ABSTRACT
Animal waste odors arising from products of anaerobic microbial metabolism create community relations problems for livestock producers. We investigated a novel approach to swine waste odor reduction: the addition of FeCl3, a commonly used coagulant in municipal wastewater treatment, to stimulate degradation of odorous compounds by dissimilatory iron-reducing bacteria (DIRB). Two hypotheses were tested: (i) FeCl3 is an effective source of redox-active ferric iron (Fe3+) for dissimilatory reduction by bacteria indigenous to swine manure, and (ii) dissimilatory iron reduction results in significant degradation of odorous compounds within 7 days. Our results demonstrated that Fe3+ from FeCl3 was reduced biologically as well as chemically in laboratory microcosms prepared with prefiltered swine manure slurry and limestone gravel, which provided pH buffering and a substrate for microbial biofilm development. Addition of a 1-g liter−1 equivalent concentration of Fe3+ from FeCl3, but not from presynthesized ferrihydrite, caused initial, rapid solids flocculation, chemical Fe3+ reduction, and Eh increase, followed by a 2-day lag period. Between 2 and 6 days of incubation, increases in Fe2+ concentrations were accompanied by significant reductions in concentrations of volatile fatty acids used as odor indicators. Increases in Fe2+ concentrations between 2 and 6 days did not occur in FeCl3-treated microcosms that were sterilized by gamma irradiation or amended with NaN3, a respiratory inhibitor. DNA sequences obtained from rRNA gene amplicons of bacterial communities in FeCl3-treated microcosms were closely related to Desulfitobacterium spp., which are known representatives of DIRB. Use of iron respiration to abate wastewater odors warrants further investigation.
Identification of odorous compounds in fresh and rotten swine manure.
