The Biodegradability of Wool Enables Wool-to- Grass ...

The Biodegradability of Wool Enables Wool-toGrass-to-Wool, Closed-Loop Recycling Henry Barker and Steve McNeil Technical Bulletin, 2015, AgResearch, Christchurch, New Zealand

 Several studies have confirmed the environmental soundness of wool products.  Ways of enhancing the biodegradation of wool textiles have been demonstrated.  Shredding post-consumer carpets for use as a fertiliser and soil conditioner has been shown to be a viable closed-loop recycling option.

The environmental impact of wool textiles Consumers of New Zealand wool are increasingly seeking reassurances that the environmental impacts associated with wool growing and processing are minimised or mitigated. The production and use of wool textiles have environmental impacts that are lower than many, if not all, other textiles [1]. Wool’s ecological credentials are seeing it increasingly used in new applications such as building insulation [2], filtration [3], heavy metal absorption [4], and as a support for catalysts [5]. Wool carpets provide many environmental benefits such as improving indoor air quality and low-impact maintenance [6,7], in addition to the benefits for personal comfort and safety [8-10]. Researchers at AgResearch have been studying the recycling of post-consumer wool products, and the results are summarised here, along with key findings of other researchers. This publication is part of a series prepared to highlight developments in wool textile science and technology [6,9-10]. Wool is a key contributor to the viability of sheep farming and meat processing in New Zealand [13,14].

Enhancing the biodegradation of wool carpet mulch mats Keratins such as wool, hair, animal skin, horns, and feathers are readily biodegraded in soil by a range of microbes (fungi and bacteria) [15]. These microbes are adapted to the chemical and physical structure of keratins, utilising it as a source of carbon, nitrogen, sulphur and energy. A series of treatments were evaluated in a factorially designed study for their ability to increase the rate of carpet biodegradation [16]. Squares of treated carpet were laid pile-down on bare earth previously treated with non-residual glyphosate herbicide to remove plant growth (Figure 1). No additional ground preparation was undertaken. In total, thirty two squares of carpet (each 9090 cm) were treated and evaluated (Table 1).

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Figure 1. Trial site.

Figure 2. Carpet pile mass after three months (95% confidence interval bars).

The most effective treatments were those which increased biological activity due to favourable moisture, temperature and nutrient conditions (Figure 2). The higher moisture retention and elevated temperature under the mulch resulted in the most significant acceleration of carpet biodegradation. Phosphates, ammonium and nitrates released from the diammonium phosphate provided a favourable nutrient environment for accelerated biodegradation.

Treatment Mulch

Wax Urea Diammonium phosphate Caustic soda Heat

Table 1. Treatments to enhance the biodegradation of wool carpet Purpose Application Increase moisture content, raise Chipped-composted Cupressus macrocarpa, temperature and provide additional 75 mm thick layer over pile-down carpet source of microbes 2 Enhance moisture retention, no Applied to the back of carpet (100 g/m ) additional nutrients for microbes 2 Source of nitrogen for microbes Applied to pile as aqueous spray (25 g/m ) 2 Source of nitrogen and phosphate for Applied to pile as aqueous spray (25 g/m ) microbes 2 Partial degradation/solubilisation of pile Applied to pile as an aqueous spray (5 g/m ) Disruption of chemical bonds in wool Carpet heated at 130C for 30 minutes

Effect of shredded carpet on pasture growth Post-consumer wool carpet was mechanically shredded, incorporated into soil at 10 Tonne/ha, and the effects on the yield of Italian ryegrass, soil and grass nutrients were measured [17] (Figure 3). The levels of essential nutrients and organic carbon in the soil were increased by the shredded carpet (Table 2). The calcium and zinc came from the latex backing of the carpet, while the other nutrients came from the wool pile, and jute backing. After ten weeks, the grass grown on areas with shredded carpet was a darker shade of green than the unfertilised grass, indicating a higher chlorophyll content and therefore a healthier state. This colour difference became more pronounced as the trial proceeded, and was still evident nine months later, after the second harvest. Analysis of the grass at ten weeks showed higher levels of available elements in the grass from carpetfertilised areas than in the unfertilised areas (eg, 25% more sulphur, 17% more magnesium, 10% more nitrogen and 7% more phosphorous). After 15 weeks, the grass was again cut and weighed before and after drying. The carpet-fertilised areas gave a 24% greater dry matter yield. A second harvest, after a further ten weeks, showed an 82% increase in dry matter yield in the areas with shredded carpet (Figure 4). This closed-loop cycle (woolgrass-wool) is a very efficient form of nutrient recycling that reduces the need for inorganic fertilisers.


Figure 3. Trial plot prior to grass sowing, with fertilised, quadrants on the left and right quadrants

Component

Nitrogen Phosphorous Potassium Sulphur Calcium Carbon Chromium Zinc Sodium Total organic matter

Figure 4. Three weeks after the first harvest, the grass in the fertilised (left and right) are lusher than that in the unfertilised quadrants in the foreground and background.

Table 2. Analysis of carpet and soil components Mass of component Level in Level in added to soil control fertilised (kg/ha) soil (ppm) soil (ppm) 571 5.7 35 42 14 12 17 125 20 65 1,123 9 10 3,390 39,000 45,000 0.047 25 18 18 67,000 77,000

Increase in soil (%) 20 42 225 11 15 0 15

Results of other studies of wool biodegradation • The fertiliser value for shredded carpet applied to pasture has been estimated at NZ$75/ha [18]. Soil moisture retention, yields of grain and green fodder, and levels of available nitrogen, phosphorous and potassium were significantly increased by wool, while soil pH, electrical conductivity and micronutrient levels were not changed [19]. • Adding wool to peat-based media increased the yields of tomatoes and peppers by up to 33% [20]. When growing Basil and Swiss Chard in pots with combinations of peat, perlite and wool, the wool increased the nitrogen content of the plants [20]. The plant roots grew directly on wool fibres suggesting growth towards nutrients and/or a possible role for roots or root exudates in wool decomposition [21]. • Tufted carpets have been made entirely from wool. Wool fibre was used for the pile, primary and secondary backings and hydrolysed wool was used as the latex [22]. Such carpets are expected to have excellent biodegradability. Wool apparel readily biodegrades [23].


References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

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For further information please contact Henry Barker or Steve McNeil Tel: Email:

+64 3 3218800 [email protected] or [email protected]

This publication has been prepared by AgResearch for stakeholders in the New Zealand wool industry, and is based on current knowledge. To the extent of permissible by law, neither AgResearch nor any person involved in this publication accepts any liability for any loss or damage whatsoever that may directly or indirectly result from any advice, opinion, representation, statement or omission, whether negligent or otherwise, contained in this publication.
