Hi everyone,
I am working on how to separate microplastics (size = 100 um, density = 1.07 mg/ml) from flocs. I used sucrose 60% w/w (density= 1.28) as a medium in gradient density method to separate these particles, but it did not work. My centrifuge condition was 4000 rpm for 15 min. After centrifuge, I got two layers; water with small flocs on the top, microplastic in the thin layer between water and 60% sucrose solution, and bigger flocs in 60% sucrose solution. My desired result is to get the microplastics in the bottom and flocs in water part. I plan to use sucrose 25% (d= 1.1) which is close to the density of microplastics but may also close to density of the flocs.
Do you think this method would work for my purpose?
If you know other better method, please let me know. I would very appreciate for that.
Thank you.
Dear Pham Ngoc Dung
Centrifuge is used only to separate dense particles in the liquid. During high speed rotation the densiparticles settles at the bottom.
Hello,
I think sucrose solution density is too low to separate microplasitcs and flocs. You should use high density solution like KI solution. With using high density solution you can separate microplastics from flocs, I imagine. In my research and a research of one of the country in north Europe, we are predicting the separation of microplastics and sludge (flocs) occurs in centrifuge. May be it is true. So, in WWTP, some degree of microplastics would be circulating because of separation in centrifuge. Perhaps, if you used a slow rotation dehydrate machine like screw press dehydrater in sewage sludge treatment process, you could move microplastics to sludge from sidestreem.
Thank you.
Hi Satoshi,
Thank you so much for your suggestion. Would you mind let me know your paper or the North Europe's paper on this topic?
Actually, my system contains microplastics and bacteria, but unfortunately some of bacteria form flocs so that it is hard for me to separate microplastics from these flocs. Not many flocs there like in activated sludge sample. My experiment is batch experiment.
I just think for density gradient method, to extract particle A from particle B, we could you 2 media, one having density close to A and another having density close to B. But as your suggestion, it would be wrong. I am quite confused with this.
Pham
Hi Pham,
I know a person is studying bacteria on microplastic in North Eurpe.
I tell you ASAP.
Thank you.
Hi Pham Ngoc Dung,
Given the rather low density of the microplastic particles, you may be well-suited doing a flotation, rather than sedimentation, experiment. In this case, load your sample at the bottom of the tube and select a density range that will allow your microplastics to float up while the larger flocs may stay nearer the bottom of the tube. This is common for lipoprotein separation (namely VLDL & LDL) and you can check that literature for some general examples on the concept.
When selecting your density range, though, keep in mind that the apparent (buoyant) density of particles may not perfectly match the absolute particle density (i.e., the particles may not localize to the sucrose solution at 1.07 g/mL).
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