Wastewater, Emissions and Solid Waste
Like any production activity, especially if industrial, the tanning production process generates impacts on the environment, the extent of which is minimised through specific treatments.
Alongside the positive impacts deriving from the circular nature of leather and, in particular of the related national supply chain, Italian tanneries must also pay attention to possible effects on the environment which, if not adequately and responsibly managed, could have undesirable consequences.
Wastewater
Wastewater treatment, which on average accounts for over 60% of the environmental costs incurred by tanneries, is undoubtedly one of the most important environmental management activities.
Water is the matrix in which most processes take place, but it is not ’consumed’ within them.
From a quantitative point of view, 95% of the water used in the process is discharged. Its qualitative characteristics change, which must be re-established through appropriate purification treatments before returning the water to the environment.
The remaining amount includes the humidity that remains in the leather and the water evaporated during the production processes or contained in the waste sent for treatment.
To avoid impacts on the ecosystem, Italian tanneries have been using of cutting-edge wastewater treatment plants and consortium purifiers for almost 50 years (even before the first legislation in this regard), which are specialised in the purification of tanning wastewater (sometimes together with the civil water of the territory).
The tanneries carry out an initial separation of coarse waste from the water discharged downstream of the factory and in some cases some pre-treatments (if separate conveyance systems are present) to recover some water before sending the wastewater for purification.
Tanneries not located in production districts see to purification directly, mainly discharging into public sewers.
The high and continuous level of innovation guarantees cutting-edge levels of reduction and efficiency worldwide.
To reduce water consumption per product unit, the tanneries work to:
The consortium purifiers are an international example of cross-company collaboration aimed at environmental sustainability. Continuous investments, local and national program agreements, innovation and research have led tanning purification to reach important optimisations in water and sludge treatment lines. Purification structures have constantly evolved in the tanning territories, starting from the period in which national production took on industrial characteristics.
The current situation also sees an important contribution from tannery purifiers for the purification of civil wastewater in the area.
In light of their key role for the supply chain, all the main centralised purifiers present in the main national tanning districts are also directly involved in our wastewater analyses.
Overall in this sample, water of civil origin represents over 40% of the inputs into the purification system, while the remaining part (over 50%) is represented by water of tanning origin, residual portions of other wastewater or industrial waste in the liquid state.
The efficiency analyses derive from the relationship between the concentration of pollutant exiting the purification system and that entering it, and are carried out on the main parameters characterising the tanning wastewater.
The efficiency of the purification systems operating in the districts allows the elimination of percentages close to 100% of suspended solids, nitrogen, trivalent chromium and organic load (COD) from the processing wastewater.
The purified water is then returned to the environment with qualitative characteristics that allow its safe reintegration into natural biological cycles.
Levels of Removal of Major Pollutants in Water (treatment plants of Tuscany and Veneto Districts)
– 2022 DATA –
-97.9%
COD
COD
(Chemical Oxygen Demand)
Its value, expressed in milligrams of oxygen per litre (mgO2/L), represents the quantity of oxygen necessary for the complete oxidation of the organic and inorganic compounds present in wastewater. The index measures the degree of pollution of the water by organic residues from the leather (hide and dermis) and chemical products not exhausted in the process baths (e.g., ammonia, surfactants, sulphides, organic acids, organic solvents, tannins, resins, aldehydes, dyes, fats, etc.). The control of COD in purification occurs by combining physical interventions (e.g., filtration/screening etc.) with chemical and biological processes.
-99.5%
Chromium III
Chromium III
fibres, preventing rotting without altering softness, flexibility and original fibrous structure and for this reason it is very widely used in the tanning industry.
In its trivalent oxidation state, chromium does not have particular toxicity characteristics.
The technologies available to the industry make it possible to recover, through chemical-physical treatments, a large part of the chromium contained in exhausted tanning baths, reducing the concentrations entering the purification systems, which complete its elimination.
-95.7%
Total Nitrogen
Total Nitrogen
This is one of the key parameters in the evaluation of the polluting load, as it exerts its action at both a chemical and biological level, intervening directly in the metabolism of living organisms. It is expressed in terms of TKN: Total Kjeldhal Nitrogen, i.e., the concentration of total organic nitrogen resulting from the degradation of proteins and urea. To obtain the total nitrogen content in wastewater, in addition to the TKN, the portion of nitrogen deriving from ammonia (NH3) and ammonium salts (NH4+) used in the processes must also be taken into consideration. During the purification treatment, biological processes are mainly carried out on the nitrification/denitrification balance.
-99.5%
Suspended SolidsSuspended Solids
Indicates the amount of undissolved solids, measured in milligrams/litre (mg/L), that can be separated by filtration from a liquid sample. In tanning wastewater, it is mainly due to undissolved chemical products or residues from the degradation of the leather during wet operations and can be reduced (with a positive impact also on COD) through chemical-physical treatments.
-29.4%
Chlorides
Chlorides (Cl-)
The chlorides present in tanning waste are entirely of mineral origin, attributable to the soaking which brings the conservation salt into solution, to the ammonium chloride possibly used in deliming/maceration and to the use of sodium chloride and hydrochloric acid in the pickling and tanning. Their presence is not considered particularly worrying except for the influence that a high salt load can cause on the osmotic potential of water, on its organoleptic characteristics and for possible corrosive phenomena on pipes, linked to the greater electrical conductivity of the water.
Emissions
Atmospheric emissions represent another important environmental aspect to be monitored and subjected to continuous improvement.
Tanning production is associated with atmospheric emissions from the leather transformation processes and the auxiliary processes involved in energy production.
The emissions generated depend on the type of production process, with significant variations depending on the type of item.
To produce Italian leather, tanneries have cutting-edge technologies that follow the development of strict regulations, both national and European.
Emissions Kg CO2 eq/m2 of leather produced
No Data Found
2022 data
Emissions from boilers and energy generators release a series of gases into the air that can contribute to the greenhouse effect (such as CO2 and nitrogen oxides). For these, the corresponding equivalent CO2 content was considered as an impact indicator, calculated based on energy consumption, evaluating the direct (consumption of gas, diesel and other fuels) and indirect (consumption of electricity generated off-site) contributions.
The emission of VOCs (Volatile Organic Compounds) is instead significantly influenced by the intended use of the leather. Filters and abatement systems installed to monitor the systems minimise polluting emissions and allow the authorisation parameters to be respected.
VOC emissions per m2 of leather produced
No Data Found
2022 data
Change 2015/2022
As regards the emission of VOCs, the results obtained are continuously decreasing compared to previous years thanks to the implementation of new technologies in both the production and emission reduction phases, and to the progressive replacement of solvent-based finishes with water-based formulations.
Solid Waste
Less than 30% by weight of the raw hides entering the tannery is transformed into a finished product. The remaining amounts of organic material deriving from the raw hides are discarded during the process, generating by-products and waste. These are of varying nature depending on the phase of the cycle they come from and can therefore have different final destinations.
The European Waste Code precisely classifies tannery waste:
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 a liquid phase
04 01 04 Tanning liquor containing chromium
04 01 05 Tanning liquor free of chromium
04 01 06 Sludges, in particular from on-site effluent treatment containing chromium
04 01 07 Sludge, in particular from on-site effluent treatment free of chromium
04 01 08 Waste from fat, grease, and wax removal and stabilization
04 01 09 Waste from dressing and finishing
04 01 99 Waste not otherwise specified
The fleshing, which results from the mechanical removal of portions of subcutaneous tissue from the pelts, the hair and other solid residues deriving from the first stages of processing are not classified under current legislation as waste, but as Animal By-Products (ABPs).
Waste generated
No Data Found
2022 data
2022 data
Excluding tanning baths
data 2022
Type of waste
2022 Data
No Data Found
The main categories into which waste from tanning activities can be divided are:
- tanning liquor: derives from the activity of those tanneries (active, in particular, in Tuscany) which separate the tanning liquor for the recovery of chromium salts.
- offcuts, trimmings and dust: residues from the tanning process that are largely recovered and transformed into fertilisers and soil improvers.
- sludge: waste from finishing activities, tank cleaning and any wastewater treatment.
- packaging: deriving from paper and plastic, wood and mixed materials packaging, mostly intended for recovery.
- other sector-specific waste, such as salt, absorbent material, filters and process residues largely disposed of.
- other waste generated by service activities
Waste hazardousness
2022 Data
No Data Found
Waste destination
2022 data
No Data Found
Italian leather has made recovery its philosophy of life: 78% of the waste resulting from production processes is sent for recovery.
A very important example of such recovery is that of Chromium (III) from tanning liquor, which is then reintroduced into the production process.
Then there is waste resulting from the tanning preparation phases (such as fleshing, etc.) which are classified as ABPs (Animal By-Products). This is biological waste that is reinserted into production cycles of other supply chains, where it is broken down into simpler molecules (peptides and amino acids), becoming biostimulants and fertilisers for agriculture: a precious nourishment for plants, collagen for cosmetics, nutraceuticals and adhesives, jellies for the food sector and pharmaceutical industry.
The waste produced from tanning to final selection (offcuts, trimmings, shavings, etc.) can instead be used to create materials for fashion (regenerated leather fibres), paper industry (paper) and more.
The management approach of Italian leather waste and by-products is: