AGRO 143 |
| Recovery of phosphorus (P) from dairy manure wastewater in an easily-dewatered form would enable farmers to manage P as a resource rather than land-apply it in excess at environmental risk. The purpose of this study was (1) to evaluate the feasibility of P recovery from flushed dairy manure wastewater; (2) to evaluate the form of recovered P precipitates; and (3) to determine effect of CO32- and Mg2+ on P precipitation from flushed dairy manure wastewater using crystallization in a fluidized-bed reactor. Wastewater was pumped directly from a dairy farm reservoir and continuously fed in parallel through four bench-scale fluidized bed reactors deployed on-site. Chemical additives (NaOH and MgSO4) required for recovery were injected directly into the zone of fluidization. Recovered P forms were assessed by X-ray diffraction, scanning electron microscopy, and micro-elemental analysis. Raising pH alone failed to recover P as Ca phosphate precipitates due to preemptive CaCO3 formation. In conjunction with MgSO4 addition, pH elevation induced crystalline hydroxylapatite (HAP: Ca5(PO4)3OH) precipitation which was documented in coatings ultrasonically removed from quartz seed grains following fluidization. Addition of MgSO4 was required to prevent CaCO3 precipitation because CO32- and Mg2+ would complex to form aqueous MgCO3 and thereby reduce free CO32- and Mg2+ activities, resulting in less CaCO3 and enhanced HAP precipitation. Addition of MgSO4 increased P recovery by 35% compared to its absence. |
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New Developments and Issues in Agrochemical Sciences
8:45 AM-11:50 AM, Thursday, August 23, 2007 BCEC -- 259A, Oral
Division of Agrochemicals |