OPTIMIZATION OF PHOSPHORUS PARTITIONING IN DAIRY MANURE USING CHEMICAL ADDITIVES WITH A MECHANICAL SOLIDS SEPARATOR.

The use of liquid aluminum sulfate (alum) and a cationic polymer to precipitate soluble phosphorus, measured as dissolved reactive phosphorus (DRP), from dairy manure was investigated in conjunction with a mechanical screw press solids separator. The ability to partition phosphorus (P) into the recovered solids would increase the feasibility of transporting P off the farm. Initial settling studies were conducted using Imhoff cones to determine the effectiveness of aluminum (AI) to P molar ratios of 2.5:1, 5:1, and 7.5:1. In the Imhoff cone tests, the DRP concentration in the treated bulk liquid was 68%, 95%, and 98% less than the control, respectively. For the mechanical separator tests, alum was added at a molar ratio of Al to P (measured as DRP, but converted to an elemental P equivalency for the ratio calculations) of 5.5:1, and alum plus a cationic polymer was tested with the alum added at an Al to P molar ratio of 7.5:1. The DRP concentrations in the manure after alum amendment at the 5.5:1 Al:P ratio (and prior to processing in the separator) and in the press liquor were 52% less than prior to alum amendment. The total phosphorus (TP) in the press liquor was not affected by alum addition because the aluminum phosphate floc remained with the press liquor when alum alone was added. With the addition of alum at a 7.5:1 Al:P ratio in conjunction with cationic polymer at a rate of 55.5 mg L-1, the DRP concentration in the press liquor was reduced by 96%. When compared to the control, waste amended with alum and polymer had 82% less TP in the press liquor, which indicates that P was partitioned into the press cake. This combined alum/polymer treatment also resulted in a 36% reduction in TS and a 71% reduction in chemical oxygen demand (COD) in the press liquor when compared to the control. Polymer addition also increased the dry mass capture efficiency of the solid separator to 81.8% compared to 65.5% in the control, but the press liquor flow rate was reduced by 81%. The combined retail cost for alum and polymer addition at the above rates is estimated to be $2.63 per 1000 L of treated manure slurry. The results indicate that a cationic polymer used in conjunction with alum amendment can effectively partition P into the press cake during mechanical solids separation. [ABSTRACT FROM AUTHOR]