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College of Food, Agricultural, and Environmental Sciences


Smart Stuff with Twig Walkingstick: Septic Secrets! (for the Week of Aug. 19, 2007)

August 19, 2007

Q. Dear Twig: What goes on in a septic tank?

A. To quote the bard, "Things you wouldn't understand. Things you couldn't understand. Things you shouldn't understand."

Ha ha! Just kidding.

My own treehouse has a septic tank. It's buried in the yard, the usual place for one. It holds 1,000 gallons, a typical size for one. Inside, bacteria digest waste and water that drain from the house's pipes. The bacteria, called anaerobic ("an-uh-ROE-bik") bacteria, don't need any oxygen. (Good thing!) The pipes include the pipes that come from my toilet, bathtub and kitchen sink.

First the stuff collects in the tank. Then it divides into layers: Sludge (solids) at the bottom. Effluent ("EFF-loo-ent"; half-clean water) in the middle. Scum on top. In time the effluent rises and goes up and out of the tank by a pipe. The pipe goes into a leach field: a stone-filled underground trench. There more bacteria help finish the job. The water ends up clean and safe. It gurgles back into the soil. Hurray!



P.S. It's gotta go somewhere! A house will have a septic tank if it isn't hooked to a city sewer.

Notes: In North America, an estimated 25 percent of households — 1 in 4 — use a septic system to dispose of their wastewater. Ohio State scientists say 980,000 households in Ohio do so. Not that most folks would ever consider it, but, "Never enter a septic tank," warns Ohio State University Extension's "Septic System Maintenance" fact sheet ( "Any work or repairs should be made from the outside. The septic tank produces toxic gases that can kill a person in a matter of minutes." Find a non-toxic tankload of details — how a septic system works, how to keep one working right, etc. — at Click on "Search," then type in "septic."

About this column: "Smart Stuff with Twig Walkingstick," a free public service of The Ohio State University College of Food, Agricultural, and Environmental Sciences - specifically, of the Ohio Agricultural Research and Development Center (OARDC) and Ohio State University Extension, both part of the College - is a weekly column for children about science, nature, farming and the environment. The reading level typically rates at grades 3.5-4.5. For details, to ask Twig a question, and/or to receive the column free by mail or e-mail, contact Kurt Knebusch, CommTech, OSU/OARDC,1680 Madison Ave., Wooster, OH 44691,, (330) 263-3776. Online at

Kurt Knebusch