The organic process wastewater and liquid waste treatment (TAPO) section consists of a complex series of treatment phases:

Storage of liquid waste delivered by tankers
The plant is equipped with two separate storage sections, one consisting of three 2,500 m3 concrete tanks covered and vacuumed to prevent the spread of odours, while the air is treated in a dedicated washing tower. Non hazardous waste intended for primary treatment can be stored here. The second section consists of tanks with a total capacity of approximately 780 m3 in which hazardous waste can also be stored for pre treatment, primary treatment or biological treatment depending on the characteristics of the waste. To prevent the spread of odours, the tanks are connected to a hydraulic seal and emissions are sent to the FIS incinerator. All facilities are equipped with the necessary safety devices, such as containment basins or high level detection filling pumps.

Chemical physical pre treatment of special liquid waste delivered by tankers
It is mainly aimed at abating heavy metals and it is carried out in a specific treatment unit by measuring out hydrated lime, ferric chloride, a complexing agent for heavy metals and a polyelectrolyte; the unit also includes the thickening and centrifugation of the sludge, which is separated for disposal;

Primary treatment
It includes the separation of suspended solids, the abatement of metals as hydroxides and part of the organic load of water. The dedicated unit receives and treats organic process wastewater flowing through pipelines from the plants of the Chemical Industry District of Ravenna and waste delivered by third parties by means of tankers. All primary treatment tanks are covered to contain the spread of odours, and the air sucked from the tanks is sent to the FIS incinerator and used as combustion air. The current hydraulic capacity of the plant, under normal operating conditions, is 1,200 m³/h. In detail, primary treatment includes:

• Flocculation: ferrous chloride and, depending on the acidity of the stream, a solution of lime milk to maintain the pH between 8 and 9 and an anionic polyelectrolyte to promote flocculation are added in a special tank;
• Clarification: the suspension obtained from flocculation passes by gravity into two primary clarifiers operating in parallel, where the abatement of heavy solids, metals and part of the organic load takes place. The sludge extracted from the two clarifiers is sent to the sludge treatment system where it is first screened by means of two rotating sieves. The coarsest solid part is separated and sent to the F3 incinerator for incineration, while the muddy suspension is sent to the thickening unit;
• Flotation: the water flowing from the clarifiers passes into two floaters where the light suspended parts both solid and oily that are difficult to sediment are removed and the organic load is further removed. The water treated in the two floaters is fed back to a 20,000 m³ equalisation tank that is placed before the subsequent biological treatment system. The extracted foam and light sludge are sent to the sludge treatment section.

Biological treatment
It consists of the pre denitrification phase in anoxic regime of present/recirculated nitrates, followed by the aerobic oxidation of COD and ammoniacal nitrogen. These phases take place within two "biological towers" with a capacity of 16,500 m³ each, in which pollutants are biodegraded by specific bacterial populations. The treatment is completed with the post denitrification and post aeration phases, which take place in a covered tank, with suction and treatment of the gaseous effluents by means of a biofilter. The decanting of the sludge takes place in three final settling tanks operating in parallel; a part of the sludge is recirculated into the treatment system while the remaining portion, the so called "surplus sludge", is sent to the sludge treatment section. The clarified waters then move on to the last phase, filtration.

Filtration
The filtration unit consists of 6 constant flow, double layer sand and anthracite gravity filters, whose function is to further reduce the suspended solids content and to further reduce the COD and nitrogen content of sludge flakes. Before being discharged into external surface water, the water exiting the filtration process undergoes a final aeration and possibly chlorination phase in a special tank.

Inorganic process wastewater treatment (TAPI)
This treatment is used to abate suspended solids contained in water flowing via pipelines from the plants of the Chemical Industry District of Ravenna. Industrial water that does not come into contact with process fluids, blowdowns from evaporation towers and runoff water from non critical paved areas are discharged into this section. The TAPI section includes the following phases: Sottotitolo: Screening, accumulation and sedimentation Inorganic process water undergoes screening before being sent to a natural sedimentation tank with a volume of 10,000 m3 that also serves as a storage tank. In the tank, the low speed of the water allows the solid particles to settle; the sludge formed by the process is sent to the sludge treatment section;

Accelerated clariflocculation
The water leaving the settling tank is sent back to a distribution well where the necessary flocculants are measured out. From there, by gravity, the stream reaches two accelerated clarifiers with a potential flow rate of 1,800 m³/h, in which further sedimentation of suspended solids takes place. The sludge separated in the two accelerated clarifiers is sent to the sludge treatment section, while the purified water is transferred to the final aeration tank, which also receives the water from the TAPO Line before it is discharged into surface water.

Sludge treatment
All sludge generated in the process is treated in this phase. Thickened chemical sludge (from the TAPO and TAPI lines) and biological surplus sludge are dewatered by centrifuges. Some of the dewatered sludge is sent to a dryer and then it is sent for disposal in landfill.