USDA uses new technology to produce syngas from manure

By Ryan C. Christiansen
Researchers at the USDA Agricultural Research Service Coastal Plains Soil, Water and Plant Research Center in Florence, S.C., are developing a new technology dubbed "wet gasification" to convert wet livestock manure slurry directly into synthesis gas without pretreatment.

According to the USDA, the main feedstock characteristic requirement for wet gasification is that it must be pumpable as a liquid, which means that swine and dairy manures with 85 percent to 95 percent moisture content can be fed directly into the system. Other feedstocks, such as poultry litter or municipal solid waste, would need to be pretreated with a certain amount of water before they could be gasified in this way. It's also possible to mix wet and dry waste feedstocks to increase the moisture content of the overall mixture, thus making it pumpable.

The U.S. DOE Pacific Northwest National Laboratory is developing a ruthenium-based metal catalyst for the technology, the USDA said. Ruthenium is used in platinum and palladium alloys for wear-resistance and in titanium alloys for corrosion resistance.

Under processing conditions of 662 degrees Fahrenheit, wet gasification destroys pathogens, odor-generating organic compounds and hormones in as little as 15 minutes, which is exponentially quicker than the days and months required to process manure using anaerobic digestion, the USDA said. However, the USDA estimates that the annualized costs for a wet gasification system, including both capital and operating costs, is $375 per animal unit compared with $85 to $95 per animal unit for an anaerobic digestion system. Most of the higher cost is related to the fact that the wet gasification system is still in the research and development stage. Additional catalyst research might substantially lower capital costs for wet gasification, the USDA said.

The environmental advantages of wet gasification are that oxygen-demanding wastes, estrogens and odorous compounds are removed during gasification, and pathogens are totally killed, the USDA said. Most of the nitrogen can be recovered as ammonia for fertilizer, and the water byproduct can be treated to provide livestock with drinking water.