Preliminary Results On The Use Of Clay To Control Pyrodinium Bloom - A Mitigation Strategy

The frequent and expanded occurrence of Pyrodinium bahamense var compressum blooms in the Philippines since 1983 has prompted the need to find mechanisms to control the harmful effects of these toxic dinoflagellates. A promising method now being explored is the use of powdered clay minerals which when added to the growth media is capable of flocculating with the algal cells. In this study, the efficiency of ball clay, brown bentonite, and Malampaya Sound sediments to remove Pyrodinium cells in seawater was tested. The addition of 1 g/L of suspended ball clay to 50 mL of cultured Pyrodinium cells (~1.037 x106 cells/L) removed 99.56% of the algal cells after 2.5 hours. Prolonging the exposure time to 5 and 24 hours showed no significant increase in flocculation. Brown bentonite and Malampaya Sound sediments showed low to moderate removal efficiency not exceeding 70% and 50%, respectively. The effect of ball clay addition on seawater chemistry showed no change in ammonia concentration but nitrate decreased after 5 and 24 hours of clay addition. Results for nitrite and phosphate were however more variable