A candidate technology of the North Carolina Agreements Project:
Development of Environmentally Superior Technologies
per Agreements Between the Attorney General of North Carolina
and Smithfield Foods, Premium Standard Farms and Frontline Farmers

Solids Separation-Reciprocating Wetland

Reciprocating Wetland Cells

This project is located on Corbett Farm #2 in Duplin County, North Carolina. It has been in operation since late 2002, treating waste from 1,600 finishing pigs. This technology employs wetland cells or basins in which alternating anaerobic and aerobic conditions are created to remove nitrogen from the waste stream. The technology provider is BioConcepts, Inc., Al Privette, president.

The waste stream from the houses in which pigs are housed flows first to a settling tank for solids separation. The remaining liquid then flows to the reciprocating wetland cells. The cells are earthen basins with synthetic liners. Each cell is filled with gravel, which acts as a surface on which microbes reside. The liquid from the settling tank is pumped back and forth between the cells. As a cell fills with liquid, anaerobic conditions are created, which promotes denitrification (the conversion of nitrate to nitrogen gas, which enters the atmosphere). As liquid is removed from a cell, aerobic conditions are created, which promotes nitrification (the conversion of ammonia in the waste stream to nitrate). The system is designed to remove nitrogen (in the form of ammonia) from the waste stream by turning it first into nitrate, then into nitrogen gas. The atmosphere is predominately nitrogen gas, so this form of nitrogen is harmless. Liquid has a six-day residence time in the cells. Liquid leaving the cells is recycled to the pig houses to be used to move waste from the houses. Any excess liquid is applied to land.

Technology Evaluation

J. Mark Rice
Department of Biological and Agricultural Engineering
North Carolina State University
Raleigh, NC
voice: 919.515.6794
FAX: 919.513.1023
e-mail: jmrice@eos.ncsu.edu

System Diagram

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