Barbara Kiser

Books & Arts editor for Nature.

Circularity is at the core of eco-design, the production methodology in which waste is repurposed and environmental impacts such as raw-material use are reduced through reuse and recycling. But if that loop is a lasso for reining in excess, the reality — as US philosopher Ralph Waldo Emerson wrote in the industrializing 1840s — remains that “Things are in the saddle,/And ride mankind”. The scale of global waste and its proportionate economic and environmental costs is gargantuan.

The Trent 1000 engine: Rolls-Royce has run a recycling programme for more than a decade. Credit: Rolls Royce

Some 269,000 tonnes of plastic litter the world's oceans, and vast industrial cast-offs such as manure lagoons and slag heaps blight landscapes. What lurks beneath is daunting. Landfill swallows much domestic and construction waste, where residual energy is lost and decomposition under anaerobic conditions creates a stream of problematic subwaste, from the powerful greenhouse gas methane to leachable contaminants such as benzene. The United States sends 40% of its food to landfill and discards 70–80% of the 145 million tonnes of construction and demolition debris that it generates each year — even though much of the wood, metal and minerals is recyclable. In 2012, Europe sent almost half of its 2.3 billion tonnes of waste to landfill. And that is just stuff: up to 50% of industrial energy input becomes waste heat.

Faced with this entrenched dynamic, how can closed-loop systems become the norm? One answer is to integrate them into circular economies — wheels within wheels. This model looks to extend the life of products at the 'use' stage, retaining value and designing out harmful by-products such as toxic substances, to create the perfect habitat for ecologically innovative companies.

For a model that slots so neatly into eco-thinking, the circular economy is a surprisingly venerable concept. In 1966, economist Kenneth Boulding hatched the idea of “a stable, closed-cycle, high-level technology” in his seminal paper 'The economics of the coming spaceship Earth' (see A. Rome Nature 527, 443–444; 2015). Five years later, in a Life magazine interview, systems theorist R. Buckminster Fuller — an advocate of 'more with less' design from the 1920s — declared that pollution “is nothing but resources we're not harvesting. We allow them to disperse because we've been ignorant of their value.” That year also saw the publication of Design for the Real World (Pantheon), an influential manifesto by Viennese educator (and ally of Fuller) Victor Papanek, who inveighed against designers creating “whole species of permanent garbage to clutter up the landscape” and called for a socially inclusive, environmentally responsible design ethic.

The 1970s saw significant practical developments. US landscape architect John T. Lyle pioneered 'regenerative design' focused on local, renewable resource use. Swiss architect Walter Stahel (see page 435) codified existing ideas and developed key new ones as principles for his Product-Life Institute in Geneva in the 1980s. More recently, German chemist Michael Braungart and US architect William McDonough (who had collaborated with Lyle) established the product and system certification Cradle to Cradle (a coinage of Stahel's), which treats industrial flows as metabolic and waste as nutrients (C. Wise et al. Nature 494, 172–175; 2013). Their book Cradle to Cradle (North Point) was published in 2002.

THE CIRCULAR ECONOMY A Nature special issue

Such design revolutions are essentially longitudinal collaborations between generations, as historian of technology Walter Isaacson has revealed (J. Light Nature 514, 32–33; 2014). Meanwhile, eco-design has moved on from the isolated gizmos and warranties of the 1970s, such as Germany's 'life cycle' eco-label, Blue Angel. New ventures are designing circularity in from the off, as the case studies here demonstrate. Enterra in Vancouver, Canada, recycles unsold organic food to feed fly larvae, which it then harvests as livestock feed (see 'Transform waste into protein'). AeroFarms in Newark, New Jersey, grows up to 4 million kilograms of baby leafy greens a year in vertical indoor 'fields', without pesticides and using 95% less water than in field farming.

A number of grand old companies are retrofitting circularity. BAM Construct UK (of the Dutch Royal BAM Group, founded in 1869) focuses on disassembly — ensuring that the raw materials it uses are either interchangeable or easily separated, and that components can be dismantled (see 'Design for deconstruction'). UK aerospace-engine powerhouse Rolls-Royce plc has cut raw-material use, cost and emissions through its recycling programme, Revert (see 'Create consistent supply systems'), which emphasizes 'power by the hour' and remanufacturing.

Academia and governments are also waking up to circular thinking, from China (see page 440) to Europe. British sailor and circumnavigator Ellen MacArthur aims to speed the transition through her eponymous foundation in Cowes, UK, which has synthesized existing knowledge to educate on, and catalyse innovation towards, the circular economy, collaborating energetically with businesses as well as design and engineering universities. On board are Delft University of Technology in the Netherlands; the University of Bradford, UK, which established the first circular-economy master's degree in 2013; and, under a fellowship with the philanthropic US Schmidt Family Foundation in Boca Raton, Florida, a consortium of 12 universities including the Massachusetts Institute of Technology in Cambridge, Tongji University in Shanghai, China, the Indian National Institute of Design in Ahmedabad and Imperial College London.

Collectively, all this constitutes a great deal more than a gleam in Buckminster Fuller's eye. Yet if the circular economy is an ecosystem for green innovation, it is primarily an island one: wildlife corridors are few. No city, region or country has embraced the vision fully. And the urbanizing, consuming and wasting world does not stand still: the Organisation for Economic Co-operation and Development estimates that the global middle class (with all its material hankerings and 'disposable' income) will swell to 4.9 billion by 2030 (from 1.8 billion in 2009). Meanwhile, the evolving industrial worldscape — a welter of start-ups, monocultures and multinationals, most clinging to business-as-usual — contributes a dynamic unpredictability.

There are problems, too, with the circular model itself. Martin Charter, director of the Centre for Sustainable Design at the University for the Creative Arts in Farnham, UK, notes a “lack of overall clarity over the concept. Perhaps just 100 companies worldwide have adopted a true circularity mindset as a core strategy.” As for the circular mantra of switching to the digital, data centres waste an average of 90% of the energy that they consume (30 billion watts, equivalent to the output of 30 nuclear power plants) and account for 17% of technology's carbon footprint. Although the circular 'business case' looks remarkable (global management consultants McKinsey and Company estimate that it could add US$2.6 trillion to the European economy by 2030), the fact that business remains central to the vision is a vulnerability. The growth economy impedes sustainability. In 2014, for instance, Chevron and a number of other big oil companies retreated from investments in renewables because of poor returns. Business competitiveness and 'disruption' can hinder the collaboration that is central to eco-design. UK design engineer Chris Wise has noted that the practice of using 'least materials' is at odds with the construction industry's prime aim of selling more materials (C. Wise et al. Nature 494, 172–175; 2013). The 'rebound effect', in which designed efficiency leads to greater use or consumption, is a related conundrum.

The thirteenth-century artist Giotto reportedly proved his genius by drawing a perfect circle. The cycles of the biosphere, from water to soil, are wonders of economy. So the idea of a circle strikes a deep chord in us. But one look at any large city reveals disconnection, pollution and social inequality. Can we square the circular economy?

Andrew Clifton: Create consistent supply systems

Sustainability manager — engineering and design, Rolls-Royce, Derby, UK.

Engineers work on a Rolls-Royce BR725 engine. Credit: Rolls Royce

The increasing pressure placed on resources through population growth and the rising demand for energy creates a challenge for industries reliant on consistent supply of materials. Rolls-Royce — which designs, develops, makes and services integrated power systems for use in the air, on land and at sea — meets the challenge with an advanced recycling programme called Revert. This is a collaborative effort between Rolls-Royce and its material suppliers that has been implemented across 100 manufacturing facilities.

Products for aerospace applications have to withstand extreme operating conditions. Components of an aircraft's gas-turbine engines will experience temperatures ranging between −40 °C and 2,000 °C; during take-off, the loadings on the engines' front fan are equivalent to suspending 9 double-decker buses from each blade.

Such demands necessitate the use of alloys of exotic metals such as rhenium, hafnium, nickel and titanium to provide the performance, efficiency and weight savings required for today's advanced aircraft engines. Rolls-Royce uses more than 20,000 tonnes of these alloys each year, and to safeguard supply of strategic material and reduce costs it is continually working to recycle as much as possible. But recycling materials for reuse as aerospace components is not as simple as mainstream recycling, such as that of aluminium cans or scrap steel. The necessarily high quality of the material and the complexity of the alloys requires many additional safeguards if the material is to be recycled for reuse.

Enter Revert. Begun more than a decade ago, the programme is designed to help reduce costs and risks while also reducing environmental impact and safeguarding material supply. Through Revert, metal removed during the manufacture of components and from unserviceable engine parts is collected, segregated by specific alloy type, cleaned of all coatings and contaminants, and returned to the material supplier for recycling. This additional level of stewardship produces a very high-quality recyclate with the necessary chain of custody and certification for the material supplier to be able to process it back into aerospace-grade alloys.

Revert is thus a triple win — providing value to the supplier, the user and the environment. The material supplier benefits from a reliable source of high-quality material to feed back into their production processes. Rolls-Royce benefits by securing long-term agreements with material suppliers that safeguard supply in exchange for the return of the Revert material. Society and the environment benefit through a reduction in environmental impact, and job creation — Revert has created some 60–70 jobs local to the Rolls-Royce site in Derby, UK, to collect and process material. The programme has cut demand for virgin material, generating energy savings of more than 300,000 megawatt-hours per year (equivalent to powering 27 million homes for a day), and a reduction in carbon dioxide emissions of 80,000 tonnes per year (equivalent to the amount emitted by the average family car circumnavigating the world 13,000 times).

Almost half of a used aircraft engine can be recycled and safely used to make a new engine.

As a result of Revert, much of the material used by Rolls-Royce can be reused as part of a closed-loop system. Between 90% and 100% of the titanium and nickel alloys removed during machining operations, such as milling and turning, are captured and reprocessed back into aerospace-quality material. In addition, almost half of a used aircraft engine can be recycled such that the recovered material is of high enough quality to be safely used to make a new engine. Any metallic materials that cannot be Reverted, owing to either cost or limitations in technology, are recycled as part of mainstream recycling programmes local to Rolls-Royce operations.

Revert is making a big difference. It is reducing Rolls-Royce's demand for raw materials, and it is significantly lowering costs, energy use and greenhouse-gas emissions.

Andrew Vickerson: Transform waste into protein

Chief technology officer, Enterra Feed Corporation, Vancouver, Canada.

Credit: Source: Enterra Feed Corporation

Fish farms and other livestock-production systems use wild forage fish such as herring and anchovies as feed ingredients in the form of fish meal and fish oil. However, as the Food and Agriculture Organization of the United Nations reports, many of these forage fish species are fully exploited, and some are depleted.

When environmentalist David Suzuki and engineer Brad Marchant met in 2007 on a rafting trip in northern Canada, Marchant wondered about alternative sources of feed. Pointing to the end of his fishing line, Suzuki asked, “Why not insects?” That idea sparked the creation of Enterra Feed Corporation in Vancouver, Canada, of which Marchant is chief executive.

Marchant, who has a track record of creating start-up companies in industrial applications of biology, saw insects as potentially solving two major global problems — a lack of sustainable feed, and wasted food. (Most of the complex nutrients in organic waste end up in landfill, compost or waste-to-energy facilities, or anaerobic digesters.) Insect larvae, he realized, could become part of a closed loop, consuming recycled food and being harvested to create a renewable source of nutrients for livestock. Feeding waste to insects allows nutrients to be recovered and used as a valuable source of protein and fat, naturally bioconverted (see 'Circulating on the fly').

The black soldier fly can turn waste food into feedstock and fertilizer. Credit: Paul Hudlow

Unsold food — primarily fruit, vegetables, breads and grains from local grocers and food processors — arrives every day at Enterra's Vancouver facility. This feedstock is mixed in large tanks to produce a balanced diet for the large, protein-rich larvae of the black soldier fly (Hermetia illucens). At current capacity, the larvae at Enterra's facility can consume up to 100 tonnes of food a day. The adult fly, which has non-functional mouthparts, does not bite or even eat: it relies instead on energy stored during the larval stage to fly and reproduce.

The 6 million adult flies in the hatchery produce a constant supply of eggs. Once hatched, the larvae are fed daily for about three weeks. Each load of feed is consumed within a few hours — a fraction of the weeks or months needed to break down food in composting or waste-to-energy facilities.

Once the larvae are ready to be harvested, they are mechanically sifted to winnow out the 'frass', or manure. This is treated separately as a natural fertilizer certified for use in organic crop production. Approximately 1% of the harvested larvae are returned to the hatchery to produce more flies and eggs. The rest are processed into feed; dried, heat treated and packaged in bulk, they contain 40% protein and 40% fat, and can be shipped as is as a source of protein and oils, or turned into separate meal and oil. The larvae meal can be used in animal feed as a direct substitute for resource-intensive ingredients such as fish meal and soya-bean meal.

More than 70% of Enterra's sales have been to the United States. In January, the company received approval from the US Food and Drug Administration and the American Association of Feed Control Officials Ingredients Definition Committee to use the dried larvae as feed in salmon farming. Approval for poultry and other livestock are expected shortly. The path to approval has been slower on home territory; an application has been pending with the Canadian Food Inspection Agency since 2012. Enterra hopes to sell its products in Canada to truly close the loop on recycled food on a local scale, by producing renewable nutrients for the local feed industry, using locally sourced inputs. With US$7.5 million in capital spent and 21 full-time jobs created so far, Enterra plans to enter into partnerships globally, including in Europe, the United States, South America and Asia.

Nitesh Magdani: Design for deconstruction

Director of Sustainability, BAM Construct UK, Hemel Hempstead.

The town hall in Brummen, the Netherlands, was built to be disassembled and recycled. Credit: BAM Bouw en Techniek

With sustainable construction company BAM Construct UK, I help to develop buildings that are fit for purpose and perform as intended for their whole lifetime. My focus is passive design, renewable and modular materials and buildings with low energy demand. Major influences have been the Cradle to Cradle approach and architects who explore biomimicry, such as Antoni Gaudí and Santiago Calatrava. The circular-economy model has provided a larger organizing idea with which to synthesize these strands, because it is predicated on using materials that can retain asset value for longer and can eventually be taken back to their biological or technical cycles — reused, repurposed or remanufactured — to reduce waste and unlock new economic opportunities.

BAM's first 'circular' pilot project is the town hall in Brummen, the Netherlands. The client had outgrown its existing building and needed a larger space for at least another 20 years. With Rau Architects in Amsterdam and its sister company Turntoo, we offered a 'building as material bank' to maximize value for the municipality (given that it may wish to move its offices in time). Our competition-winning offer took into account the full costs of the building over its 20-year occupancy, and provided greater price certainty than conventional approaches. Key to this was that after 20 years, components of the building (such as structural timber and metals) could be returned, under contract, to suppliers, unlocking a minimum 20% of their residual value. This 'closed loop' approach reduces manufacturers' reliance on virgin materials and diminishes price volatility.

Technical elements designed for disassembly include the overall shell, cladding, internal partitions and cooling. The design avoids coatings and resins wherever possible to make parts interchangeable and allow separation of valuable raw materials. Components have to retain value over time, so we bring partners such as electronics suppliers and manufacturers Philips and 8Point3 to the table. Many of our projects also incorporate prefabricated elements, so design proceeds through a standardized procurement process to reduce production costs, as well as increasing residual values for key components to more than 50%.

Transparency through the supply chain is essential, so our work has to be highly collaborative.

Beyond materials, we look at systems and processes such as the cost of dismantling, logistics, and storage of components, how it is done, and by whom. We decide who takes responsibility and ownership of the materials during and after the use phase. Transparency through the supply chain is essential, so by its very nature, our work has to be highly collaborative. Sander Holm, a key sustainability leader at our Dutch sister construction and engineering company BAM Bouw en Techniek, notes, “manufacturers and suppliers must sit at the table together as soon as possible. This kind of co-creation delivers more innovation, and also a higher residual value.”

We are currently starting a project with The Great Recovery, a sustainability network launched in 2012 by the RSA (formerly the Royal Society of Arts) in London, to encourage designers, manufacturers and recyclers to co-create solutions for material reuse. We are using 'teardown' methodology, in which production systems are scrutinized to tease out problems and opportunities for 'designing up' to circularity. BAM will focus on processes key to the circular economy, including building-information modelling, a digital shared-knowledge resource used to make decisions about a building's life cycle, such as resource productivity.

At the moment, there is no guarantee that buildings or products designed with natural materials or for deconstruction will be reused. And there is little information on existing building stocks and their potential for sustainable renovation. This must change. One of BAM's challenges is the need to educate the value chain — encouraging our industry towards procurement with an eye to the longer term, and switching to 'performance or take-back' contracts, which keep the responsibility for maintenance, durability and replacement of parts with suppliers. Through the UK Supply Chain Sustainability School, BAM has hosted the first of a series of workshops to work through some of the barriers to circular-economic models. Building on our status as leader in the Dutch Benchmark Circular Business Practices 2015, we are gradually moving from focusing on waste reduction in the construction process to reducing waste over a building's life cycle.