Turning On-Farm Waste Into Energy

The George family have lived at Brookside Dairy since 1781. They have expanded their dairy herd to 550 dairy cows, kept in a 200- by 300-foot freestall barn with 326 stalls in 2001.

The high ventilation barn features 28 five-foot fans at one end that produce a 7.5 mile per hour wind to keep the cows cool during hot weather. A sprinkler system uses water to cool the cows, and rubber matting on the floors provide cushion for the cows as they walk through the barn.

With the expansion came increased electricity costs for the new barn and more manure waste with the additional cows. The Georges began researching options to address the new issues that arose, specifically an anaerobic methane digester.

Mr George says there were several reasons - "economics, odour control and the resulting better quality fertiliser" - for considering a digester on their dairy operation.

The Georges sought help from Jim Resh, of the Indiana County Conservation District, to investigate installing an on-farm digester. They found a digester would meet the specific needs they were considering.

The renewable energy produced through the biogas is set up to offset the farm's electricity use and/or sell the power at wholesale rates to the local utility.

The conversion to biogas results in less odour-causing compounds in manure in a typical liquid storage system.

The breakdown of manure in the digester converts the organic nitrogen into ammonium which, when spread on the fields, is more readily available when taken up by the plants, allowing for less nutrient runoff. The process also reduces weed seeds in the fields, causing less weeds growing among the crops.

The digestion process also reduces methane, a greenhouse gas, emissions which would otherwise remain in the atmosphere for nine to 15 years.

After deciding it was a viable option and met the needs of their farm, the Georges secured an Energy Harvest Grant from the Pennsylvania Department of Environmental Protection which is designed to help fund projects that address energy and environmental issues.

They opted to install an anaerobic digester, which means no oxygen is involved in the process of using the cow manure to produce a biogas of methane and carbon dioxide. Microorganisms in the manure perform the decomposition process.

The manure is removed with automatic alley scrapers from the barn and is combined with waste water from the milking parlor, along with food wastes from a local brewery and Pittsburgh restaurants.

Four times a day, 3,000 gallons of manure is pumped into the digester, which holds 260,000 gallons.

"The digester is like a cow -- it likes to be fed at the same time with the same quality feed every day," said Mr George.

The digester is a 14-feet deep concrete pit and covered with a dome made of plastic and cloth. A 100- horse power motor that is run on the biogas operates a 90 kilowatt generator to keep the digester in constant motion. All the machinery is automated and run through a computer system.

The manure spends one month rotating in the digester at 98 degrees Fahrenheit after which it is pumped to the manure solids building where the nutrient-rich liquid, or effluent, is pressed out to a 400,000 gallon holding pit. The effluent is pumped from the pit and spread onto the fields every two months.

The separated dried solids are used for bedding the freestalls, which require 20 tons per week to keep the stalls clean and dry.

Pennsylvania is home to more than 50 operational or proposed anaerobic digesters, with more than half in the Chesapeake Bay watershed. Most digesters are located on dairy and swine farms.

The capital costs for installing a digester are dependent on many factors including number of animals, type of digester and site-specific conditions. The estimated range is from $500,000 to more than $1 million.

Mr George believes, in the five years since the digester was installed, Brookside Dairy has already seen the benefits of the investment.

"The digester produces enough energy to power the farm in addition to 55 homes each day," said Mr George.

"We've also seen an improvement in the quality and yield in the crops with the better fertiliser we can spread on the fields, and we've had no negative effect on the cows' health as a result of using the solids for bedding."

All told, the time and cost involved in adopting this project has had a positive effect on Brookside Dairy, making good business and environmental sense.