Phosphate poses one of Florida’s
ongoing water-quality challenges, but a process developed by Univ. 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 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.”
