The physicochemical treatment plant includes the following sections:
- Treatment of oily emulsions: In this section, the oil fraction is separated from the aqueous fraction, the aqueous fraction is then sent for physicochemical treatment, while the oil fraction is sent for recovery/disposal.
- TCF1 first stage physicochemical treatment: Comprising two treatment lines in parallel with a planned flow rate of 25 m³ per hour. During this stage, after homogenisation, the flows are subjected to neutralisation and precipitation of the metals in an alkaline environment.
- TCF2 second stage physicochemical treatment: Comprising two treatment lines in parallel with a planned flow rate of 25 m³ per hour. Clariflocculation takes place in this section with flocculating and complexing agents for heavy metals and precipitation through the addition of anionic polyelectrolyte. The water leaving the section is sent to the Baiona Ecological Centre wastewater treatment plant for final biological treatment.
- TCFA physicochemical treatment section: Comprising a physicochemical treatment line (with a capacity of 25 m³ per hour) with the addition of reagents such as lime, flocculating agents, polyelectrolyte, sodium hypochlorite and adsorbing material. The waters leaving the TCFA may, if necessary, undergo further treatment for the abatement of heavy metals at the TCF2, described above or, alternatively, they can be sent to the Baiona Ecological Centre wastewater treatment plant for final biological treatment.
- Sludge treatment (thickener): In this section, the sludge leaving the previous treatment sections undergoes thickening and is sent to the adjacent DISIDRAT sludge treatment plant for filter-pressing and then sent for disposal.
- Accumulation, equalisation and recirculation section (VP tank): An integral part of the physicochemical treatment plant, this section receives the wastewater from the 2.6 km and 3.8 km facilities which already conform to the biological treatment. The flows are stored and homogenised in a tank with a capacity of 600 m³ before returning to the Baiona Ecological Centre wastewater treatment plant via the connection comprising 2 underground pipes approximately 4 km in length.
The DISIDRAT plant is designed to treat various types of pumpable, semi-solid and powdery waste with the main goal being to obtain matrices (waste).
The non-hazardous pumpable sludge treatment line comprises the following sections:
- Receipt and storage section: The pumpable sludge is stored in semi-underground tanks with an overall capacity of over 4,000 m³. There are two pre-storage tanks, with a capacity of approximately 70 m³ each, inside each of the two main storage tanks, at the unloading stations. The waste goes from the pre-storage tanks to the main tank via the overflow channel. Inside the main tank, the sludge is kept moving to prevent excessive sedimentation of the solid part by means of a mechanical system comprising horizontal axis propeller stirrers located at the bottom of the tank (4 stirrers in each tank). For both tanks, the pre-storage area has a bucket crane for collecting and transferring the heaviest part of the wastewater (sediment). The material collected in this manner is loaded onto dedicated sealed dump trucks or vehicles with sealed tanks to be transported to the neutralisation section for subsequent processing on the semi-solid sludge processing line.
- Treatment section: The sludge is subjected to conditioning with specific reagents before being subjected to mechanical dehydration through filter-pressing. The sludge, which is constantly stirred in the storage tanks, is transferred through single screw pumps to the conditioning line tanks. The conditioning line is designed to prepare the sludge for the dehydration process through filter-pressing: the sludge passes through the reaction tanks, where it is in constant movement and where the reagents needed to optimise the filter-pressing and to immobilise pollutants such as FeCl2, Na2S and Ca(OH)2 are added. The dehydrated sludge leaving the filter press is discharged into an area underneath, enclosed on three sides by a separation and containment wall, and is then collected by a tractor loader and transported either to the semi-solid sludge deposit area or to the semi-solid sludge processing area. The resulting waters are conveyed to a recirculation well and then transferred to the process water storage tanks before being transferred to the physicochemical treatment plant for subsequent treatment and/or sent for recovery to the tank for the preparation of milk of lime required for the filter-pressing process.
The hazardous pumpable sludge treatment line comprises the following sections:
- Receipt and storage section: The hazardous pumpable sludge is stored in semi-underground tanks with an overall capacity of roughly 1,500 m³. This section works in the same way as the section for non-hazardous pumpable sludge described previously.
- Treatment section: Here the sludge is subjected to consolidation and neutralisation. The sludge is transferred from the storage tanks for treatment via two single screw pumps, with independent lines to the semi-solid sludge processing section.
The semi-solid matrix treatment line comprises the following sections:
- Receipt and storage section: The semi-solid sludge and earth arrive at the plant in vehicles that unload them in dedicated areas covered by roofs; the powdery waste, however, is unloaded into silos which have an overall storage capacity of 360 m³.
- Treatment section: Here the waste is subjected to the consolidation and/or neutralisation process through the addition of reagents such as lime and/or cement in variable amounts; other additives such as zeolites and silicates can also be used. The sludge is processed on two distinct lines which have the same capacity and can operate in parallel. One line is usually dedicated to hazardous waste, and the other to non-hazardous waste.
The first neutralisation line normally dedicated to hazardous waste treats pumpable sludge and semi-solid earth and sludge in addition to the powdery waste stored in silos. The semi-solid sludge/earth may be directly inserted into the mixer through a special lid using the tractor loader, or may be loaded into a hopper which dispenses the material into a system of conveyor belts connected in succession to a drum screen. The sludge enters the reactor/mixer to which the powdery waste and the hazardous pumpable sludge stored in the tanks described previously are added. The plant has a capacity of over 200 tonnes per day, based on an 8-hour working day. Inside, the waste and any raw materials are mixed using a system of counter-rotating screws.
The second neutralisation line generally treats non-hazardous waste: biological sludge and semi-solid earth and sludge.
There is a dispensing line with a pump that adds liquid reagent (complexant for heavy metals) and a related dissolving system; this line is not equipped with crushing equipment.
There are also three 60 m³ silos for reagents such as cement, lime, zeolites and silicates.
Both neutralisation lines are equipped with semi-automatic, high pressure washing systems.
From both lines, the hazardous and non-hazardous sludge is unloaded inside a closed building maintained in vacuum conditions where it is left to react for at least 24 hours. Subsequently, it is transferred using a wheel loader to storage bays.
The plant has been constructed using the best technology currently available, both in relation to protecting the area and the environment, and with regard to the effectiveness of the treatments. The treatment activities (filter-pressing and neutralisation) are carried out in closed sheds kept in vacuum conditions through the aspiration of exhaust air. The captured air flow is sent for treatment in scrubber towers, where specific chemical reagents are also added to increase the efficiency of pollutant and odour abatement.
The protection of groundwater and soil is guaranteed by waterproofing with a high density polyethylene (HDPE) sheet placed under the entire plant area. The plant is also served by a sealed HDPE sewer system which collects all the waters generated by the processing and sends them for treatment at the adjacent physicochemical treatment plant.