Hidetsugu Sasaki

Pollution of coastal sea water and sulfate reducing bacteria in connection with microbial corrosion of metallic materials in desalination plants

Abstract The qualities of sea water and bottom sediment in Tokyo Bay were investigated in relation to the activity of sulfate reducing bacteria. Higher concentration of organic substance and larger number of the bacteria were observed in surface layer than in bottom layer of the sea water influenced by polluted rivers. This result reveals that polluted river water spreads widely in surface layer of the sea, and that the bacteria grown in bottom sediment near the estuaries are carried in with the flowing water. In the sediment greater number of the bacteria and considerably higher organic content were found than in the sea. Anaerobic incubation tests of the sediment resulted in generation of hydrogen sulfide, which revealed that bottom sediment itself possessed enough content of organic substance and variety of bacterial flore to generate hydrogen sulfide. It follows that, in the operation of desalination plants using polluted water, quite natural attension that bottom sediment must not be taken in, proved to have important meaning for the prevention of microbial corrosion.

Corrosion Resistance of Materials in Concentrated Solutions of Iodine and Iodide (Environment of the 1st Stage Reaction)

Magnesium-Iodine cycle is based on the four main reactions containing corrosive iodine and iodide at temperatures of 150 to 700C, therefore the selection of construction materials for this cycle is very hard and the study of that is prime importance. The study was shared for every basic reaction and allotted to four laboratories. This part 1 report summarized the experimental results of exposure of metallic and nonmetallic materials to some testing environments corresponding to the first stage reaction. Among the four basic reactions only the environment of the first stage reaction is an aqueous solution. And then the corrosion behavior in this environment appeared somewhat specific unlike that in the environments of the other three stages. The metallic materials selected from the viewpoint of corrosion resistance were tantalum, niobium and zirconium; and the corrosion resistance of the first two metals was almost perfect. But these three metals are very expensive and then not practical as construction material except special parts such as a nozzle. Therefore it is prefered to develop the non-porous coating method of these metals on some inexpensive metal. On the otherhand, almost all nonmetallic materials (oxide ceramics, ceramics coating, carbon products, plastics et al.) absorbed the solution of iodine and iodide without regard to their corrosion resistance. Then the practical evaluation of nonmetallic materials for the first stage reaction seemed difficult and was reserved for some time.