GHGMP Feature Articles

New composting process beats the weather and avoids urban-sprawl conflicts

Pilot project paves the way for successful liquid manure compost system

A B.C. lower mainland company is fine tuning a process that can compost liquid hog manure in an odorless and environmentally-sound manner in a densely-populated region that records as much as 48 inches of rainfall over a six-month period.

It is a technical challenge, admits Dr. John Paul, a former Agriculture Canada research scientist, who launched Transform Compost Systems Ltd. in Abbotsford about seven years ago. He holds a PhD in soil microbiology and soil nutrition from the University of Guelph. While the company is familiar with designing more conventional composting systems, this is their first system using liquid hog manure.

Paul evaluated a pilot liquid manure composting system on a 300-sow farrow-to-finish Abbotsford-area farm over the past year. His company is now building a farm-scale system, designed around a covered concrete pit or channel. The composter is designed to convert about half a million gallons of liquid manure into a nutrient rich, dry organic fertilizer. It will handle about half of the farm's annual manure production. The rest of the manure will be applied to cropland and a woodlot.

"With the loss of nearby cropland for manure application, these producers needed to find another option for handling manure," explains Paul. In earlier work with the hog producer, he had evaluated various manure composting processes - including anaerobic digestion. A process described as bio drying actually intensifies and accelerates the conventional dry composting process. After six to eight weeks, the liquid manure is converted to a dry organic fertilizer with higher nitrogen content than conventional compost. "The process relies on using the heat energy within the manure to evaporate the moisture," says Paul.

When land is limited

An environmentally sound and economical liquid manure composting system provides another manure management option to hog, dairy and poultry producers, and in some parts of the country, beef operations using liquid manure systems. But, it is particularly good news for producers also dealing with urban pressures and the challenge of managing manure on a limited land base.

"We haven't answered all the questions yet," says Paul. "But we have a process that appears to provide another nutrient management option. It is clean and odorless and perhaps most importantly, resolves the issue of trying to land-apply large manure volumes."

The liquid manure composting project was initiated through contribution by the soil sector of the federal Greenhouse Gas Mitigation Program for Canadian Agriculture. The program, designed to raise producer awareness of greenhouse gas issues and demonstrate practices that help reduce emissions, is administered by the Soil Conservation Council of Canada. Across the country, producer-lead organizations such as the Abbotsford Soil Conservation Association are part of provincial Taking Charge teams, which direct demonstration projects. The development of the farm scale system has some financial support from the Pork Industry Development Fund and the Agriculture Environment Initiatives program, administered by the B.C. Agriculture Council.

Paul's bio drying composting process eliminates much of the methane gas associated with manure storage, filters out ammonia which contributes to odor, and will make it easier to better manage soil nutrient requirements reducing the risk of surplus nitrogen being leached from the soil, or lost to the atmosphere as nitrous oxide, a potent greenhouse gas.

A unique process

While there are similarities in dry and liquid manure composting processes, there are also striking differences. A common dry-manure system involves blending nitrogen and carbon sources - manure with straw or wood chips, for example - windrowing or piling the material on top of the ground and turning it every few weeks to incorporate more oxygen to complete the process over several months.

Transform's liquid composting system at Abbotsford involves construction of a 20-foot wide x 250-foot long, watertight, concrete channel or pit. Due to high fall and winter rainfall, the channel will be covered with a double polygreenhouse shelter.

The liquid manure, which contains six to eight percent solid material, is pumped from storage pits under the floor of the barn and blended in the channel with a bulking agent such as dry horse manure. "We're aiming for a mixture with 65 to 75 percent moisture," says Paul. "Other litter sources could be used such as shavings or wood chips and we have used poultry litter in the past. Dry horse manure works well and also assists in improving environmental sustainability in the horse industry."

The liquid manure/bio drying process has a few key unique elements compared to conventional windrow composting.

The system uses aeration pipes that lie on the floor of the channel and pump air into the composting material. It is computer controlled to add airflow and oxygen as required. Another difference is continuous mixing. Rather than turning a windrow once every few weeks, this system uses a posthole-auger type device, mounted on a rail above the channel, that travels back and forth continuously mixing the compost material.

Heat in the 65 to 80 degree Celsius range, produced by composting material, evaporates moisture, which is removed from the shelter through a ventilation system. The ventilation system is equipped with a biofilter to remove ammonia.

A sequential batch

As well, rather than being a straight batch system that stops "working" before another batch is started, Transform has developed a sequential batch process - with more liquid manure continually added to the process.

"Once we make the initial blend of liquid hog manure and dry horse manure, we expect to add more liquid manure likely every couple days," says Paul. The exact timing hasn't been determined, but eventually adding liquid hog manure will have to stop so the batch can actually complete the composting process.

"At some point we won't add any more liquid hog manure," he explains. "We'll continue aeration and mixing until the composting process is complete and we will have a relatively dry, high-nutrient, organic fertilizer. The channel will be cleaned out and new batch will be started." The complete process should take about eight weeks.

An 11 by 20-foot aerated bunker was used in the pilot project to evaluate the process. With proper ventilation and use of bio filters, it is an odorless process, says Paul. "And the end product is odorless as well " he says. "If we are going to develop these systems in areas where farms are close to urban centres or rural acreages they have to be odorless."

Commercial product

The bio drying composting process, which retains more nitrogen in the compost than a conventional windrow system, produces an organic fertilizer with potential commercial value. Paul expects the product could be bagged and marketed to home gardeners or used for high value commercial crops as well as lawns and sports fields.

Paul estimates the capital cost of building the farm-scale system at about $100,000. That will include the cost of the concrete pit, aeration and mixing equipment.

"By today's standards, a 300 sow farrow-to-finish operation isn't a large hog farm," says Paul. "But we're still evaluating how the full-scale composting system will perform. If it performs as we expect, there's no reason the scale can't be increased or the system duplicated to handle larger manure volumes."

Design and engineering work for the farm-scale project is now underway. It is expected the system will be built and operating by early 2006.