Ecoespanso S.r.l. was established in 2001 with the aim of managing sewage sludge sustainably and improving the environmental impact of the entire tanning process. Since July 2014, management of the facility has come under the control of Consorzio Aquarno, which reorganised its structure to ensure greater integration with the wastewater treatment plant and optimise operational synergies. The facility primarily treats sludge produced by Consorzio Aquarno. It is located in Santa Croce sull’Arno and is authorised for sludge storage, centrifugation, and thermal treatment operations, with sludge transported through a sludge pipeline. The maximum treatment capacity of the centrifugation section exceeds 1.3 million cubic metres of sludge per year, while the thermal section can receive up to 12 tonnes per hour. The treatment process produces a sintered granulate that can be sent for recovery or disposal operations.
8|10K
tonnes of sintered granulate produced as the final treatment residue
600K+
cubic metres of sludge treated every year
The sewage sludge produced by Consorzio Aquarno reaches the Ecoespanso facility through a dedicated sludge pipeline. The two types of sludge leaving the wastewater treatment plant (biological sludge and chemical sludge produced by tertiary treatments) are transferred through two separate pipelines. The biological sludge, which represents the majority of the sludge produced, flows into a single storage tank with a capacity of 3,000 m³, while the chemical sludge feeds into a 50 m³ tank.
The thickened sludge (about 3% suspended solids) is subjected to centrifugation to obtain shovelable sludge with a dry solids content of 26–30%. This operation makes it possible to reduce the mass to be treated by approximately ten times. The separated liquid is sent back by pipeline to the wastewater treatment plant in Santa Croce sull’Arno.
Sludge drying takes place in three moving-belt dryers, divided into two sections (one with two stages and one with a single stage), which raise the dry solids content to around 90%. The hot air is recirculated by fans, while the steam produced is partly retained and partly condensed in the heat recovery section.
The production of sintered granulate takes place through the pyrolysis and sintering of dried sludge in two rotary kilns connected to allow the continuous passage of the material.
The syngas produced by the pyrolysis of sludge has a calorific value equal to one third of that of methane and is recovered as fuel in the post-combustion chamber. The gases leaving the post-combustion chamber are conveyed to a flue gas treatment line, where dust and NOx are removed using urea. The heat produced at this stage is recovered through an economiser that generates superheated steam, which is reused in the drying kilns, reducing the consumption of fresh steam. The flue gases, cooled in a water column, are dedusted through bag filters and treated in scrubbers for acid removal before discharge. The collected dust, which may contain hexavalent chromium, is treated in reduction reactors with ferrous chloride.
Santa Croce sull’Arno (Pisa)
Via del Bosco, 283
Transparent Administration
Consorzio Aquarno spa Registro Imprese PISA P.IVA e Cod.fisc. 00857500508 R.E.A. PISA PI026-8385 Capitale sociale € 800.000 i.v.
