Investigation on the microwave heating method for the control of biodeteriogens on cultural heritage assets

Several organisms, like bacteria, algae, cyanobacteria, lichens, and fungi have their natural ecological niche on monumental stones, wall paintings and in hypogean environments where they can play an important role in the physical-chemical deterioration and aesthetical alterations of the support materials. In order to control this biodeterioration process, during conservation, chemical formulates with biocidal action are usually applied (before and after cleaning interventions). This procedure has been most recently reviewed in order to limit the risk for the substrate and the operator, decrease the environmental pollution and avoid the possible selection of microorganisms resistant to the most used biocides. An alternative methodology based on physical approach is proposed. Microwave heating has been already used with different degrees of success for the treatments of some biological agents on several materials and supports, such as nematodes and other pathogen organisms from soils, grain storage insects and wood beetles in the cultural heritage field. For the control of biodeteriogens on the artistic surfaces has been adopted a system based on new type of applicator that limits the heating to the thickness of the patinas preserving the substrata from thermal stress. Several lichens and black fungi have been isolated from cultural assets of historical interest, and they have been used to test, in laboratory, the microwave heating technique in order to develop a new control methodology for the above mentioned organisms. The advantages of microwaves with respect to conventional techniques (mechanical methods, biochemical and chemical methods, biological and other physics methods) are: the safety for the cultural asset and for the operator, thanks to the low-interaction with the substrate and penetration depth. The first results are very promising and the methodology can be directly applied on site. The use of the proposed microwave heating method to kill biodeteriogens can avoid the application of chemicals formulates potentially dangerous for substrates and environment.