Washing Plastic (V4)
Washing plastic is essential in the recycling process and at the moment it is mostly done by hand – a very time-consuming process.
While working with plastic films I came in contact with water and plastic and the advantages but also dangers it has to offer. Shredding film has turned out to be a challenge because of overheating and dust. My only solution for this was to work with a water-cooling system. I got familiar with the dangers of microplastic in water, the dirt and chemicals, and filtration processes. I changed my focus and now I am working on everything which has to do with washing. Starting before shredding and ending with a clean and dry workable material.
Washing plastic is a very broad topic and it contains many different steps. Each of them is important and I will spend the next months on researching, experimenting and updating you guys – I hope, together with your help, we can create a way to make it possible, that small workshops are able to work efficiently and save for the environment.
Creating clean plastic demands different machines, which have to function in a workflow. Designing this process seems to me as important as designing the machines so I will also work a lot on how the different work steps could look like.
So what have I done so far:
After gathering all the information from @mathijsstroobers topic washing plastic and some research I have defined and started to work on the different steps – Cutting and prewashing, shredding with water, collecting the shreds in a mesh bag, modifying a washing machine, drying and most important filtering.
Experiment | Using a sander to agitate
Another method we experimented with was agitation using the vibration of a sander – we made a quick and dirty prototype by strapping an old sander to the bottom of a bucket of water. The sander agitated the water quite a bit, however plastic remained dirty after ~15 minutes of agitation.
The biggest observable differences in cleanliness are between the shredded but uncleaned plastic and the five minute mix – There seems to be a diminishing return once you past the five minute mark. There was also a large difference between the 30 minute mix and the laundry cycle. The laundry cycle brought the plastic back to a bright, vibrant white, which the mixer failed to do.
Once the plastic plates were rinsed, I wet-shred them (shred them while spraying water into the shredder). Then I mixed the shreds in a bucket for a total of thirty minutes, removing samples at five minute intervals in order to learn how much time is needed to effectively clean the plastic with the mixer. After 30 minutes, I washed the remaining plastic in a mesh bag in the laundry machine to see how it’d compare.
As a starting point, I selected plates with a range of dirtiness from pretty clean to very dirty to see if there’s a limit to the mixer’s effectiveness. Some of the plates had a lot of contamination so I put them through a mix cycle prior to shredding them in hopes that it might remove some of the large, loose contaminants. This method turned out to be a good way to remove loose contaminants prior to shredding, however it did result in some plastic shreds being created and left behind in the water (the plates were extremely thin – i don’t think this would be an issue with thicker plastics)
To get a better understanding of how well the mixer worked, we collected some dirty plastic waste from local dumpsters – a majority of the waste was contaminated with food. We found a large amount of the same type of dirty plastic (white plates w/ tomato sauce) so we decided to use these as a control for our first tests with the mixer.
@brunowindt thanks, so if you have had wastewater emptied directly into a sump, have you taken any kind of observations or measurements about how much or what plastic or other contaminants appear/float/settle in that tank before you try to pump and filter them out?
We’ve been looking at a second-hand inline filter that someone gave us from the dairy industry, with a 2-layer reusable steel mesh filter, apparently 154 and 80 microns in size, and I wonder whether to be concerned about anything smaller being generated by abrasion.
@morayreachout exactly I designed basically a pool filter, as we need quite frequently cleaned water and the washing also needs high pressure. There might also be ways to use a gravity filter for slower washing cycles. But also I choose the pressurized filter, as I can clean it easier with backwashing.
@morayreachout Thanks for your feedback!
I am working at the moment on an updated file with all the information we have so far and I am gonna post it here as soon as it’s done.
About the sand based filter couplings, I use the big pipes for pressure reasons. About the connection to the washing machine, originally it was connected with an adapter, but the small pipe system inside the machine increased the pressure too much, so I removed lots of the “intestines” of the machine and we have a direct connection to the washing barrel now! But more to that soon!
In general, there are still many things to figure out. Especially about pre-treatment, as in label removing etc.
Also about the bill of material, we can give more detailed info later on, but it is not crazy expensive especially if you try to source things second hand etc.
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