One of the most critical factors affecting production quality in leather processing facilities that handle raw hides and skins is the control of microbial load. Raw hides are highly susceptible to bacterial growth due to their high content of protein, blood, fat, moisture and organic matter. If the microbial activity that begins after slaughter is not properly controlled, it may quickly lead to unpleasant odor, surface deterioration, hair root damage, weakening of the grain surface, staining and quality variations in subsequent processing steps.

For this reason, leather processing facilities require controlled hygiene and microbial load management at many stages, from raw hide reception and soaking to equipment hygiene and wastewater management. Traditionally, different methods such as salting, conventional leather biocides, hypochlorite-based disinfectants, quaternary ammonium compounds, hydrogen peroxide, ozone or UV systems are used for this purpose.

Peracetic acid, also known as PAA, is one of the oxygen-based strong chemical solutions that can be evaluated in this field. However, the role of PAA in leather processing facilities must be defined correctly. PAA is not a stand-alone main process chemical that changes the entire leather process. When evaluated in the right application areas, it is an oxidative hygiene chemical that can support raw hide reception area hygiene, odor control, surface and equipment disinfection, controlled microbial load reduction and, in some facilities, salt reduction studies.

This article technically evaluates at which stages PAA use may be beneficial in leather processing facilities, in which processes it may pose risks, and how concentrated products such as 15% PAA should be positioned.

1. The Main Problem in Raw Hide Processing: Microbial Load and Deterioration Risk

Raw hide is a biologically active material after slaughter. Blood, fat, protein, fecal residues, soil, salt, hair, microorganisms and various organic contaminants may be present on the surface and within the structure of the hide. This composition creates a suitable environment for rapid microbial growth, especially in warm weather or during long waiting periods.

If microbial activity is not controlled, the following problems may occur in the hide:

• Unpleasant odor formation

• Deterioration around hair roots

• Weakening of the grain surface

• Spotting and staining on the hide surface

• Damage to collagen fiber structure

• Irregular swelling after soaking

• Quality variations during tanning and dyeing stages

• Surface defects in the final leather

Therefore, for leather processing facilities, the reception, storage and preparation of raw hides for soaking is not merely a mechanical operation. It also requires controlled hygiene and microbial load management.

2. Traditional Approach: Salting, Hypochlorite and Conventional Biocides

One of the most common methods for raw hide preservation is salting. Salt slows microbial growth by reducing water activity. It is a practical and economical method, especially for long-distance transportation, warm climates or situations where hides cannot be processed immediately.

However, salting has significant disadvantages. Salt is largely transferred into wastewater during the soaking stage. This may lead to high chloride, high total dissolved solids and high conductivity in wastewater. The chloride load can be challenging for facilities, particularly in terms of discharge limits and water recovery.

In addition to salting, or to support its effect, some leather production facilities use conventional leather biocides. These products may be preferred to limit bacterial activity in soaking baths, improve storage stability of intermediate products such as wet-blue or wet-white, or prevent mold growth.

For surface, floor, channel and equipment hygiene, many facilities use hypochlorite-based products. Hypochlorite is a fast and economical disinfectant; however, it can be rapidly consumed in the presence of organic matter, generate a strong chlorine odor, increase corrosion risk on certain surfaces and have limitations in terms of chlorinated by-product formation.

Therefore, leather processing facilities may need alternative or supportive hygiene chemicals, especially for raw hide reception areas, equipment hygiene, odor control and wastewater outlet disinfection. PAA is one of the important options to be evaluated at this point.

3. What Is Peracetic Acid?

Peracetic acid is a strong oxidative compound formed from the equilibrium of acetic acid and hydrogen peroxide. Commercial PAA products generally contain peracetic acid, hydrogen peroxide, acetic acid, water and stabilizers.

The key characteristic of PAA is its strong oxidation capacity. It supports microbial inactivation by exerting oxidative effects on microbial cell walls, membrane structures, proteins and enzyme systems. For this reason, it is used in many areas such as food and beverage processing, water treatment, CIP/SIP systems, surface hygiene and industrial disinfection.

One of the main advantages of PAA is that it does not contain chlorine. Compared with chlorine-based disinfectants such as hypochlorite, it may offer a more advantageous profile in terms of chlorine odor, chlorinated by-product formation and certain corrosion problems. Its decomposition products are mainly acetic acid, oxygen and water.

However, these advantages do not mean that PAA is risk-free when used without control. PAA is a strong oxidizing agent. Its concentrated forms require attention in terms of occupational safety, storage, dilution and process compatibility.

4. The Basic Logic of PAA Use in Leather Processing Facilities

PAA use in leather processing facilities should be positioned correctly. PAA should not be considered a tanning chemical. A more accurate definition would be:

Peracetic acid is an oxygen-based microbial load control chemical that can be used at certain points, from raw hide reception and equipment hygiene to odor control and wastewater outlet disinfection.

This approach is important because leather production depends on many sensitive variables such as pH, temperature, salt, sulfide, enzymes, liming, pickling, chromium, fatliquoring and dyeing. Random addition of strong oxidizing agents into every bath may create quality risks.

Reasonable application areas for PAA in leather processing facilities include:

• Hygiene of raw hide reception areas

• Disinfection of transport carts, plastic crates and floors

• Support for odor control in channels and areas where organic matter accumulates

• Hygiene of drums, vessels, washing areas and equipment surroundings

• Surface disinfection after pre-cleaning

• Microbial load reduction in soaking baths through controlled pilot studies

• Disinfection support in treated or pre-treated wastewater outlets

On the other hand, PAA use in some areas should be carefully evaluated or avoided. In particular, uncontrolled PAA use in sulfide-containing processes, liming/unhairing baths, pickling, chrome tanning, dyeing and fatliquoring stages may negatively affect process balance and final leather quality.

5. PAA Use in Raw Hide Reception Areas

The raw hide reception area is one of the sections with the highest microbial load in leather processing facilities. Blood, hide fluids, organic residues, salt, hair, fat and surface contamination are present together in this area. Floors, transport carts, crates and storage areas can quickly become prone to unpleasant odor and biofilm formation.

At this point, PAA can be evaluated for facility hygiene before the actual process bath.

Purpose

The main purpose of PAA use in raw hide reception areas is not to tan or preserve the hide. The main purpose is to improve area hygiene, reduce microbial load and suppress unpleasant odor formation.

Application logic

Before PAA application, coarse dirt, blood, fat and organic residues should be removed as much as possible. PAA is consumed by reacting with organic matter. Direct disinfection on heavily soiled surfaces reduces effectiveness and increases cost.

The most appropriate sequence is:

1. Mechanical removal of coarse dirt

2. Pre-rinsing with water

3. Detergent cleaning if required

4. Rinsing

5. Application of diluted PAA

6. Sufficient contact time

7. Rinsing or air drying if required

In this application, the advantage of PAA is that it provides a chlorine-free oxidative effect and creates less chlorine odor compared with hypochlorite.

Points to consider

Since the organic load in raw hide reception areas is very high, the PAA dose should be optimized according to the site conditions. A low dose may be ineffective, while an excessive dose may increase cost and create unnecessary exposure risks for personnel.

Therefore, the first application should be performed as a pilot trial in a small area; odor, surface hygiene, personnel feedback and chemical consumption should be evaluated together.

6. PAA on Transport Carts, Crates and Equipment Surfaces

Raw hide transport equipment plays an important role in the movement of microorganisms within the facility. Plastic crates, metal transport carts, forklift contact surfaces, washing basins and drum surroundings may become sources of cross-contamination if not cleaned regularly.

PAA can be used on these surfaces for disinfection after pre-cleaning.

Advantages

• Provides chlorine-free disinfection.

• Helps reduce unpleasant odor formation.

• Supports the suppression of organic film and biofilm formation.

• Can be diluted and applied to different surfaces.

• Offers a practical hygiene solution when dosage and contact time are controlled.

Material compatibility

PAA is an oxidizing product. Therefore, corrosion risk should be evaluated especially on low-grade metal surfaces, galvanized surfaces, copper, brass, carbon steel or sensitive metal equipment. It can be used more safely on stainless steel, suitable plastics and surfaces with known chemical resistance.

A small-area material compatibility test is recommended before application.

7. PAA Use in the Soaking Stage

Soaking is a critical stage in preparing raw hides for production. This stage aims to remove salt, allow the hide to take up water, dissolve impurities and make the material suitable for subsequent processes. It is also a risky stage in terms of microbial activity.

Bacterial load may be high in soaking baths. Therefore, some facilities use biocides. PAA can theoretically be evaluated for microbial load reduction at this stage; however, this application is not as simple as surface disinfection.

Why is caution required?

Leather is based on a collagen structure. PAA, on the other hand, has an oxidative character. Under unsuitable conditions such as improper dose, long contact time, low pH, high temperature or insufficient control, the surface structure and fiber integrity of the hide may be negatively affected.

Possible risks include:

• Weakening of the grain surface

• Lightening of color or shade differences

• Stain formation

• Oxidative effects on fiber structure

• Different behavior in subsequent tanning and dyeing stages

• Changes in leather handle

Therefore, PAA use in the soaking bath should only be evaluated through a controlled pilot study.

How should a pilot study be conducted?

Two groups should be taken from the same raw hide batch:

• Control group: Existing standard process

• Trial group: Controlled PAA application

The following parameters should be monitored for comparison:

• pH value of the soaking bath

• Temperature

• Contact time

• Bath odor

• Microbial load

• Hide surface appearance

• Grain surface

• Hair root area

• Swelling behavior

• Subsequent liming and tanning performance

• Color, handle and surface quality of the final leather

For PAA application to be considered successful, odor reduction or microbial load reduction alone is not sufficient. Final leather quality should also be compared with the control group.

8. The Role of PAA in Salt Reduction Approaches

Reducing salt use in raw hide preservation is an important environmental goal for leather processing facilities. Although salt provides practical preservation for the facility, it brings a high chloride and dissolved solids load into wastewater. This may create problems in terms of discharge limits, treatment cost and water recovery.

At this point, PAA should not be presented as a standard solution that directly replaces salt. A more accurate approach is to evaluate PAA as a supportive tool in short-term preservation and microbial load control programs.

Where can it be meaningful?

• In facilities where raw hides can be processed quickly

• In leather production facilities aiming to reduce salt use

• In reception areas with odor and microbial load problems

• In facilities with well-managed pre-washing and hygiene control

• In operations with controlled storage time

Where can it be risky?

• In long-term raw hide storage

• In uncontrolled waiting conditions in warm climates

• When the processing time of the hide is uncertain

• In facilities without cold chain or rapid processing capability

• In facilities with weak dosing and process control

Therefore, the salt reduction approach with PAA requires facility-specific validation. An application that is successful in one facility may not provide the same result under different hide types, temperatures, waiting times and process conditions.

9. PAA Use in Odor Control

Unpleasant odor in leather processing facilities may arise from many sources. Microbial activity on raw hides, protein decomposition, blood and fat residues, sulfide-containing processes, ammonia formation, channel deposits and wastewater systems can all increase odor problems.

PAA does not completely eliminate odor problems on its own. However, it can help reduce odor formation, especially when the odor is microbiologically driven. It can also support the oxidation of some reduced odor-forming compounds.

Correct application points for odor control

• Raw hide reception area

• Floors where blood and organic matter accumulate

• Washing channels

• Transport carts

• Plastic crates

• Drum surroundings

• Pre-treatment wastewater holding areas

Critical warning

PAA must not be brought into uncontrolled contact with sulfide-containing liming wastes. Leather processing operations may include stages where sodium sulfide or sodium hydrosulfide is used. Uncontrolled contact between these reducing chemicals and oxidizing PAA may create safety and process risks.

If sulfide-containing baths, sulfide-containing sludge or reducing chemical residues are present in the area where odor control is planned, a technical assessment should be performed before application.

10. PAA in Wastewater and Treatment Applications

Wastewaters from leather processing facilities generally contain high organic load, high COD, high TDS, sulfide, chromium, fat, hair, suspended solids and variable pH. Therefore, PAA should not be considered the main treatment chemical for leather industry wastewater.

The more appropriate role of PAA in wastewater applications is to provide disinfection support after pre-treatment and main treatment stages.

Suitable application approach

• Preliminary settling should be performed.

• Suspended solids should be reduced.

• Organic load should be brought down to a reasonable level.

• Coagulation/flocculation should be applied if necessary.

• PAA should be evaluated for final disinfection or microbial load reduction.

Direct addition of PAA into raw wastewater may often be uneconomical because high organic load rapidly consumes PAA. This results in high chemical consumption and low efficiency.

Advantages in treatment applications

• It can offer a chlorine-free disinfection alternative.

• It may reduce the risk of chlorinated by-products.

• It can support microbial load control in final effluent.

• It can be applied in a controlled manner using a dosing pump.

Limitations

PAA does not solve chromium, high COD, high TDS, fat, hair or suspended solids problems on its own. Therefore, it should not be positioned as a replacement for technologies such as coagulation, settling, biological treatment, filtration, advanced oxidation or membrane processes.

11. Why Choose 15% PAA?

15% PAA is a concentrated product for professional use. In leather processing facilities with large-volume and multi-point application needs, it can provide advantages when used with proper dilution and dosing systems.

Advantage of concentrated use

Compared with lower-concentration products, 15% PAA requires less storage volume. The same amount of active substance can be transported in a smaller package volume. This provides advantages in logistics and stock management.

Adaptable to different application points

The same product can be evaluated for different purposes through proper dilution:

• Surface hygiene

• Equipment disinfection

• Odor control

• Channel applications

• Wastewater outlet disinfection

• Soaking bath trial through controlled pilot validation

Safer use with dosing systems

Manual and uncontrolled use of 15% PAA is not recommended. It is safer to use it with a dosing pump, dilution unit or controlled preparation procedure. This approach supports both occupational safety and cost control.

12. Risks in 15% PAA Use

The risks of 15% PAA should be explained as clearly as its advantages. This is important for both technical reliability and responsible product use.

Occupational safety risk

15% PAA is a strong oxidizer. It may be irritating to the eyes, skin and respiratory tract. Appropriate personal protective equipment should be used when working with the concentrated product.

Required precautions include:

• Chemical-resistant gloves

• Safety goggles or face shield

• Appropriate protective clothing

• Good ventilation

• Eye wash and emergency rinsing facilities

• Trained personnel

• Storage in the original container

• Separation from incompatible chemicals

Chemical incompatibility

PAA may react with reducing agents, sulfide-containing chemicals, certain metals, alkaline substances and organic contaminants. This is particularly important in leather processing facilities because sulfide-containing liming processes are commonly present.

PAA should not be used without control in the following areas:

• Baths containing sodium sulfide

• Areas containing sodium hydrosulfide

• Liming/unhairing baths

• Sulfide-containing waste sludge

• Tanks containing reducing chemicals

• Containers with high metal contamination

Leather quality risk

If PAA is to be used directly on raw hide or within a process bath, dose, time, pH and temperature should be controlled. Otherwise, oxidative effects may influence the surface quality of the hide.

Rapid consumption under high organic load

PAA can be rapidly consumed in the presence of blood, protein, fat, hair and organic matter. Therefore, PAA used without prior cleaning may be uneconomical. For best results, the principle of “clean first, then disinfect” should be applied.

13. Where PAA Can and Cannot Be Used

The following assessment can serve as a practical guide for PAA use in leather processing facilities.

14. Recommended Pilot Study Plan for Leather Processing Facilities

The most appropriate approach to PAA use is not to apply it directly across the entire facility, but to conduct a controlled pilot study. A pilot study objectively demonstrates both technical performance and cost impact.

Stage 1: Area hygiene trial

The first trial can be conducted in the raw hide reception area. This is one of the safest starting points.

Parameters to monitor:

• Odor condition before and after application

• Surface cleanliness

• Personnel feedback

• Chemical consumption

• Surface material compatibility

• Odor return at the end of the day

• Biofilm appearance in channels and floor areas

The aim at this stage is to observe the practical contribution of PAA to facility hygiene.

Stage 2: Equipment and transport vehicle trial

In the second stage, plastic crates, transport carts, drum surroundings and washing equipment can be evaluated.

Parameters to monitor:

• Microbial load after cleaning

• Odor reduction

• Residual feel on the surface

• Material compatibility

• Ease of use

• Daily application time

• Potential reduction in hypochlorite use

Stage 3: Controlled soaking trial

This stage is more technical and should be performed at laboratory or small production scale.

Application principle:

• Hides from the same batch are selected.

• One group is processed with the existing standard process.

• One group is processed with controlled PAA application.

• Both groups are taken through subsequent process stages.

• Final leather quality is compared.

Parameters to monitor:

• pH

• Temperature

• Contact time

• Microbial load

• Odor

• Swelling behavior

• Grain surface

• Hide color

• Tanning performance

• Dyeing uniformity

• Final leather handle

• Tensile, tear or other physical quality parameters

Stage 4: Wastewater outlet disinfection trial

If there is a microbial load problem at the treatment outlet, PAA can be evaluated for final disinfection.

Parameters to monitor:

• Microbial load at inlet and outlet

• Contact time

• PAA consumption

• Effect on COD

• pH change

• Odor

• Effect on discharge criteria

• Total cost

At this stage, it should be remembered that PAA is not a main treatment chemical. The product should be evaluated mainly for final disinfection or microbial load reduction.

15. Success Criteria in PAA Use

For PAA application in a leather processing facility to be considered successful, simply using the chemical is not enough. Success should be evaluated using measurable and traceable criteria.

Possible success criteria include:

• Odor reduction in the raw hide reception area

• Improvement in surface hygiene

• Reduction in hypochlorite use

• Reduction in chlorine odor

• Decrease in biofilm formation around equipment and channels

• Reduction of microbial load in the soaking bath

• No negative change in final leather quality

• Manageable occupational safety procedure

• Economically acceptable chemical consumption

• Improved microbial load control at the treatment outlet

Applications performed without these criteria cannot be evaluated in a technically reliable way.

16. How Can Ultracol® Peracetic Acid 15.0 | 15% PAA Be Positioned in This Field?

15% PAA should not be positioned as a chemical to be applied directly and without control onto raw hides in leather processing facilities. It should be positioned as a professional oxidative hygiene solution used with controlled dilution and dosing.

Ultracol® Peracetic Acid 15.0 | 15% PAA is a concentrated peracetic acid solution that can be evaluated for use in raw hide reception area hygiene, surface hygiene, equipment disinfection, odor control and wastewater outlet disinfection after pre-treatment. With proper dilution and controlled application, the product supports a chlorine-free hygiene approach in leather processing facilities.

The most important point in this positioning is the correct definition of process limits. Ultracol® Peracetic Acid 15.0 | 15% PAA should not be added without control to liming/unhairing, sulfide-containing baths, pickling, chrome tanning or dyeing/fatliquoring stages. The most efficient and safe approach is to evaluate the product for hygiene applications after pre-cleaning and for controlled process points validated by pilot studies.

17. Conclusion: PAA Is Beneficial, But Only at the Right Point

Peracetic acid use in leather processing facilities has significant potential. Especially in raw hide reception areas, odor and microbial load control, equipment and surface hygiene, reduction of hypochlorite use and wastewater outlet disinfection, PAA can be evaluated as a strong alternative.

However, it should be remembered that PAA is not a general-purpose chemical that can be added to every process bath. Leather production is a sensitive process. Uncontrolled PAA use in liming, sulfide-containing baths, pickling, chrome tanning, dyeing and fatliquoring stages may negatively affect process balance and final leather quality.

Therefore, the most appropriate approach is to consider PAA not as a “main leather process chemical” but as an “oxygen-based support chemical used in a controlled manner for raw hide hygiene and facility disinfection.”

Concentrated products such as 15% PAA can be adapted to different hygiene points in professional facilities when used with a dosing pump or controlled dilution procedure. For a successful application, pre-cleaning, correct dilution, appropriate contact time, occupational safety, material compatibility and pilot validation must be taken into account.

As a result, PAA can be a valuable solution when used at the right point in leather processing facilities. However, the highest benefit is achieved when the process limits of the product are understood and the application is carried out through a controlled and measurable pilot study.

For technical information and application recommendations about Ultracol® Peracetic Acid 15.0 | 15% PAA, you can contact Colin Kimya.

Product page: Peracetic Acid 15.0 | 15% PAA