Il Duomo di Milano

by Elio
 

Complete view of the façade of Milan ca­the­dral.

Grime on old buildings is a microbiological concern – not because microbes cause it, but because they can help get rid of it. The gray pall shrouding old buildings comes from the conversion of chalky stone such as marble (cal­cium carbonate) to gypsum (calcium sulfate), a result of atmospheric pollution. Not only is gypsum more soluble (which facilitates deterioration), but smog and mineral particles stick to it, which gives venerable old buildings a mournful cast. The conventional way to clean such faça­des is to douse them with an ammonium carbonate-EDTA-surfactant mixture. Now there is a better way.
 

A group of researchers from several Italian institutions have devised a biological cleaning method that employs sulfur reducing bacteria to convert the gypsum back into calcium carbonate. Desul­fovibrio desulfuricans is adept at that, and these researchers cleverly devised procedures for its delivery to the affected areas. Using an autotrophic organism has advantages too, in that you don't have to feed it with an abundance of organic nutrients. By several biological, chemical, and visual criteria, this biological treatment method is clearly superior to the chemical one. The bac­teria are careful workers, removing the gypsum but leaving a warm patina, and making the sur­face stronger than when they arrived. However, we must be mindful that this report deals with small scale laboratory experiments. Tackling a whole building may require considerable engin­eering development.
 

View of the left side of the Milan cathe­dral, taken from the stairs to the roof.
 

I want to bring up a personal reason for mentioning this work. I was born in Milan and lived there until almost teen age. Since we lived only a short walking distance away, I often went to the Piazza del Duomo, the Cathe­dral Square. I got to admire the cathedral and its hun­dreds of spires. As the family story goes, when I was a toddler my nanny took me into the cathedral, most likely to pray. When we got home, my Teddy Bear was missing. It turned out that I had left it in a confessional where I'm sure that it got freed of all its sins.
 

 
 

 
 

Comments

[Dan]

Wow!

I work in the Oil Business, and I know that microbes (bugs, we say) can be used to clean up oil spills, to decrease viscosity and therefore increase flow rates down hole, as well as plug up flowing wells and pipelines. I had no idea you could use them to clean up old buildings! What a great idea!

Dan (Melanies's Brother)