If they were much lighter than water it wouldn't be as much of a problem for water filtration - they'd float, and settle at the top rapidly. It would remain a large problem as far as untreated discharges though.
Stokes' Law gives settling times (or terminal velocities) for small spherical particles. Terminal velocity is proportional to (difference between particle density & water) * (particle diameter ^2)
A 0.1mm microbead at 0.9 specific gravity will float to the top at 0.54mm/s, or at 1.1 specific gravity will drop to the bottom at the same speed. A 1mm microbead will move 100x as fast. A 0.01mm microbead will move 1% as fast.
I don't see the technical issue with trying to incorporate them into settling plant workflows, only the sociological issue that we routinely underfund municipal works. It's much cheaper to ban the selling of microbeads than to deal with them via settling in a universe where engineers run everything and the environment is sacrosanct, but even so, we don't live in that universe: Raw sewage discharges are common, and such things are not seen as important so long as we're not getting cholera outbreaks. Municipal works don't have the power, political or regulative, to levy new taxes on specific consumer-good industrial practices to pay for any expansion.
Food for thought:
"there are 330,000 plastic beads in a single bottle of Clean & Clear facial scrub"
Stokes' Law gives settling times (or terminal velocities) for small spherical particles. Terminal velocity is proportional to (difference between particle density & water) * (particle diameter ^2)
A 0.1mm microbead at 0.9 specific gravity will float to the top at 0.54mm/s, or at 1.1 specific gravity will drop to the bottom at the same speed. A 1mm microbead will move 100x as fast. A 0.01mm microbead will move 1% as fast.
I don't see the technical issue with trying to incorporate them into settling plant workflows, only the sociological issue that we routinely underfund municipal works. It's much cheaper to ban the selling of microbeads than to deal with them via settling in a universe where engineers run everything and the environment is sacrosanct, but even so, we don't live in that universe: Raw sewage discharges are common, and such things are not seen as important so long as we're not getting cholera outbreaks. Municipal works don't have the power, political or regulative, to levy new taxes on specific consumer-good industrial practices to pay for any expansion.
Food for thought: "there are 330,000 plastic beads in a single bottle of Clean & Clear facial scrub"
Edit: From a student study of microbeads, it looks like sizes have a mean of 260um with a standard deviation of 100um. http://nature.berkeley.edu/classes/es196/projects/2013final/...