Friday, December 11, 2015

Microbeads happen, a sewer eye view of Microbead filtration.

When lathering in the shower, people rarely thinks of where the soap and water go. Even less thought goes to the little beads of plastic so popular in modern soaps. Portland, Oregon's shower water flows through some serious concrete tubing and into the Headworks of the Columbia Boulevard Treatment Plant. This waste is then divided into smaller channels that help divide out solid waste and coarse grit. So where in all this are those little micro beads?

Fluorescent colored microbeads have a density of 1.00 g/cm3, water has the same density of 1.00 g/cm3. Those little happy bubble beads mix in everywhere, like a cool kid at a party. Stage one Headworks does nothing to stop these little beads. 


On to the Primary Clarifiers.

The Columbia Boulevard Treatment plant has eight sedimentation tanks that can process up to 275 million gallons a day. They do this by cleaning two layers of the sewage; the very top, all the bubbles from the shower; and the very bottom, all the little nasty bits you were washing off. This is done with skimmers and paddles that separate out oils and lighter than water liquids, and heavier than water sludge.

Microbeads, floating throughout the fluids, are left behind. The beads settle in the middle of the mix. Stage two does nothing to stop these little beads.


From here the Microbead party heads over to the Oxygen Bar in the form of Aeration Tanks. These tanks are filled up with microorganisms that endless eat biomass waste. Like some kind of monster from a 1980’s horror film that feed on organic pollutants. The do this at a rapid pace when immersed in a oxygen environment. These little microbes are less than a micron in length, meaning they are roughly the size of those tiny soapy beads. They also have no interest in eating little colored microbeads.

At this stage the microorganisms, high on oxygen, party on. They do this with the little floating colored beads. The party comes to a crashing halt as it moves from the high oxygen tanks and into the Final Clarifiers. Without the constant supply of oxygen, the microbes all party to death and drift down into the bottom of the sludge. This stage uses the same approach as the sedimentation tanks. The tanks skim the top, like a kid stealing frosting off a cake, and they sweep the dead microbes back to the aeration tanks, because that oxygen bar runs on microbe flavored Soylent Green.

The microbeads now take a two mile trip through the disinfecting process and complete their journey by being dumped into the Columbia River.

Wait…Wasn’t this story about how they get cleaned out? If sewage treatment doesn’t deal with them who does?

Unfortunately, no one. There is, however, a silver lining.

Microbeads are becoming targets for legislation that blocks their use in cosmetics. Society should jump on board the ban bus, but you my humble reader are the real solution. The best method is to stop using them. Get an app, look for poly-something or other on your soap labels. If you are an Oregon resident support HB 3478 A, a ban on microbeads in personal care products.

References
  • Fendall, L. S., & Sewell, M. A. (2009). Contributing to marine pollution by washing your face: Microplastics in facial cleansers. Marine Pollution Bulletin58(8), 1225-1228.

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