[britch]

Maybe I'm being slow, but what is the obvious solution?

The article doesn't really go into how or why the Yangtze, for instance, has so much plastic. The Yangtze is is 6,300 km long. It seems difficult to prevent people from dumping in it along it's entire length.

Are thinking of setting up a filter at the mouth? Processing 4000 tons of plastic a day, including microscopic beads, doesn't seem trivial to me.

Is your assumption that there's only a few major dumpers?

[hairytrog]

It's far more fixable than filtering the water in ocean. The river mouths are probably where the plastics are most concentrated in the plastic's life cycle. You could couple the plastic filter/processing plants with other required systems like power plant cooling and desalination, so that the energy you expend to filter is being used both to filter and for a secondary purpose.