Producer-agricultural engineer develops simple system that
effectively filters out manure odors and reduces neighborhood
complaints.  Neighbors driving by NPPI's 1,500-sow, farrow-to-
finish operation near Hector, MN, don't complain about hog
odors. Biofilters, operating since the complex was built in
1997, have eliminated the majority of the odors as air is
exhausted from the barns.  Only when pits are pumped out twice a
year for application to nearby fields, do neighbors even notice
the gases given off by the manure, says Dick Nicolai.  He raised
hogs for 30 years and still owns part of the operation, but now
works as an agricultural engineer at South Dakota State
University (SDSU) in Brookings.  Biofiltration Not New
Biofiltration occurs when microorganisms mix with oxygen,
resulting in a dilution of offensive waste compounds, says
Nicolai.  Biofiltration is not new to agriculture, he explains.
The drain field for a septic tank system offers similar benefits
as the soil serves as a biofilter to break down