From manure to money:the biodigester


Darryl Vander Haak uses the state’s first dairy digester to turn cow manure into fertilizer and bedding for his dairy cattle. He has also been able to generate a small revenue stream through selling electricty generated by the plant.


To some, diversifying by turning cow poop into a revenue source sounds like a load of you know what.

But the pungent smell of manure that saturates Darryl Vander Haak’s dairy farm has become a supplemental revenue source for the 64-year-old dairyman in the form of Washington state’s first dairy digester, which produces power from methane gas.

Vander Haak started the digester three years ago with technological help from Ferndale-based heating and air conditioning company Andgar Corp., as well as funding assistance from the USDA and a Washington State University grant from Paul Allen.

The process offers multiple benefits to Vander Haak, his farm and the environment by generating income from waste.

He sells the energy created from methane gas in his dairy cows’ manure, which would otherwise act as a polluting greenhouse gas, to Puget Sound Energy. The leftover liquid from the manure, rid of bacteria and 99 percent of all pathogens through the digester process, is used as fertilizer in his fields at his farm north of Lynden — a cow patty’s throw away from the U.S.-Canadian border.

He uses the solids, which also have been rid of bacteria and 99 percent of all pathogens, and essentially look like fibrous mounds of topsoil, as bedding for the cows. This saves him $3,000 a month from the cost of sawdust normally used for that purpose. He also sells the solids to local nurseries to use instead of peat moss for fertilizer.

And still more revenue comes from a fee he charges to local food producers who dump their food waste in the digester to enhance the mixture, as well as from the carbon credits and tax breaks he gets from the venture.

The digester has so far paid for itself and a little more.

“It’s not a big revenue, but it’s a lot of added ways of making revenue,” Vander Haak said. For example, when milk prices were rock bottom a year ago, the digester offered at least some supplemental income.

If power rates increase — and Vander Haak thinks they might — his digester will be well worth the investment. Recently, one other Washington dairyman has begun producing methane power in Eastern Washington.

“If power rates tripled, every dairy farmer would have a digester,” he said.


How it works


1. Take manure

All the manure from Vander Haak’s cows is pumped into the digester — a large, 14-foot-deep underground container that holds one million gallons of manure.


2. Add heat

The digester is constantly heated to between 98 and 102 degrees, which separates the methane gas from the manure after about a month.


3. Generate power

The gas flows from the digester into a generator, then through a transformer into the power grid. It generates about 400 kilowatts per hour, enough energy for about 200 of Vander Haak’s neighbors.


4. Separate solids and liquids

The liquid from the manure is pumped back into a lagoon that fertilizes his surrounding fields, and the solids are used for cow bedding and sold to nurseries as fertilizer.

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