Disposal of animal manure is one of the biggest problems facing agriculture today. Now, scientists with the Agricultural Research Service may have found a way to convert some types into a material that can be used to help keep the environment clean.

Currently, animal waste is valued at between $3 and $10 per ton, and most of it is used as a fertilizer. Unfortunately, when added to soil, a buildup of nutrients — namely nitrogen, phosphorus and potassium — can occur, especially if it's applied repeatedly to the same area. This can lead to non-point source pollution runoff into rivers and streams as well as nitrogen leaching into shallow groundwater, which has caused some states to introduce legislation that would limit such applications.

Isabel Lima, a chemist in the Commodity Utilization Research Unit at ARS' Southern Regional Research Center in New Orleans, La., has discovered a potentially less detrimental way to utilize animal waste. She has found a way to convert it into activated carbons, which soak up unwanted pollutants and can be used for environmental remediation.

Right now, bituminous coal and coconut shells are the two materials most commonly used by U.S. manufacturers to make activated carbons. However, coal is an expensive and nonrenewable resource, costing between $60 and $80 per ton, while coconut shells are not readily available here.

Poultry litter focus

So far, Lima has focused her studies on poultry litter, which is inexpensive and available. When pelletized and activated under specific conditions, the litter becomes a highly porous material with a large surface area. In early tests, these carbons performed very well in adsorbing copper, which suggests they may do well as a wastewater filter for other metal ions. Their adsorption rate may also make them more cost effective than carbons currently on the market.

This technology could provide farmers with an acceptable way to beneficially use their animal manure, especially in environmentally sensitive areas with dense poultry populations, such as Maryland's eastern shore.

Lima was to present her findings at the WEF/AWWA/CWEA Joint Residuals and Biosolids Management Conference and Exhibition in Baltimore, Md., Feb.19-22.