Indicators for microbiologically induced corrosion of copper pipes in a cold-water plumbing system.

Corrosion damage in the copper cold-water plumbing system of a large building was investigated. An unusual combination of corrosion patterns was found on the inner copper pipe surfaces that were in contact with water. Damage was in the form of shallow cavities, a surface cover or pinprick-like pits. The corrosion system was influenced by thermal treatment and also by cefoxitin dosing. The latter fact in particular is a clear indication of microbiological involvement in this corrosive action. Different parameters, to be measured in standing water (24-h stagnation), are considered typical for this type of corrosion: the detection of Sphingomonas spec. and other species in whose cell wall regions copper can accumulate, a copper content of more than 2 mg/l, oxygen consumption of more than 4 mg/l and an increase in pH. With the help of these indicators, it is possible to recognize microbiologically induced corrosion in copper plumbing systems before pipe perforation occur.

Three steady state situation in an open chemical reaction system I.

In an isothermal continuously stirred tank reactor (open chemical reaction system) fed by sulphuric acid solutions of bromate, bromide and cerium (III) bistability (three steady state situation) is experimentally observed. This remarkable behavior, based on the instability of one steady state, has important consequences for the understanding of excitability and biochemical control mechanisms. The mass-balance equations for the reactor and the chemical mechanism of the reaction are combined into a simple mathematical model. The behavior of the resulting nonlinear differential equations is examined analytically and by a graphical integration procedure (method of isoclines). Using realistic kinetic data, the model shows the same behavior as observed in the experiment.