presence of PAC could be a promising solution for removing resistant diatoms in water treatment.