Effect of pig slurry solids on aeration efficiency and odour generation

Two laboratory-scale experiments were carried out in this study to determine the effect of slurry solids content on aeration efficiency and the odour generation potential for the treated slurry during post-aeration storage. Pig slurry with four total solids levels (0.5, 1.0, 2.0, and 4.0%) were used for both experiments. In the first experiment, the slurry was aerated and the oxygen transfer coefficient (OTC) for each solids level was determined. When the solids content increased from 0.5 to 4.0%, a reduction in OTC from about 0.59 to 0.15 min(-1) was observed. However, no statistically significant differences in OTC were found between slurry with a 0.5% and 1.0% total solids content and between slurry with a 2.0% and 4.0% total solids content, while the difference was significant between these two solids groups. In addition to OTC, the oxygen-holding capacity of the aerated manure decreased significantly with increasing slurry solids content. In the second experiment, slurry with the same four solids categories was contained in Plexiglas columns and aerated at a dissolved oxygen level of 1 mg l(-1) for 15 days. After aeration, the slurry was left in the columns to simulate long-term storage (180 days). The removal rates of volatile fatty acids (VFA), an odour indicator, by aeration were 98, 96, 67, and 31% for total solids content of 0.5, 1.0, 2.0, and 4.0%, respectively. During the entire storage period, the VFA concentrations for slurry with solids contents of 0.5% and 1.0% were consistently lower than 230 mg l(-1), indicating that the chance for offensive odour to return was moderate. In contrast, the slurry in the two upper solids categories showed VFA levels consistently higher than 230 mg l(-1) throughout the 180 day storage period. At the end of the storage, the odour detection threshold values were 531, 708, 812, and 1627 for slurry with solids content from 0.5 to 4.0%.