Biological Control of Hog Waste Odor through Stimulated Microbial Fe(III) Reduction

ABSTRACT Odor control and disposal of swine waste have inhibited expansion of swine production facilities throughout the United States. Swine waste odor is associated primarily with high concentrations of volatile fatty acids (VFAs). Here, we demonstrate that stimulated Fe(III) reduction in hog manure can rapidly remove the malodorous compounds and enhance methane production by 200%. As part of these studies, we enumerated the indigenous Fe(III)-reducing population in swine waste and identified members of the family Geobacteraceae as the dominant species. These organisms were present at concentrations as high as 2 × 10 5 cells g −1 . Several pure cultures of Fe(III) reducers, including Geobacter metallireducens , Geobacter humireducens , Geobacter sulfurreducens , Geobacter grbiciae , Geothrix fermentans , and Geovibrio ferrireducens , readily degraded some or all of the malodorous VFAs found in swine manure. In contrast, Shewanella algae did not degrade any of these compounds. We isolated an Fe(III) reducer, Geobacter strain NU, from materials collected from primary swine waste lagoons. This organism degraded all of the malodorous VFAs tested and readily grew in swine waste amended with Fe(III). When raw waste amended with Fe(III) was inoculated with strain NU, the VFA content rapidly decreased, corresponding with an almost complete removal of the odor. In contrast, the raw waste without Fe(III) or strain NU showed a marked increase in VFA content and a rapid pH drop. This study showed that Fe(III) supplementation combined with appropriate bioaugmentation provides a simple, cost-effective approach to deodorize and treat swine waste, removing a significant impediment to the expansion of pork production facilities.