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^# The conversion factor used for this data was the figure for wood of 1000 metric tonnes = 1480 cubic meters [1].

Analyses of the composition of municipal solid waste (MSW) are available for the United States of America [2] and the principality of Wales [3].  The US Environmental Protection Agency (EPA) defines MSW to include durable goods, containers and packaging, food wastes, yard wastes, and miscellaneous inorganic wastes from residential, commercial, institutional, and industrial sources.  EPA excludes industrial waste, agricultural waste, sewage sludge and all categories of hazardous wastes (the latter including batteries and medical wastes).  The proportion of plastics in MSW in each case was 9.5% and up to 11% respectively.

Figure 1:  The growth of the reinforced plastics market in the USA.

Figure 1 shows the growth of the market for reinforced plastics.  The data up to 1996 is from the Society for the Plastics Industry with the more recent data from the American Composites Manufacturers Association (e.g. US market statistics for 2005 [4]).  Note that in spite of the apparent discontinuity in sector sizes between 1996 and 1997 due to reallocation of categories, the total market figures appear to follow a sensible trend.

At the design state of any product do consider the possibility of re-use and, if that is not practical, do design for dis-assembly or recycling.

Any (re-)processing of materials will require energy. That raises issues of collection and transport, fuel efficiency and the ethics of global sourcing.  Unnecessary use of energy costs money and potentially contributes to climate change.  A European project, RECIPE: Reduced Energy Consumption In Plastics Engineering, aims to help the plastics processing industry to reduce their energy consumption.  The RECIPE best practice guide [5] provides a structured and practical approach to improving energy efficiency in the processing of plastics.

The potential routes for dealing with waste composites are summarised in a diagram (22.5KB Excel Worksheet).  In summary, the hierarchy of options at end-of-life should be:

• re-use,
• re-cycle,
• pyrolysis/hydrolysis etc for materials recovery,
• incineration with energy recovery,
• and, only if all else fails, then landfill.

Halliwell [6] has recently produced an excellent best practice guide on End-Of-Life options for composite waste.  Pickering [7] has recently published a review of the current status of recycling technologies for thermoset composite materials.

There is increasing interest in reclamation of high-value materiuals.  In particular, technologie for the recovery of short carbon fibres is being developed [8].

Composting

One alternative for bio-based materials (natural fibres and plant-based resins) is disposal by composting.  Hermann et al [9] classify "composting" into four categories as shown in Figure 2 where chemical/mechanical pulp is for paper and cellulose production (and hence probably appropriate for natural fibres).  Specific benefits of compost [9] are that:

• compost stores carbon in the soil,
• nitrogen contained in compost is an organic fertiliser,
• compost used as a soil conditioner improves the soil structure,
• compost used as a soil conditioner reduces fossil emissions arising from the use of peat.

Figure 2: Four types of biological waste treatment (after Hermann et al [9])

There are essentially two options (a) aerobic: carried out either in open air windrows or in enclosed vessels, or (b) anaerobic: required when animal by-products or catering wastes are included [10].  A typical value for mass loss during composting (for grassland in Austria) is 56% [11].  A demonstration-scale anaerobic digestion (AD) plant is operating at Dufferin (Toronto) solid waste transfer station with a mass balance (based on 100 metric tons/day) of 50% biogas and effluent, 25% digestate and 25% residue [12].  The biogas varies due to the batch operation but is typically 110 m³/metric ton with an average of 56% methane (ranges from 45-73%) by volume.  Jana et al [13] suggest that the biogas is typically 60-65% methane, 35% carbon dioxide and a small amount of other impurities".  Similarly, "pure landfill gas can contain up to 35% carbon dioxide, 65% methane and no oxygen" [14].  Further resources include BioCycle magazine and the Composting Association.

A biodegradable material is expected to reach a defined extent of degradation by biological activity under specific environmental conditions within a given time under standard test conditions [15].  Krzan et al [16] have recently reviewed the standards and certification appropriate to environmentally degradable plastics.  The biodegradation of a polymeric materials under controlled composting conditions is the subject of a number of standard methods, including ASTM D 5338 [17], ASTM D6400 [18], ASTM D6868 [19], EN 13432 [20] or ISO 14852 [21].  The EU Directive on Packaging and Packaging Waste (94/62/EC) criteria for biodegradability are set out in BS EN 13432 while the criteria in North America are set out in ASTM D6400.  The requirements of the standard include:

• biodegradation: over 90% relative to the standard (cellulose) in 180 days under conditions of controlled composting using respirometric methods (ISO14855),
• disintegration: over 90% in 3 months (ISO FDIS 16929),
• ecotoxicity: test results for aquatic and terrestrial organisms (Daphnia magna, worm test, germination test) as for reference compost,
• absence of hazardous chemicals (included in a reference list).

Organisms that possess cellulase (the enzyme which cleaves sugar from the cellulose molecule) include bacteria, some flagellate and ciliate protozoa, and fungi [22].  If an animal is to digest cellulose, it must enter into an alliance with such an organism.  For example, termites have a symbiotic relationship with fungi which provides the symbionts with a rich source of cellulose for food in return for access to glucose cleaved from the cellulose and additionally to protein, vitamins and essential amino-acids produced by the fungi.  Termites hatch without this essential intestinal flora and are inoculated with it by being fed faeces and regurgitant that contain the symbionts.  The fungal deterioration of cellulosic textiles has been reviewed by Montegut et al [23].

Milner et al [24, 25] have reported a new strain of thermophylic bacteria that can break down cellulose waste to produce useful renewable fuels for the transport industry. The Geobacillus family normally synthesise sugars and produce lactic acid as a by-product when they break down biomass in a compost heap. The re-engineered TM242 strain is claimed to produce ethanol more efficiently (yields of 10 to 15%) and cheaply than in traditional yeast-based fermentation.

Environmental impact classification factors

Azapagic has presented an analysis which permits the quantification of environmental impact classification factors.  Any (re-)processing of materials will require energy. 

The discipline of biomimetics, may have much to teach us here.  Biological systems create wastes which are raw materials for other plants and/or animals.  For an insight into how complex natural systems can evolve, see the life cycle of Maculinea Arion (large blue butterfly) and its dependence on Myrmica Sabuleti (red ant).

References:

1. Bruce Michie and Philip Wardle, EFI/WFSE Trade Flow Database, European Forest Institute, Joensuu - Finland, 2000, updated 2002.
2. Municipal Solid Waste Profile, 16 April 1997.
3. The Composition of Municipal Solid Waste in Wales, December 2003.
4. Composites Industry Statistics, American Composites Manufacturers Association, 2006.
5. Best Practice Guide for Low Energy Plastics Processing from the European Community funded RECIPE project (supported by the Intelligent Energy Europe programme) contract no. EIE/04/153/S07.38646.
6. S Halliwell, End of Life options for composite waste - recycle, reuse or dispose?, National Composites Network Best Practice Guide, 2006.
   Restricted: Download 370 KB PDF file. (NCN registrants can download the guide from NCN Best Practice Guide - Composites recycling guide).
7. SJ Pickering, Recycling technologies for thermoset composite materials: current status, Composites Part A: Applied Science and Manufacturing, August 2006, 37(8), 1206-1215.
8. Rupal Mehta, A lifeline for waste carbon fibres, Materials World, January 2010, 18(1), 6-7.
9. BG Hermann, L Debeer, B de Wilde, K Blok and MK Patel, To compost or not to compost: carbon and energy footprints of biodegradable materials’ waste treatment, Polymer Degradation and Stability, June 2011, 96(6), 1159-1171.
10. Jeremy Jacobs, The Compositing Association, private communication (e-mail), Monday 26 June 2006 08:45
11. Michael Narodoslawsky and Anneliese Niederl, Chapter 10: The Sustainable Process Index (SPI), pp 159-172 in Jo Dewulf and Herman van Langenhove (editors), Renewables-Based Technology: Sustainability Assessment, Wiley, Chichester, 2006.  ISBN 978-0-470-02241-2.
12. Nora Goldstein, Source separated organics as feedstock for digesters, BioCycle, August 2005, 46(8), 42.
13. S Jana, NR Chakrabarty and SC Sarkar, Removal of Carbon Dioxide from Biogas for Methane Generation, Journal of Energy in Southern Africa, August 2001, 12(3).
14. L Greenham and P Walsh, Carbon Dioxide Detectors For Health & Safety Applications, Petro Industry News, December 2004, pp 34-35.
15. Richard Murphy and Ian Bartle, Biodegradable Polymers and Sustainability: Insights from Life Cycle Assessment, Summary Report presented at the National Non-Food Crops Centre seminar, London, 25 May 25 2004.
16. Andrej Krzan, S Hemjinda, S Miertus, A Corti and E Chiellini, Standardization and certification in the area of environmentally degradable plastics, Polymer Degradation and Stability, December 2006, 91(12), 2819-2833.
17. ASTM D5338-98(2003): Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions.
18. ASTM D6400-04: Standard Specification for Compostable Plastics
19. ASTM D6868-11: Standard Specification for Labeling of End Items that Incorporate Plastics and Polymers as Coatings or Additives with Paper and Other Substrates Designed to be Aerobically Composted in Municipal or Industrial Facilities
20. BS EN 13432:2000 Packaging. Requirements for packaging recoverable through composting and biodegradation. Test scheme and evaluation criteria for the final acceptance of packaging, December 2000.
21. ISO 14852 (1999): Determination of the ultimate aerobic biodegradability of plastic materials in an aqueous medium - Method by analysis of evolved carbon dioxide.
22. J Scott Turner, The Extended Organism: The Physiology of Animal-built Structures, Harvard University Press, September 2002. ISBN 0-674-00985-1.
23. D Montegut, N Indictor and RJ Koestler, Fungal deterioration of cellulosic textiles: a review, International Biodeterioration, 1991, 28(1-4), 209-226.
24. P Milner, SM Martin, KL Eley, R Cripps, E Firth, C Mercier, J Robinson and T Atkinson, Development of a second generation bioethanol process using TM242 – a thermophilic bacillus,
    Autumn Meeting, Society for General Microbiology, Trinity College Dublin, 08-11 September 2008, abstracts book page 23.
25. Compost heap bacteria could help produce renewable fuel, BioTech International, September 2008, 20(4), 26.

Further reading:

1. B Adhikari, D De and S Maiti - Reclamation and recycling of waste rubber, Progress in Polymer Science , 2000, 25(7), 909-948.
2. Adisa Azapagic, Alan Emsley and Ian Hamerton, Polymers: The Environment and Sustainable Development,
   John Wiley & Sons, March 2003, ISBN 0 471 87741 7 (1st edition soft-cover).  UOP Library
3. Caroline Baillie, Green Composites: polymer composites and the environment, Woodhead Publishing Limited, Cambridge, 2004.
   ISBN 1-85573-739-6.  CRC Press LLC, Boca Raton FL, 2004.  ISBN 0-8493-2576-5.  UOP Library
4. Jack Harris, Material matters: availability of uranium, Materials World, January 2006, 14(1), 56.
5. Y Leterrier, Life Cycle Engineering of Composites, Comprehensive Composite Materials Volume 2: Polymer Matrix Composites, Elsevier, 2000, 1073-1102.
   ISBN 0-08-043720-6.  UOP Library
6. James Lovelock, The Revenge of Gaia: why the Earth is fighting back – and how we can still save humanity, Allen Lane, London, 2006.
   ISBN-13: 978-0-713-99914-3.   UOP Library
7. TJ O'Neill, Life Cycle Assessment of Environmental Impact of Polymeric Products, Rapra Review Reports, 2003, 13(12), 1-133. ISBN 1-85957-364-9.  UOP Library
8. Steve Pickering and Peter Hornsby, Polymer Composites: recycling and energy recovery, Materials World, September 1995, 3(9), 426-427.
9. Gerald Scott, Polymers and the Environment, Royal Society of Chemistry, Cambridge,  1999.  ISBN 0-85404-578-3.  UOP Library

Other resources:

• Anaerobic digestion (NNFCC, with the support of Defra and DECC)
• Eco-innovation for a Sustainable Future (European Commission)
• Plastics scorecard (Clean Production Action)