Tanning Waste Recovery
Firstly, by recovering a precious organic material – leather – the Italian tannery has historically set itself the goal of developing and managing its transformation into a material with very high added value by adopting an integrated ’circular’ approach.
Explaining how is very simple. It has created the conditions for its production waste to become raw materials for other industrial chains instead of waste, anticipating the European strategy for the circular economy by decades, which promotes the sustainable reuse of biological resources and waste for the production of goods for other sectors.
Some practices for the recovery and enhancement of waste and residues from tanning processes are described below.
From the Purification of Tanning Wastewater to the Production of Biofertilisers – Cuoiodepur Case
The Cuoio-Depur Consortium has developed methodologies that allow the agricultural reuse of sludge resulting from the treatment of wastewater from vegetable tanning, a tanning method based on the use of tannins and extracts from plant bark, obtaining organic nitrogen fertiliser that is entirely derived from natural organic sources.
This sludge is particularly suitable for the purpose, given the significant presence of organic substances deriving from plant-based extracts (tannins) and from the processing of hides. Residues of hair, mane, fleshing, hide and similar, called ’pellicino’ in Italian, are added to it.
This mixture is aimed at producing a fertiliser product known as ’Pellicino Integrato,’ which has had very positive results in terms of agronomic efficiency, as well as complying with current laws.
It is important to note that in terms of classification, this sludge is not treated as waste; in fact, it is not assigned any EWC code (European Waste Code), but is treated as a by-product resulting from the tanning wastewater treatment process.
Recovery of ABP and Tanned Trimmings from Tanning Processes for the Production of Solid Fertilisers, Liquid Biostimulants, Retarding Agents for Setting Gypsum and Energy – Cases of Sicit S.p.a., Ilsa S.p.a., Hydro S.p.a.
The above-mentioned companies are located within the national tanning districts and recover tanning waste, giving it new value through highly technological processes.
In addition to the obvious contribution to the sector’s circularity efforts, these supply chains have made it possible to significantly reduce, or even eliminate, some of the most significant types of tanning waste.
For every 1,000 kg of processed raw hides, approximately 250 kg of tanned hides are produced and up to approximately 600 kg of animal by-products (ABP), including hair, fleshing and scraps (already calcined, hairless hides) and tanned waste such as recoverable shavings and trimmings, in crust or finished form.
This waste follows different regulatory regimes: in the case of ABP, the reference is EC Regulation 1069/2009; in the case of waste it is EC Regulation 152/2006.
Both are mainly composed of collagen and are transformed into protein hydrolysates, precursors of fertilisers and biostimulants for the agrochemical sector and retarding agents for gypsum for construction.
From the fleshing alone, approximately 10% of concentrated protein hydrolysate is obtained, a basic element for the formulation of biostimulants; this percentage increases to 57% by subjecting semi-finished or finished leather trimmings to thermobaric hydrolysis to obtain solid nitrogen fertiliser and to 55% by subjecting wet blue to enzymatic or chemical hydrolysis to obtain an aqueous solution of protein hydrolysate (the figure may vary slightly depending on the degree of dilution).
Biostimulants are high quality and agronomically efficient products, totally biodegradable and without risks for public health and the environment. They are ‘smart’ fertilisers, supplements for crops in difficult environmental and stress conditions, which strengthen the plant’s natural defences against diseases, parasites and climate change.
Their use allows to reduce the use of fertilisers and especially agrochemicals: they are able to modulate the release of nitrogen based on the plants’ needs and act on plant development, improving the chemical, physical and biological characteristics of soil.
The difference between fertiliser and biostimulant is that the former restores nutrients in soil and must be used in large amounts, while the latter activates the immune responses of plants and is used in minimal amounts.
The hydrolysis processes to obtain amino acids and peptides for the agricultural sector have opened up the possibility of obtaining an interesting product for the construction sector as well: retarding agents for setting plaster, an amino acid-based additive that allows for easy workability and spreading without it coagulating too quickly.
Another interesting use of the fleshing is the production of energy. This waste is made up of a significant amount of fat, which is separated, subjected to an esterification process and subsequently sold to energy production plants. The esterification process is necessary to improve the efficiency of fat combustion and to avoid damaging the plants.
Gelatine and Food Proteins from Collagen – Lapi Gelatine Case
In this case, the processing residues from tanneries are used for the production of gelatine intended for human consumption in the food, pharmaceutical and nutraceutical sectors.
All the materials are certified, appropriately traced and processed in full compliance with the mandatory regulations applicable in the health and hygiene sector, so as to guarantee food safety.
Some products destined for the food chain are made using crusts and lime splits, but also scraps full of proteins: collagen, artificial casings, gelatines and food proteins which are essential, for example, for the production of gummy sweets and gelatines for preserved meats.
In the pharmaceutical sector, food gelatines are instead used to produce capsules for medicines; by enclosing the active ingredient, they serve to mask unpleasant flavours.
Gelatine is particularly suitable in this case, as it has the characteristic of being thermos-reversible at the temperature of the human body and this allows the drug to be released once it reaches the stomach.
Hydrolysed collagen is used in the nutraceutical sector for the production of energy bars, drinks and food supplements.
Other by-products not intended for human consumption can be transformed into technical gelatines, glues, pet food and edible pet toys.
Inert Granulates for Construction and Bituminous Conglomerates – Aquarno Case
The technological and plant innovations adopted at the purification level by Aquarno have significantly reduced the volumes of sludge deriving from purification treatments destined for disposal, transforming them into a secondary raw material.
This was possible through a specific recovery process which, starting from the dehydration and drying of the sludge, through the pyro-sintering of the same, led to the production of a sintered granulate; after mixing with calcium carbonate, this granulate is used for the production of inert granulates for construction and road foundations.