Technology Used to Remove Sand, Incinerate Manure

By Ron Johnson, Dairy Editor
Thursday, March 15, 2007 12:18 PM CDT

Ever since the invention of the pitchfork, technology has been applied to manure management.

And so it continues.

One item of manure handling technology is sand settling lanes. These lanes remove sand used for bedding from manure before it goes into storage.

Brian Holmes, a UW-Madison agricultural engineer, talked about sand settling lanes during last week's Manure Bioconversion Technology Conference at Madison. Sand settling lanes are not "brand new," but they are gaining interest, Holmes said.

He described a "typical flush-flume and sand settling lane" system. Manure is scraped or flushed into a concrete lane. Sand, being heavier than manure, settles to the bottom of the flume, much like particles of gold settle out in a prospector's pan.

From there, the sand is cleaned out of the flume and piled to dry. Some farms, noted Holmes, use two settling lanes. That way, one can be used to settle out a new batch of sand while a previous batch gets a longer drying period in the second lane.

Meanwhile, separated manure is pumped into one or more storage lagoons or pits. Many farms use pumps that can move 2,000 to 2,500 gallons of liquid manure per minute. These pumps are fitted with screened inlets to keep out debris.

Sand settling lanes are built wide enough to let a skid-loader in an out. Their length can vary, depending on the space available and their slope. Their slope is usually very slight - about 0.25 percent, according to Holmes. Actual lane depths range from eight to 12 inches, although walls along the lanes can be several feet high.

There are other aspects to these systems, too. Ramps that allow equipment access, sand drain slabs and sand mixing and storage slabs are often included.

Separation, digestion

Not many dairy farms that use sand as bedding also try to run the manure through an anaerobic digester. But Fond du Lac County's Lake Breeze Dairy is doing just that.

Holmes briefly described what he called a "fairly complex" system. It includes a railroad tank car mounted 15 to 20 feet off the ground at one end of the freestall barn. This tank holds the system's flushing water.

There's also a manure pump, two rotating separators that remove the sand, two anaerobic digesters and a pair of generators that produce electricity from the methane gas that's a product of manure digestion. In addition, three screw presses take digested manure solids to storage or to long-term storage basins.

Manure burned

Technology has also brought methods to burn manure and at the same time create usable energy. Mark Wiese, Greenleaf, talked about the manure incineration he and his brothers, Ken, Dick and Dave, use on their 2,000-cow Wiese Brothers' Farm in southern Brown County.

He described the commercial Elimanure system they use as a "first-of-a-kind process designed to consume dairy manure." In it, a "biodryer" dries liquid manure to about 12 percent solids. These dried manure solids are then fed into a combuster, where they are burned.

This burning of the manure heats water. Steam from the hot water powers a turbine. The result is electricity from burned manure.

But the Wieses chose this method of manure management for reasons other than its ability to produce electricity. The Environmental Protection Agency (EPA), he explained, classifies their 3,700-animal unit operation as a "large" farm, and with that classification come certain rules regarding manure management.

For example, the EPA's "confined animal feeding operation" (CAFO) rules require large dairy farms to reduce the amount of phosphorus in the soil and the amount applied. They also aim to reduce water pollution. Incinerating manure is one way to meet these rules, Wiese indicated.

There are other issues around manure, he pointed out. Wiese noted the "extreme pressure in northeast Wisconsin to eliminate land spreading of manure. And, for their farm, more land is needed to apply manure than for growing feed for the cattle, he added.

Urban expansion in the area also convinced them to invest in a method that burns the manure. With manure there's usually odor, but by incinerating manure, the odor is gone. All that's left to apply to fields after burning is concentrated ash.

That also lowers application costs. Wiese said his farm's manure incinerator has eliminated the need to haul some 4,500 tanker trucks of manure each year. Instead, they now apply 90 small trailer loads of ash annually.

Disease-causing organisms in manure have also become a concern. But when manure is burned, these pathogens are gone.

While anaerobic digesters are the answer for some farms, Wiese said that was "not an option" for him and his brothers. Digested manure not dried and used as bedding still has to go someplace, such as farm fields.

The bottom line for their farm, Wiese concluded, was to "get the manure off the land." They've done that by burning manure.

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