Aerobic Microbiological Corrosion of Water Pipes (Parts I and II)

Tubercles found inside pipes in which water is flowing, in addition to large quantities of amorphous ferric hydroxides, contain iron bacteria surrounded by sheaths. Inoculated sterile tap water with an appropriate iron source, will provide a strong growth of iron bacteria. These bacteria, while not the direct cause of corrosion, primarily oxidize Fe+2 into Fe+3 whereby they gain the energy necessary for the assimilation of carbon dioxide. Iron bacteria sheaths assist in formation of a membrane relatively impervious to oxygen and in the process decrease the quantity of oxygen in the immediate vicinity, forming a micro-electrochemical cell. Experimental confirmation of the premise is claimed through the use of differential aeration cells created by using germ filtered water with and without inoculation with iron bacteria. Iron bacteria play a decisive role in initial formation of the differential cells but a minor one in establishment of anaerobic conditions under the tubercle during the main period of the corrosion. After tubercle formation corrosion proceeds practically independently of the metabolic activity of iron bacteria. Inhibition of further corrosion is attempted by changing the equilibrium of the water to form a layer of chalky rust on the tubercle.