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I <br /> Scope of Work <br /> The scope of work for this project is to provide all labor, materials, supplies, and <br /> equipment necessary to dredge, dewater, weight and stockpile 2,000 dry tons of <br /> biosolids from the Water Pollution Control's Recirculation Channel. <br /> Process Description— Dredging I <br /> APG plans to remove the slurry from Recirculation Channel with a high volume <br /> cutter head style auger dredge. The dredge has a cutter head that is mounted on <br /> the end of a hinged boom that can be lowered to the depth of the sludge. The <br /> cutter head augers the material to the dredge pump which transports the sludge <br /> through an 8-inch pipe and then discharges into a screening tank at the processing <br /> setup area. The screening tank will remove debris and will serve as a process <br /> buffer between the dredging and the dewatering to allow for optimization of both. <br /> The screening tank is agitated to keep the slurry consistent. The slurry will be <br /> drawn from the screening tank and pumped to the centrifuge(s) via Variable <br /> Frequency Drive (VFD) driven feed pump(s). The variable frequency drive allows <br /> for regulated speed control of the feed pump and therefore variable pumping rate <br /> to the centrifuge. Each centrifuge has its own feed pump to allow for process <br /> optimization of each centrifuge individually. <br /> A polymer make down system allows for the mixing and hydration of polymer <br /> flocculent that will be used to aid the separation process. The hydrated and aged I <br /> polymer is metered using a VFD driven positive displacement pump. The VFD <br /> permits the precise flow and regulation of the polymer so that the correct dose is <br /> added for optimal separation while minimizing waste. <br /> The slurry and polymer flow will both be measured using magnetic flow meters <br /> and the polymer will be added to the slurry with a static in-line mixer to blend the <br /> two. The polymerized slurry will then be injected into the centrifuge where the <br /> separation will take place. <br /> The centrifuge has two main elements, a bowl that provides the mechanical <br /> separation and a scroll conveyor inside the bowl that augers the solids portion to <br /> the solids discharge end of the machine. The scroll conveyor is coupled through <br /> a planetary gearbox to the back drive motor. The bowl motor and back drive <br /> motor are both VFD driven. For the bowl this means that the amount of separation <br /> force, or "G" force is controllable by varying the bowl speed. Varying the back <br /> drive speed controls how quickly the material is augured out of the bowl, which is <br /> used to achieve a balance of optimum cake dryness and polymer dosage. <br /> r City of Everett 2020 Blosolids Removal Project—Work OrderilUT 3705-11 March 6,2020 - Page 2 <br />