4 Systemic change: Zero pollution, circular economy

4.1        Introduction

Treatment to clean our sewage is essential to protect human health and the environment. Waste water treatment is also expensive, resource intensive and can generate significant greenhouse gas emissions. In seeking to protect the environment from micropollutants generated by our modern way of living, we solve the issue by adding yet more resource-intensive solutions, creating more waste and emissions. In our focus towards ensuring the water cycle is respected,  we have developed a linear solution – missing the circularity which sewage treatment should represent. This approach is an unsustainable way to resolve an issue of a “waste” that will be continuously generated.

A central problem that we create for ourselves is the use of substances which are harmful to the environment, traces of which can enter the water system from our homes, schools and workplaces. Some of these substances are essential and alternatives may not be available. But for others, achieving the aims of the Chemicals for Sustainability Strategy provide for a long term solution. Transitioning to a society where chemicals and products no longer contain substances of concern[1] both advances zero pollution and also allows circularity, within the product as well as the “waste water” chain. In advance of achieving that ambition, we will nevertheless have to manage pollutants already in use and circulation.

Historically, we have left it to water managers to solve society’s waste problem, at the end of the pipe. But already more sustainable solutions are being trialled by innovative utilities, villages and cities. By recognising the central role that waste water treatment can play in a circular, zero pollution economy, full power can be applied to achieve systemic change.

[1] i.e. those with persistent, toxic, bioaccumulative and mobile characteristics

4.2        Re-thinking “urban waste water treatment”

As a society, we have gone to considerable lengths to address the harm that our untreated sewage causes to human and environmental health. The 1991 UWWTD required that Member States provide collection systems and treatment of waste water, which has led to significant improvement in Europe’s water quality.

But, this has come at considerable cost – financial, in pollutants to water and greenhouse gas emissions, and, as we look ahead to a changing climate, with new challenges. More intense rainfall in parts of Europe is leading to more frequent surface water flooding and discharge or runoff of pollutants. In other areas, lack of water resources is becoming a key concern. Demographic change can lead to over- and under-capacity in water utilities such as UWWTPs, reducing their efficiency.

Practically, we have built a system which requires dilution of a nutrient and energy-rich natural resource by clean water, mixing that with other potentially harmful substances, then draining or pumping this mixture through an extensive pipeline network to a central point. Here, energy is used to aerate and pump “waste water” through various filters and treatment facilities, dry out the solid material and then discharge the cleaned water. Disposal of the sewage sludge faces continual challenges for politically-acceptable and economically-viable routes. This linear approach focuses on water quality, giving much lower priority to other environmental dimensions.

There are other ways to manage our sewage safely and with much less infrastructure. Keeping the sewage from toilets separate from other contaminated “grey” water, such as that from washing, allows alternative, water-less treatment to kill pathogens and recover the nutrients and or energy (Zeeman and Kujawa-Roeleveld, 2011). Meanwhile, less intensive treatment, or no treatment, allows the grey water to be reused where quality demands are lower, e.g. in parks and gardens. Such decentralised schemes can operate at a very local scale, e.g. buildings and streets.

Clearly, such approaches are niche in the near term. Conventional safe treatment and management of human waste mostly relies on expert engineers and water managers, and the infrastructure in homes, schools and workplaces mostly relies on connection to waste water treatment plants. Experiments with building-focused sewage treatment and water reuse have already shown the problems associated with construction mistakes, where effluents from other non-drinking water systems in buildings have been introduced into the drinking water distribution system, compromising human health (EC, 2021). Less immediate, environmental harm may be caused if the waste from ourselves and our houses continues to be contaminated with micropollutants (Zintz et al, 2021; Comber et al, 2014). However, households with individual treatment systems such as septic tanks tend to be careful not to poison those systems (Mulder, 2019). Realising the ambitions of the Chemicals Sustainability Strategy over the longer term is key to reduce harmful micropollutants at source. “Hybrid grey and green” water infrastructure combines centralised and decentralised water treatment, leading to reduced water loss, increased water reuse, optimising the exploitation of alternative water sources in a circular economy, and strengthening resilience against climate change events (WE, 2020).

One of the features of such a local approach is that it already provides the opportunity for small, remote or under-served communities to tackle sewage treatment in areas where that is still lacking, and to develop skills and capabilities in “new” technologies (or rather, re-learning traditional recycling). New developments in urban areas, such as the brownfield site at Buiksloterham (see text box), can provide opportunities in purpose-built, decentralised treatment approaches.

Text box: Case study – Collaboration, city level - Amsterdam, the Netherlands.

In Buiksloterham, a collaboration between the water board, municipality and housing corporation is piloting a study on separation of waste water at source, to test the sustainability of decentralized sewage treatment. An innovative vacuum sewer and floating treatment plant has been built with a capacity of 1550 p.e., with vacuum toilets installed in 47 floating homes.

The  traditional waste water sewer system is replaced by a multiple sewer system, which consists of  a vacuum pipe with a small diameter for  the concentrated collection of sewage and a free-fall pipeline for grey water. This collection method enables efficient local water treatment and raw materials (phosphate), heat and energy (biogas) can be recovered and reused locally. This primarily provides raw materials and energy, but also saves energy through avoidance of pumping waste water over long distances.

Amsterdam plans to learn from Buiksloterham in its development of Strandeiland, a new island in IJburg where approximately 8,000 homes will be built. The water board and the municipality want to apply New Sanitation there, as well as using thermal energy from waste water and surface water to make Strandeiland energy neutral.

4.3        Zero pollution and waste water treatment

Health protection and prevention of pollution continue to be the key purpose of sewage and urban waste water treatment. Improved scientific knowledge since the 1990s has shown the presence of many pollutants in surface waters, and many of these arise from chemicals and products that we use in our homes and workplaces. Cleaning, washing and runoff introduce these into the waste water stream. Such societal and sectoral issues are beyond the capacity of water managers to resolve, but rather, require wholesale review of what substances we choose or allow to be used. Such is the role for the Chemicals for Sustainability Strategy, launched by the EC in 2020 (EC, 2020). Among its ambitions, the Strategy aims to ban the most harmful chemicals in consumer products and allow use of such substances only where essential. This is key to reducing the load of harmful chemicals into waste water. The ambition to boost the production and use of chemicals that are safe and sustainable by design should lead to lower chemical pollution over the longer term. In turn, lowered pollution loads in waste water will reduce the need for intensive treatment i.e. turning from a vicious into a virtuous circle.

Meanwhile, UWWTPs face the challenge of cleaning up waste water to meet more demanding standards set in legislation. Modelling for the revised UWWTD by the JRC has examined the costs and benefits of micropollutant removal, considering ca. 1200 chemicals assumed as a proxy of the total pollution conveyed by raw wastewater. This has shown that advanced treatment for micropollutants at all plants in Europe  with a capacity of 100 000 p.e. or more could reduce the overall toxicity of discharged effluents by about 40% (JRC, 202x).

The decisions taken to addressing sewage treatment through any particular approach are necessarily local. Water managers aim to optimise according to local requirements and possibilities: ensuring and enabling circularity principles form part of those considerations is the role of policymakers. Where trade-offs come into play, ensuring the protection of human health and the environment should take primacy.

4.4        Circular economy – from “waste water treatment” to resource recovery

The goal of a circular economy is to manage natural resources efficiently and sustainably (EEA, 2016). Respecting planetary boundaries through increasing the share of renewable resources while reducing the consumption of raw materials and energy, and at the same time cutting emissions and material losses, meets goals set both for sustainability and business efficiency. The Circular Economy Action Plan under the Green Deal seeks to accelerate the transition towards a regenerative growth model and move towards keeping resource consumption within planetary boundaries, thereby reducing Europe’s consumption footprint (EC, 2020). Three principles underpin the detail for a circular economy:

• Eliminate waste and pollution
• Circulate products and materials
• Regenerate nature

Source: Ellen MacArthur Foundation, n.d.

Water in the environment follows a natural cycle that secures water resources by regulating water flow and ensuring water quality. On the other hand, in systems created by people that follow a linear model of economic growth “take-make-consume-dispose”, the quality of water is reduced, becoming unfit for further use both by humans and ecosystems (Stuchtey, 2015).

From one perspective, sewage and waste water are the waste products from human life. However, these also form part of natural cycles that urban waste water treatment is at least already partly successful in recreating, such as returning cleaner water to the environment and sludge to land. However, the approach to date has neglected some areas, such as greenhouse gas emissions, and been unable to fully address others, such as micropollutants in urban waste water. The transition of UWWTPs from “pollutant removal facilities” to resource recovery facilities has been foreseen by the sector, with a wide range of technologies for water reuse, energy and resources recovery, despite limited, full-scale application (Kehrein, 2020; Veolia, n.d.).

Whilst some progress has been made in water utilities transitioning to a circular economy,there remain two significant drawbacks: a difficult regulatory environment and opaque market conditions.   The complexity of the “landscape” for implementation of circularity becomes clearer (Fig 4.1).

Figure 4‑1 Challenges in shifting from a linear to a circular system

Source, EEA, 2020

Implementing circularity more fully in the UWWT sector will extend the context of supply and demand in which water utilities operate, as well as the regulatory framework, since single sector approaches will not be able to deliver the desired outcomes.  Challenges to the waste hierarchy are already arising, with some innovative operators presenting mono-incineration of sewage sludge with phosphorus recovery, as circular practice. Circularity will result in an increased range of products, such as reused water, energy, nutrients and other resources. Quality will need to be regulated, while reflecting use which is fit for purpose - already the Waste Water Reuse Regulation (2020) has taken steps in this direction. Customers across different economic sectors e.g. energy, agriculture and industry, need to play an active role in defining the quality of products. Specific value chains, embedded in local or regional economies, may need to be established for specific products or services. Taken together, delivering circularity will require adaptation of existing institutions and regulatory practices. Holistic, integrated water management is required which does not necessarily follow conventional administrative, sectoral, political and geographical boundaries. It will need to build on broad-based engagement and partnership ( Stuchtey, 2015; IWA, 2016; Arup et al., 2018). 

4.5        Accelerating the transition

Sewage treatment is an essential service which can provide clean water, nutrients and renewable energy. However, in its current operation it uses significant amounts of energy, leads to significant emissions of greenhouse gases and produces sewage sludge in large quantities which may represent disposal problem for utilities. The shift from “waste water management” to “resource hubs” is already happening in some forward-thinking towns and utilities (text boxes).

 Text box: Case study – Net zero emissions - Scottish Water, UK

Scottish Water have a target to reach net zero GHG emissions by 2040. Some actions are directly in their control, such as improving energy efficiency and hosting renewable energy. But others require efforts to influence customers and supply chains, such as the amount of water people use, removing surface water from sewers, and reducing emissions in the cement they buy (Scottish Water, 2021). They have identified areas for innovation, such as low energy treatment methods; ammonia and methane recovery; the need for digital and analytical tools; low/zero emissions materials for investment and operations.

Text box: Case study – Energy efficiency and recovery - Marselisborg UWWTP, Denmark

In 2005, Aarhus City Council decided to upgrade and consolidate its municipal waste water treatment system, which at that time comprised of 17 smaller facilities. The Danish water sector aims to be climate and energy neutral by 2030.

Marselisborg UWWTP has increased plant efficiency and reduced energy consumption by optimising its processes. It now produces 50 % more electricity than it needs for UWWT and 2.9 GW of heat for the district heating system. Energy-saving technologies include an advanced control system, a new turbo compressor, sludge liquor treatment and optimisation of the bubble aeration system. This has resulted in saving approximately 1 GWh/year (c.25 %) in power consumption. By implementing energy efficient solutions and producing biogas from the sludge, the utility is able to cover almost all the energy needed for the whole water cycle - from groundwater extraction, to pump stations, water distribution and waste water treatment.

While solutions adapted to the local situation are necessary for sewage treatment, the characteristics which are necessary to achieve a transition to more sustainable approaches can be set out. Innovation can play major role in enabling circularity.  More efficient technologies, which eg reduce energy costs of resource recovery and increase recovery rates are perhaps obvious, but innovation also applies to new partnerships extending across public administration, research, industry and citizens, with new business models and new forms of water governance (Martins et al, 2013; Moore eta al, 2014; EWA, 2014). Sustainability, nature-protection ideas and citizens can contribute to the exploration of alternative domestic, communal, and public approaches. The Strategic Implementation Plan for EIP Water identifies several areas, such as water re-use and recycling; water and waste water treatment; the water-energy nexus; and cross-cutting issues including water governance; decision support systems and monitoring and financing (European Commission, 2012a). Digitalisation can help in the delivery of improved efficiency and productivity, and faster monitoring to inform decision-making (Mbavarira and Grimm; EC, 2021). Connecting to Stakeholders beyond Traditional Boundaries provide mechanisms to promote a shift towards markets for recovered resources and sustainable technologies, using perhaps Integrated Resource Management as a process to bring together all the resource groups. This allows optimisation of the supply and demand for resources, and for opportunities and synergies to be taken into account, helping to place recovered resources in appropriate value chains. Practically, achieving circular practice can require intense efforts by all players, not least in the area of enabling legislation (text box).

Text box: Case study – Legislative barriers to urban phosphorus recovery - NL

Phosphorus can be recovered in different products from sewage sludge, for example as struvite (which can be used as a slow-release fertiliser) or in ash following mono-incineration (where the sludge is not mixed with other wastes). In the Netherlands, experiments to recover struvite from UWWTPs at full scale started in 2006, but introduction to the fertiliser market was hindered by the classification of struvite as a waste, with the Fertilisers Act prohibiting use of wastes. A change in legislation was supported by extensive studies examining struvite use as a fertiliser and various initiatives of the Dutch Nutrient Platform, in particular the Dutch Phosphate Value Chain Agreement signed by more than 30 businesses, research institutes, non-governmental organisations and the Dutch Ministry of Infrastructure and Water Management, to initiate a sustainable market for reusable phosphate streams (Nutrient Platform, 2021).  Use of struvite and other two recovered phosphates as fertilisers was eventually approved from 2015.

4.5.1        De-centralised solutions for circularity

One of the empowering aspects of sewage treatment is that local conditions lead to necessarily local solutions (APE, 2019). There are tools for individual houses, small villages and towns, up to major cities.

Decentralised waste water management is used to treat and dispose, at or near the source, relatively small volumes of waste water, originating from single households or groups of dwellings located in relatively close proximity (less than c. 3–5 km) and not served by a central sewer system connecting them to a regional UWWTP. While still needing a local collection system, this is likely to be much smaller and less expensive than those used for conventional, centralized treatment, especially when the greywater components have been separated human waste (Capodaglio, 2017). Decentralised systems focus on the on-site treatment of waste water and on local recycling and reuse of resources contained in domestic waste water. They are particularly attractive because of the possibility of reducing long-term treatment costs. The systems can be easily adapted to local conditions, capacity can be added incrementally and quickly. As such they can serve as alternatives to conventional expansion/refurbishment of the sewer network and thus could help to save funds in the short and long terms. Remote control and monitoring contributed to operation and management improvement and resolved problem with lack of skilled personnel.  Decentralised solutions enable introducing source separation between urine and faeces, and possibly grey water through toilet systems or other water saving systems which can further enhance resources and energy recovery. 

Decentralised solutions in general will tend to be compatible with local water use and reuse requirements where locally treated water could support agricultural productivity or (in more urban areas) be used as a substitute for drinking water for uses which do not require such high quality (e.g. landscaping, surface storage, recreation, groundwater recharge, industrial application/ cooling) (Capodaglio, 2017).

The decision to implement a decentralised solution to waste water treatment needs is usually made or discussed at the local level, and local stakeholders are usually more proactive when considering these systems. Stakeholder involvement can help in establishing closed loops for local reuse of recovered resources and thus contribute to establishing viable value chain for recovered resources as a part of local economy. As such they can serve as sources of valuable novel approaches, and testing laboratories for new concepts that can be extrapolated at larger scales.

4.5.2        Individual action

For those of us living in areas where our sewage and waste water disappears down the pipe, our influence on reducing the environmental impact of UWWT might seem somewhat remote. But we all have a part to play.

• Water efficiency. Using water more efficiently not only saves water, but also the energy put into treating it and pumping it to the tap, and then the resources to take it through the UWWT process.
• Avoid putting harmful pollutants down the sink and drain. Then they do not need to be removed from the water - if indeed, it is possible to remove them. Safe disposal of pollutants is usually offered by local councils. Leftover medicines can be taken back to pharmacies.
• When replacing clothes, textiles and furniture, consider those which are made of environmentally-friendly materials if possible. This helps avoid pollutants in such products being washed out and then eventually reaching the sewer system.

4.6        What needs to change

With no change to current direction, the trajectory for UWWT in Europe is for more energy-intensive treatment, to remove micropollutants about which we are becoming increasingly aware. Concern about pollutants transferred to sludge during water treatment will continue to limit opportunities for using sewage sludge in application to land, leading to increased demand for incineration and problems for regions lacking such capacity. Infrastructure investment costs will continue to increase, along with the GHG emissions embedded in concrete, plastics and steel for sewer networks and treatment plants.  

Water managers are skilled at optimising processes within their remit. UWWTP processes can be optimised to improve energy efficiency. GHGs released during treatment are being reduced and more energy recovered from the UWWT cycle, such as in biogas and through heat recovery. Nutrient recovery, particularly of phosphorus, is driving innovative utilities towards solutions such as mono-incineration and finding applications for reuse of remaining ash.

Accepting this situation with no change risks accepting an unsustainable lock-in (EEA, 2020).

Addressing long-term sustainability in this area means fundamentally reviewing the purpose of sewage treatment. In the long term, protecting human health and the environment from sewage and waste water does not necessarily require the major infrastructure programme that we have developed. Decentralised and nature-based solutions, such as constructed wetlands and source separation schemes, allow for low input, effective sewage treatment, while at the same time producing local environmental benefits such as green space. The treatment solution at any particular place has to reflect the local situation, but more sustainable approaches should be enabled.

Achieving a circular economy in sewage treatment is a long term project and is dependent on many contributors. From realising the Chemicals Strategy for Sustainability to prevent micropollutants reaching sewage from our homes, to enabling legislation at all levels, to establishing viable markets for recycled products. Such are the needs to transition to the sustainability envisaged by the Green Deal.