Milk tankers.
April 16, 2020

Using Dumped Milk to Feed Anaerobic Digesters

 |  By: Jim Dickrell

At first glance, it appears anaerobic digesters might be a good outlet for dumped milk. The high levels of fat and protein in milk can be a good feed source for digester bacteria, and boost methane production as a result.

But do so with caution, urges an article by the Michael Best law firm based in Wisconsin.

The firm says there are two things to consider. The first is biological and the second is regulatory.

•  Biology. “Introducing too much high-energy milk [to the digester] can cause microorganism die-off or imbalance in the microorganism mix. If those things are avoided, other problems can result when milk is removed from the substrate stream.

“Put simply, the ramp up and ramp down of milk introduction into the digester needs to be managed carefully and scientifically.”

•  Regulatory. “If your digester is producing gas to generate Renewal Fuels Standards (RFS) credits, putting milk in the digester will change the type and value of those credits.

“Gas produced exclusively from manure generates credits known as ‘D3 RINS’ under the RFS program. But when you add food sources in addition to manure, the digester loses its D3 RINS qualification, and may be eligible only for ‘D5 RINS’ under RFS.”

That’s important because D5 credits are worth only about half as much as D3 credits. Stay tuned. The U.S. Environmental Protection Agency is expected to release further guidance on the enforcement of this distinction during the ongoing milk disposal crisis, say Michael Best attorneys.

For more information on using milk in digesters, click here.