Executive summary

The European Green Deal sets an ambitious agenda “to transform the EU into a fair and prosperous society, with a resource-efficient and competitive economy where there are no net emissions of greenhouse gases” (EC, 2019).

Sewage treatment is an essential service which can deliver clean water, nutrients and organic fertiliser. It can and should contribute to delivering the Green Deal, while recognising that the primary priority is to protect human health and the environment from harm caused by insufficiently treated sewage.

EU water legislation has focused on the water cycle, improving water quality and aiming to restore biodiversity. The Urban Waste Water Treatment Directive 1991 (UWWTD) has led to improved water quality in Europe, but urban waste water treatment plants (UWWTP) still represent the major point source of pollutants to Europe’s waters (EC, 2019; EEA ). Compliance with the UWWTD requires building collection and treatment facilities, usually involving use of energy-intensive materials such as concrete and steel, with energy-intensive operation, while not covering greenhouse gas emissions of methane and nitrous oxides (Fig ES-1).

Water managers have already identified ways to become more energy efficient and reduce operational greenhouse gas emissions (GHG). Some UWWTPs generate more energy than they use, through biogas generation and waste water heat recovery. Some towns and operators have ambitious plans for “net zero” GHG emissions and are intensively reviewing their infrastructure and processes. Alternative approaches to energy-intensive treatment include constructed wetlands which in addition can provide green space for citizens, and decentralised approaches which treat and dispose, at or near the source, relatively small volumes of waste water.

Sewage treatment should be recognised as integral to resource recovery, rather than “waste management”. Incentives for reuse and recovery are needed to enable use of a range of products recovered from the waste water stream. Legal barriers limiting use of recovered resources should be revisited.  Coherent legislative frameworks for all relevant sectors along potential value chains should be in place to enable recovered resources to enter the market.

Solutions for sewage and urban waste water treatment are necessarily local and need to take into account the local situation. An optimal approach for a densely-populated city is unlikely to be the same as for a low density, rural population. At legislative level, a focus on the desired outcome could provide flexibility for local solutions.

A significant blocker in realising circularity in sewage treatment is the presence of harmful chemical pollutants in waste water. This leads to the need for intensive treatment to remove them and then the presence of persistent pollutants in sludge, making that unsuitable for reuse on land. Breaking this cycle requires the successful implementation of the Green Deal “Chemicals Strategy for Sustainability”, so that harmful pollutants are no longer present in the sewage.

Achieving a circular economy in sewage treatment is a long term project and is dependent on many contributors. Case studies show the opportunity. At national and regional level, social acceptance of change is crucial for successful implementation. Strategic goals, giving industry and the public confidence in long term direction, enable investment in innovative approaches. Certification schemes can build public confidence in circular products and improve social acceptance. Collaboration across sectors and partners is essential for a successful outcome. At municipal level, projects require significant local input and energy.