Recently, Arsutoria Tannery has published a series of articles that talk about the tanning district of Santa Croce sull'Arno, focusing mainly on the Aquarno purifier with an interview with its Director, on the “Tubone” and “Acqua 360” projects, and finally on the plants sludge treatment.The articles highlight how the Santa Croce purifier with recent projects and interventions has become an efficiency model that the world observes and envies us.
Aquarno purifier: in the tannery, there will soon be only refined recovery water
The tanning district of Santa Croce sull'Arno is one of the largest tanning areas in Europe with over 250 tanneries. From the point of view of environmental respect the Aquarno purifier, a centralised system at the service of the leather district active since 1974, today is at the centre of an impressive connection project of the purification system, the so-called “Tubone”.
The possibility of recovering treated wastewater is one of the most interesting results that will bring “Tubone”. The president of Assoconciatori, Alessandro Francioni explains the new integrated system will redistribute “refined” water directly to tanneries, which no longer have to emit water from the subsoil. Soon it will be possible to use only recovery water to tan the skins in a perfect circular economy perspective.
The system is not limited to the de-pollution of all waste waters produced by the tanning pole, which are released clean in rivers; the purifier is connected to a treatment and reduction system of muddy materials resulting from the treatment that processes them to be reused in other sectors, such as in the construction industry. It is also important to remember that the chromium used in the tanning processes is returned to companies through a careful recovery process. Even residues and scraps of leather processing are recovered and destined for other uses, such as scientific and cosmetic ones. There are two distinct treatment lines inside the purifier, one for civil waste and one for industrial waste.
The Santa Croce water treatment plant is managed by the Consorzio Aquarno which constantly collaborates with major research institutions, university departments and other accredited companies in order to always test new plant solutions that further reduce sludge production and odor emissions, as well as to improve and make the purification yields even more effective.
Interview with the Director of the Depuratore Aquarno, Nicola Andreanini
The chemical engineer Nicola Andreanini, director of Depuratore Aquarno, in the interview illustrates the main strengths of the tuscan tanning district water treatment: “One of the distinctive elements of a purifier's features is certainly the one linked to the destruction of the pollutants to be removed. Consider that we are able to obtain removals greater than 98.5% of the concentrations of incoming pollutants. In this particular period, another element distinguishes us and makes the most of all the efforts and the energies involved in minimising environmental impacts. I am referring to the substantial elimination of landfill disposal as a destination for the sludge flow produced by the purifier. For many years now we have been dealing with the entire sludge flow produced by the purifier at the sludge treatment plant in via S. Andrea where the outgoing inert, which after the various treatments to which it is subjected, represents a tenth of the incoming mass flow, is anyway going to be recycled in the construction industry.”.
Andreanini points out the new tank specifically dedicated to the temporary storage of rainwater will soon be operational. In this tank the incoming water will be collected during periods of heavy rainfall so that it can be stored temporarily, without weighing down with an excessive hydraulic load on the functionality of the plant, in order to be subsequently treated downstream after the most intense precipitation period.
In the first instance we want to ensure the purification of domestic waste of large areas of the regional territory where the purification is currently too fragmented and does not allow to obtain satisfactory results. Secondly we intend to exploit this new arrival in order to have a water flow that can be appropriately refined and then be returned into the production sites in place of the waters emitted from the subsoil. The arrival of domestic wastewaters is scheduled for 2021 and it is therefore likely that the system will be fully operational in the following year.
During the interview the "Acqua 360" project is mentioned, closely linked to the "Tubone" project. The Acqua 360 project aims to test technologies that will be used for refining domestic wastewaters. It is a good-sized pilot plant which has allowed us to test, together with the three partner tanneries of the initiative, the characteristics of the water refined in the production processes. The results were encouraging as there were no indications against the use of this recovery water instead of the well water commonly used by the partners.
The “Tubone” project: a 200 million euro work for a more efficient and environmentally friendly water reorganisation system
The so-called “Tubone” is the new system of water reorganisation of 42 municipalities in Tuscany, which will have its fulcrum ar the Aquarno purifier of Santa Croce sull'Arno and will be fully operational within the next three years.
The project is part of the Program Agreement for the Protection of Water and was created with the dual aim of adapting the Valdinievole purification system and supporting the Santa Croce leather district by supplying refined water to the tanning industries which will no longer have to draw their needs from the water table. The “tubone” will pass through almost all the Municipalities of the Valdinievole, to get to Santa Croce where it will bring the treated wastewater to the leather district.
The project involves the construction in three years of a piping system of about 50 kilometres, of which the “tubone” is the main part. The latter will have a length of over 30 kilometres and its diameter will reach, to the maximum extent, almost one metre. The project involves the expansion of the Santa Croce treatment plant which will see a significant increase in the water to be purified and a consequent and progressive disposal of about twenty small water treatment plants in the territory which, in some cases, will become accumulation tanks.
The “Acqua 360” project
One of the most interesting aspects of the new Tuscan civil and industrial water treatment system is linked to the “Acqua 360” research project, which is experimenting how to purify and refine civil waste water and then re-use it in the tannery. As part of the project, funded under the ERDF Tuscany 2014-2020 ROP, was create a pilot plant (ACQUA 360 plant) for the purification and refining of civil wastewater with the aim of producing a sufficient amount of process water which is supplied to the 3 tanneries involved in the project. Thanks to the tannery tests, we are proceeding to validate the water purification process and the feasibility of re-use. Project partners are DeltAcque, the Aquarno purifier, Poteco, Archa Laboratories and the San Lorenzo, Settebello and Victoria tanneries which are already experimenting.
Over the years, the technological innovations introduced during the purification phase have significantly reduced sludge production to be disposed of. The flows involved are however still significant and for this reason we have worked to further reduce the volumes by studying their possible reuse.
The Ecoespanso plant of Santa Croce is entirely dedicated to the treatment of sewage sludge produced by the Aquarno Consortium and the Tanning Consortium of Fucecchio.
This is where the process starts, which is divided into 5 phases: dehydration (centrifugation), drying, pyrosintering of dried sludge, energy recovery and fume treatment, production of inert granulates for the construction industry (HSC) and bituminous conglomerates (HBC) for asphalts, containing the KEU (sintered granulate).
Since the 1980s, the Consorzio Cuoio-Depur, which manages the centralised urban waste water treatment plant at Ponte a Egola, studies possible forms of reuse in agriculture of its sludge with high organic protein content.
In particular, efforts have been focused on identifying possible formulations made by mixing the protein sludge obtained by the tannery purification with products deriving from the same production cycle and in any case already recognised as fertilisers.