Wisconsin State Journal: Cow Pies and Potato Peels Can Make Wisconsin Dairy Farms More Sustainable

By Mark Crave

Things have never been easy for dairy farmers here in America’s Dairyland. The work is hard, and milk prices barely cover farming expenses most years.

Wisconsin farmers who survive often do so by innovating. Today, each Wisconsin cow produces twice the milk one did in the 1980s, due to advanced breeding techniques and feed formulations, superior milking machines, digital record-keeping and high-comfort barns. We’re making more milk from fewer cows, less feed and water. Today’s farmers are spending wisely, wasting nothing and becoming more sustainable.

One of the most important ways dairy farmers can continue to innovate is to recycle our manure in a more beneficial way. Rather than storing manure in pits or stockpiles and then spreading it on fields, we can first use it to make renewable energy by employing anaerobic digestion.

This process is as old as nature itself and has been used for decades in farming and wastewater treatment. Certain types of microbes efficiently break down organic matter in an oxygen-free environment. When these microbes digest manure, they produce biogas, which then is piped out of the digesters.

Biogas is about 60% methane. It can be used as is to generate power on a farm, or it can be converted to nearly pure methane — the same substance as the natural gas we use for cooking and home heating. But methane created by digesting manure is renewable, not a fossil fuel. Selling this renewable fuel offers farmers added income, and the benefits don’t stop there.

In addition to producing valuable energy, the digestion process breaks down manure into a nutrient-rich material called digestate, which has far fewer pathogens than manure and is almost odor free. Importantly, though, the digestate retains the manure’s soil-friendly nutrients.

Because the digesting microbes remove so many pathogens, farmers can confidently fertilize their crops with the digested manure, all but eliminating the need for imported fertilizers. This increases uptake by the plants, which improves crop production.

Recycling manure in this way stops methane from going up into the air. This is important because, as a greenhouse gas, methane traps heat in our atmosphere. By anaerobically digesting manure, we can trap and use that methane as a substitute for fossil fuels.

Anaerobic digesters are only in use at Wisconsin’s larger dairies now because of the scale needed for economic viability. Digesters are expensive to build and operate, so you need enough digestible material for the investment in digesters to make economic sense. Small and mid-sized farms also could become more sustainable and bring in a non-milk revenue source if they team up our cheese and snack makers using co-digestion.

Co-digestion means digesting more than one type of material in one tank. Crop residues, grass clippings and food waste are great partners with manure when digested together. Like manure, these organic materials produce valuable renewable energy. They also reduce the massive amounts of food waste that use up dwindling space in Wisconsin’s landfills.

Wisconsinites send about 854,000 tons of food waste and scraps to landfills each year, almost 300 pounds per person. These scraps come from dinner plates, grocery stores and food processing facilities.