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Pisa Liquid Waste Treatment Plant (Chemical-Physical Biological)

Via C. L. Ragghianti, 12 - Pisa

Herambiente Servizi Industriali

Page updated 1 July 2019

 
    Authorised treatment capacity
    the maximum quantity of waste authorised for chemical-physical treatment is 75,000 t/year, of which 40,000 t/year comes from third parties and the remaining part is produced within the platform. The maximum quantity of waste authorised for biological treatment is 75,000 t/year, of which 13,000 t/year comes from third parties and the remaining part is produced within the platform. The acid neutralisation plant can treat up to 5,000 tonnes/year of waste.
    Authorised storage capacity
    1520 t (chemical-physical) + 235 t (acid neutralization).
    Waste accepted
    liquid special waste, hazardous and non-hazardous waste.

    Chemical-physical section
    The chemical-physical treatment plant has a capacity of 25 m3/h and consists of the following sections:

    • discharge of liquid wastewater, with grate system,
    • incoming wastewater storage, with 2 tanks of 200 m3 each and 12 tanks of 60 m3 each,
    • equalisation,
    • treatment by addition of chemical reagents
    • sedimentation by means of 2 lamella settler elements
    • storage of treated water with 2 tanks of 200 m3 each;
    • sludge storage with 4 tanks of 30 m3 each acting as thickeners;
    • sludge dewatering by centrifuge.

    The plant uses a coagulation/flocculation process for the abatement of heavy metals and suspended solids by adding coagulant (ferric chloride), pH corrector (hydrated lime) and polyelectrolyte. Separation between the liquid and sludge phase is carried out in a lamella settler.
    The incoming waste, delivered by tankers, before being unloaded, is sampled and analysed in the laboratory.
    The entire treatment process is managed by operating personnel with the help of PC-based control.
    The chemical-physical plant is equipped with an exhaust ventilation system that abates the exhaust air from the treatment and storage tanks and from the sludge from chemical-physical treatment.

    Biological Section
    The biological treatment plant consists of the following sections:

    • equalisation,
    • SBR aerobic treatment (nitrification and denitrification)
    • balancing tank
    • final finishing of the water (filtration on sand, activated carbon and ion exchange resins, microfiltration and reverse osmosis and treatment with UV lamp)
    • internal discharge or reuse of treated water.

    Specifically, it includes the following components:

    • equalisation tank,
    • biological aerobic treatment tank,
    • balancing tank,
    • sand filtration,
    • filtration on activated carbon,
    • filtration by microfiltration and reverse osmosis,
    • filtration on ion exchange resins,
    • disinfection with ultraviolet rays,
    • final storage of treated water,
    • technical rooms (blowers, electrical panels, RS and UV, reverse osmosis),
    • canopy over the filtration plants,
    • microfiltration booth.

    The biological treatment is an SBR (Sequencing Batch Reactor) type unit.
    The equalisation tank has a capacity of 750 m3, corresponding to about 2 days of incoming material.
    The treatment tank has a capacity of 1,400 m3 and by alternating the oxidation and mixing phases can carry out the oxidation/nitrification and denitrification processes.
    The balancing tank, with a capacity of 360 m3, can accumulate the right quantity of wastewater to be sent to the subsequent finishing treatments that require a constant lower flow rate that is more distributed over time.
    Before discharge into the sewer and/or reuse, the water can be accumulated in 3 tanks of 150 m3 each from which samples will be taken and analysed in order to define the destination of the water itself, which may be: direct discharge into the sewer, storage tank for internal reuse, equalising tank EQ-01 if the water needs further treatment.
    The final filtration phase is carried out by means of filters on sand, activated carbon and ion exchange resins.

    As an alternative to the filtration system on ion exchange resins, a microfiltration and reverse osmosis section can be used.
    The discharge of purified wastewater, when not reused internally, takes place after storage of the water in three tanks of 150 m3 each and prior analytical control to ensure compliance with the limits required by Italian Legislative Decree 152/2006 for discharge into surface water.
    The treatment, aeration and equalisation tanks have exhaust ventilation systems and the flow is treated by means of a biofilter.

    Acid Neutralisation Section
    The neutralisation section, which can be used independently of the chemical-physical plant, has a capacity of 5,000 t/y and consists of:

    • 3 tanks of 28 m3 each (AF1, AF2, AF3) for storage of acid waste (sulphuric acid, hydrochloric acid, hydrofluoric acid)
    • 2 tanks of 28 m3 each (AD1, AD2) for storage of weak acid solutions
    • 1 alkaline solution storage tank (BF1) (raw material or alkaline waste)
    • neutralisation reactor (N1)
    • exhaust ventilation line and vent treatment
    • cooling system

    Acid neutralisation takes place in the N1 reactor equipped with a cooling system with a special tower. In the batch process, about 5 m3 of acid solution is reacted for each treatment cycle, with the addition of alkaline solution (NaOH or sodium aluminate, raw material or waste) for the reaction. The neutralised solutions are transferred to two intermediate storage tanks, each with a capacity of 10 m3, to check that neutralisation has taken place and are then sent to the two thickeners and from them to the centrifuge.
    The reactor and acid storage tanks have an exhaust ventilation system with a dedicated fan that conveys the exhaust to two wet towers for neutralisation.

    Waste type approval
    Specific waste control procedures apply both when defining contracts with customers (the 'type approval' phase) and upon accepting deliveries to the plant.
    The compliance of the quality of the incoming waste with the corresponding approval is checked by means of visual and analytical inspections, carried out instantly, periodically and on a 'spot' basis, including collection of waste samples. After checking, the waste is sent for the treatments defined in the approval phase.

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