Sewerage service and treatment system

Once it has been used for various civil purposes, water is collected through the sewer system and sent to the wastewater treatment plants. The treatment process enables the removal of pollutants via physical processes (filtering, sedimentation, flocculation) and biological methods (aerobic and/or anaerobic decomposition of the organic substance with bacteria), and the production of sludge.
With 860 treatment plants (of which 489 managed by Acea Ato 2, Acea Ato 5, AdF, Gori and Gesesa), the total volumes of water processed by the Group main companies¹⁹⁷ in 2022, were 940 Mm³, of which 759 Mm³by Acea Ato 2, Acea Ato 5, Gori, AdF and Gesesa¹⁹⁸. The total number of treatment plants has decreased, from 895 plants in 2019 to 860 in 2022, on the basis of the project for centralisation of treatment of wastewater in order to streamline the service, which involves the main Companies (see infobox for more details on Acea Ato 2). The volumes of wastewater treated and the percentage coverage of sewerage and treatment services, out of the total number of users served by the aqueduct, for Acea Ato 2, Acea Ato 5, Gori, AdF and Gesesa are shown in Tables 57 and 58. The sewerage networks managed in 2022 total 22,004 km, of which 13,225 km relate to the five Companies listed.

Table no. 57 – Volumes of wastewater treated by Water Companies operating in Lazio, in Campania and in Tuscany (2020-2022) (Mm³)

(*) Since 2020, Gesesa began installing flow meters at the entry to treatment plants. Estimated data.

Chart no. 56 – Sewer networks of the main Group Companies in Italy (2022)

NOTE: The kilometres in the chart refer to georeferenced data.

The water in output from the plants cited, after having undergone the purification treatments described, has chemical and biological properties compatible with the life of the receiving body of water and in accordance with the parameters established (as per Italian Legislative Decree no. 152/2006).
Almost 100% of the wastewater treated, which can be defined entirely as “fresh water”, containing less than 1,000 mg/l of total dissolved solids, flows into bodies of surface water. Only 0.2% of the water treated by Acea Ato 2, 0.9% of the water treated by AdF and 24% of the water treated by Gori is discharged into the sea, representing approximately 4% of total water treated²⁰⁰. The portion of water discharged into the sea travels through underwater pipes, following treatment at the coastal treatment plants of the Sorrento Peninsula (Sorrento, Massa Centro and Marina del Cantone), the island of Capri (Gasto, Occhio Marino and La Selva) and Foce Sarno.
The main basins affected by discharge are presented in Table no. 59.

Table no.58 – Percentage coverage of the sewer and purification services for total user accounts of the Water Companies in the NFS (2020-2022)

(*) The 2022 data include an estimated percentage of users in newly acquired municipalities not yet migrated to Acea Ato 2's commercial systems.

Table no. 59 – Hydrographic basins affected by discharges of Companies within the scope of NFS

NOTE: prior to discharge, wastewater is treated in the treatment plants managed by the Companies themselves.

The companies operating in the water sector are committed to increasing the capacity and efficiency of their treatment plants by upgrading certain facilities and decommissioning others (see the box on Works by Acea Ato 2).

The Company manages treatment processes in line with the provisions of the authorisations required for each plant and on the basis of the regulatory context in which they operate. The discharge limits are established for each plant, through an authorisation issued by the competent administrative body, which, on the basis of technical and environmental assessments during evaluation, may set stricter parameters compared to those applicable nationally. In this regard, for example, the regulatory framework in which Acea Ato 2 operates is characterised by prescriptive standards for discharge which are generally higher than the national regulatory reference level, while Acea Ato 5 is subjected to stricter authorisations regarding the quality of water discharged than those established by sector-wide regulations. This is a precautionary approach.
The companies that perform analyses to verify the proper treatment of water report the percentages of non-compliance with discharge limits, which are very low relative to the total quantities analysed: 2.8% for Acea Ato 2, approximately 0.8% for Acea Ato 5, 0% for Gori, 3.4% for AdF and 0.3% for Gesesa²⁰¹.

Chart no. 57 – Analytical checks on wastewater, total and by Company (2022)

The 135,906 controls conducted by Acea Ato 2 on wastewater confirmed the high purification standards achieved by the treatment process. In the “historic” area managed by Acea Ato 2, which includes Rome and Fiumicino, the main treatment plants treated in 2022 approximately 510 million of cubic metres of wastewater, a figure that is slightly lower than the previous year (516 million cubic metres in 2021). Considering also the smaller treatment systems and the plants of the municipalities acquired in OTA 2 (a total of 164) a total volume of 589 million cubic metres of wastewater treated (602 Mm³ in 2021).
Table no. 60 shows the figures of the most important parameters from the main treatment plants of Acea Ato 2, Acea Ato 5, Gori, AdF and Gesesa. Other indicators of the efficiency of purification are described in the section Key environmental performance indicators – Water Segment of the Environmental Accounts.

Table no. 60 – Output parameters of the main treatment plants managed by Acea Ato 2, Acea Ato 5, Gori, AdF and Gesesa (2022)

The sludge produced during the treatment process is mostly sent for recovery of material (see Intermediation and Transport of Waste in the Environment section, and the chapter on Waste). 
In 2022, actions continued to reduce the quantity of sludge produced by treatment plants managed by the Group Companies. For more details on the activities carried out by individual companies to reduce sludge production and improve the efficiency of waste treatment processes, refer to the section on Management and Minimisation of Waste Produced in the chapter on Waste.
In 2022, Acea Ato 2 obtained authorisation to build two plants to upgrade the biogas produced by the anaerobic digestion processes at the Roma Nord and Roma Est treatment centres for the production of biomethane (through a refining process) and its introduction into the gas network managed by Italgas Reti. The production of biomethane, which when at full capacity is estimated to reach a total of around 2.6 million Sm³/year, will be incentivised from January 2024²⁰². Finally, please note that both projects were included on the final list of projects eligible for funding under the National Recovery and Resilience Plan (NRRP)²⁰³.

197 Data relating to the number of treatment plants, the volumes treated, the size of the networks and the controls refer to the main Group companies operating in the water sector, including three subsidiaries not consolidated on a line-by-line basis. Acque, Publiacqua and Umbra Acque.
198 Gesesa started installing the first flow meters on certain plants in 2020 and estimating the quantities of wastewater treated; this activity continued in 2022 as well.
199 Plants that discharge into the sea for the Company Gori are those on the islands of Capri, the Sorrento Peninsula and that of Foce Sarno.
200 The discharge of water, as for intake, occurs in areas at potential risk of water stress, as defined by the cited Aqueduct Water Risk Atlas.
201 The percentages correspond to the M6 value, as defined by ARERA, except for Gesesa, which reports non-compliances according to an alternative calculation method and for which the M6 data was not available at the time of publication.
202 In November 2022, the GSE accepted the qualification requests submitted by the two plants for admission to the incentive issued under Article 6 of the Ministerial Decree of 2 March 2018: ten-year incentive relating to the production of advanced biomethane, so called as it is produced from an advanced raw material such as the sludge deriving from the treatment of urban waste water.
203 Investment “1.1 Action Line C of the NRRP”, but with a payable amount of zero due to exhaustion of the relevant budget ceiling (MITE Decree of 21/12/2022).