Plants Clean Waste Water and Grow Better by Eating Fish Poop

Fish farmers have a big problem with the water they raise their fish in. The farmers can't dump the wastewater in streams because the wastewater is loaded with fish poop. That poop can be bad for rivers and streams because it's loaded with nutrients. But Paul Adler, a horticulturist at the Appalachian Fruit Research Station in Kearneysville, West Virginia, uses plants to clean up the water so that it can go back into streams even cleaner than it was before.

What are nutrients? A) A beaver-like rodent from South America? B) An atomic particle? C) Wastes such as nitrogen, phosphorus and organic matter that come from raising fish?

Too many nutrients in the water can actually kill fish. The nutrients encourage algae--one-celled plants that sometimes appear as a green slime. Other microbes that eat the algae take oxygen from the water. Without enough oxygen, the fish can't survive.

To help clean up fish waste, Adler turned to plants. First, he built a trough that the wastewater runs through. Then he placed potted plants like lettuce and basil at the top of the trough so that the water runs through pots which have holes in them. The roots of the plants soak up the nutrients from the water. Plants can take more nutrients than they need at the time and store them for later use.

After the water runs through the trough and through many potted plants, Adler and colleagues take out the remaining solid waste to make fertilizer. When added to the soil, this stuff makes the plants grow better and produce even more lettuce and basil. Straw can be added to the waste to make a compost material for growing potted plants.

Now that the water is clean, it can be used on other crops or it can be released back into streams, where it won't hurt the fish.

—By Doris Stanley, formerly, Agricultural Research Service Information Staff

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