Here's a project that I've been following for a long time that I wanted to share, because (a) it's a really great goal, and (b) they're going about developing this the right way, with real-world testing and troubleshooting.
The Ocean Cleanup is a project designed to clean up ocean garbage patches, and they've just arrived at the great pacific garbage patch for their second set of large-scale tests. I follow a lot of ecology forums and news sites, and there's a constant stream of pie-in-the-sky solutions to various problems that are technology-oriented, as opposed to being problem-oriented (in other words, trying to apply a favorite technology or engineering solution to a problem, as opposed to looking at the problem and figuring out an optimal, cost-effective solution).
The current solution they're testing involves net collection system suspended between two very slowly-moving vessels, and is roughly 500m wide, about 1/3 size of the intended eventual modules. Their estimates are that a fleet of about 15 deployments of these can clean 50% of the actual garbage in one patch per year (major diminishing returns there over time), and is supported by a planned network of river-based plastics collection units, which they're currently working on deploying in the 1000 worst-polluting rivers (responsible for 80% of all river-generated plastics).
Anyway, the current 002 system in the Pacific is going to be really interesting to follow over the next couple months as they complete this phase of testing.
https://twitter.com/TheOceanCleanup/