Waste technology borrowed from municipalities and industries is now being used on a North Carolina pork operation.
In the subsurface-flow of a reciprocating wetlands’ system, manure solids from barn flush water settle in an underground tank. Liquid is pumped into two wetland cells, each filled with 42,000 cubic feet of gravel and some plants. The liquid is then pumped back and forth between the cells.
This reciprocation promotes both anaerobic and aerobic conditions for high-level microbial activity within the cells. BioConcepts officials, the company providing the technology, say it will eliminate almost all manure odor, and greatly reduced organic matter and ammonia. They say it will substantially reduce phosphorus levels as well.
The novel system treats wastewater from a 1,920-head, feeder-to-finish operation on a Murphy Farms’ operation in Duplin County, N.C. It is one of 18 technologies that North Carolina State University researchers are evaluating under Smithfield Foods’ agreement with the state attorney general.
The process works like this: Two barns with under-slat pits are flushed automatically every 10 hours into a solids-settling tank. After the solids settle, the remaining water is pumped out to fill the first cell. Any sludge collected is returned to the primary lagoon for digestion.
The wastewater remains in the first cell for one to five hours – depending on its dillusion strength. It is then pumped to cell two, where it remains for one to five additional hours before it is pumped back to the first cell.
At any given time, one cell is nearly empty while the other is almost full. Pumping liquid back and forth allows fresh air to enter the void space between and around rocks in the cell. This reciprocation is critical to allow the bacteria to “eat” nutrients in the swine manure.
As more water comes into the first cell from the dosing tank, excess cleaned water from the second cell is pushed out into a day tank. There it can be used to recharge the two barns’ flush tanks.
The two cells are sized to hold six days worth of the operation’s flush water. This residence time is required to treat high-strength manure using about 60 reciprocations. (Wastewater from municipalities needs only 1.5 days.)
The system is fully automated. Should a pump malfunction, fail-safe features automatically sound alarms and dial up the farm’s operator to report the problem.
This particular system costs about $300,000 to construct, and electricity costs run $150 to $200 a month. Fixed and operating costs, including an allowance for time, are estimated to total slightly less than 2 cents per pound per live hog in the buildings.
According to Mark Rice, North Carolina State’s agricultural engineer in charge of project evaluation, it will be early 2004 before researchers can say how well the system works on the farm and pinpoint a final operation cost.