Systems reduce costs, create value-added products
By CAROL RYAN DUMAS
In a sleepy area of Idaho's Gooding County, big things are going on at Big Sky West Dairy.
With 4,000 cows, the dairy has a lot of manure to manage. It has to keep a tight handle on land application of phosphorous and mitigate odors offensive to its rural neighbors. New technology is helping with those constraints, conserving water on the dairy and creating the potential for value-added products.
The dairy and Ag Power Partners began operation in December 2008 of a GHD Inc.-made methane digester; its energy is sold to Idaho Power's grid.
The digester can produce about 1.2 megawatts, said Brad Weg, biogas and renewable energy construction regional manager for ANDGAR.
The process begins in the free stalls. The dairy scrapes its alleys into a flush flume that delivers the manure to a staging area. There, screens separate solids from liquids. The thicker manure is pumped to the digester, and the thinner liquid goes back into the flume.
"We don't use clean water, and we don't recirculate lagoon water," said Marty Tolle, Big Sky's environmental coordinator.
Clean water would overwhelm lagoon capacity, and lagoon water would create more odor, he said.
The pump delivers the manure to the digester daily at 8 percent solids. The stream exits the digester at 5 percent solids, which is about 40 percent total solids destruction, Weg said.
The digester effluent then goes to the solids-separation process, where two different systems are used. One system removes solids for bedding and the other removes phosphorus and solids from the liquid stream headed to the lagoon.
"Conventional methods, at best, bring 20 percent phosphorous separation," Tolle said. Band-press technology has allowed them to get an 85 percent phosphorus-separation rate.
The process has decreased the dairy's cost of hauling raw manure off the dairy.
"What we're doing today in comparison with prior practices is cost-effective," he said.
The dairy could eventually capture added value from the more nutrient-concentrated dry matter by selling it for compost or bagged gardening products.
"When we get it to a point that we can sell it, that's a home run for everyone," Weg said.
But the reason for installing the new technology was to better meet state and county requirements and control odor, Tolle said.
"We wanted to have complete control with nutrient management," he said.
Phosphorous is a limiting factor when it comes to land application of dairy waste. And odor control is a huge benefit for the dairy industry, he said.
Marv Patten, Dairy Bureau chief for the state Department of Agriculture, said he cannot recall any complaints coming into the agency since the system started operating.
"I see this, from a regulator's viewpoint, as being a plus-plus for the dairy industry and the community," he said. "It's an economically viable means of meeting nutrient-management requirements and being more socially acceptable."
ANDGAR Corp.: www.andgar.com
Environmental Resolutions: Troy Hartzell, vice president, 208-280-1857.