Waste-to-energy, composting, disposal of liquid waste and related services

[GRI - 103-1], [GRI - 103-3], [GRI - 302-1], [GRI - 302-4], [GRI - 306-4],

Chart no. 53 illustrates the types of processing and recovery of materials or energy for the Environment Segment.


Chart no. 53 – Incoming volumes of waste managed by type of plant/activity (2021)

Grafico 53


In the context of circular-economy logic, after maximum recovery of materials, the recovery of energy represents a key phase, which provides energy and economic advantages and leads to a notable volumetric reduction and the biological stabilisation of waste, minimising disposal of this waste in landfills without processing.

In addition to the activities already described of solid and liquid waste treatment and anaerobic-digestion lines at composting sites, Acea Ambiente also manages the waste-to-energy process through the plants of San Vittore del Lazio and Terni. The two plants are operat- ed according to the certified Environmental Management Systems and registration with the European EMAS III scheme (see also Cor- porate identity, Management systems).

In its current configuration, the San Vittore del Lazio plant is the largest in the Latium Region and plays an important role in the management of municipal waste, both for the advanced technol- ogies used for its construction and for its considerable treatment potential135. It is composed of three independent waste-to-energy lines designed to be fed with Solid Recovered Fuel (SRF), with the

following characteristics:

  • 52 MWt of thermal power for line 1 and 56.7 MWt of installed thermal power for each of the other two lines, for a total thermal power of approximately 165 MWt
  • 9 MWe of electric power for line 1 and 15.1 MWe for each of the other two lines, for a total power of approximately 44 MWe;
  • approximately 400,000 t/year of SRF, sludge and other waste at full treatment capacity.

Acea Ambiente has submitted an application for the creation of a fourth waste-to-energy line, enabling full processing of waste en- tering the plant in the case of shutdowns for upgrading or scheduled maintenance, as well as treatment of sewage sludge in compliance with the indication of the Waste Management Plan approved by the Latium regional authority. The application is moving forward through the procedure and is awaiting final approval.

In 2021 307,391 tonnes of waste were processed by the waste-to-energy plants and approximately 268 GWh of electricity was generated, in line with 2020 figures.

Table no. 52 – The San Vittore del Lazio waste-to-energy plant: operating data (2019-2021)

  u. m. 2019 2020 2021
incinerated fuel t 340.531 319.122 307.391
gross electricity produced GWh 276,27 269,38 267,74
conversion efficiency (*) kWh/kg CSS 0,81 0,84 0,87

(*) Relationship between gross electricity produced and quantity of SRF converted to energy.

The Terni plant is composed of a waste-to-energy line and has the following characteristics:

  • 52 MWt of thermal power installed;
  • 6 MWe of electrical power installed;
  • 120,000 t/year of pulper waste (paper mill waste resulting from the pulping of waste paper), as the maximum potential for incoming

The waste-to-energy plant is also equipped with photovoltaic sys- tems, the primary system on the pulper waste pre-treatment area and a secondary system on the adjacent building, which in 2021 generated approximately 444 MWh of electricity, with around 61% consumed on site and the remainder sold to the grid.

In 2021 99,730 tonnes of pulper waste were processed by the waste-to-energy plant and approximately 89 GWh of electricity was generated, up on 2020 figures.

For data on the emissions of both waste to energy plants see the chapter Air emissions, in addition to the data in the Environmental accounts.

Table no. 53 – Terni waste-to-energy plant: operating data (2019-2021)

  u. m. 2019 2020 2021
waste-to-energy paper mill pulper t 94.092 90.215 99.730
gross energy produced GWh 80,93 76,77 88,67
conversion efficiency (*) kWh/kg pulper waste 0,86 0,85 0,89

(*) Relationship between gross electricity produced and quantity of pulper waste converted to energy.

In 2021, certain experiments were completed applying circular-economy logic to waste-to-energy plants:

  • development of a plant solution aimed at recovering sodium bi- carbonate and calcium chloride dihydrate (reaction by-prod- ucts) from the treatment of Residual Sodium Carbonate (RSC), deriving from the neutralisation phase of the acid fumes pro- duced by the waste-to-energy plants, currently under contract, and the start of activities to define the industrial scale-up
  • treatment of fly-ash and bottom-ash for the recovery of the inert fraction present and treatment for the elimination of haz- ardous characteristics, and initiation of activities to define the industrial scale-up

Please also see The commitment to research and innovation in the chapter Institutions and business.


In Umbria, the Company Acea Ambiente manages an important systems hub for waste treatment, recovery and disposal, ensuring the integrated cycle of municipal solid waste and equivalent materials, produced in the regional basin that includes all municipalities in the province of Terni. The landfill site is also authorised to receive special waste.

The hub includes the following main plant sections: mechanical biological treatment of municipal solid waste, composting and refining of the organic fraction of the sorted waste and disposal in landfills. Management takes place in accordance with the certified Management Systems (see the section Management systems in Corporate identify), with the goal of maximising recovery of materials (production of high-quality compost) and supporting both the produc- tion of renewable energy (utilising biogas produced for energy) and the reduction of waste sent to landfill.

In 2021, total waste entering the plant was 108,361 tonnes. 67% (approximately 72,500 tonnes) was sent to landfill and almost all of the remainder was sent to the anaerobic digestion and composting section of the treatment plant for the production of biogas and compost.

The end product resulting from the aerobic process is refined and subsequently analysis for its chemical and physical classification as high-quality compost, for us for commercial growing, environmen- tal restoration and, in general, for maintaining green areas.

At the Orvieto site there are two energy production plants pow- ered respectively by the biogas produced by the anaerobic section of the treatment plant and by the biogas produced naturally by the landfill site. The latter is collected through a supply network and sent to two internal combustion engines that transform it into electricity, which is then sold to the local public grid.

The electricity generated is broken down as follows:

  • approximately 6 Mm3of biogas and 4.7 GWh of energy were produced at the treatment plant in 2021;
  • approximately 6 Mm3of biogas and 9.3 GWh of energy were produced at the landfill site.

Overall, approximately 14 GWh of electricity was fed into the grid. (for further details, see the Environmental Accounts.)

The Orvieto hub is also equipped with a photovoltaic plant owned by Acea Produzione, which did not generate energy in 2021 as it was undergoing upgrading works.


Experimentation is currently underway with the University of Tuscia on high-quality compost produced by the Orvieto plant hub, to- talling approximately 3,560 tonnes in 2021, for use as agricultural fertiliser, applying the direct product and sowing wheat crops on land at the plant itself.

In addition to the Orvieto site, Acea Ambiente has three other composting plants in Aprilia, Monterotondo Marittimo and Sabau- dia respectively.

At the Aprilia plant the deed of seizure expired on 18 March 2021. Thanks to upgrading and expansion works, completed in 2020, the plant can recover up to 120,000 tonnes/year of organic waste, with production of electricity and thermal energy integrated with the pre-existing composting section. Furthermore, in 2021, with issue of the new Integrated Environmental Authorisation (IEA)a compost bagging line and a line for production of SRF from plant waste were installed. Both of the lines were created and approved during the year and will be operational from January 2022. The Monterotondo Marittimo plant has a recovery capacity for the or- ganic fraction of municipal solid waste, garden waste (grass cuttings and material from pruning), and sludge, of (70,000 t/year. Both sites have implemented a new anaerobic digestion and composting section, which enables recovery of electricity and thermal energy. For details on the quantities of biogas and energy produced, see the chapter Energy segment and the Environmental Accounts.

At the Sabaudia plant, operations were suspended from 31/10/2019, to allow upgrading work on the plant136. The liquid waste treatment section is currently inactive. Upgrading work will enable a capacity of 60,000 t/year.


In 2021, Aquaser, which loads, transports, recovers and disposes of waste produced by treatment plants, managed a total of 390,000 tonnes of waste (493,000 tonnes in 2020).

With regard to intermediation, during the year Aquaser took charge of approximately 155,000 tonnes of waste, of which 134,000 tonnes of sludge is attributable to the Group’s water companies137, and in particular approximately 76,600 tonnes to Acea Ato 2, Ac- quedotto del Fiora and Acea Ato 5. The dried out and dehydrated sludge coming from the three Companies was sent to the following end destinations:

  • 68% to material recovery operations (pretreatments aimed at agricultural use and composting);
  • 13% to recovery of energy (waste-to-energy);
  • 19% for

Also this year, due to regulatory constraints direct spreading was not used in agriculture.

Aquaser used its own means to transport approximately 45,000 tonnes of non-hazardous waste


The Demap plant, located in the province of Turin, carries out selec- tion and implementation of recycling for plastic and plastic/metal packaging. Specifically, it handles the storage, selection, sorting and separation of single and multi-material waste originating from sepa- rate waste collection, such as plastic material and metal packaging, for subsequent recovery. The Demap plant is affiliated with the Corep- la Consortium, a group of companies established pursuant to Italian Legislative Decree 22/97 to organise and manage post-consumption plastic packaging, and performs its activity on the basis of a contract for the selection of waste plastic packaging with the Consortium it- self. In 2021 approximately 57,000 tonnes of material entered the plant and were then processed for final separation and recovery.

Another 10,500 tonnes of waste were handled by Berg in the role of broker, even though the main business involves the storage and processing of hazardous and non-hazardous liquid waste, as illus- trated below138. See also the Environmental Accounts.


The Group treats liquid waste on behalf of public and private Com- panies through the Companies Acque Industriali and Berg and the Bio Ecologia plant, merged into Acea Ambiente.

Acque Industriali performs brokerage services and treatment of liquid waste for private and public companies, as well as activities connected to the integrated water cycle, primarily consisting of the recovery and disposal of organic sludge, through management of four main platforms located in Pontedera, Pisa Nord, Empoli and Poggibonsi, which received over 92,400 tonnes of liquid waste in 2021. In addition, the Company provided brokerage services for ap- proximately 54,000 tonnes of waste during the year.

Acque Industriali uses technologies that support recovery of raw materials contained in waste, energy savings and efficient use of resources, such as stripping/absorption of ammonia in a closed cycle that enables recovery of ammonium sulphate, which can be used as an agricultural conditioner. In 2021, approximately 219,700 kg were produced. In addition to the above, the Company provides services for design, creation and management of plants for the treatment of wastewater for third parties, decontamination of polluted sites and environmental consulting for the management of plants, investing in research and development in the relevant sectors, in collabora- tion with recognised Research Bodies. For details of the type of in- coming waste, the resources used, the waste produced and other specific information, see the Environmental Accounts.

The Berg plant is a polyfunctional platform for the storage and pro- cessing of hazardous and non-hazardous waste, authorised for the sale and brokerage of waste and the creation of plants for treatment and processing of liquid waste.

Specifically, the plant has two departments: storage and treatment of liquid waste and storage and treatment of solid waste. In 2021 the plant processed approximately 133,000 tonnes of waste, both sol- id and liquid, and provided brokerage services for a further 10,500 tonnes of waste.

The Bio Ecologia139 plant in Chiusi handles the chemical/physical and biological treatment of non-hazardous liquid waste140 and treatment of sewage. In 2021 approximately 93,000 tonnes of liquid waste were processed and approximately 149,000 m3 of wastewater.

135With reference to Decree Law 133/2014 (referred to with the name “Sblocca Italia”), the plant has been defined as a strategic structure of primary national interest for the protection of health and the environment, as per Latium Regional Decree no. 199 of 24/04/2016.
136The plant has been shut down for the whole of 2021. At the end of the upgrading work it will be possible to continue with publication of the call for tenders for definitive planning and creation of the new composting plant. The upgrading project will increase the treatment capacity to 60,000 t/year of incoming waste.
137The data detailed here for the sake of completeness concerns sludge for which Aquaser has managed the entire supply chain, from loading to transport and final disposal, originating from the following Group Companies: Acea Ato 2, Acea Ato 5, Acquedotto del Fiora, Umbra Acque, Publiacqua, Acque and Acea Molise.
138In 2021, Bio Ecologia did not carry out any waste brokering activity.
139(*) On 1 May 2021, Bio Ecologia Srl was merged by incorporation into Acea Ambiente.
140The quantities of liquid waste authorised for treatment (excluding wastewater) have a maximum limit of 99,900 tonnes/year./span>