Recovery and recycling of post-consumer waste materials. Part 1. Generalities and target wastes (paper, cardboard and aluminium cans)

Abstract

Recycling of post-consumer waste materials is gaining increased interest due to public awareness, legislative promotion and imposition, economic benefits and appropriate technologies being available. The present paper does not deal with municipal solid waste as such, but only with the recyclable constituents. The paper does not aim at presenting recycling process details and/or fundamental research results, but reviews the major recyclables with their reuse potential, recycling technologies used, problems, solutions and potential areas of future research and development. These target recyclables include paper and cardboard, aluminium cans, glass beverage bottles, scrap metal and steel cans, scrap tyres, batteries and household hazardous waste. The present paper sets the overall picture and deals with paper, cardboard and aluminium cans only. A second part of the paper assesses the other target recyclables. The assessment of the waste availability, the existing and currently developed recovery and recycling technologies, and the economically rewarding markets while recycling, stress the technical, economic and environmental importance of this waste management sector. The activities associated with the recovery and recycling of post-consumer wastes require a strong sustainable engineering input at all phases of the treatment, from input quality control, to the selection of the most appropriate technology and the delivery of the recyclables as readily reusable feedstock.

Keywords:

• post-consumer waste
• recycling
• paper
• cardboard
• aluminium cans

1. Introduction

Recycling, curbside, segregated collection, sustainability, materials recovery facilities, landfill bans and tipping fees, municipal solid waste (MSW), refuse-derived fuels, waste-to-energy and other words or descriptions have become part of our daily vocabulary. In the era of growing awareness of sustainable development, it appears no longer viable or acceptable to deal with MSW as an unfortunate flow of materials to be disposed of by landfilling or incineration. MSW contains a multitude of products that can be recycled: a new solid waste management strategy has hence emerged, environmentally more desirable and part of the sustainability objectives. MSW indeed contains a variety of products, present at varying weight percentages depending on, for example, source, location and public awareness in waste segregation.

An illustration of such average composition, albeit per group of the main constituents only, is given in Figure 1. Clearly, there is potential for feedstock recycling.

Figure 1 Average composition of MSW (updated from Lund 1993).

The present review paper does not deal with MSW as such. It concentrates on major recyclables including paper, aluminium cans, glass beverage bottles, plastics, scrap metal and steel cans, end-of-life tyres, batteries and household hazardous waste. Minor components such as wood, leather and textiles are not dealt with. Food scraps and clean yard waste are now commonly and successfully recycled through composting or anaerobic digestion. The methodologies and technologies used in the treatment of this ‘green’ waste are not covered by the text, since involving a totally different approach and dedicated plants.

This paper does not aim at presenting recycling process details, but rather focuses on the major recyclables with their reuse potential, recycling technologies used, problems and solutions. These ‘case-studies’ will be preceded by some general views about the recycling sector, the related legislation, the targets, priorities and markets.

2. Recycling: a growing field of sustainable development

Recycling is the solid waste management strategy which is clearly the environmentally preferred method of solid waste management. The general public's perception of what recycling is, remains often limited to those visible elements including curbside programmes, recycling centres, segregated waste collection, etc. and a vague understanding that this is good for the environment because these materials do not go to a landfill or incinerator. This view also usually encompasses a demand to recycle a greater variety of materials than is practically or economically feasible at this time and needs a clear understanding about what can and cannot be recycled (Green and Perry 2007).

The legislation must promote and impose recycling of those materials in the waste stream that are selectively easy to separate and for which known and relatively stable markets exist. In addition, these definitions ignore previously established industrial recycling efforts based on purely economic needs of avoided cost of disposal and intrinsic value of industrial raw material-derived waste.

Recycling occurs for social, economic and legal reasons. The social aspect relates to protecting the environment and conserving resources. The economic aspect is due to avoiding cost of environmentally acceptable disposal of waste and the commercial value of recyclables (Lund 1993; Green and Perry 2007). Finally, in response to both public demand and a growing lack of alternative waste disposal methods, governments impose recycling and include a variety of economic and civil penalties and incentives in order to encourage recycling.

A successful recycling programme starts with the separation of materials before they are mixed with wastes: this imposes the use of separate containers at home or in the workplace. The containers are removed at appropriate intervals to the processing facilities. These containers may be rigid (organic waste, household hazardous waste), paper or plastic bags (plastics, cans) or even bundled (paper, cardboard, wood trimmings). Glass is most commonly collected in centralised and dedicated containers for clear and coloured glass. If the degree of separation is inadequate and wastes are commingled, the processing plant needs to be equipped with sorting technology. This development of centralised material sorting facilities is gaining popularity, although efficient sorting equipment is still in full development, and the subject of advanced research. Waste-to-energy plants increasingly employ separation systems to recover non-organic materials, either before or after incineration. The recovery after incineration can recover ferrous and non-ferrous metals by using simple technology. Separation prior to incineration mostly focuses on selectively removing the inorganic waste fraction, leaving the combustible materials to generate refuse-derived fuel. Technologies for upfront separation are more complex but can recover a wide variety and high quality of recovered products. Composting of mixed waste has met with limited success and is even prohibited by several governments, due to the potential presence of contaminants such as glass, heavy metals, etc. Only composting of the organic fraction of household waste and of clean yard waste is currently favoured, although still limited in its application for lack of significant markets.

While recycling is a must, the market for those materials has often been ignored or misunderstood with barriers encountered through both competition with existing products manufactured from virgin feedstock, and the sensitivity to the relationship between supply and demand for materials. The effect on the economy and a better view on the integration of recyclables within the current product markets must certainly be given additional consideration in the future.

3. Legislative evaluation

Over the past decade, numerous new legislation concerning solid waste reduction, recycling and recovery has been issued, both in the USA (EPA 2009) and in the EU (European Commission 2009). Within the EU, Global Framework Europe plays an increasingly decisive role in the development of the legislation of European countries. National and regional initiatives have to fit into these European directives. The key European initiatives related to sustainable production and consumption are listed in Table 1.

Table 1 Key European initiatives for sustainable production and consumption (European Commission 2009).

Year	Topic
2000	Lisbon Strategy of Economic and Social Renewal
2000–2005	European Commission's Social Policy Agenda
2001	The Community Guidelines on State Aid for Environmental Protection
2001	Commission Interpretative Communication on Environmental Considerations in Public Procurement
2002–2006	6th EU Framework Programme for Research and Technological Development
2002	6th Community Environmental Action Programme
2002	Commission Communication on Corporate Social Responsibility
2002–2006	EU Consumer Policy Strategy
2003	IPP
2004	Communication on Member State's Use of Market-based Instruments in Environmental Policy
2004	EU Environment Technology Action Plan
2005	Thematic Strategy on Waste
2006	REACH
2006	Sustainable Development Strategy
2006	Commission Interpretative Communication on Social Considerations in Public Procurement Directive 2006/12/EC on Waste (former Waste Framework Directive 75/442/EC)

The thematic strategy ‘Taking sustainable use of resources forward – A Thematic Strategy on the prevention and recycling of waste’ determines the long-term goal for the EU ‘to become a recycling society that seeks to avoid waste and uses waste as a resource’. As resources that are introduced into the market sooner or later totally or partly turn into waste, and all productive activities generate a certain amount of waste, measures must be taken in order to reintroduce that waste into the economic cycle. Directive 2006/12/EC of 5 April 2006 on Waste (the former Waste Framework Directive 75/442/EC) sets out the course for the European waste legislation, but is currently under review to introduce concepts of by-product and the end-of-waste status.

The new European regulation on chemicals registration, evaluation, authorisation and restriction of chemical substances (REACH) contains provisions concerning chemical substances as such, in preparations and objects. As waste materials are excluded, in principle, there is no overlap. The following question however arises: when is waste no longer waste? In other words, when does the waste legislation apply, and when does REACH? The discussion on REACH is therefore directly linked to the conversion point of waste to product.

The principles of the Integrated Product Policy (IPP) are defined in a Communication of the European Commission and the Greenbook on IPP. These principles and instruments will encourage producers to create new product generations that are ‘greener’ than their predecessors. To boost the production and purchase of ‘green’ products, the European Ecolabel was introduced in 1992, to encourage both sustainable production and sustainable consumption (European Commission 2009). Products or services carrying the European Ecolabel have a reduced environmental impact during their lifespan, but are otherwise of a similar quality to equivalent products. The governments are important actors in the sale of these products. The EU tries to encourage green public procurement among its own institutions and government bodies and among the authorities of the different member states. In March 2004, the Council and Parliament approved two new directives on ‘public procurement’. These contain provisions regarding the integration of environmental factors into public tenders, as explained in the handbook ‘Buying Green! A handbook on environmental public procurement’ (European Commission 2009).

The situation in the USA is more complex, since federal laws and state/district laws are put into place, whereas the EPA also plays an important role in developing appropriate solid waste management strategies (EPA 2009).

One of the EPA's publications, ‘The solid waste dilemma: an agenda for action’, addresses the EPA's goal of managing 25% of the USA's MSW through source reduction and recycling (EPA 2009). Although the 25% goal is not a federal law, the EPA provides recommendations to reach that goal and has published numerous reports regarding waste reduction and recycling.

In regulations proposed under the federal Clean Air Act, the EPA proposed that waste-to-energy incinerators be obliged to reduce the amount of garbage they burn by 25% through recycling and composting. The EPA sees this plan as a way to cut toxic substance emissions, reduce the amount of land-filled ash and promote its goal of 25% national waste reduction.

The national waste reduction and recycling legislation is on the move as a result of organised opposition to land disposal of solid waste and general public awareness of the need to reduce the amounts of wastes in general. The basis for the legislation was in many cases the lack of available landfill capacity, the ‘not-in-my-backyard’ syndrome, the escalating expense of waste disposal and the environmental consequences of disposal (Lund 1993; EPA 2009). Most states have already issued necessary laws, whereas other states have replicated portions of laws from other states that have developed viable solutions. Solutions proposed include recycling, composting and waste reduction strategies. The federal government will moreover need to provide the legislation for waste reduction to some rural states that have not yet developed the needed waste reduction legislation.

4. Recycling: targets, priorities, quality control and marketing

4.1 Targets and priorities

The initial success of the recycling programme will depend on how it is integrated in the existing waste management with landfilling or incineration as today's common final disposal methods. The ultimate success will depend on the public participation, where some citizens will genuinely want to help the environment, whereas most citizens will only participate as a result of legal or economic incentives (Wilson 1997).

Legislation is certainly a key factor, with bans on the disposal of, for example, tyres, batteries, yard waste, household hazardous waste, etc. The recycling venture will therefore need short- and long-term targets to guide its implementation and assess its progress and effectiveness subsequently and continuously.

Short-term targets focus on planning and orientation to encompass all actors (community, processing plant, marketing of recyclables). Long-term targets will then consider programme expansion, additional marketing efforts, legislation and effectiveness of the programme.

Typical short- and long-term targets are presented in Table 2.

Table 2 Typical short- and long-term targets (Keoleian and Menerey 1994).

Short-term targets	Long-term targets
Prepare a complete recovery and recycling plan	Meet targets and implement methods of improvement
Determine priority recyclables to be collected	Explore recovery of secondary recyclables
Assess and secure markets for recyclables	Identify additional markets and negotiate long-term contracts
Establish appropriate processing plants and capacity	Explore methods to reduce costs, expand plants
Promote recovery/recycling targets with the public (education, promotion)	Continuously ensure public awareness and discipline
Implement curbside, drop-off, segregated waste collection	Improve collection systems
Train and motivate recycling staff	Assess programme effectiveness
Keep clear records of achievements	Continuously evaluate achievement records
Live up to mandatory legislation	Stimulate new legislation, if necessary

In recent years, some authorities (e.g. in Continental Europe) have imposed a strictly segregated collection system and applied weight-based waste disposal fees for residual waste products, while making the collection of segregated recyclables (glass, paper, metal, etc.) free of charge. Under these pay-per-weight systems, citizens can be expected to try reducing the quantities of residual garbage, while at the same time participating in the recycling initiative at little or no charge.

4.2 Quality control is essential in recycling

The success of materials recycling depends upon (i) its ability to consistently turn waste products into high-quality and marketable end products; (ii) ensuring a stable market for the end products; and (iii) produce in a cost-effective manner. Quality control measures are hence essential at all stages of the process from source segregation, professional collection and delivery, to pre- and post-process inspections (Lund 1993; Wilson 1997).

Contaminants should be avoided. The end markets for recycled glass are, for example, sensitive to contamination by ceramics, lead glass, light bulbs, laminated glass, etc. To maintain glass quality, contamination should be avoided and recycling should apply sorting techniques to eliminate these contaminants, yielding a higher price for the high-quality end product. Consumers' education, adequate process design and well-managed operation are the keys to produce high-quality recyclable materials.

Quality control problems arise at all stages of the recycling process (Lund 1993):

• Cross-contamination can occur when residents have to separate the recyclables into specific multi-bins, e.g. ceramics should not be disposed of in the glass containers.

• The presence of hazardous wastes within potentially recyclable feedstock, e.g. paints and light bulbs.

• Handlers and transporters face difficulties to monitor the presence of commingled materials in the bin collection programmes.

• Central sorting and processing facilities can be controlled with difficulty due to technical inefficiency, leading to 20–30% rejects. With large-scale curbside collection programmes, rejects are normally limited to some 5–10% of the total incoming tonnage.

• Health and safety hazards associated with manual pre-sorting and the difficulty to remove smaller rejected objects effectively.

Recyclable products are subject to severe materials specifications: e.g. aluminium should not contain iron and lead in excess of 1%, recyclables should have limited moisture content, plastics should not contain excessive percentages of non-conformity materials, etc.

In view of this necessary and strict quality control, analytical procedures (visual inspection, laboratory analyses) are stringent and important, albeit a function of the waste material being considered.

4.3 Marketing

The marketing of recyclables has become a real business as can be witnessed from the numerous website-announcements when opening ‘recycling markets’, or ‘plastics’, or ‘glass bottles’, etc.

A recent Organisation for Economic Co-operation and Development (OECD)-review, ‘Improving Recycling Markets’, is an extensive guide that includes a thorough strength/weakness analysis, required policy measures and recommendations (OECD 2007; OVAM 2009).

Price volatility in the markets for recyclables is a given fact, although the markets for many classes of potentially recyclable materials are growing, and prices are overall rather stable or on the increase. This is illustrated for a variety of curbside materials (residential mixed paper, newspapers, cardboard, glass, metals and plastic bottles) in Figure 2. The figure gives the weighted average market price for large quantities, ready for transportation to end-users, and is adapted from reference Zero Waste (2009).

Figure 2 Illustration of the average value of curbside recycled materials (adapted from Zero Waste 2009).

Causes for the price movements are reviewed in the same reference (Zero Waste 2009), and include:

• supply increases from new curbside recycling programmes (1980–1990);

• general economic slowdown (1980–1990);

• manufacturer feedstock build-up during the 1991 Gulf War;

• increase in recycling capacity and demand (especially paper; early to mid 1990s);

• manufacturer feedstock build-up in anticipation of continued increases or supply shortages (1994–1995);

• recession in Asian economies (late 1990s); and

• unanticipated paper shortages especially in China, Mexico and Indonesia (1998–2000).

The numbers on the figure show the average weighted value, indicating that prices move up substantially from a lower €46.2/tonne in the early 1990s to €89.6/tonne during the most recent 2001–2002 downturn. This is primarily due to an upward trend for mixed paper. Prices for other recyclables, by contrast, show no particular up or down trend over the same period. Whereas fluctuations can be detrimental to a recycling programme, the combination of different materials may experience less revenue volatility. Also, the negotiation of long-term contracts that feature price limits and/or revenue/risk sharing is recommended. Finally, the development of a local manufacturing demand for recycled feedstock will limit price fluctuations. The OECD report deals with important additional issues.

The growth of markets for many classes of potentially recyclable materials is due in part to policy incentives, but also to more general commercial conditions. In many cases, their development is supported directly by public authorities through measures such as collection schemes for recycled materials, deposit–refund systems and public procurement schemes.

The constraints in the markets for many potentially recyclable materials arise, in many cases, because such markets possess characteristics that undermine their efficiency. Factors such as information failures, technological externalities and market power can affect the prices, quantity and quality of materials traded.

A good communication between sellers and buyers is necessary. Sellers should make appropriate documentation available (quantity and quality), to guide the buyers while entering the market. Buyers should moreover possess full information about quality of the final product manufactured from recycled materials. This lack of in-depth knowledge was thought to be a problem for recycled paper in former years, and continues to be a problem for retreaded tyres and other materials.

Manufacturers should moreover be rewarded in the market for designing products that are recyclable: in many markets, the increased complexity of product design and material use has driven up the cost of material recovery significantly. Clearly, novel product design and material use must generate benefits – otherwise, companies would not make such investments. In the absence of market signals that reflect the net benefits of recyclability, product design will be inefficient. Plastic packaging is an area in which such problems seem to be important.

More generally, trade in recyclable materials can incur significant search and transaction costs (Zero Waste 2009). The markets are often diffuse or occasional, and in some cases include market participants with little market experience. Under such conditions, it can be burdensome for buyers and sellers to find each other, and to negotiate a ‘fair’ price due to the heterogeneous and uncertain nature of the commodities being exchanged.

Whereas the virgin material markets may increase the use of recyclable markets, it may also be that markets for recyclables may be reducing recycling rates. Where markets are local in nature (construction and demolition waste), or when there are significant economies of density (waste paper and bottles), there is an issue of market power in the recycling itself.

5. Target post-consumer waste recovery and recycling sectors

5.1 Paper and cardboard

The production of paper became industrialised in the nineteenth century and has been growing since then to a production level of approximately 100 million tonnes in 2008. The demand for paper and cardboard shows no slackening, due to the growth of advertising, communication, personal care and international trade. The paper and cardboard industry is large and growing faster than most industries. Over the past decade, its overall production in Western Europe has increased by more than 40%, and it has become a vital part of the economy, generating an annual turnover of more than €400 billion. The European paper and pulp industry is united in the Confederation of European Paper Industries (CEPI), founded in 1992 and representing today 95% of the European pulp and paper industry in terms of production (CEPI 2008, 2009; Paper Online 2009). The largest European paper producer is Germany (22%), followed by Finland (13%), Sweden (12%), Italy (10%) and France (9%). The main pulp producing countries are Sweden (28.8%) and Finland (27.8%). Asia is the world leader in producing paper and board (38.5%), followed by Europe (29%) and North America (25.6%) (CEPI 2008).

Paper recycling has increased significantly throughout the 1990s. To achieve even better results, the European Declaration on Paper Recovery was issued. After paper products have been consumed, they can start a new life as a secondary raw material: this cyclical process means that forests are a renewable source of raw material and that the eco-cycle is closed and balanced (European Declaration on Paper Recovery 2009; Paper Online 2009).

5.1.1 Pulp and paper and cardboard production

The primary raw material for the paper and cardboard industry is derived from trees, even using the parts of the tree that are left after wood has been used for other commercial purposes. Cellulose fibres in the wood are separated from one another by a pulp mill, then washed and screened to remove any remaining fibre bundles. Pulping can be either mechanical by applying shear forces or chemical by cooking in a digester with chemicals. Paper made of chemical pulp has better strength and brightness, but the procedure is more expensive than when mechanical pulp or recovered paper is used. The resulting pulp can be used directly for the production of unbleached paper, or it may be bleached to produce quality papers that do not discolour during storage or go yellow when exposed to sunlight. Bleaching in Europe is only allowed by elemental chlorine-free or total chlorine-free bleaching for environmental reasons (Lund 1993; Paper Online 2009).

As shown in Figure 3, two main fibrous raw materials are now used in papermaking: wood pulp and recovered paper. In addition to these raw materials, a number of additives, auxiliary chemicals and dyes can be used. The industry uses 42% of recycled fibres and 43% of virgin pulp, the rest being other pulp (1%) and non-fibrous materials (14%). The raw materials are fed into a pulper, diluted with up to 100 times their weight of water and subjected to severe mechanical forces, to completely separate the fibres. The resulting slurry is then pumped through various types of mechanical cleaning devices and into the paper machine (Paper Online 2009).

Figure 3 Process of papermaking.

5.1.2 Recovery and recycling

The paper industry has recycled paper and cardboard for over 600 years. Used paper has become an increasingly important raw material source, not at least because of the ease of recycling, for almost any paper can be recycled: newspapers, cardboard, packaging, postal mail, magazines, catalogues, greeting cards, wrapping papers, etc. It is important that these papers are kept separate from other household waste, as contaminated papers are not acceptable for recycling (Paper Online 2009; Paper Recovery 2009).

Recovered paper should not be considered as waste, but as secondary raw material: the use of recovered paper extends the life cycle of wood fibres. Production of new paper by using recovered paper is, however, only possible if virgin fibres are simultaneously introduced in the recycling process. Wood fibres can be reused four to six times: every time a fibre is recycled, it loses some of its strength and the fibre length decreases. In Europe, the average utilisation rate for paper was 47.5% in 2002, which means that for every kilogram of new paper produced, 0.47 kg of used paper is consumed as raw material (CPI 2009; Paper Online 2009).

The majority of the recovered paper (52%) is derived from industrial and commercial sources. Due to the growing demand for recovered paper, additional sources are tapped: households (38%) and offices (10%). The industrial and commercial sources are often the easiest, cleanest and most economical to collect from. Today, there are over 60 recognised grades of waste paper in Europe, categorised into five main groups by the CEPI and the Bureau of International Recycling (BIR). Ordinary grades contain a substantial amount of short fibres, and are used for the production of mixed paper and board, grey board, mixed newspapers and magazines, corrugated paper and board. Medium grades contain unsold newspapers, printed white shavings, sorted office paper, coloured letters, white books, coloured magazines. High grades predominantly contain white papers made from virgin fibres. Kraft grades generally come from brown unbleached packaging materials such as paper sacks and corrugated boxes: these grades are very suitable for recycling into new packaging, due to their long, strong fibres. Special grades, the final grade, tend to be uneconomic to sort, and so they are used in the middle layers of packaging papers and boards (Friar and Max 1993; Paper Online 2009).

Broadly speaking, the production process for recycled paper is the same as for new paper but, as the recovered fibres have already been used, they have to be cleaned after pulping. For certain uses, the fibres have to be de-inked too: printing ink is removed from paper fibres, using a combination of mechanical action and chemical means (alkali and detergents). Afterwards, the cleaned fibres can be mixed with virgin ones. The added quantity of virgin fibres depends on the grade of paper being produced: newspapers and corrugated materials, for instance, can be made from 100% recycled paper, whereas printing paper requires some virgin fibres (Paper Online 2009).

Unfortunately not all of the paper products can be collected or recycled, e.g. cigarette papers, wallpaper, tissue papers. The share of these products is estimated to be about 19% of the total paper consumption in Europe (Paper Online 2009).

During the last decade, paper and board consumption has progressively increased. It is estimated that, by 2010, 66% of all paper and board will be recycled: this indicates a significant improvement, compared to only 38.8% in 1990 (CEPI 2008; European Declaration on Paper Recovery 2009; Paper Recovery 2009).

Paper represents approximately 40% of the US solid waste and 85% of post-consumer waste recovered for recycling. Nearly, 32% of the paper produced in the USA is now reclaimed. This recovery rate indicates the importance of recycled paper for the production of paper products in America. Paper continues to increase in importance in business and private lives. Because paper is the most prolific waste material, it presents a great solid waste management challenge. Many recycling opportunities are provided by a strongly growing paper-recycling industry (Friar and Max 1993).

5.1.3 Environment, sustainability and R&D potential

Paper is based upon wood and thus biodegradable, recyclable and a source of energy after use. The pulp and paper industry is therefore well fitted to meet the challenge of sustainable development. Over the last two decades, the industry has improved the efficiency of its processes, and has reduced energy (up to 25% of the total manufacturing cost) and water needs, as well as emissions to air (CO₂, SO₂ and NO _x due to the combustion of fossil fuels) and water.

Recycling induces a reduction in energy consumption of 40%, according to the Energy Information Administration, to 64% as claimed by the BIR. Another advantage of recycling paper is the reduction of landfills. Furthermore, according to the US EPA, recycling causes 35% less water pollution and 74% less air pollution than making virgin paper. Recycling 1 tonne of paper saves 17 mature trees, 26 m³ of water, 2.3 m³ of landfill space, 320 litres of fuel oil and 15 GJ of electricity (BIR 2009; EPA 2009).

There remains a need for research and development in the sector of recycling paper and cardboard. A major problem is related to the de-inking, currently performed by chemicals and mechanical energy. Improvement options should be further investigated, such as ultrasonic de-inking, the use of high-pressure water jets, or the development of neutral pH de-inking using more active surfactants. Within the currently used technologies, the sludge from de-inking contains heavy metals and other contaminants that require attention.

Another problem inherent with recycled paper is the loss of quality and strength, due to cellulose fibre degradation within each cycle. Although this problem is currently overcome by mixing recycled paper with virgin paper, fundamental research is needed to achieve the same goal of strength retention, while further increasing the portion of recycled pulp. Other issues of interest are finding uses for the degraded fibres, efficient separation methods and improved methods and equipment for paper recycling. The economics of recycling could moreover be improved by developing methods that reduce waste water and deal with the design of cheaper and smaller paper mills near to waste paper sources.

Expanding the paper recycling industry to include a greater portion of the paper-product mix would also reduce both the solid waste generation and the consumption of wood reserves.

Efficient recycling is, however, compromised by many of the additives used in higher grades of paper. For example, coated stocks contain clay, pigments and other ingredients in such large amounts that the yield of paper vs. sludge volume is not economically attractive at present prices. Though improvements in processing might reduce the handling problems, at this time only changes in consumer desires or expectations can change the content of coated stocks in the waste paper stream. Future decisions regarding the content of paper may also be influenced by increasing costs for dealing with these wastes: costs that will be passed on to the consumer.

5.2 Aluminium cans

5.2.1 Aluminium

Aluminium is the third most abundant element (8% of the earth's crust), and it is extracted from bauxite. It is found in rocks, clays, soil and vegetation combined with oxygen and other elements, though never in its metallic form. It was discovered some 160 years ago, but a viable production process was established only 100 years ago. Today, more aluminium is produced annually than all other non-ferrous metals combined (approximately 15 million tonnes in 1985 against 35 million tonnes in 2005; ALUPRO 2009; EEA 2009).

In 2002, the total aluminium consumption in Western Europe was 8.86 million tonnes, of which 3.6 million tonnes was recycled. Between 1980 and 2002, the average consumption has increased from 14 to 22 kg per capita (ranging from 34 kg in Austria to less than 10 kg in Portugal; Jacobsen et al. 2004).

Aluminium is a valuable material, due to its light weight (2700 kg/m³), strength, corrosion resistance (by naturally generating a protective oxide coating), durability, ductility, formability and conductivity (of heat and electricity). Moreover, aluminium is 100% recyclable without loss of quality, as recycling does not affect the metal structure (EEA 2009).

The aluminium production process involves two main stages. First, aluminium oxide present in bauxite ore (a mixture of aluminium oxides, iron oxides and clay) is refined by dissolving in a caustic solution, settling out, filtering and heating to evaporate the water. In the second stage, the alumina is mixed with molten cryolite at about 900°C in a pot (a large electrolytic cell) lined with pitch and coke (acting as a cathode). Then, a carbon anode is inserted in the pot, and a strong electrical current passes through. Due to this electrolytic melting process, the aluminium oxide dissociates into molten aluminium and oxygen. The aluminium is then collected and cast into ingots (ALUPRO 2009).

In 2004, aluminium was mostly used in the automotive and construction sectors (63%), and packaging accounted for 16%. However, these packages are likely to constitute a much larger share of waste generation, due to their shorter lifespan than other aluminium products. Consumption of aluminium products is increasing, but so are the recycling rates. Recycling of aluminium waste from cars and buildings is relatively easy, yielding high rates (92–98% in 2002). However, the recycling rate of aluminium cans is only half that amount (46% in 2002), as collection is more challenging and less profitable. Recycling rates of aluminium cans differ significantly between countries, as illustrated in Figure 4 (Jacobsen et al. 2004).

Figure 4 Recycling rate for aluminium cans by countries (adapted from Jacobsen et al. 2004).

The European Aluminium Association represents the aluminium industry in Europe and aims to secure sustainable growth of the market, while maintaining and improving the image of the industry (EEA 2009).

5.2.2 Aluminium beverage cans

Aluminium packaging has many structural advantages and is by far the lightest complete barrier packaging material. As a result, raw material costs and energy resources are saved. The beverage industry is a major user of aluminium. It is a very convenient, safe and practical material to use for packaging liquids. It does not break, is lightweight, chills quickly, is easy to open and compact, which makes it cheap to transport and handle. Its smooth bright surface is suitable for labelling (EEA 2009).

For the production of aluminium beverage cans, aluminium sheets are alloyed with manganese and magnesium for strength and ductility. These sheets are then fed into a press to cut and form the cans. Afterwards, the cans pass through a number of process steps: re-drawing, ironing, trimming, cleaning, printing and varnishing, baking, inside spraying, necking and flanging, stamping, rivet making, scoring, tabbing and shipping. Can ends are similarly stamped from an aluminium sheet, the edges are curled within the process and a compound sealant is applied within the curl. The separate pull tabs are cut and formed in two stages before being joined to the can end, after the ends have been scored to enable the metal to break under pressure (ALUPRO 2009).

5.2.3 Aluminium recycling

Today, recycled aluminium accounts for about one-third of the worldwide aluminium usage. Recycling is an essential part of the industry and makes economical, technical and ecological sense (EEA 2009).

New and old scraps are mixed together in the recycling process. New scrap (surplus material that is discharged during the fabrication of aluminium alloys) comes directly from the manufacturing industry and is recycled for 100%. Old scrap (car cylinder heads, window frames, old electrical conductors, etc.) is collected by an efficient network of merchants, dismantlers and scrap processors: they use shredders, magnetic separators and sink-and-float installations to separate the aluminium from other materials (EEA 2009).

European recycling rates for aluminium are high: 90–95% for transport and construction applications and 60% for beverage cans in 2005. Incentives to recycle aluminium products after use are strong, since the material can be recycled indefinitely without loss of quality, and because of the high intrinsic value. In 2006, 5.2 million tonnes of recycled aluminium were processed in Europe, and about 40% of the European aluminium demand was satisfied by recycled material (ALUPRO 2009; EEA 2009).

Aluminium and its alloys can be melted and superheated to about 800°C and re-cast for the manufacture of products with the same properties as primary aluminium. Aluminium cans and foil are recycled separately because they are slightly different alloys: it is thus important to collect them separately (ALUPRO 2009).

5.2.4 Recycling aluminium beverage cans

Used beverage cans are processed to remove the interior lacquer coating and the outside product display printing inks. When the aluminium scrap is of appropriate quality, it can be remelted in a process that requires only 5% of the energy needed to produce the primary metal (EEA 2009). Recycled aluminium cans are used again for the production of new cans or for the production of other valuable products (engine blocks, building facades and bicycles). In Europe, almost 50% of the aluminium used for the production of new beverage cans comes from recycled aluminium. In some European countries, collection rates are as high as 80–93% (Benelux, Scandinavia and Switzerland), whereas the mean collection and recycling rate of aluminium beverage cans in Western Europe only amounts to 62%. The evolution in consumption and recycling of aluminium cans is shown in Figure 5. The sudden increase in recycling in 1995 was due to a new can design in which the can ends were also made from aluminium (before only the can bodies were), so the cans could be recycled as a whole (EEA 2009).

Figure 5 Aluminium beverage can usage and recycling rates in Western Europe (adapted from EEA 2009).

Aluminium cans are shredded and the shredded material passes through a magnetic drum separator to remove steel (a contaminant to the process). Then, the lacquer from branded and decorated cans is decoated by blowing hot air through the shreds. Eventually, the aluminium is remelted to produce ingots, which are rolled into sheets and then supplied to can makers to produce recycled cans (ALUPRO 2009).

In 2006, the total number of aluminium cans consumed in Europe amounted to 28.3 billion units; in 2007, it rose to 32 billion. This growth occurred particularly in Northern and Eastern Europe, whereas several Western European countries demonstrated more steady growth rates (Recycling Portal 2009).

5.2.5 Environmental impact of recycling aluminium cans and R&D prospects

Recycling aluminium cans saves energy, because it only requires 5% of the total energy needed to produce new cans from bauxite. Moreover, for every tonne of aluminium recycled, about 8 tonnes of bauxite and 4 tonnes of chemicals are conserved. There is also a substantial saving in waste management costs, and less landfill space will be needed, which results in cost savings in landfill development, management and remediation.

The major R&D achievement of the past decades was the development of a new can design, where can ends were also made from aluminium (before only the can bodies were): this made the recycling of the whole can possible.

There, however, remain technical environmental problems to be solved, although of a lesser extent, i.e. the removal of lacquer from branded and decorated cans and the appropriate treatment of decoating air.

Future R&D will moreover mainly focus on economic improvements as the development of thinner can bodies (currently about 0.11 mm thick) will even further improve the life cycle assessment (LCA) of aluminium cans, already positive in comparison with its competing glass and plastic liquid containers. The introduction of 500 ml cans on the market will further improve the LCA results of the aluminium can as a container for beverages.

6. Conclusions

Recycling of post-consumer waste materials is gaining increased interest due to public awareness, legislative promotion and imposition, economic benefits and appropriate technologies being available.

This paper, part one of two parts, has presented general views about recovery and recycling and focused on the potential reuse and recycling, problems and solutions for paper, cardboard and aluminium cans.

Part 2 of the paper deals with recovery and recycling techniques of additional post-consumer waste, i.e. glass beverage bottles, plastics, scrap metal and steel cans, end-of-life tyres, batteries, and household hazardous waste.