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Remove microplastics from the water cycle by filtering and treating greywater from washing machines

KetkiDave
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Remove microplastics from the water cycle

Begin small. Begin strong. Sure-footed. The Washing Machine Project is proof. Helps millions, especially women free up their time, use less water, spend less money, and be happier, by simplifying something seemingly simple as washing laundry.

My job here is to design a microfilter that removes microplastics from the greywater and makes is reusable. But I don’t think it ends there. Let us remove microplastics from the water cycle, not just change its location from water to soil. Let me explain. The microplastics removed from the water are retained by the filter. Once the filter media is clogged up, either it is cleaned for reuse or disposed. If cleaned using chemicals, this involves further pollution of water, by moving microplastics, plus chemicals to dark-grey water, or black water, depending on how you dispose the washed-out liquids. Once the filter reaches its end-of-life, whether disposable or reused, it usually ends up in the landfill. Companies like Tesco and Brita recycle their filters, but the filter media cannot be reused, it ends up in the landfill. Thus, we are producing microplastics through clothes and cleaning products, this ends up in grey water, which ends up in the soil through landfill even when you filter it.

700,000 microfibers can be released from a single load of laundry (Napper and Thomson, 2016, Doi: 10.1016/j.marpolbul.2016.09.025). Microplastics are defined as pieces of microplastic smaller than 5mm. Microfibers are generally bigger than microbeads, which are defined as less than 1mm in size. They are less than 10µm in diameter. Assuming that the majority in laundry greywater are polyester-based, the density of polymer is 1. 25 g/cm3 (1.04 - 1.46 g/cm3), a median of 5 µm diameter, 2.5mm length, gives 42.93µg microplastics per wash.

Global average weekly plastic consumption

(Published on edition.cnn.com dated 2019/06/11)

Although that might seem like a miniscule amount, the International Union for Conservation of Nature (2017) estimate that ‘35% of all microplastic contamination in the oceans’ is from laundry greywater, and this amounts to a staggering 32,550 – 82,600 tons by 2014 estimates. A team of researchers led by Utah University scientist found that plastics keep breaking down into smaller and smaller sizes and now can be found in rainwater and the air we breathe. We do not notice them due to their micro and nano sizes, but they affect our health, and in the ocean, they affect sea-life. The nano plastics are even more harmful to life than micro plastics. Therefore, it is important to remove nano plastics as well, and not just microplastics. And not just remove them, return them to harmless non-toxic basic constituent blocks, which are naturally available.

basic needs

higher needs

Usability

Aesthetics

Information and reliability

Functionality

Hierarchy of user experience needs based on Maslow’s model of needs

The process

The connecting link between The Washing Machine Project and microplastics in the oceans is made by installing a water filtration device to the drainpipe of the washing machine.

The filtration device must not: add more rubbish to the environment, so therefore be preferably carbon neutral, or in the least low carbon. It should be fully biodegradable at the end of life.

The organic and inorganic matter retained by the filter should be biodegraded or made use of another way.

Product:

a micro-filter that removes micro-plastics from the greywater from the washing machine so that it can be re-used or secondary purposes. If it can be drinkable, that would be super!

To understand product functionality from the user’s point of view, the following pain points were identified:

Pain points:

1) water emptied from the washing machine to bucket by hand using the drain hole. A pipe could be provided to make this easier. Should filter be a part of this pipe, or in the bucket?

2) Durability, life of the filter. It should last as long as possible. A year is acceptable.

3) Cost of the filter. The entire washing machine costs about $120. The filter should not cost more than $10 to the consumer.

4) Disposing off the micro and nano-plastics that get filtered – reuse or compost

5) cleaning of the filter

6) RE-use of the filter

7) recycling options

8) end of life – fully compostable filter

9) selective filtration? – keeping minerals and removing microbes, is that possible

10) any dissolved substances in the water that needs removal before reuse of water

11) non-plastic filter required

12) embodied carbon minimisation

13) end of life and circularity of filter

14) easily accessible to all or most parts of the world

The kind of solution users would like:

  • Easy to fix, easy to store
  • Easy to clean
  • Made from non-polluting materials, non-toxic materials, as children might open it up at the end of its life, or play with it, instead of disposing it off
  • Affordable
  • Potable water / drinking water preferred, minimum standard is secondary uses – washing, gardening, etc.

Aesthetics:

Good to look at, does not collect dirt, simple shapes, simple lines for the filter; beautiful looking, and aesthetically pleasing shape for the micro and nano plastic processor acrylic pot.

Usability:

In this model, usability refers to the ultimate ease of using, where the product goes beyond its function and starts fulfilling other needs and becomes very convenient, and therefore a pleasure to keep.

Here, the filtration device satisfies this by being very easy to connect. So that it can also act as a pre-filtration device for any kind of water storage, by connecting it to the tap using a hosepipe.

The microalgae not only digests the plastic using the PETase enzyme implanted in it, but also produces useful biomass, which could be sold collectively, or used individually as food supplement.

Figure 1: Sediment depth filtration

Depth filtration method is employed to remove sediment. Research with available filters and cartridges in this range in the market and at RS components suggests that the nominal filtration rate of these filters is 1-10 µm. The best filters are made with tight non-woven layers of microfibre sheets that are tightly spun together to form a filter cartridge. These are less dense towards the outside, and more dense towards the inside.

An inner hard pipe core is required to ensure that when the filter is cleaned using back flushing, the cartridge fibres do not lose their form. For industrial use, for high temperature, cotton fibres with stainless steel core is used. Since we do not require high temperatures such as 120C that they require, we are able to replace this with eco-friendly sustainable bamboo core. Bamboo cores are being used to produce durable water bottles, and industry is well-developed that can source good quality bamboo, and manufacture it to requirements.

The cartridge is built using a combination of jute cellulose nano fibre whiskers needle punched together to form non-woven membrane. These have shown to be able to filter nano particles. Antimicrobial treatment is done using chitosan and vegetable dyes has shown to make it resistant to bacteria, better conductor of electricity, and thus a better filtration medium. It has also shown to be better at keeping its form after cleaning using back flushing, compared with glass wool in some studies.

Jute micro and nanofibre  along with unmercerised cotton fibres will be used to produce the cartridge. No existing manufacturers make this, though facilities for jute fibre nonwoven membranes and cotton filter cartridges do exist. So this will be an innovative product.

The outer shell is built from repurposed moulded bamboo, made using bamboo fibres and plant-based resin adhesive. Water jugs using this material are being sold, so the industry exists.

 

Costs:

Inner core: £5, filter cartridge: £3.70, outer shell: £5, assembly manufacture and additional costs: £2.

These are bulk manufacture estimated costs based on available products. The picture above is of water bottles 7.5 cm diameter available in different lengths, made in Assam, India. Similar bamboo industry exists in Vietnam, China and other countries.

 

Sustainability, culture and costs:

These filters are used in places where either 1) water is scarce, 2) there is poverty, 3)refugee camps, or 4) sustainability enthusiasts.

Keeping these in mind, the product has been designed to be flexible, and easy to use.

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