In comparison, the membrane technology Mukhtar and his associates have been testing is relatively simple.
Gas-permeable tubing is submersed in a tank of liquid manure. A very dilute solution of sulfuric acid is pumped through the tubing, which has a porosity of only 2 microns. To put this in perspective, a typical human hair is 70 microns in diameter.
The method takes advantage of a property of dissolved gases described by Fick's first law of diffusion. A high concentration of a dissolved gas, such as ammonia, will migrate to regions of lower concentration. As the concentration of ammonium is high in the liquid manure and low to zero in the permeable tubing, the ammonium is drawn into the tubing and out of the liquid manure.
Also, the migration is enhanced by ammonium being a base and chemically attracted to the acid in the tubing.
The name of the tubular membrane they used is "expanded polytetrafluoroethylene, which is usually abbreviated ePTFE," Mukhtar said.
The product has several uses including blood filtration and synthetic blood vessel and even dental floss, he said, and once was prohibitively expensive. But with the expiration of several patents for this material and its uses, the cost has dropped dramatically, allowing its use for other applications.
Mukhtar said the next step is to scale up from the small bench model to a large tank, perhaps 100 gallons, he said. The team also wants to experiment with how little tubing can be used, and how dilute the acid solution can be, while still capturing about 50 percent of the ammonium within a reasonable amount of time.
They are also looking ahead to learn how to economically scale up the process for use on the farm.
"Obviously, we can'
|Contact: Robert Burns|
Texas A&M AgriLife Communications