A newly developed technique could capture the nitrogen compounds released in the liquid waste from confined livestock facilities, such as concentrated animal feeding operations, and turn it into fertilizer. The cost of the the capture process could then be offset by the sale of the fertilizer.
Saqib Mukhtar, of the Texas A&M University, developed the technique to reduce contamination from animal rearing facilities.
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"Excessive ammonia emissions from animal feeding operations are considered a source of odor and environmental pollution," Mukhtar said in a press release.
The nitrogen also fuels algae blooms causing dead zones in bodies of water, as well as contaminating ground water.
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"Once emitted, ammonia may contribute to formation of fine airborne particulates in the presence of certain acidic compounds in the atmosphere," said Mukhtar. "And it may even be a constituent of nitrous oxide, a potent greenhouse gas."
Mukhtar believes his technique is superior to other methods because of its simplicity and that it produces a valuable economic commodity, ammonium sulphate fertilizer. Usually this fertilizer is made in reactors mixing ammonia with sulphuric acid. The United States imports much of this fertilizer from Canada.
Mukhtar's method uses gas-permeable tubing submerged in a tank of liquid manure. A dilute solution of sulfuric acid is pumped through the tubing, which has a porosity of only 2 microns. The tiny holes keep unwanted materials out, but allow the ammonia dissolved in the liquid manure to pass through.
The nitrogen compounds diffuse into the tubing because of the concentration difference. The acidity of the solution also helps to draw the ammonia into the tubing. It then reacts with the sulphuric acid solution to produce ammonium sulphate.
"Remember, we are capturing ammonia with this process," Mukhtar said. "Not just scrubbing it as other processes do. We might be able to return part or all of its cost of the process as ammonium sulfate, an expensive fertilizer."
Ammonium fertilizers contain nitrogen which plants need to grow and stay green.
Another advantage of Mukhtar's process which wasn't mentioned in the press release is that it could help reduce farmer's dependence on synthetic fertilizers.
Conventional production of nitrogen fertilizers uses the energy intensive Haber-Bosch process to pull nitrogen out of the air. Most manufacturers then use methane from natural gas to provide hydrogen. The hydrogen reacts with the nitrogen and various catalysts while under pressure to produce ammonia.
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Producing more ammonia fertilizers from animal waste would also reduce demand for natural gas and help agricultural economies produce materials they need from their own waste stream without reliance on the fossil fuel market.
The process still needs to be scaled up from the lab to the industrial level before it can really be useful.
"Obviously, we can't use a 'gazillion' feet of tubing in a large manure lagoon," Mukhtar said. "Potentially, what we could do is divert some of the flushed manure in a much smaller basin and apply membrane technology to extract ammonia from it."
Tags: Chemistry, Conservation, Food, Food Chain, Pollution
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