This story in the Sacramento Bee reports on a fantastic business that does just that and which Sacramento is very fortunate to have based here.
“Crates filled to the brim with watermelon rinds, bushy pineapple tops, lettuce scraps and grass clippings each weigh in at nearly a ton.
“One might be inclined to call this “organic waste.” But not Clean World Partners: This is biodigester food.
“It’s feeding day for the four huge cylindrical tanks of the biodigester on the grounds of the American River Packaging plant in North Natomas. Nearly 10 tons of leftover plant matter are being dumped into the mouth of the digester and stuffed in with a garden fork.
“Without breathing any greenhouse gases into the atmosphere, the biodigester will turn these scraps into electricity and less than a ton of solid compost and fertilizer.
“It works like a cow’s stomach, says Kathryn Oliver, environmental engineer at Clean World Partners (CWP). Taking in food, the biodigester produces carbon dioxide and methane, or “biogas.” But unlike a cow’s burps and farts, its gases are turned into electricity with a microturbine. And it is far less pungent.
“It is about two weeks, says Oliver, “from the day that the apple goes in to when the apple is biogas.”
“The conversion is the work of legions of bacteria. They are the critical residents of the biodigester and the cow’s (and probably your) stomach.
“The bacteria naturally carry out a process called anaerobic digestion. Digestion, because they break down the food scraps. Anaerobic, because they do it without oxygen.
“From a science perspective, it’s not new,” says Warren Smith, co–founder and senior vice president of business development at CWP.
“Anaerobic digestion has long been used to get rid of organic waste, and is common throughout Europe. Dairy farms will transfer cow manure to large lagoons, where anaerobic bacteria go at it. Water treatment plants use it to dispose of leftover sludge.
“The difference with CWP’s biodigester is its ability to efficiently handle lots of solid material. Most anaerobic digesters can only digest material that is 9 percent solid. In contrast, theirs can take half-solid, half-liquid material.
“A carrot is one-fifth solid. To digest it with technology at water treatment plants, you would have to add a lot of water and use “really expensive blenders,” explains Smith.
“Instead, the CWP biodigester grinds up the material to the consistency of “really thick oatmeal,” says Oliver, without adding much water. This mostly solid slurry travels through pipes to the biodigester’s tanks.
“Handling this high-solid material efficiently would not be possible without technology developed by University of California, Davis professor Ruihong Zhang.”