Interactions Between Scenedesmus Obliquus And Heavy Metals

The study of the interactions between algae and heavy metals is of great importance for bioassay of toxic metals and the biotechnology to remove heavy metals from wastewater. But the mechanisms are still poorly understood in the literature. In this thesis, the effection of four heavy metals(Cu²⁺,Zn²⁺,Pb²⁺ and Mn²⁺) on the growth offive spieces of scenedesmus obliquus were investigated.In this dissertation, there are two aspects on heavy metals showed a high toxicity on the growth of the algae. One is sole heavy metal was toxic with algae and the other is each two of four heavy metals were toxic with algae. The concentration of algae was suppressed by the concentration of heavy metals. It is found out the EC50 of Cu²⁺,Zn²⁺,Pb²⁺ and Mn²⁺ was on scenedesmus obliquus in 48 and 96 hours. As a result, EC₅₀ of four heavy metals in 48 hours were:Cu²⁺2+< Zn²⁺2+ and the toxicity was Cu²⁺>Pb²⁺>Zn²⁺>Mn²⁺. Furthermore, in 96 hours, EC50 of four metals were: Cu²⁺2+< Pb²⁺2+ and the toxicity of them was: Cu²⁺>Zn²⁺>Pb²⁺> Mn²⁺ . Each two together of four heavy metals showed different effects on toxicity which was Synergistic effect and Antagonistic effect. For example, when the joint action of Cu²⁺, Zn²⁺ was the same concentration, the toxicity showed on Synergistic effect in both 48 and 96 hours. However, when they jointed together with the same toxicity, the toxicity showed on Antagonistic effect in 48 and 96 hours.Moreover, it was also studied that the adsorption capacity of scenedesmus obliquus was different in different conditions such as temperature, pH, Algae's amount used and time. According to adsorptive capacity and Transformed rule of scenedesmus obliquus adsorped to sole heavy metal, it can be determined by different adsorption capacity to different heavy metals.Obviously, these conditions could change adsorption efficiency. In this example, the pH was between 3 and 5, adsorption efficiency was best, while the temperature was between 20°C and 30°C, adsorption efficiency might enhance as the temperature elevated.