Flushed Dairy Manure: a Case Study

Sunny Day Farm was the home of the highest producing registered Jersey herd in the world at the time this study was conducted. The cows are housed in a freestall barn and manure is removed from the barn using a flush system. The manure treatment system on this farm includes the following components in series: an inclined stationary screen separator, a two–chambered settling basin, and a lagoon. Samples were taken to quantify the performance of the existing manure treatment system. The inclined stationary screen separator removed 60.9% of the total solids, 62.8% of the volatile solids, 49.2% of the TKN, 52.2% of the organic–N, and 53.1% of the total P. The complete on–farm manure treatment system removed 93.0% of the TS, 95.6% of the VS, 74.0% of the TKN, 91.1% of the organic–N, and 86.1% of the total P. In addition, settling experiments were carried out with flushed manure (unscreened) and effluent from the mechanical separator (screened) to determine how well settling of dairy manure could be enhanced with a polymer (PAM) and aluminum sulfate. Addition of 250 to 400 mg PAM/L to screened and unscreened dairy manure significantly increased the removal of total and volatile solids, organic–N, total P, Cu, and Zn. The optimum amount of PAM to add was 300 mg/L for screened and unscreened manure. Settling of flushed dairy manure for 60 min following an application of 300 mg PAM/L removed 76.1% of the TS, 80.3% of the VS, 80.8% of the COD, 45.7% of the TKN, 72.3% of the organic–N, and 61.8% of the total P. The largest amount of TKN and total P was removed by a two–stage separation process that combined the stationary inclined screen separator followed by gravity settling with a polymer or aluminum sulfate. Enhancing the gravity stage with 300 mg PAM/L removed 71.1% of the TKN and 86.0% of the P. Application of 3,194 mg alum/L removed 71.1% of the TKN and 99.6% of the total P.