Microbial ecology of biofilms in swine wastewater treatment systems for odor abatement

Animal waste odors arising from products of anaerobic microbial metabolism create community relations problems for livestock producers. This dissertation project focused on microbial approaches to odor abatement of swine wastewaters and consisted of two main studies. The first study tested the hypothesis that biological reduction of iron by bacteria in swine manure slurries is accompanied by degradation of odorous compounds and abatement of offensive odors. We showed that FeCl3, a flocculating agent commonly used in municipal wastewater treatment, stimulated dissimilatory iron reduction by bacteria growing in biofilms on limestone gravel in static swine manure microcosms. Biological but not abiotic iron reduction was accompanied by reductions in concentrations of volatile fatty acids and phenols, which were used as odor indicator compounds. Enrichment of dissimilatory iron-reducing bacteria in microbial biofilms was also demonstrated by ribosomal RNA intergenic spacer analysis (RISA). Although FeCl3 is widely used to flocculate solids and remove phosphorus from waste waters, our results demonstrate that it also can promote anaerobic respiration for odor abatement. The second study explored odor abatement in a subsurface flow wetland consisting of four sequential tanks filled with limestone gravel used to treat swine wastewater prior to land application. Wetland treatment performance was evaluated by comparing influents and effluents during (1) initial operation with undiluted wastewater; and (2) after spring re-establishment of Scirpus spp. with diluted wastewater. Odor abatement was measured by gas chromatography analyses of odor indicator compounds and by human sensory evaluation of headspace gases from the final effluents. During the first four months of operation with undiluted wastewater, plants did not become established due to excessively high NH4+-N concentrations (1500--1800 ppm). Although the unplanted wetland caused significant reductions in total solids and odor indicator compounds, concentrations of these compounds in the effluents still exceeded human sensory thresholds. Thus, only four out of ten panelists detected significant improvements in odor unpleasantness after wastewater passage through the unplanted wetland, while no panelists detected significant improvements in odor intensity. (Abstract shortened by UMI.)...