Use of flocculants in dairy wastewaters to remove phosphorus

Additions of alum (Al-2(SO4)(3)), ferric chloride, and polyacrylamide solut ions were tested in th laboratory for their effectiveness to increase nutri ent removals, especially phosphorus (P), by sedimentation from flushwaters with 1% dairy manure solids. Alum and ferric chloride significantly affecte d TS recovered, pH, and amounts of P, TKN, K, Ca, Zn, Cu, Mn, and Na remain ing in the effluent as compared with control sedimentations without additiv es. effects on P removals were greatest with removal curves best fitting a quadratic polynomial (r(2) = 0.96 for P). However, the linear regression co efficients for P with a linear only model (r(2) = 0.93) were considered to be good estimates of average removal rates (4.0 mg P removal/mmol Al+3 for alum, 5.36 mg P removed/mmol Fe+3 for ferric chloride). Polyacrylamide trea tments were not different from control sedimentations at the concentrations tested. Field studies tested 0, 0.9, and 1.8 mL/L additions of alum soluti on (4.4% Al by weight) to dairy manure flushwaters (0.33% TS and 41 mg P/L) that previously had been subjected to sedimentation and screening. Managem ent scenarios tested, utilizing 4100 L tanks, were single-fill (batch), 3-f ill continuous flow, and 6-fill continuous flow. Removals of 11 to 17 mg P/ mmol Al+3 added (0.9 mL alum/L) were higher than in the laboratory experime nt. All removal efficiencies in laboratory and field experiments with eithe r alum or ferric chloride were well below theoretical efficiency of one mil limole of P (31 mg) precipitated as phosphate with one millimole of Al+3 or Fe+3 but lower efficiencies are expected when organic compounds are presen t that can blind these ions. These studies demonstrated that reduction of P in dairy manure wastewaters to low levels is possible with additions of al um or ferric chloride solutions. However, the economics of these procedures did not appear favorable.