Overview
The Industrial Sludge Treatment Plant (ITFI) in Bologna is designed to treat liquid waste and industrial sludge.
The plant is located in an area adjacent to the wastewater treatment plant of the city of Bologna and has two different treatment sections.
Chemical physical section for leachate and industrial waste: it consists of three different continuous clariflocculation treatment lines, one of which can be used to purify waste with high surfactants using the Fenton process.
SLS section solid/liquid separation for the treatment of sewage wastewater and sludge: the waste is desanded and screened, then it undergoes a centrifugation and flotation phase.
Discharges from the two sections flow into a final interposition tank before the effluent is sent to the IDAR wastewater treatment plant in Bologna.
A number of upgrades in the 1980s and 1990s made the plant increasingly adequate and safe with the building of concrete tanks and a yard with HDPE liners with inter liner monitoring wells to check for leaks, and the building of pre treatment plants for chemical physical sludge, sludge from cesspools and roadside drainage, and leachate from landfills.
Page update 5 December 2022
Form
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Total authorised capacity:
149,000 t/year (input) of which 5,000 t/year of hazardous waste -
Accepted waste:
Liquid and muddy waste (such as waste from cleaning roadside drainage and cesspools; sludge from chemical physical treatments and production processes; landfill leachate; process water and mother liquors)
The plant consists of two treatment sections, each designed for the different types of liquid waste.
Desanding, screening and hydrodynamic filtration section
This is the section dedicated to wastewater from cleaning sewer pipes, storm drains, roadside drainage etc., which have a high solids content, mainly sandy material. The line consists of three receiving tanks in parallel, each with a capacity of 15 m³, equipped with a sloping discharge pad, a coarse material screw pump with discharge into filter bags, and a sewage sludge lifting pump to send the sludge to the subsequent screening, hydrodynamic filtration or centrifugation stages. The screening phase is designed to remove coarse materials in suspension that are found in particular in septic tank discharge, and it is carried out by means of a mechanical grid and microgrids with a filter basket. The solid material is collected in bags and laid on the yard to complete dehydration before disposal. The liquid fraction is instead sent to the hydrodynamic filtration or centrifugation stage after adding a polyelectrolyte, with an overall average solids removal yield of 99.5%. The aqueous residue is sent to a 600 m3 final interposition tank and then sent for biological treatment in the adjacent IDAR wastewater treatment plant of the city of Bologna.
Chemical physical treatment section
It consists of two parallel chemical physical clariflocculation wastewater treatment lines and a chemical physical treatment line with Fenton reagent. The treatment is carried out before the wastewater is sent for biological treatment in the IDAR wastewater treatment plant. The incoming sewage sludge is stored in 5 tanks with a capacity of 10 m³ each and 4 tanks with a capacity of 35 m³ and undergoes sampling and analytical testing.
In the clariflocculation treatment, primary sedimentation takes place in a waterproofed tank with a capacity of 3,000 m³ in which the waste is homogenised and mixed according to its chemical characteristics in order to favour the precipitation of metals in insoluble form (hydroxides and sulphides). The settled sludge is continuously extracted and filter pressed, while the liquid fraction flows together with the leachate into a 650 m³ equalisation tank, equipped with mixers and an aerator, which ensures a homogeneous feed, in terms of composition and flow rate, to the subsequent chemical physical treatment stages. This occurs through the two distinct stages of clariflocculation: an acidic one, in a 10 m³ tank with the addition of hydrochloric acid and ferric chloride for the flocculation of colloidal particles, followed by a basic one, in which the effluent is supplemented first with an aqueous solution of calcium hydrate to promote the precipitation of metals and then with an aqueous solution of anionic polyelectrolyte in two separate reactors. The stream is then sent to a 35 m³ settling tank, common to both lines of the chemical physical processing plant, for sludge precipitation. The clarified material is then sent to the 600 m³ final interposition tank. The sludge collected from the bottom of the settling tanks is sent to a 35 m³ thickener to increase the dry solid concentration and then to the filter press section for final dewatering.
In addition to clariflocculation, the plant is equipped with a chemical physical treatment line with Fenton's reagent (hydrogen peroxide sulphuric acid bivalent iron), which can effectively treat waste characterised by peculiar contaminants such as poorly biodegradable organic compounds (detectable as "refractory COD"). The sewage sludge from the 100 m³ storage tank is fed with a nominal flow rate of 5 m³/ha into a 15 m³ reactor, equipped with mixers, in which the reagents are measured out. The reaction mixture passes through communicating vessels into two separate 5 m³ neutralisation reactors in which an aqueous suspension of calcium hydrate and polyelectrolyte is added to promote metal precipitation. The mixture is sent to a 35 m³ settling tank for sludge precipitation and separation. The clarified material obtained in this way is sent by gravity into the final interposition tank. The sludge collected from the bottom of the settling tanks is sent to a 35 m³ thickener to increase the dry solid concentration and then to the filter press section for final dewatering.
Accumulation, equalisation and recirculation section
The flows from the various treatment lines channelled into the final 600 m³ interposition tank are sent via dedicated piping to the IDAR wastewater treatment plant for subsequent biological treatment. Water recirculated into the IDAR wastewater treatment plant undergoes analytical testing (on line and off line) and in the event of non compliance, the contents of the final tank may be sent to special storage tanks for further treatment The sludge produced, sedimented and filter pressed/centrifuged, is disposed of at authorised plants.
Desanding, screening and hydrodynamic filtration section
This is the section dedicated to wastewater from cleaning sewer pipes, storm drains, roadside drainage etc., which have a high solids content, mainly sandy material. The line consists of three receiving tanks in parallel, each with a capacity of 15 m³, equipped with a sloping discharge pad, a coarse material screw pump with discharge into filter bags, and a sewage sludge lifting pump to send the sludge to the subsequent screening, hydrodynamic filtration or centrifugation stages. The screening phase is designed to remove coarse materials in suspension that are found in particular in septic tank discharge, and it is carried out by means of a mechanical grid and microgrids with a filter basket. The solid material is collected in bags and laid on the yard to complete dehydration before disposal. The liquid fraction is instead sent to the hydrodynamic filtration or centrifugation stage after adding a polyelectrolyte, with an overall average solids removal yield of 99.5%. The aqueous residue is sent to a 600 m3 final interposition tank and then sent for biological treatment in the adjacent IDAR wastewater treatment plant of the city of Bologna.
Chemical physical treatment section
It consists of two parallel chemical physical clariflocculation wastewater treatment lines and a chemical physical treatment line with Fenton reagent. The treatment is carried out before the wastewater is sent for biological treatment in the IDAR wastewater treatment plant. The incoming sewage sludge is stored in 5 tanks with a capacity of 10 m³ each and 4 tanks with a capacity of 35 m³ and undergoes sampling and analytical testing.
In the clariflocculation treatment, primary sedimentation takes place in a waterproofed tank with a capacity of 3,000 m³ in which the waste is homogenised and mixed according to its chemical characteristics in order to favour the precipitation of metals in insoluble form (hydroxides and sulphides). The settled sludge is continuously extracted and filter pressed, while the liquid fraction flows together with the leachate into a 650 m³ equalisation tank, equipped with mixers and an aerator, which ensures a homogeneous feed, in terms of composition and flow rate, to the subsequent chemical physical treatment stages. This occurs through the two distinct stages of clariflocculation: an acidic one, in a 10 m³ tank with the addition of hydrochloric acid and ferric chloride for the flocculation of colloidal particles, followed by a basic one, in which the effluent is supplemented first with an aqueous solution of calcium hydrate to promote the precipitation of metals and then with an aqueous solution of anionic polyelectrolyte in two separate reactors. The stream is then sent to a 35 m³ settling tank, common to both lines of the chemical physical processing plant, for sludge precipitation. The clarified material is then sent to the 600 m³ final interposition tank. The sludge collected from the bottom of the settling tanks is sent to a 35 m³ thickener to increase the dry solid concentration and then to the filter press section for final dewatering.
In addition to clariflocculation, the plant is equipped with a chemical physical treatment line with Fenton's reagent (hydrogen peroxide sulphuric acid bivalent iron), which can effectively treat waste characterised by peculiar contaminants such as poorly biodegradable organic compounds (detectable as "refractory COD"). The sewage sludge from the 100 m³ storage tank is fed with a nominal flow rate of 5 m³/ha into a 15 m³ reactor, equipped with mixers, in which the reagents are measured out. The reaction mixture passes through communicating vessels into two separate 5 m³ neutralisation reactors in which an aqueous suspension of calcium hydrate and polyelectrolyte is added to promote metal precipitation. The mixture is sent to a 35 m³ settling tank for sludge precipitation and separation. The clarified material obtained in this way is sent by gravity into the final interposition tank. The sludge collected from the bottom of the settling tanks is sent to a 35 m³ thickener to increase the dry solid concentration and then to the filter press section for final dewatering.
Accumulation, equalisation and recirculation section
The flows from the various treatment lines channelled into the final 600 m³ interposition tank are sent via dedicated piping to the IDAR wastewater treatment plant for subsequent biological treatment. Water recirculated into the IDAR wastewater treatment plant undergoes analytical testing (on line and off line) and in the event of non compliance, the contents of the final tank may be sent to special storage tanks for further treatment The sludge produced, sedimented and filter pressed/centrifuged, is disposed of at authorised plants.
