Can You Harvest Waste?

Composting for fun and profit.

Cover Photo:  Twelve-inch lateral pipes every 2 feet on-center are installed to capture the heat from composting material.

It is no secret that farmers have mastered the ability to harvest a crop. Many farmers are discovering that they are also able to harvest energy from their natural surroundings: the wind and sun and the waste on their farms to generate power, cut operation costs and, in some cases, identify new sources of income.

Medium and large-scale livestock farms are finding ways to implement renewable energy alternatives for financial and environmental reasons.

“Ninety-eight percent of all modern agriculture relies on natural gas, petroleum and fossil fuel byproducts,” said Josh Nelson, director and partner of AgriLab Technologies. “It is projected and anticipated that fossil fuel costs will double in the next two to four years.”

Composting organic material and converting it into useable energy is one way farms can reduce their dependence on fossil fuels. All farms generate organic waste that can be composted. For livestock farms, that organic material comes in the form of manure. Composting is either an aerobic or anaerobic process; both of which have the potential to generate energy. Anaerobic composting is based on fermentation and occurs when little to no oxygen is present. Anaerobic Digestion Systems (ADS) are being installed on farms to capture methane, a natural byproduct of the anaerobic composting process. Nelson cautions that ADS systems can be costly to install and can be dangerous because methane is explosive and odorless, making a leak hard to identify.

The middle of the barn where all of the heat from the composting material is collected and converted into usable energy.
The middle of the barn where all of the heat from the composting material is collected and converted into usable energy.

Conversely, aerobic composting requires oxygen to decompose. Rather than producing a gas, aerobic composting produces heat, which can be captured and reused as a source of energy. Traditionally, aerobic composting is set up in a chamber or an outdoor windrow and requires continuous flipping and turning to provide enough oxygen. Nelson has developed a system that will allow aerobic composting inside a dedicated facility.

“We know that we can generate 1,000 BTUs per ton of material being composted per hour from properly managed composting material,” Nelson explained. Depending on the size of the farm, enough energy can be produced to power the entire operation with excess that can be sold back to the public power grid.

Seven years ago, New York farmer Sean Quinn began composting all of the bedding used on his 2,000 heifer replacement farm. His deep-rooted passion for conservation led him to research ways to reduce waste even further on his farm. Through his research, Quinn met Nelson and committed to installing a Passive Aerated Windrow System (PAWS) on his farm.

The technology used on Quinn’s farm is simple. First, he built a 55-by-130-foot barn and divided it in half. Two cement walls were poured to create separate production areas, allowing for expansion as the volume of composting increases. Twelve-inch diameter PVC pipe and fittings were laid every 2 feet on center to direct the heat from the compost into a manifold system where the heat will be captured and used to generate hot water and electricity for the farm. Ideally, the final composted material will be clean enough to be reused as bedding for the older heifers on the farm.

6-inch piece of drainage pipe at the isobar array, the fundamental component of the thermal heat recovery system.
Looking into the 36-inch piece of drainage pipe at the isobar array, the fundamental component of the thermal heat recovery system.

A 36-inch piece of ADS pipe is the foundation of the entire process. Inside 10 stainless steel ISO #10 pipes fill the chamber. This isobar array assembly is sealed and charged with a refrigerant fluid designed to capture and transfer the heat. During the process, the isobar will also create condensation. “Because the system is a sealed environment, theoretically the water from the condensation should be pure enough for drinking water for the calves,” Quinn explained. The water will undergo testing before being used, but in Quinn’s quest for zero waste on the farm, his goal is to use the water for the herd.

Though the pipes are exposed during construction, everything will be insulated before being used to avoid heat loss. “The key thing is to conserve energy and not to use any fossil fuel,” Quinn emphasized. Each of the PVC ball valves that will control each zone within the barn will be manually operated. “I will be in and out of the barn all day, it’ll be easy to monitor each zone and turn the valves on or off as necessary,” he added. Using the same materials as those used with outdoor woodstoves, it is possible to transport the heat generated up to 500 feet with minimal loss for easy use on the farm, Nelson noted.

Even though the project took five years from the time it began until its completion in the fall of 2010, Quinn is eager to benefit from the exceptionally high return on investment. The thermal heat system will generate more hot water and heat than the farm can actually consume. “We expect to save $220,000 annually on energy costs. If a second phase of the project can be implemented, then electricity can also be produced, and then the savings will double. More testing will be necessary to determine the feasibility of the second phase,” he said.

close-up view of lateral pipes
A close-up view of lateral pipes used to transmit the heat captured by composting material.

A thermal heat recovery system is not only for large-scale livestock facilities. Farms with as few as 25 to 30 head of cattle have the ability to produce enough compostable material to benefit from a thermal heat recovery system. “Enough manure is generated on a dairy of this size to heat all of the buildings on the farm,” Nelson noted. Despite an initial investment ranging from $37,000 to $100,000, depending upon the size of the system, Nelson urges farms to consider a thermal heat recovery system because the benefits will outweigh the investment.

Not only will a thermal heat recov-ery system reduce utility expenses, it also provides additional benefits that lead to reduced expenses. “Composting shrinks the volume of material you have to haul away by 35 to 45 percent,” Nelson explained. That equates to fewer trips, less fuel and decreased labor associated with moving the material.

“A lot of people don’t realize that the planet loses 1 percent of our topsoil annually,” Nelson explained. Properly composted material can be spread over working fields to counteract soil erosion and increase the fertility of the fields. Well-managed compost can also provide income. “High-quality compost typically goes for $45 to $50 per yard. Farms can sell the abundance of compost they have and generate additional income,” he concluded.

Editor’s note: This article originally appeared in the February 2011 issue.