TECHNOLOGY SPOTLIGHT Optimization of Waste Sludge Thickening/Dewatering
The P6 PolyMix® Difference: A Case Study Biosolids sludge management has become exceptionally challenging for municipalities due to population increases creating greater wastewater treatment demand. This increased demand results in greater amounts of biosolids to process and dispose of, both economically and efficiently. Municipalities are now charged with finding new and creative solutions to handle the growing volume of wastewater biosolids. The patented P6 PolyMix® system optimizes various sludge thickening processes, specifically the belt filter press (BFP), but also screw presses and centrifuges. Optimization is addressed in the location of polymer introduction into the sludge, the process of how the polymer is mixed with the wastewater sludge, the volume of flow that is fed to the dewatering equipment, and the reliability of the press feed pump. As a result of these optimizations, the potential for reduced polymer consumption and cost, the potential for drier cake solids, the near elimination of feed pump maintenance, and the ability to process two to three times more
volume than that of conventional dewatering systems makes the P6 PolyMix system a powerful addition to a municipality’s sludge handling process
Background The conventional process for BFP sludge thickening is to pump dilute neat polymer into an injection ring located after the BFP feed pump between the pump and the BFP (Figure 1). Immediately after the polymer injection ring, a highshear mixer is used and is required to properly mix the polymer with the sludge particles so that the BFP can squeeze the water from the solids. The high-shear mixer immediately breaks the long-chain polymer strands into smaller pieces, resulting in increased polymer consumption and blinding off of the BFP belts. This system creates back pressure through the high-shear mixer, resulting in increased pump discharge pressure and horsepower (HP) requirements. Before the advent of the P6 PolyMix system, this was the normal process mode
Figure 1. Conventional High Shear Belt Filter Press Pumping Process
for conditioning sludge prior to delivery onto a BFP. On the other hand, the P6 PolyMix system optimizes the BFP sludge conditioning and mixing process (Figure 2). The dilute neat polymer is pumped into the P6 InjeX™ chamber ahead of the BFP feed pump. The P6 InjeX chamber receives the dilute neat polymer for initial mixing with the sludge, and then both flow into the P6 PolyMix feed pump, where final mixing and pumping are performed. The P6 PolyMix feed pump is a boundary layer/viscous drag centrifugal pump that gently “pulls” the sludge and polymer together through the pump. As it passes through the bladeless flat discpac (disc impeller), the sludge particles are gently mixed in a nonmechanical shear manner. The sludge particles and polymer are gently pulled through the discpac in a spiral motion from the discpac eye (center) outward to the pump discharge. The boundary layer/viscous drag pumping action creates a homogeneous slurry of polymer/solids, resulting in large, easily dewatered flocs. This process
also has the effect of conditioning the polymer strands by “pulling them through” the pump and unwinding the polymer coils, as opposed to “pushing them through” the pump. This conditioning of the polymer and sludge allows for more available charged sites on the polymer strands to attract the oppositely charged biological particles in the sludge for greater flocculation with less polymer. The homogeneous sludge/ polymer slurry is transferred without any additional mixing or damage to the floc to the BFP for dewatering/ thickening. The P6 PolyMix feed pump, with its boundary layer/viscous drag pumping principle, is illustrated in Figure 3. The gentle nonmechanical shear pumping action protects the pump from wear, and the product, which, in this case, is the delicate biological floc, from damage or degradation. Since the flocs, after forming, are not mechanically sheared and not broken apart with a high-shear mixer valve, less polymer is required to achieve excellent flocculation and better dewatering. Continued on page 10
Figure 2. P6 PolyMix Belt Filter Press Pumping Process
Technology Spotlight is a paid feature sponsored by the advertisement on the facing page. The Journal and its publisher do not endorse any product that appears in this column. If you would like to have your technology featured, contact Mike Delaney at 352-241-6006 or at mike@fwrj.com.
8 May 2022 • Florida Water Resources Journal
