Changes in hog manure in a flow-through anaerobic storage tank

Bench scale anaerobic flow-through storage tanks were fed screened hog manu re from a farm housing 10 000 hogs in pens flushed with water. The tanks we re operated at room temperature, at different hydraulic residence rimes (HR T): 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 initia l rapid settling of the organic matter was complete in 2-3 days and was fol lowed by slow stabilization of organic matter. At HRT above 30-35 d the eff luent pH has reached an equilibrium at 8.2 and effluent non-filtered BOD5 d ecreased below 1300 mg l(-1).