Grinding tests indicate that Abrasit-coated materials show less loss of material when compared to cast and ductile iron. Click here to enlarge imageTo combat these conditions, grit chambers are typically placed just after a plants' bar racks, but squarely ahead of all treatment activities (i.e., primary sedimentation tanks, etc.). Pumps are required in these areas to move the wastewater forward in the process, and — until recently — the pumps subjected to duty in these harsh, grit-filled areas were known primarily for their minimum life and maximum maintenance requirements. (Typically, pumps employ cast iron for casting and impeller components, which is highly vulnerable to grit-filled liquid.)
The abrasive character of grit makes it a particularly significant concern relative to the reliability and operating expense of these wastewater pumping systems. Even small increases in abrasive grit content can have devastating affects on pump casing and impeller life. Grit-filled wastewater has the very real effect of abrasively altering pump and impeller surface geometries — degrading the hydraulic capabilities of pumping units. Often, the erosive effect reaches a point where the danger of clogging rises to unacceptable levels.
Approaches that place pumps outside of the grit chamber have been tried, but generally, have not proven to be cost-effective. Until now, it has just been a situation that the industry has had to "live with" and "pay for" with added maintenance, as well as more frequent pump purchases.
Fortunately, advances in the hardness levels of the pump components that come into direct physical contact with grit-filled wastewater now provides system operators with a cost-effective response to today's increased grit levels.