Pant Water treatment?

i noticed a really interesting set up at my school recently. the teacher has set up a 4 tank system, my guess is around 60 gallons total. one tank has a few plants, 2 gold fish, and a pleco, the next tank in the series is a empty except of a later of silty mud, then a tank with much more mud and stuff in it, a tank FULL of plants. the last tank is full of wierd non rooting sea weed esk stuff, a bunch of snails and the roots of a tropical vine looking thing. the whole set up is by a big windo with a lot of day time light. the only thing running on the set up is a small water pumo to power the syphon system to circulate the water throught the series.

My teacher explained it a bit to me but i didnt really catch much of it, he said something about mangrove trees working well, and being sort of popular for filering water in aquariums. Has any body heard this? Does anybody know anything about setting up a sytem like this? has it done already?

I would really appreciate anybodies thoughts on this, thank you.

You can set up a low tech tank w/out a filter to it if that's the question yes. And for it you can use various plants to achieve the "natural" filtration that the plants will do. Mangrove's are popular for this set up especially then if you'd like to have a open tank as they'll nicely grow out of the water.