USE OF FLOCCULANTS IN DAIRY WASTEWATERS TO REMOVE PHOSPHORUS

Abstract

Additions of alum (Al 2 (SO 4 ) 3 ), ferric chloride, and polyacrylamide solutions were tested in the laboratory fortheir effectiveness to increase nutrient removals, especially phosphorus (P), by sedimentation from flushwaters with 1%dairy manure solids. Alum and ferric chloride significantly affected TS recovered, pH, and amounts of P, TKN, K, Ca, Zn,Cu, Mn, and Na remaining in the effluent as compared with control sedimentations without additives. Effects on Premovals were greatest with removal curves best fitting a quadratic polynomial (r 2 = 0.96 for P). However, the linearregression coefficients for P with a linear only model (r 2 = 0.93) were considered to be good estimates of averageremoval rates (4.0 mg P removed/mmol Al +3 for alum, 5.36 mg P removed/mmol Fe +3 for ferric chloride).Polyacrylamide treatments were not different from control sedimentations at the concentrations tested. Field studies tested0, 0.9, and 1.8 mL/L additions of alum solution (4.4% Al by weight) to dairy manure flushwaters (0.33% TS and 41 mgP/L) that previously had been subjected to sedimentation and screening. Management scenarios tested, utilizing 4100 Ltanks, were single-fill (batch), 3-fill continuous flow, and 6-fill continuous flow. Removals of 11 to 17 mg P/mmol Al +3added (0.9 mL alum/L) were higher than in the laboratory experiment. All removal efficiencies in laboratory and fieldexperiments with either alum or ferric chloride were well below theoretical efficiency of one millimole of P (31 mg)precipitated as phosphate with one millimole of Al +3 or Fe +3 but lower efficiencies are expected when organiccompounds are present that can bind these ions. These studies demonstrated that reduction of P in dairy manurewastewaters to low levels is possible with additions of alum or ferric chloride solutions. However, the economics of theseprocedures did not appear favorable.