An option could be the use of

commercial filter papers (e.g., with pore size of 20-25 micron or larger) used in laboartories, allowing to separate the smaller particles and to retain paramecia

Thanks Paola,

However one issue with paramecia is that they have an elongated oval shape and they will pass through a 20µm pore...

See if they are positively phtotactic, in which case they are can segregated with the help an adequate source of artificial light & then scooped out from the rest of the contaminating particles. 

How many cells do you need? Pasteur pipette is a nice tool to have some cells.

You can look for 10/um mesh for sieving. If you do not obtain it directly, contact some milling company: they use it to separate fractions of flour.

Parameciun is not phototactic but negatively geotactic. But do not be so sure in the result: centrifuge with a speed sufficient to separate 10 /um particles will kill the ciliates.

If you chave a culture of Paramecium in a test tube in (e.g., barley) grain, the ciliates will be found just in one layer, according to oxygen vs. food concentration. If your particles are able to sediment, within one or two days you will be able to have a chance to pipette ciliates from such layer.

As well, chemotactic behaviour may be used: connect your sample by long capillar tube (without bubbles!) with the vessel containing some attractive solution - cultivation media, traces of pepton, etc. (bacteria are not so attractive as the cultivation medium for them; it was published in ciliate investigation-prehistory). With some good lack, ciliates would migrate from your dirty sample. Such attempt was used to isolate axenic/monoxenic cultures.

Good luck

Cheers

Miroslav Macek