centrifugation: its advantages and its limitations

Centrifugation has undeniably taken over the dewatering market over the recent decade. This is mainly due to its advantages:

• continuous dewatering in an enclosed unit, reducing olfactory nuisances and the cost of deodorising premises;

• compact installation in a unit that remains salubrious and clean if it has been properly designed (the machines are washed automatically);

• the installation can operate unmanned if the sludge is relatively constant. All mechanical safety mechanisms constitute part of the standard equipment and, with the new sludge concentration sensors, unit automated operated has become reliable;

• major increase in dry solids contents which, for certain sludges, come close to the dry solids content produced by filter presses (4 to 6 points of additional dry solids content compared with older low pressure machines).Refer to table 21 where dry solids content and polymer consumption are compared with those for belt filters:

• suitable for all sludge types, even the most difficult and such as especially oily sludge:

• in-line operation (without buffer tank) when the centrifuge precedes a thermal dryer or a furnace:

• dewatering without a filtering medium and, therefore, without the attendant limitations (washing…);

• possibility of altering machine functions very quickly; more or less thorough dewatering to more or less sustained thickening and this is done merely by altering operation variables quoted in high pressure centrifuges.

On the other hand, some limitations remain significant, without, however, undermining the success achieved by this appliance:heavy polymer consumption (table 21), high energy consumptions, protection against noise inevitable, reduced but specialised maintenance, need for a stand-by unit in many cases.

Table 21. Comparison between a centrifuge (C) and a belt filter (FAB)

Photo 21. 5 D7LL Andritz – La Farfana WWTP (Santiago-Chile)

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