“Biochar” More Effective, Cheaper at Removing Phosphate from Water

Phosphate poses one of Florida’s ongoing water-quality challenges. A process developed by University of Florida researchers using partially burned organic matter called biochar could provide an affordable solution, however. The process also yields methane gas usable as fuel and phosphate-laden carbon suitable for enriching soil.

Phosphate is used to make fertilizers, pesticides, and detergents. Florida produces about one-quarter of the world’s phosphate, and its surface waters sometimes contain large amounts. 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 such as high cost, low efficiency, and hazardous byproducts.

A laboratory study demonstrating the effectiveness of biochar for phosphate removal is published in the current issue of the journal Bioresource Technology. Bin Gao and Pratap Pullammanappallil, assistant professors in University of Florida’s agricultural and biological engineering department, say that crop wastes could provide raw material for the biochar.

The study involved beet tailings, which are culled beets, scraps, and weeds removed from shipments of sugar beets destined for processing to make sugar. In the United States, sugar beets are grown primarily in the Northeast and upper Midwest, but the technology can be adapted to other materials. “It’s really sustainable,” Gao said. “We will see if it can be commercialized.”

The researchers collected solid residues left after beet tailings and fermented them in 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-quarters of the phosphate, which was much better than that removed by other compounds, including commercial water-treatment materials. The phosphate-laden biochar can also be applied directly to soils as a slow-release fertilizer.

The research team plans to investigate whether biochar could remove nitrogen from wastewater, as nitrogen can also stimulate algae growth in surface water. They have also been testing the potential for biochar to purify water of heavy metals including lead and copper.

 Perhaps the biggest challenge the 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 according to Dave Malmskog, the company’s business development director at Moorhead.

The university has filed a patent application for the phosphate-removal process and wastewater treatment facility representatives have shown interest in the technology.