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<br />GRIT REMOVAL <br /> <br />Grit removal follows screening and flow measurement. A vortex grit unit is recommended to <br />replace the existing basin. <br /> <br />The circular concrete grit tank design forces the flow in a vortex, depositing grit on the flat <br />bottom of the tank. Paddles operated by a smail drive unit sweep the flat bottom of the tank <br />and force grit towards the central grit hopper. The paddle action .also serves to fe-suspend <br />any organic material. The forced vortex design results in low head loss through the system, <br />even at peak flows. The grit tank would have piping to convey grit slurry through a grit <br />pump to the grit cyclone and associated grit classifier, which further dewaters and cleans the <br />grit prior to conveyance to a dumpster for final disposal. <br /> <br />Based on the evaluation, one 7.0-MGD grit unit is recommended to handle future plant <br />influent flow and side stream flow described later. An uncovered tank, located east of the <br />Pretreatment Building is proposed. Most vendor designs indicate a tank diameter of 10 feet. <br />The short detention time of the process makes it unlikely that significant odors would <br />develop, and so odor control is not included. <br /> <br />Alternatively, a dual grit tank system could be installed. Two, 4.0 MGD grit tanks would <br />provide adequate future PHWW flow capacity. Initially, one 4.0 MGD grit tank would be <br />installed north of the existing grit tank. An additional 4.0 MGD grit tank would need to be <br />installed at the site of the existing grit tank to meet future peak flows. <br /> <br />The grit tank would be located east of the building with the grit slurry pumps, described later, <br />located approximately 14'-0" below grade inside the Pretreatment Building. Cleanout <br />connections would be provided to assist with flushing the grit line. The grit slurry would be <br />periodically withdrawn and pumped to the grit classifier unit (equipped with a cyclone) to <br />further dewater grit. HRG intends to use the existing grit conveyor and classifier. Grit <br />suction and discharge lines would be kept short to minimize the potential for plugging. <br /> <br />Alternative models for the grit system are shown in Table 3. <br /> <br />Table 3.. Grit System Altemativ~ <br />Manufacturer Model Flow, MGD <br />Jones and Attwood JetaGrit Trap 7.0 <br />Smith & Loveless Pista Grit Chamber 7.0 <br />USFilter/Envirex Vortex Grit System 7.0 <br />XGT™ 300 Grit RemowlSystem 7.0 <br />WesTech Vortex Grit Chamber 7.0 <br />I Cost does not include concrete tank or equipment installation <br /> <br />Manufacturer Cose <br />$50,000 <br />$62,000 <br />$52,000 <br />$40,000 <br />$41,500 <br /> <br />A channel would be built to flow out of the existing IS-inch grit tank bypass north into the <br />new grit tank. The wastewater flow would turn 270 degrees and then flow east away trom <br /> <br />7 <br />