Here’s an interesting way in which a problem is helping to solve itself.
Algal bloom — toxic plants that grow in water in hot weather — feed off nutrients contained in runoff from farm fertilizers or town wastewater.
It also occurs offshore, for example in Florida last year, where thousands of tons of marine life were laid to waste, and coastal communities lost millions of dollars in tourism revenue.
But there is a way in which growing algae can actually help to clean bodies of water, and be harvested and used for feed and fuel. It’s called an algal turf scrubber. First, an algal bloom is cultivated — usually in a man-made, stream-like channel — then water from a bay or lake is diverted to run over the bloom, feeding it with runoff nutrients. This essentially puts the algae to work as it pulls nitrogen, phosphorus, and carbon out of the water, cleaning it before the water is fed back into the original source.
The public works department of the town of Durham, NC, conducted a pilot study which put an algal turf scrubber to work cleaning up a local reservoir. The scrubber was a raised channel, 500 feet long by one foot wide, which moved 29,000 gallons of water per day and harvested nearly 11,000 pounds of algae and solid waste. The result: phosphorus and nitrogen were reduced in the reservoir by a third and a quarter respectively. The Durham team is seeking approval from local government to build a larger version.
The benefit of removing the polluting nutrients from the water is clear — a reduction of algal breakout on the body of water being treated. But that leaves another problem: what to do with the algae that grows during the process of treating the water? The turf scrubber channels need to be cleaned weekly as the algae grows quickly with all the nutrient-rich water feeding it. Fortunately, there are a few uses for the algae once it has been harvested — including using it in animal feed and biofuels.
At the port of Baltimore, MD, Stephanie Lansing from the University of Maryland feeds her weekly harvest into an anaerobic digestion system, where microbes break down the algae and turn it into methane biogas. In turn, the gas runs a fuel cell, which produces a modest amount of electricity that can charge batteries, and power fans and lights. Not a bad dividend from sludge.
These algal turf scrubbers could never combat the kind of coastal problems Florida had to deal with last summer — but it’s an intriguing experiment which could help fight the problem of chemical runoff in lakes and other slow-moving bodies of water.
The first video shows the Durham pilot program:
The second shows Stephanie Lansing and her colleagues with their algal turf scrubber in Chesapeake Bay in Baltimore:
Related front page panorama photo credit: Adapted by WhoWhatWhy from Lake Erie harmful algal blooms (NOAA Great Lakes Environmental Research Laboratory / Flickr – Public Domain).
