Huls Dairy


Montana must have been the most beautiful place we visited.


Huls Dairy, a family operation for 100 years, was recently the recipient of the Blue Ribbon Small Business Award from the US Chamber of Commerce, one of only 75 small businesses in the US given this recognition. Dan Huls, the farmer and operator of the digester, was very accommodating to our schedule and happily gave us a tour of his digester that has been years and $1.2 million dollars in the making. The Huls are known for sharing their farming knowledge with the community and beyond to help everyone understand where our food comes from. See their website for extensive information on their dairy, the digester and contact details. In summary, the Huls milk 370 holsteins after an expansion in 2003. At the time of the expansion, they already had plans to build an anaerobic digester for the manure. The anaerobic digester, completed in 2008, is the only one in the state of Montana using cow manure as a substrate.


When we pulled up to a big green barn, Dan and his brother, Tim, first approached us on their dirt bikes—we knew right away that this would be a fun trip with a bunch of characters. (The farm is owned by the four Huls brothers and their wives.) Dan, we later learned, earned five (I believe) championships for racing Moto Cross in the Rocky Mountain area.

Holding Tank

First we saw the holding tanks for the manure. They were mixed to keep the solids suspended before being pumped to the digester.

Induced Blanket Reactor

Two anaerobic digesters were run in parallel, each 30,000 gallons.The digesters were built by Andigen. Dan expected the digester to be able to accomodate the waste of 700 cows, but his 370 cows put the digester at maximum capacity. About two-thirds of the project was financed by government grants. The trouble was the grant money did not arrive until after the project was finished so the Huls had to find loans for the two years of construction. Josh Keller at Rocky Mountain RC&D was instrumental in organizing the financing and cash flow for the project.

In addition to the energy that could be produced from the digester, Dan was motivated to use anaerobic digestion to reduce odor. The population of the Bitterroot valley in which the dairy is located is growing dramatically and Dan knew that it was only a matter of time before neighbors complained of the odor if the manure was sent to open lagoons to decompose. The anaerobic digester was a proactive way to reduce odor.


The anaerobic digester is an Induced Blanket Reactor (IBR) which I had not heard of before. The diagram is my attempt to explain how the internals work. The digester was recently developed and patented by Andigen in Utah.

Digester Building

The digester is housed inside an insulated building to maintain mesophillic temperature during Montana winters that go below zero.The technology does not mix the digestate or heat the digester. The influent is heated to 105˚F before loading into the digester. Digester maintains a temperature of ~98˚F by maintaining the building in which the digester is housed at ~85˚F. The object of the IBR is to keep the solids low in the tank and let the liquid rise—I assume to keep new influent from leaving in the effluent. The HRT is the shortest I have heard of at 5 days. Influent is about 7% TS and effluent is 3%.


The biogas is used to heat the influent stream using boilers. The digester system was designed to send the unused biogas to a generator to sell electricity back to the grid. This worked for a bit but the cost of keeping the generator running was too much and hence it is no longer in operation. You can see that the generator was pieced together from disparate sources, most obviously a car exhaust manifold and muffler. Dan chose this generator over other generators because this was the only one on the market that worked with software capable of sending electricity to barn operations when the power from the street was out and sending electricity to the grid the rest of the time. In the end, the software wasn’t able to make the switch at all. I believe Dan said it was the hydrogen sulfide in the biogas which has caused the generator to break down so frequently.

Afterburner Afterburner2

But the final product of the digestate may be the most interesting part of the whole operation. This year Dan has developed a brand of fertilizer called Afterburner Boost which hit the shelves of 8 lawn and garden in shops in the area for about $9 per bag of which Huls Dairy gets a 50% cut. I was impressed by the logo and even more impressed when I heard that Dan designed it himself. The fertilizer is the dewatered digestate which has been left in a pile outside to decompose for a year. The “1.6/0.6/1.0” on the bag above refers to the NPK content. Dan tested for NPK before leaving the fertilizer in pile for a year so he could print the bags. As it turned out, the fertilizer nearly doubled in N, P and K after a year so he will have to update the bags for next year. While we were on the tour, Dan received an order for more Afterburner from a store that had sold out. This stuff was going like hotcakes!

Fiber Separator Fiber Separator2

The digestate is dewatered with the Bauer Separator. At the front of the machine is a spring loaded door which applies pressure to the digestate so that water is forced through the screen (seen in the right photo) while the fiber is passed through the machine. Dan says this cost about $30,000. Some of the fiber is used as bedding for the cows.


The fiber is left in piles for a year. The darkest pile is the oldest.

Liquid Fertilizer

The liquid is stored in a pond and eventually spread on crops and on fields used for grazing. Dan says that they haven’t had much trouble with pipes freezing in the cold Montana winters.

Dan said that the local power company that bought the electricity was happy to do so; the electric company could now say that it was using renewable energy. But power companies aren’t always so happy buy electricity from home-scale renewable sources. In some states such as Utah, well-meaning politicians have required that electric companies buy the power at the rate sold to customers. This means that power companies loose money on the transaction. This has led to electric companies to push legislators to decrease the incentives for installing renewable resources to decrease the amount of power they will have to buy at a losing price. Perhaps the free-market approach in Montana is a better solution.

Huls Dairy
1769 Simpson Lane
Corvallis, MT 59828

About Kyle David

Thinking about distribution in developing countries
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