Flocculation of Swine Manure: Influence of Flocculant, Rate of Addition, and Diet

Manure was collected from growing pigs (22–48 kg) fed one of 11 diets varying in total and available phosphorus content. Reduced phosphorus diets were amended with feed additives intended to improve availability of phytate phosphorus. Diets were replicated over three feeding periods resulting in 33 manure samples. Collected manure samples were diluted (final solids content approximated 2.4% total solids) and poured into Imhoff cones. Five flocculants plus a control were added at each of three concentrations and the diluted mixtures allowed to settle for 10 minutes followed by a second 10-minute settling period. Volume of settled material was recorded following each settling period. At the end of the second settling period (20 min of total settling) supernatant was poured off and frozen for future phosphorus analysis and settled solids were weighed and dried for total solids determination. Phosphorus and solids recovery was calculated. Results indicated that Al2(SO4)3 and FeCl3 were the most effective flocculants. Little improvement was observed when the flocculant was added at a concentration of 625 mg/l compared with 250 mg/L. Both flocculants recovered more than 85% of solids and more than ß 70% of the phosphorus. Addition of Al2(SO4)3 at a concentration of 625 mg/l increased phosphorus removal to 90%. Diet and feeding period were significant influences on results. As the pigs aged, manure phosphorus was more soluble, possibly explaining the observation that less phosphorus was settled in feeding period 3 compared with periods 1 and 2. As producers consider nutrient management options, feed-tofield strategies should be implemented.