Environmental Protection

Ammonia Emissions Reduction Method Patented by USDA

The USDA has patented a process to capture and recycle ammonia from livestock waste, which could help farmers reduce harmful emissions and concentrate nitrogen into a liquid to sell as fertilizer.

The U.S Department of Agriculture (USDA) patented an ammonia emissions reduction method that was developed by Agricultural Research Service (ARS) scientists in Florence, South Carolina. ARA is the chief research agency of the USDA and responds to climate change and promotes international food security.

The system uses gas-permeable membranes that are similar to materials already used in waterproof outdoor gear and biomedical devices. Using these materials, the scientists recorded an average removal rate from 45 to 153 milligrams of ammonia per liter per day when manure ammonia concentrations ranged from 138 to 302 milligrams of ammonia per liter.

When manure acidity decreased, ammonia recovery increased. For instance, the scientists were able to recover around 1.2 percent of the total ammonia emissions per hour from manure at pH 8.3. The recovery rate managed to increase 10-fold to 13 percent per hour for manure at pH 10.0.

In a follow-up study, the scientists immersed the membrane module into liquid manure that had 1,290 milligrams of ammonia per liter. After nine days, the total ammonia concentration decreased about 50 percent to 663 milligrams per liter and acidity increased from pH 8.1 to 7.0. This meant that the gaseous or free ammonia in the liquid—the portion of the total ammonia linked to ammonia emissions--decreased 95 percent from 114.2 to 5.4 milligrams per liter.

The scientists used the same process in 10 consecutive batches of raw swine manure and ended up recovering concentrated nitrogen in a clear solution that contained 53,000 milligrams of ammonia per liter.

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