| As a kind of global oceanic disaster, Harmful Algal Blooms (HABs) have increased in frequency, intensity and geographic distribution, seriously threaten human health, marine environment and fishery resources, brought a great amount of economic loss on marine aqualture. Studying new, economical and effective HAB mitigation methods has important scientific significance and application prospect. In this dissertation, we studied the effect of clay on the fundamental psychological index of China common I-LAB species, and put forward methods of clay surface modification in order to improve the removal efficiencies of clay mineral. In addition, the inorganic flocculants MMH and PSMS were used in HAB mitigation for the first time, and the environmental and ecological effect of above agents were investigated accordingly. The main results are as follows. 1. Study on screening of clay minerals About 30 kinds of clays were collected from home and abroad to investigate their removal efficiencies on HAB organisms Heterosigma akashiwo and Alexandrium tamarense. Experimental results showed that the coagulation efficiencies of HAB organisms varied with clay kinds markedly, and the chemically treated kaolinite, the clays from wuxian, suzhou and WHOI showed higher coagulation capability. The coagulation curves of these clays on Heterosigma akashiwo andAlexandrium tamarense indicated that the maximum removal rates varied with clay kinds and I-LAB species. Compared with H. aka.shiwo, A. tamarense was easy to be removed. 2. Psychological effects of clay on HAll organisms The effects of kaolinite on the growth, chla content, photosynthesis and respiration of H. akashiwo and A. tamarense were studied. Results showed that kaolinite inhibited the growth, chla content and photosynthesis of FLAB organisms, and the inhibition effect enhanced with time and clay concentration, which was considered as due to reduction on light and change on trophic environment of algae after adding clay. In addition, the inhibition of kaolinite varied with algal species, A. tamarense was more sensitive than H akashiwo. 3. Study on preparation of inorganic flocculants and their coagulation on HAll organisms The preparation of inorganic flocculants MM.I-I and PSMS (including PSAC and PSAS), and their coagulation on I-JAB organisms were studied in this part. In the process of MMH preparation, Mg/AL molar ratio and temperature were investigated. MMH prepared under the condition of Mg2/Al32 had higher removal efficiencies and coagulation rates on Heterosigma akashiwo and 1.5 mmolAl3~/L were obtained as the economic dosage used to coagulate Heterosigma akashiwo. 3-factor, 3-level orthogonal test were designed to prepare PSAS, and the optimum conditions were: concentration of Si022%, Al3/SiO21 and pH=4. Coagulation experiments showed that the removal efficiencies PSAS varied with HAB species due to different size, structure, locomotion and extracellular excrete of algal cells, and were much higher than that oftraditional flocculant AS.4. Studies on clay surface modification and coagulation mechanisms In order to improve the removal efficiencies of clays on HAB organisms, insertion reaction method and surface adsorption method were used to prepare modified clays. Preparation experiments showed that the optimum preparation conditions for the two methods were: prepar...
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