The Ecology of Recycling

While not on the front line 
of climate solutions, recycling of waste materials, wastewater, and wasted energy is a locally available and highly desirable means of reducing greenhouse gases. One potent greenhouse gas, the methane emitted from landfills and wastewater, accounts for about 90 per cent of greenhouse gas emissions from the entire waste sector. That amount is 18 per cent of human-caused methane emissions globally and about three per cent of total greenhouse gases, according to the Intergovernmental Panel on Climate Change.1 Diverting waste bound for landfills and putting it to good use, then, is an obvious and proven means for conserving land and resources, as we have known for a long time; we can now add the knowledge from numerous studies that these practices also bolster climate protection.

This article draws on examples from around the world to describe the climate effects of 1) household recycling and reuse, 2) the cyclic resource flows across clusters of companies known as "industrial symbiosis", and 3) far reaching policy proposals for national scale resource use. It draws lessons from the system's perspective provided by industrial ecology, a new field resolutely focused on the flows of material, energy, and water through systems at different scales, from products to factories to countries and regions.

How does resource reuse affect climate? Cycling energy through cogeneration, reuse of agricultural wastes, or recovery of energy-intensive materials such as aluminium, reduces greenhouse gases. Since most commercial energy is produced from burning fossil fuels, the power generation sector emits more greenhouse gases than any other industrial sector. Cycling materials for use in other production processes reduces the lifecycle impacts, when compared with virgin materials that must be extracted from the earth and then transformed and transported through numerous stages. Recovered resources free up land and capital for other opportunities that would have been required for the equivalent amount of goods to be made from virgin resources. Cycling water means using it more than once, a critical and increasingly urgent practice where water is scarce owing to expected changes in precipitation patterns brought on by climate change. To capture these concepts, industrial ecologists use the term "embedded utility": the total amount of the water, energy, and materials used for all different lifecycle stages of a product from beginning to end.2 Embedded utility is central to industrial ecology: if a product is landfilled, these resources are lost.

Household Waste and Recycling
Study after study in the last five years from Brazil to Canada and from Europe to Asia affirms the ability to quantify greenhouse gas emissions from household waste on a lifecycle basis. Each of these lifecycle studies finds a clear, positive impact of recycling and reuse on reducing greenhouse gasses, principally because of recapturing, rather than discarding, the embedded energy, water, and materials used to make the products in the first place. These studies have included "upstream" (production stage) impacts, such as the effect of replacing virgin materials with recycled ones, as well as "downstream" (waste management) impacts that result from alternative strategies such as landfilling, incineration, composting and recycling. The sum of upstream and downstream amount to a dual benefit from recycling. Even when the emissions from collection trucks and additional transport to recycling facilities are included, greenhouse gas savings prevail.

The scale and mechanism of greenhouse gas reductions for a particular location, however, depend on the specific materials involved, the extent of recovery, the availability of markets, and the mix of fuels avoided through recycling of resources. Recycling metals carries a large energy benefit, while paper recycling often contributes to forest carbon sequestration benefits. Replacing power generated by oil or coal, two carbon-intensive fuel sources, adds more greenhouse gas benefits to recycling than replacing power generated from renewables or hydro energy. Thus, there are no universal claims, but significant regional differences occur when measuring comparative climate impacts from waste recycling and disposal.

There are now many tools to calculate greenhouse gas impacts of different solid waste management options and materials. One example is the Environmental Benefits Calculator of the Northeast Recycling Council in the United Sates, which estimates the environmental benefits of a selected study area based on the tonnages of materials that are source reduced, reused, recycled, landfilled, or incinerated. The Calculator, a Microsoft Excel-based tool, incorporates findings from several lifecycle studies based on "typical" facilities and operating characteristics in the United States.3 The Brazil study measured in detail the greenhouse gas impacts of individual materials, including aluminium, plastic, paper, steel and glass.4

With some exceptions for mixed or contaminated materials that are difficult to categorize or recycle, a broad array of policy programmes is available to reduce climate-related impacts of waste management. Some of the most successful programmes include recycling pick-up from homes or drop-off at district centres; requiring residents who generate a lot of waste to pay more than those who generate less ("pay as you throw"); instituting policies that originated in Europe and are diffusing quickly in Asia that require producers of goods to play a larger role in taking back products (extended producer responsibility); and assessing fees and taxes on categories of goods such as tyres or batteries, or on landfill use overall.

Industrial Symbiosis
While geographic concentrations of industry are often heavy generators of greenhouse gases associated with global climate change, impacts can be modulated through collaborative approaches. Emerging from industrial ecology is the notion of "industrial symbiosis": where a cluster of geographically proximate companies exchange material by-products, energy, and water in a mutually beneficial manner, such that waste from one industrial process becomes the feedstock for another. Through such systems, transportation costs and emissions are minimized and embedded utility is conserved, enabling greenhouse gas emissions to be greatly reduced at the industrial scale.

A simple but prevalent reuse of an industrial by-product is fly ash from coal plants used to make concrete. A British expert estimated that there were 600 million tonnes of coal ash worldwide in 2000.5 For each tonne of fly ash that is substituted for Portland cement to make concrete, the dual benefit is realized: not only is a tonne of material being diverted from landfill downstream, but assuming reasonable transportation distances, close to one tonne of carbon dioxide is also avoided upstream.6 Still, using the United States as an example, over 50 per cent of coal fly ash winds up in landfills.7
At the level of an industrial district, there are numerous cases of multi-firm exchanges of process by-products. The most famous of these includes over 20 exchanges across eight member companies and many other ancillary operations in Kalundborg, Denmark. The primary partners in Kalundborg include an oil refinery, a power station, a gypsum board facility, a pharmaceutical plant, and an enzyme manufacturer. They share ground water, surface water, wastewater, steam, and fuel, and also exchange a variety of by-products such as coal ash and synthetic gypsum that become feedstock in other processes.8

An even larger example is in Tianjin, China where over 80 exchanges of materials, energy, and water across companies have been identified at the Tianjin Economic-Technological Development Area (TEDA), which hosts some 60 international Fortune 500 companies.9 Preliminary analysis at TEDA indicates substantial greenhouse gas reduction from process energy recovery and energy cascading (such as condensate recycling), significant water reuse, and savings in transport, given the shorter distances these materials travel in and around a region rather than being shipped in from more distant areas. Staff of the National Industrial Symbiosis Program (NISP) funded by the British Government routinely use publicly available conversion factors to assess the greenhouse gas impacts of every industrial exchange they broker across parties. In the last four years, NISP reports having diverted over five million tonnes of waste from landfill, saved nearly eight million tonnes of virgin material from use in the United Kingdom, while eliminating over five million tonnes of carbon emissions throughout its industrial network.10

Far-Reaching National Policy Proposals
Given the benefits to the climate of source reduction, reuse, and recycling over other waste options, it is not surprising that some Governments have been interested in implementing these practices on a national basis. Germany and Japan are credited with the earliest legislation to encourage more recycling-oriented societies. In 1994, Germany passed the "Act for Promoting Closed Substance Cycle Waste Management and Ensuring Environmentally Compatible Waste Disposal" with the explicit goal of conserving natural resources and providing for sound waste disposal.11 In 2000, Japan enacted the "Basic Act for Establishing a Sound Material-Cycle Society" and in 2003, established the "Fundamental Plan for Establishing a Sound Material-Cycle Society", seeking reductions in waste disposal and increases in jobs in businesses related to promoting recycling and the sound material-cycle society. Japan has taken this logic to the international community through its "3R Initiative" to urge waste policy based on the 3Rs of "reduce, reuse, recycle" that was agreed to at the G8 Summit of 2004.

Most recently, China enacted, as of 1 January 2009, "The Circular Economy Promotion Law" a progressive and far-reaching policy based on the need to balance China's rapid economic growth with the realities of a deteriorating environment. The "circular economy" is defined comprehensively in the law referring to the reduction, reuse and recycling of resources during the processes of production, circulation and consumption.

It is important to keep in perspective that while climate-related impacts of waste management are significant, many other waste-related issues must also be addressed, from air pollution, to water quality at waste management sites, to land degradation and resource scarcity. In the least developed countries where waste scavenging is prevalent, often in highly organized pods of the informal economy, numerous social, economic, and public health issues accompany waste management decision-making. Still, climate impacts in the waste sector are projected to rise by another 20 per cent by 2030, according to a study by McKinsey & Company. On the reduction side, a full 60 per cent of the potential to abate these increases could be achieved through recycling.13

Historically, increases in waste generation have had a clear statistical relationship with gross domestic product per capita: the stronger the economy, the more waste. Yet some countries have successfully decoupled economic growth from waste. Even with more income, less landfilling means more source reduction, reuse, and recycling which, in turn, reduces climate impact. Early studies about "green jobs" indicate that recycling and composting create much more employment than disposal, providing opportunities for training, employment, and new investment in next-generation waste technologies. Cascading benefits from technology and innovation for conserving and reusing materials, water, and energy are growing and are likely to make an enormous difference in decreasing climate impacts from waste.


1 Bogner, J.E., 2007. "Mitigation of global greenhouse gas emissions from waste: conclusions and strategies from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. Working Group III (Mitigation)" Waste Management & Research, 26 (1), pp 11-32.
2 Graedel, T. E and Allenby,B. Industrial Ecology, 2nd Edition: (New Jersey, Prentice Hall, 2002)
3 See:
4 Pimenteira, C., 2004, "Energy conservation and CO2 emission reductions due to recycling in Brazil", Waste Management, 24 (9), pp 889-897.
5 Tenenbaum, D.J., 2007. "Recycling: Building on Fly Ash Waste", Environmental Health Perspectives, vol. 115, no. 1, Jan 01.
For comparison, 600 million tons is approximately twice the amount of municipal solid waste generated in the US every year according to US EPA.
6 O'Brien, K. et al, 2009, "Case Study Reducing GHG Emissions from the Concrete Industry", The International Journal of Life Cycle Assessment; Springer.
7 American Coal Ash Association, 2008, 2007 Coal Combustion Product (CCP) Production & Use Survey Results (Revised), September 2009.
8 Symbiosis Institute, Kalundborg, Denmark,
9 Shi, H. and M. Chertow, 2009. "Developing Country Experience in Eco-Industrial Parks: a Case Study of the Tianjin Economic-Technological Development Area in China." Working paper. Yale Center for Industrial Ecology.
10 National Industrial Symbiosis Programme,
11 "Kreislaufwirtschafts-und Abfallgesetz-KrW-/AbfG." Federal Law Gazette (BGBl) I 1994, 2705
12 The Basic Act for Establishing a Sound Material-Cycle Society, Act No.110 of 2000, Japan. This is sometimes translated into English as the "Recycling-Based Society."
13 McKinsey & Company, 2009, Pathways to a Low-Carbon Economy.