With water shortages looming in the future, we need new ways to clean water that's been fouled by human waste, agricultural runoff and industry. A new article published in BioScience (free PDF link) shows that we can use naturally-occurring algae as a filter. The plants would not only make the water suitable for re-use, but could also allow us to harvest pollutants for fertilizer and even biofuel.
Algal turf scrubbers (or ATS) have been known for decades, and they are looking more attractive as demand rises for cheap and effective ways to clean water. The scrubbers are usually large outdoor fields, where the algae uses sunlight as a fuel source to pull nitrogen and phosphorous out of the water, and replaces them with oxygen. While traditionally used in large inland sewage treatment plants, the ATSs can also be modified to work in open water, so they don't take up useful space on land.
Once you've sucked up the pollution from the water, what do you do with the algae? There's the fun part. The infusion of nitrogen and phosphorous make the algae into an excellent fertilizer, and with a bit of work you can even turn it into a biofuel. Once a week you can harvest the algae, and it functions as a fertilizer about as efficient as commercial options. The researchers are quick to point out that turning it into biofuel isn't yet efficient enough to turn a profit, it does help to recoup costs, and is another benefit for the system.
At least one company is already working on a commercial application of ATSs, but there's more in the works. There's talk of making 3D meshes to grow the algae more efficiently, and of mobilizing screens of them into the ocean to help with runoff from cities.