Separation of manure solids from simulated flushed manures by screening or sedimentation

Feces and urine were collected separately from individual cows fed corn silage-based (50% of dry matter) diets which were supplemented with distillers dried grains plus solubles or soybean meal to be 14 or 18% crude protein (CP). Fecal samples from 30 cows were screened using wet sieving and vibrating screens (nested in series); sizes were 3.35, 2.00, 1.40, 1.00, and 0.50 mm. Effluent passing the screens contained 60.2% of total solids (TS), 86.3% of nitrogen (N), and 94.3% of phosphorus (P). Solids caught on the five screens (largest to smallest) accounted for the following percentages of materials: 14.6, 9.4, 2.8, 4.3, 8.6% of TS; 5.7, 3.1, 0.8, 1.3, 2.8% of N; 2.2, 1.2, 0.3, 0.6, 1.5% of P. In another study, a 100 g composite sample of urine and feces from each of 44 cows, mixed in proportion to the amount excreted, was diluted to 1 L with water and allowed to settle for 1 h in a graduated cylinder. Supernatant and sediment were separated by decanting. Supernatants were analyzed for N content, sediments for TS content, and these amounts were subtracted from analyzed contents of samples to obtain reciprocal fractions. Overall, the sediment contained 66% of TS and 45% of N. Estimates of sediment amount made at 5, 10, 20, 40, and 60 min by recording best-defined line between supernatant and sediment suggested sedimentation was 89% completed by 5 min. In a second sedimentation study, simulated manure flushwaters (0.5, 1.0, and 1.5% TS) were treated with additives as follows: (1) 0.75 g of CaCO3 plus 0.50 mL Fe2(SO4)3 solution/L, (2) 0.75 g of CaO plus 0.50 mL Fe2(SO4)3 solution/L, (3) 0.50 mL Fe2(SO4)3 solution/L plus five drops of a commercial polymer, and (4) control (no additives). Precipitates with CaCO3 and CaO treatments contained 92% of the TS, 69% of the N, and 31% of the total potassium (K); the CaO treatment precipitated appreciably more P (93% of total) than other treatments; and treatment with Fe2(SO4)3 plus polymer precipitated the least TS and N. These data indicated a potential to remove more manure solids and N from flushed manure by sedimentation than by screening.