Dewatering System Comparison (Centrifuge and Auto-Vac)
Of the many dewatering system choices, two machines are often mistaken as the same technology due to their physical similarities. These systems would be the centrifuge and the rotary vacuum drum filter.
Both systems have skid mounted cylindrical drum filters that are used to separate liquids and solids; and that’s about all they have in common.
A centrifuge offers “nominal” filtration whereas the Auto-Vac® provides “absolute” filtration. In relation to particle filtration size, the centrifuge typically filters down to 5 micron; Auto-Vac® filters down to 0.5 micron.
When dewatering non-settleable solids, a centrifuge needs polymer to capture smaller than 5 micron particles, where the Auto-Vac requires very little to no polymer (just a pin-floc). The volatile spin on centrifuges requires heavy doses of polymer to maintain a molecular bond. The “spin cycle” often shreds polymer bonding.
A centrifuge cannot function without polymer nor can it operate efficiently with a polymer overdose. The Auto-Vac® will filter slower and less efficient, but will still filter. Variances in the waste stream, such as heavy slugs of solids could also debilitate a centrifuge.
The purpose of dewatering is to reduce water weight in order to landfill or transport the filtered solids economically. Centrifuge generates from 11% – 15% dry solid content by weight; Auto-Vac up to 45% dry solid content by weight.
Upfront capital costs will fluctuate with the materials of construction; both machines typically fall within the same dollar amount. Both dewatering systems have ongoing consumable costs, but maintenance should be factored in as well.
There are only five moving parts on an Auto-Vac®, all of which require light duty maintenance consisting of scheduled cleaning and lubrication. Auto-Vac® parts are available commercially. A centrifuge requires the rotor assembly to be rebuilt at least once a year. The cost to rebuild the rotor assembly is 1/3 to 1/2 the cost of a brand new centrifuge (annually – sometimes biannually). Centrifuge systems have an intricate bearing and shaft assembly with a very tight tolerance that requires constant adjustment and realignment (replacement and maintenance costs can be very high).