Mold Inactivation on Water Damaged Documents using Supercritical and near Supercritical CO2

Author:  Rory Dempsey, BSc., MRSC. 

Midwest Freeze-Dry, Ltd.

Abstract

To find an environmentally friendly and non destructive cost-effective restoration method of mold decontamination which effectively destroys mold and bacteria after water damage and is suitable for vellum books, paper books, documents, paper, archival records, art works and textiles. Midwest Freeze Dry has pioneered the novel use of supercritical/near supercritical CO2 for mold inactivation after water damage and applied it on cost-effective industrial scale to conserve leather books, vellum books, paper books, documents, artworks and textiles after water damage.

Introduction

Our unique cost-effective mold treatment is the best for leather books, vellum books, paper books, documents, artworks and textiles after water damage. Why?

Most of the commonly used mold treatments such as regular heat sterilization, methyl bromide, ethylene oxide and ozone bleaching can damage or destroy the vellum book, paper book or legal document being treated along with the mold and/or damage the environment.

At Midwest Freeze Dry no ozone bleaching or environmentally dangerous chemicals are used to treat mold on leather books, vellum books, paper books, documents, artworks and textiles after water damage and there are no harmful gasses or waste to be disposed of. Instead we have adapted a Cost-effective scientific freeze drying process which is normally used to decaffeinate coffee to kill molds. Independent clinical tests prove that we are capable of reducing molds by 95%. Our cost-effective treatment uses near and supercritical carbon dioxide which effectively destroys molds and bacteria after water damage and is suitable for books, documents, archival records, art works and textiles. Our cost-effective method has taken us seven years to develop. It is non destructive and cost-effective environmentally safe unlike other methods.

The first step is that the water damaged documents and water damaged books is blast frozen to minimize large ice blocks which can damage the paper in your water damaged leather books and vellum books, paper books, or documents further.

Normal freeze drying is a good second step if the water damaged textiles and water damaged books and water damaged  documents being treated contain water but is not without its draw backs. Freeze drying removes the water, but on its own freeze drying is an unacceptable form of treatment for mold on books, papers, and documents after water damage. This is because mold has a protective mechanism within its life cycle which can help it to survive against such extremes as freezing and desiccation. When this occurs mold forms rough, thick walled protective coatings protective called zygosporangia which allow it to become metabolically inactive until such time that conditions improve (conditions where the temperature is warmer and there is more water). Many laboratory suppliers make use of this mechanism and commercially freeze dry mold samples to sell to researchers. So normal freeze drying is not enough, further treatment is required.

Midwest Freeze Dry  innovation is that after freeze drying the process of decontamination is continued using a series of other techniques. After freeze drying the material is treated with plasma. The plasma is generated using a dielectric field and a special mix of gases which are all contained in a customized vacuum chamber. 

Plasma is considered by physicists to be a fourth state of matter. It is a highly ionized neutral gas in which the number of free electrons is approximately equal to the number of positive ions. Particles present in the plasma such as ions and free radicals have a high activity and do the work on the moldy documents, papers, photographs, manuscripts, maps, slides, microfilm, microfiche,  x-rays and books.  Their high activity is related to the process pressure.

After plasma treatment the leather books, vellum books, paper books or documents are treated with carbonic acid. Carbonic acid (H2CO3) is a dibasic acid which is formed when carbon dioxide is dissolved in water. It is a chemical reaction which occurs in nature when rain water is formed.

CO2 (gas) + H2O(aq) ↔  H2CO­3 (gas)

Under special controlled conditions this carbonic acid is introduced along with applied heat and effectively sterilizes the affected material being treated including the mold. This may occur due to the unique mass transfer properties of super critical / near supercritical CO2 which may allow the fluid to penetrate the cell walls and interact with the intracellular components of the mold. This Cost-effective sterilization is a function of both the proximity to the fluids critical point and the chemical nature of the fluid itself.

Materials And Methods

To test our treatment we used conventional microbiological procedures and did multiple tests on areas of water damaged mold infested documents. We took samples before and after treatment and then analyzed the samples. The samples were also independently analyzed.

Media - Potato Dextrose Agar.

Materials - Petri dishes.

Methods - Serial dilutions.

Conditions – Aseptic conditions. Samples were incubated at 37°C in a constant temperature growth chamber.

Results And Discussion

Midwest freeze dry were able to identify the most prevalent mold present and to take a colony count. The most abundant molds were identified as the common paper molds Fusarium, oxysporum and Penicillium notatum. The colony counts were measured in Colony Forming Units (Cfu’s).

Midwest Freeze Dry’s in house test results were able to show that the mold had been reduced by 2-3 log orders (5 samples taken - mean initial cfu’s 28,000 , mean final cfu’s 1,307 a reduction of 95.33%) and were consistent with an independent laboratory’s results, but with the added advantage that the results were available after 48 hours.

While growing cultures may permit greater accuracy in speciating some fungal organisms present, the ability of spores to grow and compete on laboratory media can differ significantly with their ability to grow and compete on a more real world substrate such as a file, document, book or textile.

However, for our needs the use of this type of analysis is very useful. Firstly it gives us a feel for the degree of mold infestation and thus the level of treatment required. Secondly as the mold is being grown on an agar plate the humidity conditions are very high, almost 100% RH, particularly while the agar is wet. As humidity is perhaps the single most important factor which affects mold growth, cultivation on agar should give living mold the favorable conditions that it needs to reactivate, release its haploid spores and re-colonize its new substrate. In short using this method lets us know that we have done our job.

Consider the reality; molds have a high natural incidence. Penicillium and Fusarium for examples have 6% and 5% presence respectively in an average sample of outdoor air. This fact combined with molds complex survival mechanisms make 100% mold eradication an unachievable goal. Our results were a 95.33% mean reduction which we consider a good outcome as the mold was significantly eliminated and important documents were saved and rendered safe to normal handling.

A few or trace amounts of fungal spores in surface sampling should be considered background and be expected. In this investigation our methods were tested on fungal species that were found on documents the most significant but not exclusively being common paper molds Fusarium, oxysporum and Penicillium notatum. We are conscious that these are not the only fungi that which infest books, legal documents, works of art and personal collections but we feel that these our methods could be applied equally to any rapidly growing, asexually reproducing fungus.

Why Choose Midwest Freeze Dry

Midwest Freeze Dry has 25 years experience in Cost-effective restoration.

We are a specialized and dedicated firm that uses the most up to date scientific methods to treat water damaged books and water documents. Our non ozone treatment excels after water damage to vellum books, paper books, documents, paper, archival records, art works and textiles. We spend a large proportion of our time in the research and development of new non chemical technologies to be applied to the restoration and conservation of water damaged books and water damaged documents and are consulted by other conservation professionals daily.

Midwest Freeze Dry acknowledges that freeze drying alone does not kill mold. We believe that further treatment with supercritical and near supercritical CO2 is a satisfactory and environmentally safe mold treatment for materials after water damaged documents and water damaged books. No Ozone is used in any of our processes because our research has shown it degrades paper by bleaching causing accelerated aging and consequently fading, loss of tensile strength and cuts down the life expectancy of vellum books, paper books, documents, paper, archival records, flight logbooks , art works and textiles.

Our new non ozone process has been used to treat numerous libraries, collections, legal documents and as an alternative to replacement in insurance claims.

In addition to our unique non ozone mold treatment we provide a number of supporting restoration services.

Our team can ascertain the level of damage caused by fire, soot, smoke, water,  and mold to water damaged  leather books, water damaged  vellum books, water damaged paper books and water damaged  documents, including on site assessment and can co-ordinate with your staff to ensure that your disaster response is timely, efficient and does not cause the situation to worsen saving you time and money.   

We can co-ordinate with your staff to catalogue and to pack and safely ship all your books and documents.

At your request your books and documents can be clipped, cleaned and re-filed.

We Specialize in Services including Low Cost Vacuum Freeze Drying:

Cost-effective Vacuum Freeze Drying for Water, Fire, Smoke and Soot Damaged Materials: