Mikrobielle Werkstoffzerstörung – Simulation,Schadensfälle und Gegenmaßnahmen: Untersuchung der Beständigkeit von keramischen Werkstoffen

Microbial deterioration of materials – simulation, case histories and countermeasures: Testing of the resistance of ceramic materials Testing of microbiologically influenced corrosion of ceramic materials by biogenic sulphuric and nitric acid corrosion is well described and applied for constantly moist buildings like sewage pipelines and cooling towers. The complex situation on historical buildings of natural sandstones has not yet been investigated in the laboratory. A double-chamber cabinet and a test system for the simulation of chemically (gaseous pollutants), combined chemically and microbiologically (gaseous pollutants plus nitrifying bacteria) and solely micro biologically (nitrifying bacteria) influenced corrosion of natural sandstone is presented. A high stone moisture was essential for the growth of nitrifying bacteria on test stones. Under optimum conditions a nitrifying biofilm developed on the calcareous Ihrlersteiner green sandstone, reducing the evaporation from the stone surface. Biofilm cells adapted well to high concentrations of gaseous pollutants (1,065 μg/m³ sulphur dioxide, 850 μg/m³ nitric oxide, and about 450 μg/m³ nitrogen dioxide): in the simulated smog atmosphere. The mean metabolic activities of ammonia oxidizers were 11 times and those of nitrite oxidizers 30 times higher than mean values of samples from historical buildings. The microbiologically, influenced nitric acid corrosion alone was 8 times stronger than the chemically influenced corrosion by the simulated smog atmosphere. If sulphur dioxide was added, the microbiologically produced nitrite was removed by chemodenitrification. Thus, the combined attack of nitrifying bacteria and gaseous pollutants did not result in an increased corrosion, but the nitrifying biofilm promoted the formation of gypsum.