As for dehydrators for treating sewage sludge, the use of dehydrators made of metal filtering materials is spreading rapidly, and a high-efficient twin screw press dehydrator has been developed with a view to achieving a lower moisture content in sludge that is hard to dehydrate, as well as space saving and energy saving. Figs. 1 and 2 show an outline of the conventional machine and the developed machine. The developed machine allows shear force to be applied to sludge by rotating the two screws in opposite directions, and therefore the machine makes it possible to reduce cake moisture content even when supplied with sludge which is hard to dehydrate, as compared with the conventional machine.
The purpose of research was to make an experimental comparison of the dehydration performance of the high-efficient twin screw press dehydrator with a conventional screw press dehydrator in the treatment of anaerobic digested sludge.
I show below result provided from this research.
1 Investigation of the influence on sludge properties
Table 1 shows the result of investigation. With the developed machine, the cake moisture content was 2.0 - 2.7 percentage points lower than that with the conventional machine.
2 Investigation of influence due to seasonal changes
In any season the cake moisture content with the developed machine was 2.0 - 2.9 percentage points lower than that with the conventional machine; therefore it is clear that it can function well without the effect of seasonal changes.