Published on 10/18/01

Recycling System Makes Most of Manure

The manure from dairy cattle can be recycled in an environmentally friendly way. No, not just in compost. It can actually provide energy, feed and maybe even drinking water for cattle, says a University of Georgia scientist.

Finding ways to effectively use the manure on dairy farms is a problem for farmers. And to stay competitive, dairies are now raising more cattle on less land. It's becoming critical to find ways to handle all that waste.

Larry Newton, an animal and dairy scientist with the UGA College of Agricultural and Environmental Sciences, says the manure doesn't have to be a problem anymore. In fact, it can be a valuable resource.

Newton and a team of UGA engineers, scientists and economists have created a manure management system that can take recycling to the limit. It can clean up the environment, maintain a healthy water supply and even help cows give more and better milk.

Working out a system

Newton's system combines parts of other systems, such as fermentation and hydroponics, that effectively dispose of human and some industrial wastes in cities.

"We just have to find the right management that works for cattle and then work out the economics to see if it's worth the producer using the system," Newton said.

The process

To start the process, the manure is flushed from the dairy barns where cows are kept and milked. It's then placed in a settling basin. The solid waste settles to the bottom. The liquid waste is then siphoned from the top and sent to a machine called an anaerobic digester.

The remaining solid waste in the basin can be composted or treated to produce a product more easily transported away from the dairy and applied as fertilizer.

The digester uses a fermentation process without oxygen to produce methane gas, which reduces the odor.

"The main purpose of the digester is to convert the plant nutrients in the liquid waste into more digestible forms for plant roots to absorb," Newton said.

The nutrient-rich wastewater is then sent through greenhouses, where forage plants are grown in trays using the wastewater without soil. This is called hydroponic production.


The methane gas from the digester can power water heaters or heat the greenhouses where the digester liquid is used to hydroponically grow the forage plants cattle can feed on.

After the plants filter and absorb the nutrients from the digester liquid, it could potentially be used for the cattle's drinking water. This would reduce the use of water pumped from the groundwater supply.

Newton is confident the system will work. But it may not be for everybody.

"It will be there as an option for some producers, especially those with a limited land base for dairy," he said.

Newton will test his system at the Coastal Plains Experiment Station dairy facility in Tifton, Ga.

"That's what we (farm scientists) are here for," he said. "We can test to see if things like this work and where they might fit into a farmer's operation."

Extra benefits

Because of the change in seasons and feeding practices on most dairies, fresh forage is not always available to cattle. But cattle that feed on fresh forage could produce more milk, Newton said. This could help farmers and shoppers. Newton's system could provide year-round forage.

A bonus is that conjugated linoleic acid is found in highest concentrations in the meat and milk of animals that eat fresh forage. Conjugated linoleic acid has been found to reduce bad cholesterol and the growth of certain cancers, Newton said.

Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.