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Hog manure plus mortalities equals compost

March 19, 2008  by Tony Kryzanowski

A composting vessel for
mortalities developed by hog producer Puratone Corporation can also be
used for hog manure, either on its own or as a mixing agent with

A composting vessel for mortalities developed by hog producer Puratone Corporation can also be used for hog manure, either on its own or as a mixing agent with mortalities.

compost1The Biovator: primarily a long, insulated galvanized vessel.

While the science to convert manure into compost is well-established, intensive hog and poultry businesses now have a new means of converting dead animals into valuable compost.

Hog production company Puratone Corporation has developed a composting device called a Biovator that can convert about 2 lbs. of mortality mixed with wood shavings to about 1.6 lbs. of pathogen-free and nutrient rich compost.


While it was developed to help intensive livestock producers efficiently manage mortality, the Biovator will also compost manure, either on its own or as a mixing agent with dead animals. However, using manure as a mixing agent does decrease the capacity of the vessel because it has less carbon content. Carbon is a key ingredient in the composting process, and more manure needs to be added to achieve the same carbon content as wood shavings. Therefore, using manure reduces the amount of space in the vessel for dead animal parts.

“Bedding compost can be run through as-is because the carbon to nitrogen ratio is close to that required for proper microbial activity,” says Shawn Compton, general manager of the Biovator division at Puratone Corp. “The dry component of separated hog manure will also compost nicely but may require the addition of straw or shavings, depending on the tested carbon to nitrogen ratio.”

Since arriving on the market in 2004, more than 70 Biovator units have been sold in North America. The product is marketed in the United States by Seven Star Enterprises, of Mankato, Minnesota.

Compton says the technology is unique to the livestock industry. It was developed by Puratone out of necessity to find an alternative dead stock disposal method to rendering and outdoor composting in bunkers. The company is first and foremost a hog producer, managing operations with a total of about 60,000 sows, as well as a feed mill business.

“Puratone was looking for a better mortality management method that addressed its concerns related to biosecurity,” says Compton, “so they conducted a significant amount of research and development into industrial composting, which resulted in the Biovator.” It worked out so well that they decided to market the product.

Paustian Enterprises, an Iowa-based farrow-to-finish hog producer, purchased a Biovator as an alternative to incineration or rendering in 2005.

“It’s probably worked beyond our expectations,” says company co-owner, Kent Paustian. “It does a good job. Originally, I had figured the payback versus the fuel we used in our incineration method to be about three years. That was before the jump in fuel prices. The payback ended up being barely over two years.” He adds that his calculation includes the extra expense of having to purchase wood shavings.

Kent co-owns the business with his brother Ross, and father, Dale. The operation manages about 900 sows on a farm about 20 miles west of Davenport, and the family business has been in operation since 1973.

compost2Biosecurity is the main driver for farms opting to install a Biovator. The farms are anxious about the number of vehicles coming and going. And economically, composting is said to be cheaper than incinerating and rendering in some areas.

The Biovator is primarily a long, insulated galvanized vessel with a stainless steel shell that costs about $1,000 per foot. There are three sizes available: a starter unit for operations that need to dispose of 175 lbs. of mortality per day, a mid-sized unit at 350 lbs. per day, and the largest unit at 500 lbs. per day.

“The largest Biovator is geared more for a 3,000 sow, farrow-to-early-wean operation where you will need that 500 lbs. of capacity per day,” says Compton.
That was the size purchased by the Paustians because it fit with their production output. The ease of operating this composting device – in addition to the fuel savings – has improved the task of dealing with dead animals at the Paustian operation.

“We sure don’t miss working with the incinerators,” says Kent. “Not only do you have fewer mechanical parts with the Biovator and no issues like smoke to deal with, we were also always having to clean out the ash and that sort of thing from the incinerators. With the Biovator, there are no environmental problems.”

Rendering, instead of incineration, was an alternative for the Paustians, but that raised issues of biosecurity. Compton says biosecurity is the primary concern for the majority of Puratone’s customers.

“The biosecurity issue is the main driver at this point,” says Compton. “People just don’t want vehicles coming and going. Economically, composting is a lot cheaper than incinerating and rendering in some areas.”

This composting technology is really geared toward the hog industry because the Biovator method is a continuous flow method. The nature of raising hogs can almost guarantee a continuous flow of dead animals. The Biovator needs organic material from dead animals and shavings added to it at least once a week to maintain the heat of the conversion process within the vessel. The cattle industry does not operate that same way, with a guaranteed flow of dead animals.

However, Compton says one way to keep the composting process active is to use the vessel to compost manure when it is not active with dead carcasses. He says intensive cattle producers should conduct a careful cost-benefit analysis to see if the Biovator makes sense for them. The technology has – so far – proven itself within the hog and poultry sectors.

When selecting a site, one important issue to consider is how close the site is to the mortality exit door, for efficient management of carcasses. In extreme cold conditions, distance to a winter exhaust fan should also be considered, so that heat can be provided from a barn facility to the vessel as required, so that the temperature in the vessel can be maintained at above 100 degrees Fahrenheit.

The vessel should also be located near power and water sources, and near a supply of wood shavings or manure, which must be added to the carcasses to achieve proper composting. Finally, the unit should be placed on level ground.

compost3This composting technology is really geared towards the hog industry because the Biovator method is a continuous flow method, and the nature of raising hogs can almost guarantee a flow of mortalities.

The composting vessel consists of a slowly rotating steel drum that has steel paddles mounted on the inside walls. The paddles are mounted in a spiral-shaped pattern at varying spaces to allow material to move in one direction at a consistent speed inside the vessel so that good biological activity can be achieved. It has loading, inspection and discharge openings. The discharge opening has a screen that allows only compost to pass through, while stopping large bones from being discharged.

The vessel is supported on side steel rollers as well as a front pillow block. The steel rollers are supported by a steel skid. It rotates at a speed of four revolutions per hour.

The recipe for the conversion process consists of measured quantities of mortalities to wood shavings and water. Although many Biovator owners use wood shavings as a carbon-based additive, any granular organic material with high carbon content should work. Long fibrous material, like hay or cornstalks, can be used. However, these materials have poor moisture retention properties.

Users can save on the purchase of wood shavings by substituting the manufactured compost itself for a portion of the wood shavings additive.
Puratone says experience to date indicates that up to 50 percent of the fresh shavings requirement may be substituted with finished compost.

After the vessel is loaded, the composting process begins.

While anaerobic activities are underway inside the carcasses, aerobic micro-organisms are also in action through the vessel, breaking all organic matter down into humus-like material that is consistent in quality and can be used as a soil-enhancing agent, says Puratone.

With any biological process, odor can sometimes be a concern. Puratone says that if the vessel is not overloaded, the proper temperature is maintained and the carcasses are totally covered with enough wood shavings, odors are sufficiently suppressed or absorbed. Using an insufficient amount of additive material is the single greatest factor causing odors in and around the vessel.

Paustian says it took about a month to establish the optimum recipe of wood shavings to dead animals and afterbirth to deliver consistently high-quality compost. However, the Biovator has run problem-free and continuously since its installation in 2005. He says they have gotten excellent service support from Seven Star Enterprises, including an upgrade on a door seal to deal with some minor seepage. Even after a couple years in operation, he says the supplier continues to maintain contact with them.

The composting temperature inside the Biovator must remain higher than 100 degrees Fahrenheit. In less than seven days in summer or 14 days in winter, the bulk of the composting process is finished and the operator can discharge the compost and pile it up, or recycle it back into the composting vessel with the addition of more mortalities and less wood shavings.

Each pound of carcass requires about .07 cubic feet of wood shavings. Other input combinations involving various amounts of wood shavings, liquid hog manure and recycled compost work equally well.

Paustian Enterprises gathers and spreads the compost generated by the Biovator on its farmland, although the amount is not sufficient to have reduced their need for commercial fertilizer.

Compton says another potential market for the Biovator is in slaughterhouse applications. However, Puratone Corp. will have to engineer a unit capable of handling much more capacity, given the amount of organic material generated daily by these operations.


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