Changes in Hog Manure in a Flow-Through Anaerobic Storage Tank

Bench scale anaerobic flow-through storage tanks were fed screened hog manure from a farm housing 10 000 hogs in pens flushed with water. The tanks were operated at room temperature, at different hydraulic residence times (HRT): from 3 to 90 days. Some 80% of the total solids and some 35% of BOD5,nf settled out from the screened hog manure in a matter of hours. This initial rapid settling of the organic matter was complete in 2-3 days and was followed by slow stabilization of organic matter. At HRT above 30-35 d the effluent pH has reached an equilibrium at 8.2 and effluent non-filtered BOD5 decreased below 1300 mg l−1.