Heat from sewage treatment plants to towns: four proposals to avoid wasting energy
A report by the SHIFT think tank identifies the regulations that need to be amended and the incentives that need to be put in place to foster synergies between water services and district heating
Wastewater holds an energy resource that is almost entirely overlooked: heat. The billions of litres of water that flow through the sewerage networks every day maintain relatively stable temperatures throughout the year, ranging between 10 and 20 degrees Celsius. This characteristic makes it possible, through the use of heat pumps, to raise the temperature of the heat transfer fluid to the required levels and thus supply urban district heating networks. Transforming sewage treatment works into energy hubs capable of supplying heat to cities is the central objective of the first Climate Paper published by SHIFT, a think tank focusing on public policies for the ecological transition, promoted by the CAP Group, which brings together businesses, utilities, research centres, universities, associations and stakeholders.
This objective can be achieved through four concrete measures, aimed at legislators and regulatory authorities, as set out in the document, thereby transforming a European obligation into an industrial opportunity. The Waste Water Directive (EU) 2024/3019, which came into force on 1 January 2025, requires treatment plants with a capacity exceeding 10,000 population equivalents to achieve energy neutrality by 2045. Furthermore, the Energy Efficiency Directive (EU) 2023/1791 sets binding milestones for efficient district heating networks as early as 2028. However, the implementing decrees have not yet been transposed into Italian law.
The overlooked energy potential
An analysis by the Politecnico di Milano cited in the report estimates that two sewage treatment works within ten kilometres of an existing district heating network could provide around 144 GWh of recoverable heat per year, equivalent to approximately 40 per cent of the heat currently fed into the network. In Peschiera Borromeo, the CAP Group has built Italia’s first integrated district heating and cooling plant powered exclusively by biogas produced from sewage sludge. The sludge, treated in anaerobic digesters, produces biogas which is converted into electricity and heat. The surplus heat – converted into cooling energy in summer – supplies a shopping centre, a municipal building and a block of flats. Total investment: approximately 3 million euros, of which 1.7 million was covered by PNRR funds. Result: 2,800 tonnes of CO₂ avoided each year.
According to the report, however, the widespread adoption of these models requires a fundamental overhaul of the national regulatory framework. “61 per cent of the perceived barriers are non-technical, whilst only 39 per cent are attributable to technological or infrastructural aspects,” the research states. Key challenges include economic and regulatory barriers, the complexity of authorisation procedures, and a lack of technical expertise within local authorities responsible for planning and approving projects that integrate energy, water and urban infrastructure. The document identifies four proposals for action, each aimed at a specific institutional recipient.
First and second proposals: regulations and incentives
The first proposal identified in the SHIFT dossier, addressed to legislators, concerns the transposition of European directives. It is necessary to ensure that one thermal kilowatt-hour counts as one electrical kilowatt-hour for the purposes of calculating energy neutrality, regardless of whether it is produced with or without a heat pump. This is the so-called ‘1 equals 1’ principle, already adopted in Germany and Denmark.
