There are various different types of sludge, but let’s focus on how digested sludge and waste activated sludge are handled in a variety of different applications.
Let’s Define ‘Sludge’
Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. There are different types of sludge, including primary, secondary, digested and thickened, each with varying percent solids as a result of the wastewater treatment process.
Waste activated sludge is the surplus (mg/L) of microorganisms that must be removed from the wastewater process to keep the biological system in balance and facilitate further stages in the water treatment process.
Digested sludge is treated sludge (aerobic or anaerobic). The purpose of the treatment is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids.
Waste activated and digested sludges are the most common types of sludge that are pumped to dewatering machines for further solids separation.
Double Disc Pumps for a Variety of Applications
Double disc pumps are excellent for transfer and dewatering feed applications where these two types of sludges are generally found. While the double disc pump is a reciprocating pump, the short stroke length provides a very small displacement per revolution and therefore a relatively smooth flow that does not affect dewatering operations.
Double disc pumps are routinely used to feed centrifuges, belt filter presses, dewatering boxes, gravity belt thickeners, rotary drum thickeners, rotary presses, screw presses, sludge bagging systems and volute presses.
Unique Technology that Keeps Sludge Moving
Double disc pumps are based on a non-captive, free disc design where two discs are positioned in the pump’s housing. This unique pump design combines the mechanism of a positive displacement pump with the principle of induced flow.
Its discs perform the duties of both diaphragm and valve, providing a double-acting, non-clogging pump action. The way the connecting rods and camshaft are arranged in the pump, a reciprocating action of the discs is created, forming a large cavity that is filled and emptied in a continuous flow.
Reduced Friction Leads to Longer Life
Large seating areas allow for low internal velocities which help extend pump wear life. Friction is reduced in the double disc pump because this type of pump does not depend on close tolerances or a rubbing action to generate flow like rotary pump technologies.
The double disc pump technology provides the lowest life cost of any positive displacement pump available due to the unique low-friction design. The typical operating life between pump rebuilds is 10,000 – 15,000 hours.
The extremely low wear rate provides a more consistent flow rate over time than close tolerance pumps that lose their efficiency as they wear, requiring increases in speed to maintain the required flow. These required increases in speed lead to an even higher wear rate.
PVP’s Double Disc Pumps are geared toward wastewater with a heavy solids content. The elastomeric discs are flexible enough to allow larger solids, rags and debris that would normally cause problems like clogging and failure to pass through the pump. The discs can still seal around those materials if they are trapped during the cycle.
The reciprocating nature of the pump design means the disc will continue on its cycle to unseat and pass fluid, with debris included, out through the discharge pipe. Depending on the pump model size, double disc pumps can handle solids up to 2 inches in diameter.
Using a double disc pump for waste activated or digested sludge in transfer or dewatering feed applications will reduce your overall pump maintenance requirements and save your facility in time and money due to the low wear rate and low life cycle costs.