Waste management cycles on a Seastead

Seasteaders will be, by necessity, pioneers in the recycling space. You can't just throw everything overboard when you're done with it, and we'll need lots of raw materials to make stuff out of. Below are the major recycling efforts we'll need to incorporate in our quest for sustainable deep-water living.

Liquid waste - 

Luxury yachts and cruise lines have long had to deal with the problem of liquid waste management, splitting the job into 3 subsystems. They typically set out with a full tank of fresh water, and empty tanks that are nearly as large for "grey water" and "black water" as well. 

Some types of water usage, such as kitchen faucets, turns into grey water, and that goes to fill up or flush toilets, which then goes to black water. Ultimately, the black water is flushed in the deep sea and we let nature scrub it back into clean water again over millennia. 

For more on that subject, check out the Seasteading Institute's "Where does the poop go" FAQ video: 
https://www.youtube.com/watch?v=Gd2FCpU5wu8

This is established technology & wouldn't change much on a seastead, but we have other waste to consider than just what goes through our pipes.

Solid wastes - 

All of our trash, down to every last banana peel, scrap of metal & plastic bottlecap, it all needs to be accounted for out in the deep because there is no junkyard. For decades seasteaders have been looking for an acceptable solution to deepsea trash recycling but it seems hopeless when we consider how bad the problem with trash & recycling is even on land today. Basically, just 9% of all the plastics you throw into a recycling big can be recycled at all!

https://www.youtube.com/watch?v=5-quksK76Rw

Plastic waste -

Thankfully, a couple of very interesting new developments are in testing these days. Chemically they do work, but the only question is if they are going to be practical to use at scale. 

The first has already been highlighted in this short video by the seasteading institute: Recycle waste plastics into building materials for seasteaders: 

https://www.youtube.com/watch?v=t02KFwHDeKs

There is much promise here for creating a concrete replacement, because the process isn't as energy intensive as a recycling plant typically is.

The second new development is even more useful; convert waste plastics into a hydrocarbon biofuel! Aduro Clean is one publicly-traded company that claims it can do exactly that: https://adurocleantech.com

If this process is perfected then such biofuel would naturally become a major source of energy generation on most seasteads. 

However, now that 3D printers are common, I personally feel that the technology which most quickly takes us from an empty coke bottle to a printer filament spool will be the one we most need to pursue. Making biofuel out of our waste plastic wouldn't be an unwelcome use case, but creating just about every physical object we need would surely trump that usage by far.  

Organic waste -

Most biological waste like banana peels, eggshells, paper & coffee grinds will have no trouble finding a home in compost bins, which then, with the help of a few worms, become soil for seasteaders to use in gardening. Naturally a lot of our solid waste from toilets can go in here too, but no one is going to want to live nearby that compost center! An air-tight system for composting stinky trash would be a great advancement we could make for a seastead.

Metal waste -

Finally, recycling metal waste would obviously need some kind of a smelting center. It would be great to see a seastead melt this stuff down and create new spars out of all waste metals out in the deep, but that process is extremely energy intensive, on par with all of the energy a large OTEC plant could produce!

Most likely, for the first 100 years or so, our metal waste would either get batched & sold to passing barges that recycle them on land, or simply dumped out in the deep. We've lost a few steel-hulled ships down there over the centuries already, so we're pretty sure the fallout is minimal from that choice.