UF researchers develop method to remove phosphate from water, using biochar

May 11, 2011

GAINESVILLE, Fla. — Phosphate poses one of Florida’s ongoing water-quality challenges but a process developed by University of Florida researchers could provide an affordable solution, using partially burned organic matter called biochar to remove the mineral.

The process also yields methane gas usable as fuel and phosphate-laden carbon suitable for enriching soil, according to Bin Gao and Pratap Pullammanappallil, assistant professors in UF’s agricultural and biological engineering department, part of the Institute of Food and Agricultural Sciences. Crop wastes would provide raw material for the biochar.

A laboratory study demonstrating the effectiveness of biochar for phosphate removal appears in the current issue of the journal Bioresource Technology.

The study involved beet tailings, which are culled beets, scraps and weeds removed from shipments of sugar beets destined for processing to make sugar, said Gao, one of the authors. In the U.S., sugar beets are grown primarily in the Northeast and upper Midwest, but the technology can be adapted to other materials, he said.

“It’s really sustainable,” Gao said. “We will see if it can be commercialized.”

UF has filed a patent application for the phosphate-removal process, Gao said. Wastewater treatment facility representatives have shown interest in the technology, he said.

Phosphate is used to make fertilizers, pesticides and detergents. Florida produces about one-fourth of the world’s phosphate.

Florida’s surface waters sometimes contain large amounts of phosphate, arising from natural sources or human activity. Because the chemical can spur algae growth, it has caused water-quality concerns in some communities.

Some water treatment plants filter phosphate from wastewater but existing methods have drawbacks, including high cost, low efficiency and hazardous byproducts.

In the study, researchers started by collecting solid residues left after beet tailings were fermented in a device called an anaerobic digester, which yields methane gas. The material was baked at about 1,100 degrees Fahrenheit to make biochar.

The biochar was added to a water-and-phosphate solution and mixed for 24 hours. It removed about three-fourths of the phosphate, much better results than researchers obtained with other compounds, including commercial water-treatment materials. The phosphate-laden biochar can be applied directly to soils as a slow-release fertilizer.

The research team plans to investigate whether biochar could remove nitrogen from wastewater. Nitrogen can stimulate algae growth in surface water.

The research team has also been testing the potential for biochar to purify water of heavy metals including lead and copper, he said. Part of the challenge involves pinpointing raw materials with the greatest affinity for a particular contaminant. And used biochar packed with toxic metals would have to be regenerated or handled as hazardous waste.

Previous UF studies have demonstrated the potential value of producing methane gas by fermenting crop waste. Pullammanappallil specializes in this area and regularly collaborates with Gao on biochar studies.

Perhaps the biggest challenge researchers face is making biomass technology more cost-effective. Pullammanappallil recently helped design, build and operate an anaerobic digester at an American Crystal Sugar Company facility in Moorhead, Minn.

The digester processed beet tailings like those used in the study, and worked well, said Dave Malmskog, the company’s business development director at Moorhead. But when the research grant funding the project ended, the company found it wasn’t practical to continue.

Nonetheless, the researchers remain optimistic that the process can be made cost-effective.

“Florida agricultural industries could benefit,” Pullammanappallil said. “You could do this with any biomass — sugarcane bagasse, citrus pulp.”