Normally, when you find plastic bags full of waste with green stuff growing inside, you don't open them up hoping that something good will come out. NASA, though, is trying to be a bit more optimistic, and the agency thinks that it can float a bunch algae bags out in disused bays, pump in waste water and pump out jet fuel. Good luck with that.
There's no question that it's possible to get algae to chow down on waste water and poop out biofuel. The question, really, is how to keep algae happy and healthy enough to do it for cheap enough and in high enough volume to make it worthwhile. Taking care of all those "enoughs" is what's been keeping the algal biofuel industry from being an algal biofuel industry at all, but NASA reckons it can fix that by appropriating chunks of unused waterfront property and using it to grow gas.
To flourish, algae need a couple things: they need ammonia and nitrates (which they can get from waste water), they need carbon dioxide (which they can get from power plant waste), and then they need a temperature controlled and protected environment, which is where plastic bags come in. Most land-based algae farms rely on tanks, and those tanks have to be cooled to keep all the algae from going belly-up, but if you instead just partially submerge plastic bags full of algae in water, you don't have to worry about it.
It turns out that a city the size of San Francisco (whose waste I personally contribute to on occasion) is capable of feeding 1,200 acres (about two square miles) worth of floating algae bags. These bags, in turn, would create well over two million gallons of biofuel per year. It would be cheap, it would only moderately sully the San Francisco waterfront, and it would be safe, too: even if a broken bag disgorged its algae and wastewater contents into the sea, the algae would all just die, and the (treated) wastewater is released out into the ocean anyway.
So far, NASA has spent two years and $10 million on this concept, and the next step is a comprehensive cost analysis to figure out if this is all really worth it or not. If it is, start looking for algae bags to come to a beach near you.
Via Tech Review