Process Water:
Averting Environmental and Economic Peril

Water used in the processing of phosphate into the phosphoric acid that is used to make fertilizer hit the news again thanks to the string of hurricanes that whipped through central Florida this fall. During Hurricane Frances, a pond full of process water on top of a phosphogypsum stack in Riverview suffered a dam breach and millions of gallons of the acidic water spilled into the environment.

Cargill Crop Nutrition (now Mosaic Co.), the owner of the Riverview stack, was able to keep a lot of the water on its property, but some streamed off the property and into Archie Creek which empties into Hillsborough Bay. Process water is high in nitrogen and phosphorus, which over an extended period of time enables algae to thrive. The algae, in turn, can reduce the amount of oxygen in the water, killing marine life. Process water is also acidic and contains dissolved solids that can quickly kill aquatic life. While much of the water was treated to lower the acidity and the rain diluted the spill, the impact on the surrounding environment is not yet known.

Hurricane Jeanne caused another spill of 4.5 million gallons of process water from Cargill's Bartow Facility. The spill was contained on mined lands before it reached Peace River.

The threat of such spills made process water a regulatory, legislative and research focus in recent years. Experts at the Florida Institute of Phosphate Research (FIPR) have been asked to sit on committees to evaluate ways to avoid spills in the future and to find ways to improve the quality and lessen the quantity of process water produced during fertilizer manufacture. (Background information on process water issues)

In response to a 1997 spill of fifty million gallons of acidic water into the Alafia River that caused a massive fish kill, FIPR funded research to investigate the environmental impacts of using lime in the river to neutralize acid. The research showed that the lime will not improve the survival of fresh water fish, but it would significantly help the saltwater fish.

More recently, FIPR has formed a special Technical Advisory Committee (TAC) to seek short-term and long-term solutions for reducing the volume of process water the industry generates, improving the quality of the water that is stored and finding a better way to clean it at a reasonable cost. Like other FIPR TACs, this group of environmental, phosphate industry, consultant, academic and DEP experts is the point of exchange for technical ideas and information.

A need to manage the water and close abandoned phosphogypsum stacks, combined with concern about corporate financial liability and what will happen to the process water when companies close operating stacks in the next 10-20 years has increased interest in finding ways to improve the quality and decrease the quantity of process water.

In February 2001, Mulberry Phosphates (the company that owned the stack that was the source of the spill in 1997) filed for bankruptcy and abandoned its phosphate operations, which include two phosphogypsum stacks in Mulberry in Polk County and one at Piney Point in Manatee County. Florida’s Department of Environmental Protection (DEP) had to step in to empty the ponds and close the stacks.

In the fall of that same year, Tropical Storm Gabrielle dumped 19 inches of rain on the stack at Piney Point, threatening to cause the process water cooling ponds on top of the stack to overflow. A spill from the stack would have threatened Bishops Harbor, a prized estuary.

Through two heavy rainy seasons, DEP maintained the water levels in the Piney Point stack by transporting water to phosphate companies willing to take it, paying for water cleaned by a reverse osmosis process and liming, dumping some of the treated water in Bishop’s Harbor and getting an emergency permit from the U.S. Environmental Protection Agency (EPA) to barge more than 200 million gallons of treated water into the Gulf of Mexico and dump it. Meanwhile, DEP contracted with Cargill Crop Nutrition to close the stacks in Mulberry, saving DEP $30 million of the estimated $50 million closing costs.

Emergency efforts to manage and close the abandoned ponds cost the state of Florida almost $100 million and $60-$70 million more is needed to permanently close the sites. The money has come from a Trust Fund established to pay to reclaim land mined before reclamation became mandatory in 1975. The Trust Fund is financed with a portion of the severance tax the phosphate industry pays for the phosphate it mines.

FIPR is working to define the environmentally sound and economically viable solutions needed to avert a future crisis.

The TAC is evaluating research proposals and ideas that come to the DEP as well as those that come to FIPR. As a result, FIPR has funded projects such as a study of how an intermediary liner in the stacks might cut down on the amount of water retained in them and is examining how changes in process technology might reduce the quantity and improve the quality of process water that is generated.

Potential solutions FIPR is evaluating include demonstrating a unique Reverse Osmosis process that has the potential to clean the water faster and leave less reject behind, testing the concept of an intermediary stack liner to decrease the amount of water in a phosphogypsum stack and evaluating ways to improve the quality or reduce the quantity of the water produced in phosphate processing.

The Reverse Osmosis (RO) process, developed by IMC Phosphates (now Mosaic Co.), has a unique front-end treatment for the water. FIPR demonstrated the process at a pilot plant at the Piney Point stack in Manatee County. The results indicate that the system has potential to be better than the traditional RO process currently being used at Piney Point. A major benefit is that this process produces more clean water, leaving behind less contaminated sludge (reject) that will have to be dealt with later. The demonstration ended June 1, 2004. It proved the process did not scale the membrane, which is a problem with the traditional RO process, and the pilot identified and fixed glitches in the system.

Process operators feel strongly enough about the results to have answered a Florida Department of Environmental Protection (DEP) Invitation to Negotiate (ITN) to use the FIPR/IMC process to provide the closure of the Piney Point Phosphates Phosphogypsum Stack System. It is hoped that the system could be used in the future at other phosphate processing locations to clean process water well enough for release off-site without threatening surrounding habitats and waterways.

Billions of gallons of the water are used at the plants where phosphate is reacted with sulfuric acid to make the phosphoric acid used to make fertilizer. A by-product of this reaction is phosphogypsum. The process water is used to transport the phosphogypsum to the top of the stacks where it is stockpiled. The water then is retained in huge cooling ponds at the top of the stacks before it is recycled back to the plant.

Typically process water never leaves company property. It is recycled to plants, cutting down on the mount of fresh water that is pumped from the ground. If water needs to be released off-site, companies must obtain an emergency permit from the DEP and treat the water to neutralize the acidity and, depending on the situation, get rid of the ammonia.

While FIPR considers process water a critical research topic, it is not something the general public gives much thought to unless the water spills.

December 2004