For a future project, we are looking for for waste processing efficiency (read cleaning, shredding, sorting) and shredder efficiency.
In the coming weeks I will post my findings on washing, solutions for washing and the shredding routine.
More about shredding efficiency you can find here.
I did some tests on washing PET and HDPE. I choose these two because of the high abundance of the materials and also because PET does sink while HDPE floats.
I seperated the materials on type and then made two equal batches of the material. One batch PET and one batch HDPE I washed before shredding and one batch of both materials I did wash after.
I figured out that washing before shredding is more time consuming but has some advantages. Especially oily substances are easier to remove on bigger parts by washing them with some cloth. Also it prevents the shredder from getting dirty.
However I think the best process is first cutting and cleaning the dirty products (especially oily substances) than shred than clean in water and then dry.
This is mainly because you can make this in a more streamlined process.
During washing the shreds I noticed some things that can be important in the further research (first picture):
Oil floats (obviously) so it is floats in the same layer as the HDPE.
PET sinks to the bottom of the container resulting that it gets mixed with the dirt.
Microplastics which get in the water should get handled and filtered with care. (see last picture
Right now I will continue on washing process optimization.
Open for feedback 🙂
First small scale sieve for sieving shreds. The mesh is a little bit too coarse so the shreds ‘leak’ a little. Searching for finer sieve.
Together with Dave, I came up with the idea to shred and wash plastic at the same time. With siphoning technique you do not need a pump,although how I need to transfer the water back to the top by hand.
The first impressions are pretty good and it will probably further explored in version 4. However, due to time constraints, I am not focussing on this principle.
But it is nice food for thought.
Watch a short video here
Nice one @mathijsstroober – I was already thinking about combining those two processes (shredding + cleaning), cool to see it being tested!
For the upward transport of the water, we could use an archimedes screw (maybe using the rotation of the shredder motor to run the screw as well, i think it won’t need a lot of power).
And probably would be good to have some sort of filter there, so the water gets cleaned in between every cycle.
Yes, you are right. But as mentioned.. this will be for a later research. It maybe needs another frame etc…
Testing sieve sizes
As a part of the washing research, I did test different sieve meshes. I wanted to see which mesh is the best for further research. The fabric were different kinds of mosquito meshes. As result I figured out that the meshes do not difer much in filtering qualities: The plastic was caught but the dirt got through. It looked like plastic did stick less to on of the meshes.
After filtering with one of the three coarse meshes, I also filtered with the finest I could find. Although it caught the same size of plastics, the water stil had signs of microplastic.
i’m looking into a solution as well. i am evaluating 2 options right now:
1. converting a regular washing machine with a more fitted sieve
2. use sieves in combination with vibrating housing, enabling more easy to built extensions like multi-stages of cleaning
is there are already a certain mesh size you could recommend to get started ?
Hey @mathijsstroober !
Very interesting to see your results !
I was thinking about a point : after microplastics come nanoplastics 🙁
all the effort you put in there will not manage to seperate micro/nano plastic particles from the dirt or any other things ? Is there a minimal size of “remaining plastic in the sieve” your are aiming for ?
I have sorted to clean up my plastic from glue (mainly) once reduced in size; and i am wondering if the washing wouldn’t be more effective while the plastic is still in its whole piece. The shredding would then operate on a clean plastic and we could imagine a system which vacumes all the output of the shredder and maintains it together. The main cleaning is from glue and dirt, so i think it would take less effort & be less risky to do it before shredding. ( Though the industries tend to shred then wash, they are operating tons of plastic at the same time; being at a much smaller scale, process may be rethought ?)
The mesh research would be very interesting for the vacuum bag ? :p need to push the research
Anyhow, these thoughts i just pushed aren’t there to bring you down on the research; cuz we need as much intel as possible to make all this possible !
edit : sorry just saw the video now ! so the sieve would be for that system ok ! i’m curious, what are you adding to you water to clean the shredder plastic ? what is the diameter size of the holes of your schredder sieve there ? Maybe that size impacts also on the amount of micro/nano plastic created through the schredding process; OOoor those micro/nano plastics could get collected in the bucket underneath and be reagglomerated together through a special very very very thin sieve ?!
Nice feedback, your are right on some points. About micro/nano plastics. I want to have the cleaning water in a pretty closed process. Only it water is really dirty it can be changed. Filtering the water can be done with something like sari cloth. Old sari, is really fine and also able to remove cholera bacteria. Read here more about this.
However, thoroughly cleaning plastic before shredding takes a lot of time and is more difficult because sometimes you need to cut it in small pieces in order to remove all the dirt. Also a great thing to do is to let the pieces scrub itself. Which works better with shreds than cut pieces of plastic. Otherwise all the pieces need to be cleaned by using cloth and wiping all the debris.
One thing to take in to consideration is that except glue and dirt, oil is also something to remove. Right now I think it works best to first clean the oil/ grease and then do shredding and washing (dirt/glue).
Also I know PP is on small scale, but I am researching efficiency to recycle as much as possible. Making it more attractive to wash also after shredding
Have you though about using a sand filter to remove the micro plastics?
That would be very easy to replicate by other people.
Not sure about speed though.
I was reading through your posts and wanted to give you an alternative to caustic soda have a look a this thread https://www.quora.com/Are-there-any-alternatives-to-sodium-hydroxide-lye-in-making-soap
I believe I will have an answer and will post in a few weeks just need to finish tests
Very interesting topic, points and tests @mathijsstroober.
It might be relevant to mention that we have focused mainly on ocean plastic waste as well as HDPE-cans from gas stations.
Currently we have washed before schredding. My biggest concern about washing after or simultaneously is that the contaminated plastic will dull the knifes in the shredder a lot faster. Any thoughts or empirical indications regarding this?
Some [semi-random] process thoughts on cleaning and separating the shredded plastic.
* Fluidized beds
* something like a fractionating column for density separation?
Some process thoughts on cleaning the wash water.
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