Milk house wastewater flows and characteristics for small dairy operations

Water meters were used to indicate milk house wastewater flow rates in the milk houses of 16 dairy operations with between 41 and 130 milking cows. Wastewater samples (7 to 21) were taken from the first septic tank providing primary treatment of the milk house water to measure pH, biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), total suspended solids (TSS), fats, oils and grease (FOG), total phosphorus, total Kjeldahl nitrogen (TKN), and ammonia nitrogen concentrations. Average water flow rates across the 14 dairy operations without parlors ranged from 8.6 to 35.3 L/d/cow. Milk house water use per cow per day on individual farms varied by between 146% and 400%. Overall average BOD₅ concentration across all sixteen operations was 1.44 g/L while individual farm averages ranged from 0.50 to 4.52 g/L. Overall average COD concentration was 2.26 g/L; farm averages ranged from 0.72 to 6.28 g/L. Overall average TSS concentration across all operations was 686 mg/L, farm averages ranged from 181 to 1,537 mg/L. Average FOG concentration was 477 mg/L, farm averages ranged from 45 to 1,334 mg/L. Median average pH level was 6.8, farm levels ranged from 5.9 to 8.0. Average phosphorus concentration across all operations was 56 mg/L, farm averages ranged from 18 to 101 mg/L. Average TKN concentration was 81 mg/L, farm averages ranged from 33 to 179 mg/L. Average ammonia concentration was 34 mg/L, farm averages ranged from 12 to 98 mg/L. Based on these results the authors recommend using 19 L/d/cow for the design milk house wastewater flow rate for milk houses for dairy operations with 130 or fewer cows. For sizing aerobic treatment units and infiltration systems, the authors recommend using 1.5 g/L for the design effluent BOD₅ concentration for a milk house only. For designing irrigation land application systems based on annual TKN and P per cow for milk house only sites, the authors recommend using 0.6 and 0.35 kg/cow/yr, respectively.