Yes, indeed, we have flushing toilets at Stonyfield, but no, that’s not what we’re talking about here. When we make yogurt, we have to clean up afterward—much like you do after cooking at home. Luckily, it’s not nearly as messy as your kitchen may be after cooking, because for us, it’s all inside the pipes that run through our factory! But we do wash and sanitize all the equipment regularly—and that generates “wastewater,” or water mixed with small amounts of milk, yogurt, fruit, sugar, and cleaning solutions.
When our factory grew to a point that we needed to pre-treat this wastewater before it left the “Yogurt Works” and headed to the municipal treatment plant, we knew we wanted to use a very environmentally responsible type of treatment—one that didn’t require a lot of energy or chemicals, or generate a lot of waste.
A traditional dairy wastewater treatment plant uses quite a bit of energy and generates biosolids (or “sludge”) that need to be hauled offsite to be managed. While it was not the typical choice for a dairy company, we chose our anaerobic digester because it generates very little waste, yet makes some of its own energy.
The upfront cost was 17% higher than other systems, but the operating costs are much lower, due to 40% less energy use and more than 90% less waste generated (and therefore 90% less waste to pay to have hauled away!). We expect it to save $3.5 million over the first 10 years of operation.
So how does it work?
The wastewater flows through drains in our factory to a short pipe underground that delivers it to our wastewater treatment plant. At the treatment plant, bacteria eat the stuff that’s in the wastewater, and cleaner water goes out into our local sewer system.
The bacteria, which we often call “bugs” even though they are not insects, also burp out a gas that we collect and use to make energy. The bacteria like to live in a hot tub-like environment, around 95° F.
And all this happens in a pretty darn big “hot tub”! Our digester is about 30 feet tall and 100 feet across—or a total of about 1,800,000 gallons. That’s the same as 2 or 3 Olympic-sized swimming pools!