Concerns have been growing in recent years over the growth and spread of hypoxic areas, or Dead Zones, in the world's oceans and large lakes. These zones were created in part by excessive nutrient pollution caused by human activity that, through run-off from urban areas and rural farm land, have taken residence behind fresh water damns, in bays and estuaries and into seas and open ocean water.
These escaped nutrients, in the form of run-off created by heavy rains, slowly deplete the oxygen in the water, creating large areas of hypoxic (low-oxygen) areas that can prove deadly to marine life. In addition, with over 400 of these dead zones identified around the world, the loss of once-fertile fishing waters has affected global food production and the marine industries that support it.
One of the largest Dead Zones in the world is located in the northern Gulf of Mexico, and is being fed high-nutrient run-offs from the Mississippi and other rivers and streams that feed into back bays and open Gulf waters. While a number of contributing factors are involved in high nutrient run-off, research has discovered a leading cause can be attributed to nitrates originating from farm, dairy and ranch operations.
Research has been underway for a number of years seeking to better understand the processes involved in the development and possible solutions to prevent or improve this major environmental threat—with some degree of success. But cleaning up the problem is not a fast or easy project, and research continues as scientists continue to look at new and better ways to help eliminate these toxic zones in the waters of the world.
Knowing that algae blooms that quickly develop within these Dead Zones is the major culprit for our ailing oceans, researchers have been attempting to find solutions to curb the introduction of nitrate and phosphorus pollutants that make their way down watersheds to larger bodies of water. Eleven states are now involved in a coalition to tackle the problem, and universities and their labs have joined the massive effort to shrink or eliminate the fuel needed by these Dead Zones to grow and prosper.
Recently, a possible new tool was introduced that may further efforts to prevent nutrient pollution from reaching and enriching Dead Zone areas. Laura Christianson, Assistant Professor of Water Quality in the Department of Crop Sciences at the University of Illinois, is a skilled professional in woodchip bioreactors. She has demonstrated the potential of using woodchip-filled trenches to help filter nitrates from tile drainage water in Illinois croplands.
The approach involves creating an environment to support the growth of bacteria that will consume nitrates in the water. The biological process has been described as a nature-friendly method of eliminating nutrients caused by run-off from diverse sources like farm field and wastewater plant pollutants.
In a recent study, Christianson and several colleagues also thought about removing phosphorus by adding a special "P-filter" exclusively developed to trap the fertilizer-derived pollutant. The team tested two kinds of industrial waste products in the P-filters, both steel slag and acid mine drainage treatment residual (MDR). Researchers say phosphorous adheres to elements such as aluminum, calcium and iron contained in these products, removing it from the water.
Instead of mixing steel slag or MDR with woodchips in one large phosphorus and nitrate removing machine, the team placed a separate P-filter downstream or upstream of a lab-scale bioreactor. They ran wastewater from an aquaculture tank through the system and measured the amount of nitrate and phosphorus at several points along the way.
Regardless of P-filter type and whether the P-filter was downstream or upstream of the bioreactor, nitrate removal was consistent. However, MDR was far better as a phosphorus filter.
"It removed 80 to 90 percent of the phosphorus at our medium flow rate," Christianson said. "That was really amazing."
Only about 25 percent of the phosphorus was removed by the steel slag, but Christianson says steel slag is a lot easier to find in the Midwest.
"According to the Illinois Nutrient Loss Reduction Strategy, we're only trying to remove 45 percent of the phosphorus we send downstream. Since agriculture is only responsible for half of that, 25 percent would be pretty good," she said.
The concept is the latest tool to be developed in the fight against the Dead Zones of the Gulf, and the team says more testing and demonstrations are necessary. But they say they are pleased with the results so far and look forward to fine-tuning the process.