Challenge

For years, the West Mifflin Sanitary Sewer Municipal Authority (WMSSMA), located near Pittsburgh, Pennsylvania, hauled liquid from the smaller of its two sewage treatment plants (STP) to its larger STP for dewatering.  Hauling, labor, and coordinating dewatering schedules between both plants were costly and difficult.  They also faced a requirement to achieve higher cake solids and to provide a means for odor control.  Space constraints and staffing reductions demanded a compact, simple-to-operate technology.

Solution

The smaller plant's biosolids needs were met by installing a liquid clarifying and solids dewatering system that integrated three technologies from Siemens Water Technologies:

• Centramax™ centrifuge—its first North American installation.
• Stranco Products Polyblend® M Series polymer feed system.
• Asdor Products screw conveyor.   

The feed slurry passes into the feed distribution chamber of the centrifuge, where it quickly accelerates to the speed of the bowl.  G-forces drive the solids to the bowl wall, while the clarified liquid flows to the adjustable overflow weir.  
 
The internal conveyor turns at a slightly higher speed than the bowl, carrying the solids to the conical section where final dewatering occurs before being discharged the solids from the bowl.  The slower the conveyor moves in relation to the bowl and the longer the sediment remains in the centrifuge, the greater the liquid/solid separation efficiency.  The differential speed between the bowl and conveyor is controlled automatically, providing the maximum liquid/solids separation efficiency and highest cake solids.
 
The system is totally automated and extremely operator friendly. After what is essentially a one-button start, the system operates automatically and adjusts for variation in feed solids to maintain a high cake solids output over a wide range of operating conditions.

Results

Both plants now have dewatering capabilities, and operational efficiencies have drastically improved.  Short-term outcomes are:

• $5,000/month, on average, in cost savings at the smaller STP.
• Low operating costs and minimal repair time.
• Streamlined biosolids processing.
• Eliminated the need to coordinate dewatering schedules. 
• Higher cake solids.
• Odor control requirements achieved by eliminating hydrogen sulfide emissions.
• Small system footprint.
• Automated system operation with minimal operator attention.

Integrated technologies from Siemens Water Technologies streamlined processing and achieved more productive and efficient operations.