Introducing green conservation protocols for the preservation of waterlogged wood

Between 2016 and 2023, a Swiss-funded project aimed to enhance the conservation of waterlogged wood by developing a bacterial extraction method prior to polyethylene glycol (PEG) impregnation and freeze-drying. The protocol employed siderophores and bacteria to remove harmful iron and sulfur compounds (BT), in comparison to a chemical extraction (CT) using sodium persulfate and ethylenediaminetetraacetic acid (EDTA). Tests conducted on 500 waterlogged wood samples assessed the efficiency of sulfur and iron removal, as well as changes in wood color. The subsequent consolidation involved sequential PEG 2000 baths (8%–40%) at room temperature or 40°C for larger samples, monitored using refractometers and pH checks. Freeze-drying parameters were adjusted to critical temperatures to preserve wood morphology. Biological treatment resulted in wood reddening, while chemical treatment caused bleaching. The anti-shrinkage efficiency exceeded 75%, with an average of 90% for freshwater samples. In parallel, previously consolidated and dried wood samples were treated with a 3% agarose gel containing either chemical or biological reagents at 35°C. Treated samples exhibited discoloration, whereas control samples retained their original color. Infrared spectroscopy confirmed PEG retention in the consolidated wood, with no observed swelling. XRF analysis revealed iron removal exclusively in BT-treated samples. BT also demonstrated potential for chlorine trapping and effective sulfur removal, even in previously preserved wood. The study highlights the advantages of green extraction methods in reducing toxicity, health risks, and energy costs during conservation, offering a sustainable approach to preserving archaeological waterlogged wood.