A STUDY ON OPTIMIUM CONDITIONS FOR THE REMOVAL OF RED TIDE ORGANISMS BY MODIFIED CLAYS

The water samples from the Prawn-culture pools of Shangma Town, Chengyang District of Qingdao were collected weekly from May 9 to August 29, 1995 and the biologic species were identified. The result shows that the total amounts of phytoplankton in the water samples collected from the No.3 small pool in the northem part of the culture field reached red tide concentration on July 4 and 7. The predominant species were Phaesodactylum triconutum, Gymnodinium sp. (July 4) and Phaesodactylum triconutum, Nitzchia closterium Gymnodinium sp. and Euglena sp. (July 11), respectively. The red hde organisms were coagulated by the modified clay and the optimum conditions for removing red tide organisms were obtrined by means of the orthogonal test. The results show that an optimum formula for removing Phaesodactylum triconutum is: modified kaolin 75-100mg / L, PACS 2-5mg / L and sodiurn perearbonate 5-30mg / L. Opdmum formelae are: removing was modified kaolin 35mg / L, PACS 2-5mg / L and sodium percarbonate 7-10mg / L for Gymnodinium sp., and modified kaolin 75-100mg / L, PACS 0.4mg / L and sodium perearbonate 30mg / L for Mitzchia closterium. In all of the above formulae, the best pH was 6.0 and removal rates reached 80%-90% within 12 hours. The best formulae were slightly different with different species. Thus the formula should be selected according to the predominan species in the field waters.