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Bologna Industrial Sludge Treatment Plant

Via Shakespeare 29, Bologna

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Bologna liquid waste and industrial sludge physicochemical treatment plant (ITFI)
The plant is located at via Shakespeare 29, in an area adjacent to the purification plant for the city of Bologna (IDAR), in the north-west area of the municipality on the border with the municipality of Castel Maggiore.
As far back as 1972, before the purification plant was built, the municipality of Bologna installed three tanks in the area for collecting sewage sludge generated by private pumping firms operating in the local area.

 


    Subsequent work in the eighties and nineties updated the plant and improved its safety through the construction of tanks and a concrete yard with an HDPE liner and inter-liner monitoring wells to check for any leaks and with the construction of pre-treatment plants for physicochemical sludge, sludge from septic tanks and discharge from street drains, as well as landfill leachate.

    Page updated 26 August 2015

    Total authorised capacity
    • 120,000 tonnes/year (incoming)
    • 13,000 tonnes/year (D15 preliminary grouping)
    Types of waste accepted
    Liquid and sludge waste (such as sandy waste from street drains; organic waste with coarse materials derived from septic tanks; sludge from physicochemical treatment and from production processes; water and sludge from washing; leachate produced by landfills for municipal solid waste and special waste; process sewage sludge and mother liquors)

    The plant comprises two treatment lines, each designed for various types of liquid waste.

    1 - Sand extraction, screening and hydrodynamic filtration line.
    This section is dedicated to wastewater deriving from sewers, drains, street drains, etc., which has a high content of solids, the majority of which is siliceous material. The line comprises three parallel tanks with a capacity of 15m³ each, equipped with an inclined drainage pit, a screw for sand extraction and drainage into filtering bags and a pump to lift the sewage sludge and send it to the subsequent phases of screening, hydrodynamic filtration and centrifugation. The screening phase serves to remove the coarser material present in particular in septic tanks. This phase is performed by means of a mechanical grate and micro-grates with a filtering basket. The solid material collected in large bags is deposited in a yard to complete dehydration before disposal. The liquid fraction is sent for hydrodynamic filtration or centrifugation, after the addition of a polyelectrolyte, so that the overall removal of solids can reach an average of 99.5%. The watery residue is sent for biological treatment at the adjacent purification plant for the city of Bologna (IDAR).

    2- Physicochemical treatment line.
    This comprises two parallel physicochemical clariflocculation lines to treat the wastewater and a line for physicochemical treatment with Fenton's reagent. The treatment takes place before the wastewater is sent for biological treatment at the IDAR purification plant. Incoming sewage sludge is stored in 5 tanks measuring 10m³ each and 4 tanks with a capacity of 35m³, and undergoes sampling and analytical testing. Subsequent primary sedimentation takes place in a watertight tank with a capacity of 3000m³ in which the mixing of the landfill leachates also takes place. As the latter are characterised by a certain alkalinity and by the presence of sulphides, they encourage the precipitation of highly insoluble metals. The sedimented sludge is extracted and filter-pressed continuously, while the liquid fraction flows into a 650 m³ tank equipped with stirrers and an aerator, which enable the sewage sludge to be equalised, thus ensuring that the material sent to the subsequent physicochemical treatment phases is uniform in terms of composition and flow rate. This takes place by means of two distinct stages of clariflocculation: an acidic stage (in a 10 m³ tank, through the addition of hydrochloric acid and ferric chloride to achieve the flocculation of the colloidal particles) and a basic stage (in which, inside two separate reactors, an aqueous solution of calcium hydroxide is added first to encourage metal precipitation, followed by the addition of an aqueous anionic polyelectrolyte solution). The liquid waste is then conveyed to a 35 m³ sedimentation tank for the precipitation of the sludge. The clarified sewage sludge is then transferred by gravity to the final tank which has a capacity of 600 m³. In addition to the clariflocculation line, the plant is also equipped with a line for physicochemical treatment using Fenton's reagent (hydrogen peroxide, sulphuric acid and bivalent iron), capable of effectively treating waste with specific contaminants such as organic components that are not easily biodegradable ("refractory COD"), surfactants and solvents. The sewage sludge coming from the 100 m³ storage tank is sent at a nominal flow rate of 5 m³ per hour to the 15 m³ reactor fitted with mixing equipment. Following close contact with the reagents, the reaction mixture goes through connected vats inside two separate 5 m³ reactors to which an aqueous solution of calcium hydroxide is added to encourage the precipitation of metals, as well as an aqueous anionic polyelectrolyte solution. The mixture is then transferred to a 35 m³ sedimentation tank for the precipitation of the sludge. The clarified solution thus obtained is sent by gravity to the last 600 m³ tank. The sludge collected from the bottom of the sedimentation tank is sent to a 35 m³ thickener tank to increase the dry solid concentration and then to the filter pressing section, for final dehydration. The wastewater from the Fenton treatment and the clarified fluid from the physicochemical treatment process collected in the final 600 m³ storage tank, which also receives the water from the hydrodynamic filtration, are sent via dedicated piping to the IDAR purification plant for biological treatment. In this way, all the water treated can undergo rigorous analytical testing before it is sent for biological treatment at Bologna's purification pant (IDAR); if the content of the final tank is non-compliant, it can be returned to the physicochemical section for repeat treatment.
    All sedimented and filter-pressed/centrifuged sludge is disposed of in authorised plants.

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