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Limitations of Orthophosphates Removal from Swine Manure During Batch-Aerated Treatments

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  034153,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.13895) @2003
Authors:   Pius M. Ndegwa
Keywords:   Batch aeration, pH, oxidation-reduction potential, swine manure, and phosphorus

Previous studies on removal of orthophosphates (ortho-P) from swine manure during aeration treatments show performances ranging between 30 and 91%. This study investigated three factors believed to be potentially responsible for the wide variations as well as limiting even higher removals of ortho-P from swine manure during aeration treatments: (i) levels of insoluble-P, (ii) inadequate pH levels, and (iii) inadequate relevant metal ions. Results indicated that, removal of insoluble-P by prior aeration solids/liquid (PASL) separation and by mid-aeration solids/liquid (MASL) separation (four days into aeration process) resulted in an additional removal of 3 and 8%, respectively. Removal of insoluble-P by MASL separation significantly improved soluble ortho-P removal more than removal by PASL separation most probably because more insoluble-P is removed in the former process than in the latter process. Results also showed that upward adjustments of pH beyond that obtained from the aeration process did not significantly improve the removal of ortho-P suggesting that the pH level achieved during aeration process may not significantly limit further removal of soluble ortho-P during the aeration treatment of swine manure. Significant additional removals of 11, 9, and 5% were observed on the addition of a single dose of Ca+2 ions (80 millimoles [Ca+2]/L [Manure]) to the manure, improving removal levels to 95, 96, and 97% for the control, PASL separation, and MASL separation, respectively. Subsequent double and triple dose ups did not significantly improve the removal of ortho-P in the control or in the PASL separation treatments. Based on the results of this study, depletion of Ca+2 ions (and possibly other similarly acting metal ions) and accumulated insoluble-P, are most probably the two main factors limiting further removal of soluble ortho-P during aeration treatments of swine manure. These two factors are also likely to be responsible for the wide variations observed in the removal efficiencies because their content will vary with both feed mineral-supplementation and manure management practices.

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