抄録
Primary sludge and thickened surplus sludge were separately digested in a mesophilic and a thermophilic anaerobic digestion. As a result, the primary sludge was digested easier in the mesophilic digestion than the thickened surplus sludge. However, in the thermophilic digestion vice versa occured. On the basis of these results, a two-series digestion process with a thermophilic liquefaction of only thickened surplus sludge was proposed (hereafter called modified two-series digestion process).
In the thermophilic liquefaction of the thickened surplus sludge, the maximum volumetric loading rate of VSS of 14g·l-1·d-1 (HRT, 1.8d) could be achieved with respect to liquefaction of the sludge. On the other hand, in the mesophilic digestion of the mixture of thickened surplus sludge liquefied and primary sludge, the maximum volumetric loading rate of VSS of 8g·l-1·d-1 (HRT, 2.3d) could be achieved. In order to evaluate the performance of the modified two-series digestion process, a conventional mono-phase digestion was also investigated. As a result, the maximum volumetric loading rate of VSS in the modified two-series digestion process was about twice as much as that in the conventional process. The VSS digestion efficiency also increased up to about 10% compared to that in the conventinal process at the same volumetric loading rate of VSS.
