Wastewater, Emissions and Solid Waste
Like any industrial production activity, the tanning process has environmental impacts, which are minimized through targeted treatment measures.
Alongside the positive effects of leather’s circular nature – particularly within the national supply chain – Italian tanneries must also carefully manage potential environmental impacts. If not handled responsibly, these could lead to undesirable consequences.
Wastewater
Wastewater treatment is one of the most significant environmental management activities for tanneries, accounting for over 60% of their total environmental costs.
Water serves as the primary medium for most tanning processes, but it is not consumed in them.
From a quantitative perspective, 95% of the water used in production is discharged. However, its qualitative characteristics change, requiring purification before being safely reintroduced into the environment.
The remaining 5% includes: moisture retained in the leather, water evaporated during production and water contained in waste sent for treatment.
To minimize environmental impact, Italian tanneries have been using advanced wastewater treatment plants and consortium purifiers for nearly 50 years—even before the introduction of the first regulations on the matter. These facilities are specialized in treating tannery wastewater, sometimes in combination with local municipal wastewater.
Tanneries first separate coarse waste from discharged water at the factory level. In some cases, pre-treatment systems are also in place to recover part of the water before sending it for purification.
Tanneries located outside industrial districts manage wastewater treatment independently, typically discharging into public sewage systems.
Continuous innovation has ensured that Italy’s tanning industry maintains world-class efficiency and pollution reduction levels.
To reduce water consumption per unit of product, tanneries focus on:
Italian consortium wastewater treatment plants are internationally recognized as a model of cross-company collaboration for environmental sustainability.
Ongoing investments, research, and national program agreements have led to significant advancements in water and sludge treatment. These purification systems have evolved alongside the industrialization of Italy’s tanning sector, adapting to ever-stricter environmental standards.
Today, tannery purifiers also contribute to the treatment of municipal wastewater, highlighting their broader environmental role.
Because of their importance to the supply chain, all major centralized purifiers in Italy’s tanning districts participate directly in wastewater quality analyses.
Efficiency analyses assess purification performance by measuring pollutant concentrations before and after treatment. These analyses focus on key tanning wastewater parameters.
The purification systems used in tanning districts eliminate nearly 100% of suspended solids, nitrogen, trivalent chromium, and organic load (COD) from the wastewater.
Once purified, the water is safely reintroduced into the environment, ensuring its reintegration into natural biological cycles.
Removal Levels of Major Water Pollutants
(Treatment Plants in the Tuscany and Veneto Districts)
– 2023 DATA –
-97.8%
COD
Chemical Oxygen Demand (COD)
COD, expressed in milligrams of oxygen per liter (mgO2/L), represents the amount of oxygen required for the complete oxidation of organic and inorganic compounds in wastewater. It indicates pollution levels from organic residues (animal hair, dermis) and unused chemical products (e.g., ammonia, surfactants, sulfides, tannins, resins, aldehydes, dyes, and fats). COD reduction in purification combines physical interventions (e.g., filtration) with chemical and biological processes.
-99.4%
Chromium III
Chromium III
Basic chromium sulfate (Cr(OH)SO4) is a widely used tanning agent that binds irreversibly to collagen fibers, preventing decomposition while preserving leather's softness and flexibility. In its trivalent state, chromium is not particularly toxic. Chemical-physical treatments allow the recovery of significant amounts of chromium from exhausted tanning baths before final purification.
-95.5%
Total Nitrogen
Total Nitrogen
Total Kjeldahl Nitrogen (TKN) measures the organic nitrogen content from protein and urea degradation. To determine total nitrogen in wastewater, nitrogen from ammonia (NH3) and ammonium salts (NH4+) must also be considered. Purification primarily relies on biological processes, balancing nitrification and denitrification.
-99.5%
Suspended SolidsSuspended Solids
Measured in milligrams per liter (mg/L), this parameter represents the amount of undissolved solids that can be separated by filtration. In tanning wastewater, these solids mainly originate from undissolved chemicals or leather degradation. Chemical-physical treatments effectively reduce suspended solids, also lowering COD levels.
-28%
Chlorides
Chlorides (Cl-)
Chlorides in tanning wastewater originate from conservation salt in soaking, ammonium chloride used in deliming/maceration, and sodium chloride and hydrochloric acid in pickling and tanning. While chlorides are not a major concern, excessive salt levels can affect water osmotic potential, organoleptic characteristics, and cause pipe corrosion due to increased electrical conductivity.
Emissions
Atmospheric emissions are another key environmental aspect, to be monitored and subjected to continuous improvement. Tanning production generates emissions from both leather processing and auxiliary energy production activities.
Emissions vary significantly depending on the type of leather item being produced.
Italian tanneries use cutting-edge technologies aligned with stringent national and European regulations.
Emissions Kg CO₂ eq/m² of leather produced
2023 data
Boilers and energy generators release gases contributing to the greenhouse effect, such as CO2 and nitrogen oxides. The environmental impact is assessed using CO2 equivalent values, considering both direct (gas, diesel, and fuel consumption) and indirect (off-site electricity consumption) energy sources.
VOCs emissions depend on the intended use of leather. Tanneries minimize emissions through filters and abatement systems, ensuring compliance with authorization limits.
VOC emissions per m² of leather produced
2023 data
Change 2015/2023
VOC emissions have steadily decreased due to new technologies, process improvements, and the progressive replacement of solvent-based finishes with water-based alternatives.
Solid Waste
Less than 30% by weight of the raw hides entering a tannery become finished leather. The remaining organic material is discarded during processing, generating by-products and waste. The nature of these residues varies depending on the production phase, determining their final destination.
Classification of Tannery Waste (European Waste Code – EWC)
04 01 Waste from the leather, fur and textile industries
04 01 01 Fleshings and lime split waste
04 01 02 Liming waste
04 01 03 Degreasing waste containing solvents (without liquid phase)
04 01 04 Tanning liquor containing chromium
04 01 05 Tanning liquor free of chromium
04 01 06 Sludge from effluent treatment (containing chromium)
04 01 07 Sludge from effluent treatment (free of chromium)
04 01 08 Waste from fat, grease, and wax removal
04 01 09 Waste from dressing and finishing
04 01 99 Other unspecified waste
Certain residues, such as fleshing (mechanically removed subcutaneous tissue) and hair, are classified as Animal By-Products (ABPs) rather than waste under current legislation.
Waste generated
2023 data
2023 data
Excluding tanning baths
data 2023
Type of waste
2023 Data
Main Waste Categories in Tanneries:
- Tanning liquor: derives from the activity of tanneries (in particular, in Tuscany) which separate the tanning liquor for the recovery of chromium salts.
- Offcuts, trimmings, and dust: Used to produce fertilizers and soil improvers.
- Sludge: Derived from finishing, tank cleaning, and wastewater treatment.
- Packaging: Paper, plastic, wood, and mixed materials, mostly recycled.
- Other sector-specific waste: Salt, absorbent materials, filters, and residues, mostly disposed of.
- Other waste: Generated from ancillary activities.
The recovery processes of tanning waste are an interesting application case of circular bioeconomy. Numerous good practices are implemented throughout the leather manufacturing process to minimise, reuse and recover waste. Click here to learn more
Waste hazardousness
2023 data
Waste destination
2023 data
Italian tanneries prioritize waste recovery, with 82% of waste reintroduced into production cycles.
A very important example of such recovery is that of Chromium (III) from tanning liquor and reused in production.
Then there is biological waste resulting from the tanning preparation phases (such as fleshing, etc.) which are classified as ABPs (Animal By-Products). These waste become biostimulants, a precious nourishment for plants, and fertilisers for agriculture, collagen for cosmetics, nutraceuticals and adhesives, jellies for the food sector and pharmaceutical industry.
Offcuts, trimmings and shavings can instead be used to create materials for fashion (regenerated leather fibres), paper industry (paper) and more.
The Italian leather industry follows a coherent, modern, and sustainable waste management strategy: