A story from the field: when the smell of old paper turned sour

Khun Nong is the librarian of a small public library in Uthai district, Phra Nakhon Si Ayutthaya. The single-storey building sits right next to a local museum corner that villagers built up together over many years. It holds folding palm-leaf style manuscripts known as samut khoi, old photographs of the community, rice-farming tools, hand-woven textiles and handwritten records of the village's history. The library itself has several rows of wooden bookshelves, a children's reading corner laid with mats, and long reading tables where students come to do their homework after school. On most afternoons, a handful of older residents sit by the window reading the daily newspaper.

In late September 2026, water from the fields around Uthai spread into the district. It came into the building to roughly the height of an outstretched hand and stayed for almost a week. Khun Nong and a group of volunteers managed to lift some of the books from the bottom shelves to higher ground, but they could not save everything in time. When the water finally receded, she unlocked the door and was hit by a smell she had never noticed there before. The warm, familiar scent of old paper had become a sharp, damp mustiness that stung her nose. The books on the bottom rows had swollen, hardback covers had warped, and many spines were dotted with white and black mold. Even books on higher shelves, well above the waterline, had started to smell musty and show tiny specks of mold along the edges of the pages.

What upset her most was the museum corner. Old photographs in wooden frames had a white haze growing on the inside of the glass. Folded textiles stored in a cabinet smelled stale. Boxes of village records on the lowest shelf were damp to the touch. She knew these things were irreplaceable. She also knew instinctively that spraying them with liquid disinfectant or wiping them with a wet cloth could do more harm than good. She needed a way to deal with the mold and the smell without making the paper wet all over again.

Her situation is shared by many community libraries, school libraries, temple libraries and small local museums across Ayutthaya and the other flooded provinces this year. The water has gone, but the damage to paper collections keeps developing quietly, day after day, unless the humidity, the mold and the odor are handled in the right order.

Why libraries and local museums are especially vulnerable after a flood

Paper is food for mold. Paper, bookbinding glue, cloth covers and boards are rich in cellulose and starch, which mold can feed on very efficiently. When indoor humidity stays high for several days, mold will grow on books even if those particular volumes never touched the water. This is why a flood that only reached the bottom shelf can still leave the whole room smelling musty a week later.

Packed shelves trap moisture. Books standing tightly side by side leave little room for air to move. Moisture between the volumes evaporates slowly, and the space behind a shelf that stands against a wall is often a dead zone where damp air collects. Wooden shelving itself absorbs water at its base and releases it slowly back into the room for weeks.

Heritage items are fragile. Old photographs, samut khoi manuscripts, hand-woven textiles and handwritten documents use materials and inks that are sensitive to water, light, chemicals and rubbing. Ordinary cleaning methods can make ink run, fade colors, soften emulsions on photographs or tear brittle paper. Something that would be a routine clean-up in an office becomes delicate conservation work in a museum corner.

The building is often closed and still. After a flood, small public buildings are usually locked up while staff deal with their own homes. Without air movement or dehumidifiers, the humidity inside stays high and mold has days or weeks of ideal conditions.

The people who use it are sensitive. A public library welcomes young children, schoolchildren and older adults who read there every day. These are exactly the groups most likely to react to airborne mold spores, with sneezing, itchy eyes, coughing or asthma.

The impact: health, heritage, budget and community service

Health. Mold spores released from books and shelves into the air can trigger allergies, sneezing, a blocked nose, eye irritation and asthma, particularly in children and older people. Anyone shoveling mud out of the building also needs to watch out for germs carried by floodwater, such as leptospirosis, which can enter the body through cuts and scratches, and diarrheal illness from contact with contaminated water. Gloves, rubber boots and a well-fitting mask should be worn every time, and anyone who develops fever and muscle pain after working in floodwater should see a doctor promptly.

Historical value. Ordinary books can be bought again. Community history records, old photographs and the objects in a local museum cannot. Damage that is allowed to spread for even a few weeks can erase parts of a community's memory permanently. That makes the first decisions after the water recedes particularly important.

Budget. Public libraries and local museums usually work with very limited budgets. Deciding what to save first, what has to be discarded, and what should be sent to a professional conservator helps every baht go further. A clear plan also makes it easier to request support from local authorities or donors.

Community service. A library is a shared space for the whole community. The longer it stays closed, the longer children lose a quiet place to study and older residents lose a place to read and meet. In the weeks after a flood, when many homes are still being cleaned, that loss is felt even more strongly.

Why common clean-up methods are a bad fit for books and old documents

Spraying disinfectant directly onto books. This wets the paper all over again. Ink may run, pages can stick together, and the extra moisture becomes new food for mold. For books and documents, liquids should not be sprayed directly onto the collection at all. Liquid disinfectants have an important role, but only on floors, walls and hard surfaces.

Wiping with a damp cloth or bleach. Wiping smears mold stains into wider patches, weakens the paper and can permanently bleach the color out of covers and photographs. Bleach in particular is harsh on paper fibers and leaves a strong smell in a closed reading room.

Drying in strong sunlight. Direct sun dries things quickly, but strong light makes paper brittle, fades colors and causes covers to warp and crack. It is especially harmful to old photographs and textiles.

Air fresheners and scent sachets. They cover the smell for a short time but do nothing about the spores. Some products also leave oily or chemical residues on paper surfaces, which can attract dust and cause staining over time.

Waiting for the room to dry naturally. In the rainy season, a closed building may not dry on its own for weeks. Every day of waiting gives mold more time to spread from the lowest shelf to the rest of the collection.

The solution: ozone first, so the paper never gets wet, plus disinfection fogging for floors and walls only

For libraries and museums, World Health Disinfection (WHD) uses its ozone treatment service as the main method. Ozone is a gas, not a liquid, so it does not wet the paper. It spreads between the shelves, into the gaps between volumes and behind shelving units that stand against the walls, helping to destroy mold spores and break down the molecules that cause musty odors. When the treatment is finished, ozone breaks down back into oxygen and leaves no residue or chemical smell on the pages.

Our disinfection spraying service with Chemgene HLD4H is used only in areas without books or collection items: floors that have already been cleared of mud, the lower parts of walls, toilets, corridors, and tables and chairs once the books have been moved off them. All books, documents and collection objects are moved out or fully covered before any fogging takes place.

Why this order? Floodwater leaves bacteria and other germs on the floor and walls, and those surfaces need a real disinfectant. But the musty smell and the mold that worries a librarian most live in the books, the shelving and the air between them, which is exactly where liquids should not go. Using ozone for the collection rooms and liquid disinfectant only for hard surfaces gives each area the method that suits it.

Our step-by-step process for libraries and local museums

1. Survey and sorting. Together with the librarian and museum caretaker, we sort books and documents into groups: dry with no mold, lightly affected, wet or heavily damaged, and valuable items that should go to a conservation specialist.
2. Advice on wet books. Wet volumes are separated, air-dried in the shade with good airflow, stood upright with pages fanned open, or frozen to slow mold growth until they can be properly restored. Books that are still soaking wet should not be ozone-treated.
3. Mud removal and fogging of empty areas. Once the books have been moved, floors are washed and Chemgene HLD4H is fogged on the floor, the lower walls and the toilets.
4. Controlled-dose ozone treatment. Dry book rooms are treated with the gaps between books opened up so the gas can reach them. Concentration and time are matched to the room, and no people, pets or plants are inside.
5. Ventilation. Doors, windows and fans are opened until the ozone has broken down, before staff return.
6. Re-check and long-term care. We check odor, visible mold and humidity, and advise on dehumidifiers and regular inspection of the lower shelves.

Safety and precautions: No people, pets or plants may be in the area during ozone treatment, and the space must be ventilated properly before anyone goes back in. Our team controls the ozone dose to suit the size of each room. Ozone is an oxidizer, so at high concentrations or with very long exposure it can affect some materials, such as rubber, certain textile dyes, old photographs and artworks. Collection items of historical value and artworks should be moved out or sealed in closed boxes before treatment, and conservation specialists should be consulted on a case-by-case basis. Computers and other electronic equipment should be unplugged and covered, or moved out of the room.

How ozone works on mold and odor in a book room

Ozone is a molecule made of three oxygen atoms. That third atom makes it unstable and highly reactive. When ozone meets the cell wall of a mold spore or a bacterium, it oxidizes it and damages it. When it meets the volatile compounds that produce musty and sour smells, it breaks them down into simpler substances that no longer smell. Because ozone is a gas, it travels wherever air can travel: between the volumes on a shelf, behind the shelving, into the corners of cabinets and up into the ceiling space.

This is the key advantage in a library. A liquid disinfectant only works where it lands, and in a book room you do not want it to land on the collection. A gas, by contrast, can reach every surface in the room without adding a drop of water. After the treatment time, ozone naturally reverts to ordinary oxygen, and the room is ventilated until the level is safe again.

Ozone is not a substitute for drying, however. If a book is still wet, it will keep growing mold after the treatment because the moisture is still there. That is why drying and sorting always come first, and why we stress humidity control after the treatment too. The best results come from three steps working together: remove the moisture, treat the air and the surfaces, then keep the humidity low so the mold has no chance to return.

10 reasons libraries and museums in Uthai choose ozone treatment

1. The paper stays dry. Ozone treatment uses a gas, not a liquid.
2. It reaches between the volumes and behind shelves that stand against the wall.
3. It removes musty odor at the source instead of masking it. Read more about ozone odor removal.
4. No chemical residue on the pages. Ozone reverts to oxygen after the treatment.
5. Fewer airborne spores for the children and older readers who use the library every day.
6. A controlled dose for each room, reducing the risk to sensitive materials.
7. Floors and toilets are properly disinfected through disinfection fogging applied only where there are no books.
8. A high-level disinfectant, Chemgene HLD4H, for hard surfaces.
9. A clear plan for prioritizing what to save, helping a limited budget go further.
10. Easy follow-up care with Chemgene HLD4H spray for reading tables and the lending counter (never sprayed onto books).

In the librarian's words

"What reassured me most was that nobody sprayed anything onto the books. The team helped me decide which books needed to dry first and which could be treated, and they only ran the ozone once the books were dry. We packed the museum pieces into boxes as they suggested. The musty smell in the library has gone down a lot, and the children are back at the reading tables again."

— Khun Nong (name changed), librarian at a public library in Uthai, Ayutthaya, a story from the field

Practical guide: sorting a flooded collection in the first two weeks

The order in which you handle a wet collection matters as much as the methods you use. Here is a simple framework that a small library team and volunteers can follow while waiting for professional treatment.

Day 1 to 2: make it safe and record everything. Check electrical safety before switching anything on. Wear gloves, a mask and boots. Photograph each shelf and each box before moving it, and keep a simple list of what was affected. These records help with insurance claims, requests for budget support and later decisions about restoration.

Day 2 to 4: separate wet from dry. Move wet books away from dry ones immediately so moisture and mold do not spread between them. Never stack wet books on top of each other. Books that are only damp at the edges can be stood upright with their pages fanned slightly open in a shaded, well-ventilated room. Fans that move air around the room, not directly onto the pages, help a lot.

Day 3 to 7: decide on the heavily damaged items. Books that are soaked through, muddy or already heavily molded need a decision. Common, replaceable titles may be better discarded and recorded. Rare or locally important items can be wrapped and frozen to stop mold growing, which buys time to find a conservator. Photographs, manuscripts and textiles should be handled as little as possible and put aside for specialist advice.

Week 2: clean the building, then treat. Once the collection has been moved or dried, the building itself can be cleaned: mud washed out, floors and walls disinfected, shelving dried and checked. Only then does ozone treatment of the dry book rooms make sense, followed by ventilation and continued humidity control.

This sequence keeps people safe, protects the most valuable items and makes sure the professional treatment is applied to a space that is ready for it, so the result lasts.

Checklist for librarians and museum caretakers

• Wear gloves, a mask and boots every time you handle moldy books or walk through mud.
• Photograph and list damaged books and objects before moving or discarding them.
• Keep wet books apart from dry ones and never stack them.
• Dry damp books in the shade with good airflow, never in strong sunlight.
• Store old photographs, textiles and important documents in closed boxes, apart from the rest, and ask a conservation specialist for advice.
• Wash mud off the floor and the base of wooden shelves, and let them dry fully before putting books back.
• Run dehumidifiers in the book rooms and check the lower shelves every week for the first month.
• Keep the building's windows or vents open on dry days to keep air moving.

Frequently asked questions (FAQ)

Q: Will ozone treatment damage the books?
A: When the concentration and time are properly controlled, ozone treatment for mold and odor in an ordinary book room is a method that keeps paper dry. Rare books, old photographs and artworks, however, should be stored separately or assessed by a conservation specialist first.

Q: Will the mold stains on the covers disappear?
A: Ozone helps destroy spores and reduce odor, but the colored stains mold leaves behind may still be visible. Stains can be brushed gently with a soft brush in an open area while wearing a mask, or handled by a specialist for valuable volumes.

Q: Can books that are still wet be ozone-treated?
A: We do not recommend it. Dry them first in the shade, or freeze them to slow mold growth and restore them later. Once they are dry, ozone treatment can deal with the remaining spores and smell.

Q: Why not spray disinfectant directly onto the books?
A: Liquids wet the paper again, ink may run, and the extra moisture becomes food for mold. Disinfectant is therefore used only on floors, walls and hard surfaces where there are no books.

Q: How long does the library need to close?
A: That depends on how many books have to dry first. The ozone treatment for each room can usually be finished within a single day, including ventilation time.

Q: Is the air safe for children after treatment?
A: Yes, once the room has been properly ventilated and the ozone has broken down back into oxygen. Our team will tell you when it is safe to reopen the room.

Q: Which areas do you serve?
A: Uthai, Wang Noi, Bang Pa-in, Phra Nakhon Si Ayutthaya, Phachi, Bang Pahan and nearby areas. Contact us to check your location.

Protect your books and your community's memory

Talk to the World Health Disinfection team about planning ozone treatment for mold and musty odor in your public library or local museum in Uthai, Ayutthaya.

Book ozone treatment, click here

See our disinfection service, click here

Call 065-556-6294 · LINE @whd268 · worldhealthdisinfection@gmail.com

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Sources: WHO – Floods and health and Department of Health, Ministry of Public Health (Thailand)