Sewage Purification By Chiorella Ellipsoidea And Its Tolerant Mechanism To Cd～(2+)

By spreading on agar plates, a strain of Chlorella ellipsoidea was isolated from a polluted pond receiving wastewater from the electroplating factory. Based on its high tolerance to heavy metals, we studied the effects of Cdi+ stress on physiological characteristics and ultrastructure of C. ellipsoidea. The NH4+-N, PC>43~-P and Cd2+ purification efficiency of immobilized algae under different Cd2+ concentrations were also investigated. Under Cd2+ stress, photosynthetic rate, chlorophyll content, membrane exosmosis and nitrate reductase (NR) activity of C. ellipsoidea decreased while proline content increased. The polyunsaturated fatty acid (PUFA) content decrease was accompanied by the increase of contents of superoxide radical (C>2~) and malondialdehyde (MDA). The antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD) et al., have significant functions in resisting the Cd2+ stress. SOD and POD activities were induced in high level to eliminate and resolve excessive reactive oxygen species (ROS) in the algal cells. Catalase (CAT) activity is rather sensitive and has little function. Ultrastructural observation revealed that Cd + stress resulted in the disappearance of pyrenoid, increased starch grains and swollen thylakoids of chloroplast, increased content of vacuole and the multi-nucleus cell. This strain of C. ellipsoidea showed its rather strong ability to remove the NH4+-N, PO43"-P and Cd2+ from the wastewater. It was found that the calcium alginate has little toxic effect on C. ellipsoidea as a carrier. And the results showed that the sewage purification efficiency of immobilized algae were much higher than those ofsuspended ones. The purification efficiency of immobilized algae decreased with increasing Cd2+ concentration, and that of suspended one decreased sharply. Immobilized algae technology can be exploited as a useful means for efficient sewage purification in the future.