Don't restrict biosolids without understanding their phosphorus content, says UF expert

GAINESVILLE, Fla. — In an effort to protect Florida’s water quality, state regulations governing the application of biosolids to fields, forests and other areas may be changed – but the move could unnecessarily restrict beneficial uses of the material, cautions a University of Florida expert.

Derived from sewage sludge, biosolids can be used to fertilize plants and enrich soil, said George O’Connor, a professor with UF’s Institute of Food and Agricultural Sciences. The state recycles about 80 percent of its sludge this way, but critics say biosolids release too much phosphorus, a nutrient considered the state’s No. 1 water-quality concern.

O’Connor recently completed a four-year study showing there’s actually wide variation in the amount of soluble phosphorus biosolids contain, depending on the processing methods involved, he said. Also, some biosolids release more of their phosphorus than others.

“We’ve identified a method that can be used in the laboratory to predict how much phosphorus biosolids will release,” said O’Connor, a soil chemistry expert in UF’s soil and water science department. “This is a big step toward understanding the true environmental impact of biosolids and using them more efficiently.”

A mineral essential for plant growth, phosphorus can harm lakes and streams by causing algae blooms that block sunlight and consume oxygen needed by other organisms. Phosphorus typically reaches watersheds when rain and irrigation leach it from fertilizer and animal manure.

The UF study confirms earlier findings showing conventionally prepared biosolids release about half as much phosphorus to plants as chemical fertilizers. Biosolids prepared using
methods that result in higher phosphorus content release about the same amount of the nutrient as fertilizer, whereas heat-treated varieties release only about one-tenth as much.

O’Connor and colleague Herschel Elliott of Penn State University conducted the study with a grant from theWater Environment Research Foundation, which funds research related to wastewater treatment issues. The study will be published later this year.

Florida’s Department of Environmental Protection is preparing to revise its regulations governing the use of biosolids in so-called land applications, which include farming, forestry, construction and highway beautification, O’Connor said. There are no restrictions on the phosphorus content of biosolids, but the revisions may limit the total amount of phosphorus applied to land via biosolids.

“It’s possible Florida will adopt across-the-board restrictions on biosolids without regard to the amount of phosphorus they actually release, and that would be a mistake,” said O’Connor, who serves on the department’s technical advisory committee on biosolids regulation. “Such a move would unnecessarily restrict the use of biosolids that release phosphorus in small amounts, raising costs for agricultural producers and municipal utilities.”

The technical advisory committee will meet May 9-10 in Tallahassee to discuss proposed changes to the current biosolids land-application regulations, said Maurice Barker, residuals coordinator for DEP’s domestic wastewater section. The meeting is open to the public.

“While we will be proposing requirements, such as nutrient management plans, that are related to nutrients including phosphorus, I really can’t say for sure what requirements will ultimately be adopted in the final revised regulations,” Barker said. “We do expect the revision to be finalized by the end of the year.”

Biosolids are produced by breaking down solids in sewage sludge using naturally occurring bacteria, then sanitizing and dewatering the material. The result is a black, soil-like material that contains important plant nutrients including phosphorus, nitrogen, calcium, magnesium and sulfur; biosolids also help soil retain water.

All 50 U.S. states dispose of sewage by producing biosolids, using some of the material for land application, said O’Connor, who recently received the American Society of Agronomy’s 2005 Environmental Quality Research Award to honor his decades of biosolids research.

Florida produces 300,000 dry tons of biosolids each year and imports another 100,000 dry tons; 66 percent of the total is used in land application, 17 percent is placed in landfills and 17 percent – the highest-quality material – is sold to consumers for use in home gardening, he said. If restrictions curtailed land application of biosolids, a greater portion would probably go into landfills.

“The biggest challenge for Florida and the nation is to develop consistent, scientifically sound regulatory strategies for dealing with biosolids,” O’Connor said. “We need to take advantage of the benefits biosolids offer, but use them in ways that help us manage the overall amount of phosphorus in the environment.”

One way to reduce the possibility of phosphorus runoff would be to match specific types of biosolids to specific application sites, based on the soil’s properties and its need for phosphorus, he said.

O’Connor’s current research, funded by the Florida Water Environment Association, is investigating biosolids produced and used in Florida to determine their environmental impact.

“Right now, Florida is using multiple types of biosolids for land application,” he said. “Building on our previous research, we want to identify any products that could constitute a problem and determine how we could better manage them.”

Credits

Writer

Tom Nordlie, tnordlie@ifas.ufl.edu, (352) 392-0400

Source

George O'Connor, gao@ifas.ufl.edu, (352) 392-1803, ext. 329