Simulation of microbial attack on natural and artificial stone.
Testing of microbiol. influenced corrosion of ceramic materials by biogenic sulfuric and nitric acid corrosion has been well described and applied to permanently moist structures like sewage pipelines and cooling towers. In contrast, the complex situation for historical buildings of natural sandstones has not yet been investigated in the lab. A double-chamber cabinet (DCC) and a test system are presented for the simulation of chem. (gaseous pollutants), combined chem. and microbiol. (gaseous pollutants plus nitrifying bacteria) and solely microbiol. (nitrifying bacteria) influenced corrosion on natural sandstone. A high stone moisture was essential for the growth of nitrifying bacteria on test stones. Under optimum conditions a nitrifying biofilm developed on calcareous Ihrlersteiner green sandstone, reducing the evapn. from the stone surface. Cells in biofilms adapted well to high concns. of gaseous pollutants (1065 mg/m3 sulfur dioxide, 850 mg/m3 nitric oxide, and .apprx.450 mg/m3 nitrogen dioxide) in the simulated smog atm. The mean metabolic activities of ammonium oxidizers were 8-11 times and those of nitrite oxidizers 30 times higher than mean values of samples from historical buildings. The microbiol. influenced nitric acid corrosion alone was eight times stronger than the chem. influenced corrosion by the simulated smog atm. If sulfur dioxide was added, the microbiol. produced nitric acid was removed by chemo-denitrification. At the same time the nitrifying biofilm promoted the formation of gypsum.
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