EFFECTS OF FE AND CAADDITIONS TO DAIRY WASTEWATERS ON SOLIDS AND NUTRIENT REMOVAL BY SEDIMENTATION

Simulated flushwaters containing 0.5, 1.0, or 1.5% dairy manure solids were utilized in four laboratory experiments to test effect of chemical additives on sedimentation of total solids, N, P, K, and other mineral nutrients. Sedimentation for 20 min without additives removed approximately 64% of total solids, 20% of N, 60% of P, and 40% of K. Additives tested were Fe2(SO4)3, Fe3Cl, FeSO4, CaO, hydrated lime (Ca and Mg hydroxides and oxides), CaCO3, and CaSO4. Ferric salts were much more effective than Fe+2 and Ca salts; Fe+3 was more effective with chloride than sulfate. Adding 278 mg/L Fe (the highest level tested) from FeCl3 effected sedimentation of 89% of solids, 56% of N, 88% of P and 60% of K; an additional 358 mg Ca/L from CaO (the most effective Ca source) sedimented 4.0% more solids and 3.9% more P but had no beneficial effect on N or K. Reuse of effluent water to simulate recycling of flushwater showed little potential to reduce flocculent salt levels. Field trials determined that an Ag Pro® Manure Extractor with screen size of 1.5 mm removed approximately 30% of volatile solids by screening and flow-through sediment basins subsequently removed an additional 23%. Although, the estimated cost of flocculants versus the value of fertilizer nutrients sedimented were not favorable, potential was demonstrated for food animal producing units that flush to use flocculants to concentrate nutrients in sediment that could be exported off-farm, if necessary to meet environmental regulations. Further work is indicated to ensure workability of an economical system under farm conditions