Rachel Nuwer, Contributor
March 30, 2012 | 1 Comments
Some farmers take recycling to the extreme, to the benefit of both the environment and their bottom lines. They are the often-unheralded pioneers of waste-to-energy technology, sometimes powering entire small towns with their byproducts.
The most common waste-to-energy method is to employ methane-excreting bacteria in anaerobic digesters to turn farm waste like cow manure and rotting vegetables into biogas to heat their property and even sell electricity back to the grid. For dairy farmers making cheese, however, the process can get tricky.
Getting rid of the huge quantities of cheese whey — the byproduct of the cheese-making process — is difficult because the whey matrix is rich in fat and tends to rapidly acidify. That make it unstable in reactors. Some farmers spread the whey on their fields as fertilizer, but depending upon the size of the farm, they quickly run out of field space to distribute the stuff.
“It’s a real problem,” said Elena Comino, an applied ecologist at the engineering department of Politecnico di Torino in Italy.
Now Comino and her colleagues have proposed an easy solution in a recent study: just mix the whey with cow slurry, commonly known as liquid cow manure, to get the right pH balance.
Waste to energy
Outside of nursery rhymes, whey doesn’t come up a lot in most people’s daily lives. But it is a plentiful waste product — there are only 100 dairy farms in the U.S. that produce relatively large volumes of cheese but each one can create millions of pounds of whey in a single year. Figuring out what to do with all of this waste can be a challenge.
To figure out the perfect biogas-producing concoction, the Italian researchers tried mixing different proportions of whey and cow slurry. Through trial and error, they found that a 50-50 mix of slurry and whey yields a methane concentration of about 55 percent in the biogas. This figure compares favorably with the energetic potential associated with digestion of high-energy crops like maize. “We obtained the most convenient mix in order to produce the best biogas in terms of quantity and quality,” Comino said.
Few experiments have examined the biogas potential of co-digestion of slurry or manure with whey mostly because in the past anaerobic digestion was mainly used for wastewater treatment. But the technology is becoming more popular in Europe and North America since it benefits the environment and is an additional source of income for farmers.
“Cheese whey is a waste, but if you put it in a digester you can produce biogas so it becomes something you can reuse,” Comino said.
No more lagoons
In the past, standard practice was to keep agricultural waste like cow manure was kept in an open-air lagoon before spreading it on fields as fertilizer. During this process, methane — a potent green house gas — and other pollutants were released into the air, rainfall could cause the manure to run off and contaminate local waterways. On hot days, the manure smelled awful.
With a digester, rather than being left out in the open, the manure and whey is kept in a closed container, preventing green house gases from entering the atmosphere and further exacerbating global warming. The biogas is instead used as a renewable substitute for natural gas, propane or other fossil fuels. As for the byproduct, it can be used or sold as fertilizer.
Though European farms currently leads the way with aneorobic digesters, subsidies from state a local governments in places like Pennsylvania and Vermont are increasing the affordability for U.S. farmers to install digesters. In the U.S., there are around 160 anaerobic digesters on farms. Digesters number into the hundreds of thousands to a million for the rest of the world, according to the American Biogas Council.
Selling back to the grid
Some U.S. farmers are ahead of the curve. Charley Crave owns Crave Brothers Farm and Farmstead Cheese in Wisconsin and has been recycling cheese whey for years. He estimates that he produces about 20 million pounds (10,000 tons) of whey a year. He loads both cheese whey and manure into the digester, and says he doesn’t have “a scientific recipe” for the proportions he uses. He added that the types of cheese he produces—like fresh mozzarella he sells to Whole Foods—are naturally lower in acidity.
Crave’s says there’s only a handful of dairy farmers in all of North America who use digesters to process whey. Small dairy farms usually don’t have a cheese factory on their farm and so would have to transport the whey back to the farm. Perhaps more significantly, installing a digester can cost hundreds of thousands of dollars.
After the initial installation cost, however, the digester begins to give back. Crave sells the electricity to the power company. He uses the excess heat from the generator to heat the farm. With the digester, Crave said, “There’s probably a $20,000 a year difference between purchasing that heat and utilizing what’s available.”
Crave’s farm values nutrient management and conservation efforts, so the decision to install a digester came naturally. “We feel very fortunate to have one of the higher performing manure digesters right here on our farm,” Crave said.
Rachel Nuwer is a science journalist who writes for venues including the New York Times, ScienceNOW and Audubon Magazine. She lives in Brooklyn, NY. Feel free to contact her via Twitter @RachelNuwer.
This article was originally published on ecomagination and was republished with permission.