# Ozone-Loaded Hydrogels as an Eco-Friendly Strategy to Control Phototrophic Biofilms on Cultural Heritage Surfaces

## TL;DR

This paper explores ozone-loaded hydrogels as a sustainable and effective way to control harmful microbial growth on historical sites like ancient Roman structures.

## Contribution

The study introduces ozone-loaded bacterial cellulose hydrogels as a novel, eco-friendly antimicrobial treatment for cultural heritage preservation.

## Key findings

- OBC hydrogel achieved >90% bacterial mortality within 10 minutes and inhibited fungal spore germination.
- The hydrogel reduced microalgal chlorophyll fluorescence and restored surface color parameters on Carrara marble and brick.
- In situ applications showed suppression of green biofilm for at least two months.

## Abstract

Biodeterioration represents a major threat to cultural heritage, as microbial colonization can cause both esthetic and structural damage. The use of conventional chemical biocides raises concerns due to environmental and health risks, potential substrate deterioration, and the emergence of resistant strains. In this study, an ozone-loaded bacterial cellulose (OBC) hydrogel was investigated as an eco-friendly, broad-spectrum antimicrobial treatment in the case study of the Cryptoporticus of the Baths of Trajan (Rome, Italy), a hypogean archeological site where some structures are severely affected by phototrophic biofilms. Microorganisms isolated from a colonized wall were employed in laboratory assays. OBC hydrogel exhibited strong antimicrobial activity, with >90% bacterial mortality within 10 min, complete inhibition of fungal spore germination after 24 h, and a marked reduction in microalgal chlorophyll fluorescence comparable to heat-killed controls. Furthermore, tests on Carrara marble and brick specimens artificially contaminated with microalgae confirmed the removal of green staining, restoring surface chromatic parameters (ΔE* < 5) comparable to those obtained with a commercial biocide. In situ applications demonstrated significant suppression of green biofilm for at least two months. These findings support OBC hydrogel as a sustainable, effective, and non-toxic alternative to conventional biocides for controlling microbial and microalgal colonization on cultural heritage surfaces.