Tenaris has saved approximately 1,800 tons of sludges heading to landfills since June 2019, representing a 70% reduction in the wastewater treatment sludges produced at its Costa Volpino plant in Italy. The remaining 30% of the sludges is now the focus of project underway to repurpose them as raw material for steel production.
Costa Volpino produces cold drawn pipes from hot rolled tubes, produced at the company’s Dalmine plant, which are pickled with sulfuric acid before being subsequently processed in the transformation and finishing lines. Cold drawn tubes are used in hydraulic circuits, earth-moving machinery and in the automotive industry, among other applications.
The waste generated from the pickling, including water used for rinsing, are transferred to a chemical-physical water treatment plant, which treats the material before being discharged into surface water. At the end of the treatment process, an inorganic muddy residue is produced which is filter-pressed in order to reduce the amount of water.
The sludge from water treatment at Tenaris’s Costa Volpino plant has always been handled as waste and sent for disposal to landfills following an inertization process at waste treatment plants in compliance with current laws.
Tenaris’s research team began in 2016-2017 to develop drying technologies applicable to the type of sludge produced. This research led to the installation of a closed-cycle turbo-dryer at Costa Volpino that releases zero emissions into the atmosphere, allowing Tenaris to reduce the amount of sludge sent for disposal by about 70%, drastically reducing its humidity.
The dried sludge contains three basic raw materials for the production of steel, capable of replacing part of the ferrous scrap, ferroalloys and lime that are currently supplied from external suppliers and is therefore suitable as additive in the charge of the electric furnace, putting in motion the principles of a circular economy.
"Following the analysis carried out, we began to validate the environmental benefits resulting from the reuse of dried sludge in our production process,” said Fabio Praolini, Tenaris Environment Regional Director in Italy. “This is included in an R&D project ongoing in our Romanian steel shop, looking to find new materials to be used in the steel process, replacing raw materials, reusing waste and contributing to circular economy.”
Tenaris is participating in the RETROFEED project co-financed by the European Union within the Horizon 2020 Research Program. The project involves testing different products including the dried sludge, to evaluate materials performance in the furnace and validate the recovery option.
The evaluations are relevant to identify which of those usual waste streams can be used to replace raw materials, allowing the reclassification of waste streams to valorized products while helping to reduce landfilled materials.