The Use of Photosynthetic Microorganisms in Bioremediation

The microorganisms play an important role in selfpurification of water and soil environment as decomposers in the ecosystem. Microbial technologies, such as a activated sludge or oxidation pond processes, have been extensively applied to the treatment of industrial and domestic sewages to break down organic wastes. Another type of treatment is based on their ability to remove specific substances such as phosphorus, nitrates and heavy metals. The environmental pollution by toxic metals, especially Pb, Hg, Cd, is a potential hazard to the health and welfare of mankind. Many people in Japan suffered from diseases caused by pollution of heavy metals, such as ache-ache disease and Minamata disease. We feel misgivings about the similar environmental pollution in the developing countries, for the rapidly growing industrial operations would release heavy metals and those metals even at very low concentrations would be concentrated biologically through natural food chains. Microalgae can concentrate metals and transform them into less hazardous forms, and the use of microalgal biomass would offer a potential alternative to conventional methods for detoxification and for recovery of toxic or valuable metals. This review summarizes an information on physiological relations between heavy metals and microorganisms, especially microalgae, and presents some applications of algal biotechnology that has been developed to use microalgal biomass for bioremediation of heavy metals.