What’s the connection between fashion and sewage sludge?

When we think of fashion, we don’t often think of sewage sludge. Surprisingly, fashion plays a big part in contaminating a very important resource for the world – sewage sludge.

Sewage sludge and its treated derivative, biosolids, contain valuable nutrients for plant growth. The recirculation of these nutrients to agricultural land is an essential element of sustainable agriculture. The nutrients in biosolids vary depending on the wastewater source and the treatment used to process the sewage sludge. However, concentrations of macronutrients like nitrogen and phosphorus are much lower than those found in chemical fertilizers (Moss et al. 2002). Despite this, studies have found that the application of biosolids can supply enough nutrients to result in crop yields similar to those achieved with chemical fertilizer (e.g., McLaughlin et al 2008; Silva-Leal 2021).

We are continually buying new clothes and many of them, especially low-cost fast fashion, contain synthetic fibres (such as polyester, nylon, spandex, acrylics etc.). When clothes are washed, some of the fibres of the fabric break off into the wastewater and contribute to the increasing presence of microplastics and microfibers in our waterways. In fact, textiles are estimated to contribute approximately 9% of annual microplastics to the oceans (UN Environment Programme (2020). Sustainability and Circularity in the Textile Value Chain – Global Stocktaking. Nairobi, Kenya). If your washing machine is connected to a sewer, these fibres travel with the wastewater and end up in a wastewater treatment plant (WWTP). This would not be a problem if the fibres were readily biodegradable, but many synthetic fabrics shed microplastic fibres which are resistant to biodegradation and persist in the environment for long periods of time (e.g., Sülar and Devrim 2019). Synthetic fabrics currently make up more than 65% of textile fibre production (IFJ 2019, Figure 1). A report from Ellen MacArthur Foundation estimates that washing synthetic clothes contributes 500,000 tonnes of plastic to the ocean every year (EMF 2017, Figure 2).

In this experiment, for every kilogram of clothes washed between 640,000 to 1,500,000 fibres were released. The range relates to different fabric types. Synthetics clothes constructed from tightly twisted yarns and low hairiness appear to release fewer fibres than those with more loosely twisted yarns and high hairiness (Falco et al. 2019).

At the first stage of treatment, municipal wastewater treatment plants separate the solid (the sludge) and liquid fractions of incoming wastewater. In the process microplastics and other contaminants are concentrated in the sludge. Studies have found that, depending on treatment, between 6-12 per cent remains in the water (Iyare et al 2020). This sewage sludge can be sent to landfill, incinerated, or used as an agricultural fertilizer. If used as fertilizer it generally undergoes additional treatment to remove heavy metals and pathogens – but the microplastics from clothes and other sources remain. Okoffo et al (2021) examined archived biosolid samples from Australia and the United Kingdom (1950-2016) and found that the concentration of plastic in biosolids increased overtime in line with increased plastic production. They found minimal plastic (mostly polystyrene) in samples prior to 1990.

The processed sewage sludge, referred to as biosolids, is full of valuable plant nutrients (including nitrogen, phosphorus, sulphur, potassium, and a range of micronutrients) and is used as fertilizer on fields all over the world. There is considerable evidence that the application of biosolids improves soil organic content and increases crop yields. However, there is growing concern that biosolids are contributing to the increasing level of microplastic contamination being recorded in agricultural soils (e.g., FAO 2021). 

Many countries support the increased use of sewage sludge products in agriculture as part of a more sustainable use of resources. Using biosolids in agriculture reduces the demand for synthetic fertilizer and non-renewable phosphorus, but it is essential that this valuable product does not end up adding a long-lasting contaminant that could potentially impact waterways, soil health and food quality.  

Removing plastic from sewage sludge and biosolids is costly and currently not very successful (see UNEP 2020 for an overview of the impact of different sludge treatment options on microplastic abundance). How can we prevent the persistent plastics that are shed from clothes entering WWTP and ending up in biosolids? There are policies that may help to increase consumer awareness. These include clear labelling on clothes indicating the presence of non-biodegradable polymer content. Clothes could come with a warning if they have the potential to shed non-biodegradable fibres during washing. Some clothes shed more microfibres when first washed (Figure 3). Producers could wash this category of clothes before sale to catch the first release of microfibres.

There is general decline in fibre release with successive washings (Falco et al 2019). However other studies have found that older clothes can release more fibres than new clothes (e.g., Bruce et al 2016).

There are also published tips on how to wash clothes to limit microplastic release (e.g., plasticpollutioncoalition.org).

One approach is to reduce friction on the clothes by:

· Washing synthetic clothing less often and on a short cycle

· Using a liquid soap instead of the more abrasive soap powder

· Using cold water as hot water can damage clothes leading to increased fibre release

· Using a slow spin speed

· Avoid doing small loads of washing – when the machine is full there is less friction between the clothes during washing

· Front-loading washing machines have been found to produce less friction than top-loading washing machines

· Reduce friction even more by gently hand washing synthetic clothes

Other actions include capturing microplastics before they are discharged into the sewer. Napper et al. (2020) reviewed six products that claim to reduce microfibre release into wastewater. They found that that external water filters were the most effective devices (the best achieved a 78% efficiency at reducing microfibres entering the wastewater). Of the products used to capture microfibers in the washing machine, washing bags were the most effective (the best reducing microfibre release to wastewater by 54%). Users of these products should be educated on proper disposal of the captured microfibers to prevent them from entering the environment through other pathways – e.g., don’t wash the filter in the laundry sink!

The Ellen MacArthur Foundation (2017) has developed a set of objectives that transform the textile economy. These include decreasing microplastic release by reducing the use of synthetics in textiles and the development of non-shedding fabrics. They also stress the importance of moving away from the idea of disposable clothes by encouraging better design, longer wear and improved recycling at the end of life – all of which can help to limit the amount of plastic required for new fabrics. 

1. Take action to stop non-biodegradable fibres contaminating sewage sludge/biosolids:

· Although there are some options for reducing fibre release during washing, they are likely to be taken up only by a small portion of the population. Washing machine manufacturers should be encouraged to develop effective solutions to microfibre release.

· Industry needs to focus on producing fibres that nature can recognise and biodegrade. 

· Fully removing microplastics from sewage sludge and biosolids is currently not possible. We need to develop technologies to eliminate these contaminants so that we can benefit from nutrient-rich biosolids, and they do not become a “waste” to be burnt or dumped in landfills.

2. Encourage consumers to buy less, to repair and to recycle clothes. This requires the industry to improve durability and recyclability.

3. Hold fast-fashion manufactures and retailers accountable for clothing waste and plastic pollution. Encourage the production of biodegradable, non-shedding, and recyclable fabrics.

Bruce, N., Hartline, N., Karba, S., Ruff, B. and Sonar, S., 2016. Microfiber pollution and the apparel industry. A report for Patagonia: Bren School of Environmental Science & Management, University of California.

Ellen MacArthur Foundation,2017. A new textiles economy: Redesigning fashion’s future, http://www.ellenmacarthurfoundation.org/publications

IFJ 2020. The Fiber Year 2020 – Deceleration along the textile chain. Andreas W. Engelhardt July 16, 2020. https://fiberjournal.com/the-fiber-year-2020-deceleration-along-the-textile-chain/

IFJ 2019. The Fiber Year 2019; World Survey on Textiles & Nonwovens. Frankfurt, Germany.

Iyare, P.U., Ouki, S.K. and Bond, T., 2020. Microplastics removal in wastewater treatment plants: a critical review. Environmental Science: Water Research & Technology, 6(10), pp.2664-2675.

McLaughlin, M., Bell, M., Nash, D., Pritchard, D., Whatmuff, M., Warne, M., Heemsbergen, D., Broos, K., Barry, G. and Penney, N., 2008. Benefits of using biosolid nutrients in Australian agriculture-a national perspective. In Australian Water Association, Biosolids Specialty Conference IV. Australian Water Association.

Moss, L.H., Epstein, E. and Logan, T., 2002. Comparing the characteristics, risks and benefits of soil amendments and fertilizers used in agriculture. Proceedings of the Water Environment Federation, 2002(3), pp.602-623.

Napper, I.E., Barrett, A.C. and Thompson, R.C., 2020. The efficiency of devices intended to reduce microfibre release during clothes washing. Science of The Total Environment, 738, p.140412.

Okoffo, E.D., Donner, E., McGrath, S.P., Tscharke, B.J., O’Brien, J.W., O’Brien, S., Ribeiro, F., Burrows, S.D., Toapanta, T., Rauert, C. and Samanipour, S., 2021. Plastics in biosolids from 1950 to 2016: A function of global plastic production and consumption. Water Research, 201, p.117367.

Silva-Leal, J.A., Pérez-Vidal, A. and Torres-Lozada, P., 2021. Effect of biosolids on the nitrogen and phosphorus contents of soil used for sugarcane cultivation. Heliyon, 7(3), p.e06360.

Sülar, V. and Devrim, G., 2019. Biodegradation behaviour of different textile fibres: visual, morphological, structural properties and soil analyses. Fibres & Textiles in Eastern Europe.

UNEP 2020. Water pollution by plastics and microplastics: a review of technical solutions from source to sea. https://www.unep.org/resources/report/water-pollution-plastics-and-microplastics-review-technical-solutions-source-sea

The Marine and Freshwater Branch, UNEP Ecosystems Division.

Riccardo Zennaro, Programme Management Officer 

 Avantika Singh, Assistant for Wastewater Management

Carla Friedrich, Programme Management Officer

for their contributions and reviews.