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Using sewage sludge as fertilizer

Using organic waste presents a win-win situation for municipalities, agriculture

MADISON, WI, JANUARY 31, 2003 – Sewage sludge has the potential to boost production for certain crops while addressing the increase in the amount of waste and the growing scarcity of landfills, according to scientists at the University of Florida.

Using organic waste as fertilizer is not a new concept. Before the 1940s, when synthetic nitrogen fertilizer became widely available, animal manure and human waste were commonly used for improving crop yields around the world. This technique is receiving renewed interest as municipalities face increasing waste disposal challenges.

In a study conducted in Florida from 1997 to 2000 and published in the November/December 2002 issue of Agronomy Journal, scientists from the University of Florida’s Institute of Food and Agricultural Sciences compared the effects of different kinds of sewage sludge versus commonly used synthetic nitrogen fertilizer on the forage crop bahiagrass.

Researchers Martin B. Adjei and Jack E. Rechcigl studied yield, protein content, mineral content, and digestibility. Accumulation of heavy metals and nutrients in the crops, groundwater, and soil were also evaluated.

Funded in part by the Florida Department of Agriculture and Consumer Services, the study showed liquid forms of sludge are just as effective as traditional synthetic fertilizer. Some minerals such as phosphorus, calcium, and iron were higher in crops fertilized with sludge. In a very dry year, the water in liquid sludge can also enable nutrients to reach the crop’s rooting zone more effectively than synthetic fertilizer.

“Liquid sludge if processed and applied according to specific guidelines has the potential to boost production dramatically. It is low in pathogens, inexpensive, and environmentally safe,” said Adjei. Approximately half of Florida’s 2.5 million acres of bahiagrass are fertilized with synthetic fertilizer yearly.

Adjei added, "While we did observe negligible traces of heavy metals in crops, groundwater, and soil regardless of how the crops were fertilized, this was not significant nor surprising given Florida’s small industrial base and its successful efforts to prevent industrial sources of metals from contaminating sewage."

A survey by the U.S. Environmental Protection Agency showed the amount of sewage sludge generated in the United States increased from 8.5 million metric tons in 1990 to more than 12 million metric tons in 2000. At the same time, there has been an increase in public interest for finding alternative, environmentally sound solutions to waste disposal.

American Society of Agronomy. January 2003.