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Castelfranco di Sotto (PI) Chemical, Physical and Biological Purification Plant

Via Usciana, 65 - Castelfranco di Sotto (PI)

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Herambiente Servizi Industriali

Page update 1 July 2019

    Treatment capacity
    the maximum quantity of waste treated is 270,000 tonnes/year, of which 200,000 tonnes/year are non-hazardous and 70,000 tonnes/year are hazardous.
    Waste accepted
    liquid special waste, hazardous and non-hazardous waste.

    The plant complex consists of the following sections:

    Unloading zones
    The liquid waste treatment plant has different sections, each equipped with tanker unloading zones. The vehicles are unloaded using hoses with quick couplings to connect the tanks to the grates that are installed to remove coarse material. After the grate the wastewater is pumped into storage tanks. The unloading areas for septic tanks and industrial pumpable sludge are also equipped with desanding.

    Incoming waste storage tanks
    The storage tanks are divided by type of waste. There are 5 tanks of 100 m3 each for water from chemical-physical treatment, 2 tanks of 100 m3 each for pumpable sludge, 2 tanks of 100 m3 each serving the saline solutions evaporator, 2 tanks of 50 m3 each for the oil emulsions and surfactants evaporator, 2 tanks of 100 m3 and 1 tank of 60 m3 for the supply of the distillation solvents. Tanks are also installed for the storage of chemical reagents and the liquid waste produced by treatments.

    Chemical-physical treatment in batch reactors
    The chemical-physical treatment is carried out mainly to remove suspended solids, metals, surfactants, and hydrocarbons, before the subsequent biological process. Eight batch reactors of 70 m3 each, equipped with agitators, are used. The chemical products commonly used are ferrous chloride, hydrated lime and soda, polyelectrolyte. If necessary, specific reagents may be used for the removal of metals or surfactants. The clarified wastewater is sent to the equalisation of the biological treatment plant while the sludge produced is sent to the dewatering line.

    Dewatering section for sludge produced by chemical-physical treatment
    The sludge produced by the chemical-physical treatment is dewatered using a filter-press. The line is equipped with three plate filter presses. The sludge entering the lines is further conditioned with ferrous chloride and lime. The filtered sludge, stored in roll-off containers and semi-trailers, is sent to the Herambiente Servizi Industriali stabilisation plant, from where it is then disposed of in a landfill.

    Evaporation/crystalisation section for oily emulsions and surfactants
    Oily emulsions and wastewater with high concentrations of surfactants are treated with a triple-effect, forced-circulation, vacuum evaporator. The evaporator separates the aqueous phase which is then evaporated, condensed and sent to the biological section. The hydrocarbons and surfactants flow into a liquid concentrate, with a residual water content of about 50%, which is sent to a storage tank and fed into a static concentrator. The concentrator, heated with low pressure steam coils, evaporates further water and obtains a high calorific value concentrate that is stored in a heated tank and sent off for disposal/recovery.

    Evaporation/crystalisation section for saline solutions
    The effluents with high salinity and metals that cannot be handled by the chemical-physical plant is treated with a second triple-effect, forced-circulation, vacuum evaporator. The evaporator separates the aqueous phase which is then evaporated, condensed and sent to the biological section. The salts and metals flow into a liquid saline concentrate, with a very high dry residue, which is sent to a storage tank and fed into a scraped-type crystalliser. The crystalliser, heated with an external jacket, allows additional water to evaporate and obtain a salt that is stored in a roll-off container and sent off for disposal

    Distillation section for solvent water
    Water with a low-boiling solvent content of about 20% is sent to a distillation plant which separates the solvents from the aqueous phase. The column works at atmospheric pressure and is kept at a temperature below 100C so as to boil the solvents that boil at a low temperature, which are then condensed and stored in an insulated tank, from which they are sent for recovery. The aqueous phase of the column bottom is sent to the evaporation plants in order to eliminate salinity and high-boiling compounds.

    Biological treatment section
    The biological purification plant is fed with the wastewater from the chemical-physical treatment and from the other treatment lines and with the wastewater discharged directly (landfill leachates and septic tanks). The treatment plant consists of an equalisation section, a primary flotation treatment section and three biological lines with activated sludge. The first two lines consist of denitrification, oxidation and sedimentation. The final line has an ultrafiltration section downstream of the oxidation (MBR). A boron removal filter with selective ion exchange resins has been installed before the discharge into the industrial sewer system. The plant also includes the biological sludge dewatering line (thickening and centrifugation) and the two reverse osmosis lines which, by treating the MBR permeate, produce the industrial water needed by the entire liquid waste treatment plant.

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