Slurry treatment system gives green credits and CO₂ trade opportunities

US - Less greenhouse gas and more carbon credits per pig. These are the latest environment-friendly benefits being credited to an innovative hog waste-management system invented by Agricultural Research Service (ARS) scientists.

Soil scientists Matias Vanotti (left) and Ariel Szögi (right) and Lewis Fetterman, CEO of Super Soil Systems, discuss construction drawings of a lower cost version of the manure treatment system (background) used on a 6,000-head swine farm in North Carolina.

The system was introduced in 2004 by soil scientists Matias Vanotti, Ariel Szögi and Patrick Hunt at the ARS Coastal Plains Soil, Water and Plant Research Centre, Florence, South Carolina. It's now named the 'Super Soil System' after the North Carolina firm that now implements and markets it.

The waste handling system converts pig slurry into soil improvers and fertilizers, and removes almost all of the suspended solids, phosphorus and ammonia from the separated effluent.

In the latest research, conducted at the large commercial pig finishing operation in North Carolina, the ARS researchers found that replacing conventional anaerobic lagoon practices with the new system reduced greenhouse gas emissions by 97 percent.

It cut annual emissions from 4,972 tons of carbon dioxide equivalents to just 153 tons - indicating that the system may have a role in the fledgling CO₂ trading market, which will allow farmers to earn money based on how much carbon dioxide and other greenhouse gases they can prevent from entering the atmosphere.

Commercial reality

Super Soil Systems USA Inc. has now installed the waste treatment system on two pig production sites. The liquid treatment system is at Goshen Ridge Farms, a 4,360-head finishing farm near Warsaw, North Carolina, owned by Lewis Fetterman, Jr. The farm is under contract with Premium Standard Farms. The solid waste management portion of this project is at Timber Ridge Farms near Clinton, North Carolina. Ray Campbell, vice president of research and development for Super Soil Systems USA, is leading the project.

Liquid treatment begins with separation of the solid and liquid fractions of the slurry using polyacryalmide, a flocculating agent. The solids are then transported to the Clinton site, where they are composted and blended with other materials using a proprietary process to produce a value-added compost which is bagged for sale and use off the farm.

The liquid fraction is then circulated between a series of tanks to undergo denitrification through an anaerobic process. The liquid then flows to a settling tank, where phosphorus is removed through the addition of calcium hydroxide and a de-watering bag system. Calcium phosphate, which has value as a fertilizer, precipitates out during this process, and provides a second value-added product.

The pH of the liquid is raised during phosphorus removal, which kills bacteria and viruses. Roughly 80 percent of the liquid is recycled through the pig houses, while 20 percent is used to irrigate crop fields.

Further Reading

Manure Treatment System Erases Greenhouse Gases
Super Soil Systems USA (PDF 3 pages)

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