20 of 74  Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 3: Plant Description  3.3.4.7 Primary Clarifiers 3_Vol3_d4.3_Section 3_Plant Description_GIR_rev08  For emergency situations, a bypass line at downstream of the primary clarifiers shall be provided and  this line shall be connected to treated effluent discharge line. The bypass of this unit shall be  controlled by means of the weir type penstock. This penstock shall be channel type weir penstock with  double spindle and fully watertight. It shall be proportioning and electrically driven actuators. The  width of the overflow weir shall be designed and constructed by considering the second stage  maximum flow rate. The hydraulic height of the overflow penstock shall be adjusted by considering  the first stage maximum flow rate. Therefore this unit shall work as bypass when this penstock is  open, otherwise it shall work as overflow. The surface scraper moving on the whole surface of the tank shall ensure collection and transport of  floating sludge via screw conveyer system or chain track system or any other system which can  remove floating materials by force. Surface scum and floating materials shall be removed from the  tanks and should be conveyed to the drum sieve to be located on the distribution chamber of primary  clarifier. The waste from drum sieve shall be disposed to a container with a capacity of 5m$^{3}$. Outlet  water of the sieve shall be discharged into this distribution chamber tank. The primary clarifiers shall be designed for the removal of readily settleable solids and floating  materials and, therefore, shall reduce the suspended solids content. The purpose of the primary  clarifiers is to remove a substantial portion of the organic solids from the untreated wastewater, with a  resulting decrease in the organic and solid loadings of the biological unit.  Primary treatment efficiencies shall be based on the following assumptions  The primary clarifiers shall be designed, constructed and equipped regarding the requirements set in  Table 2-1. The maximum flow (Q$_{WW,h}$) of the related stage requirements shall be met for the unit. Primary Clarifiers shall be constructed in either circular or rectangular shape. The sludge shall be  collected into sludge hoppers by scrapers that are mounted on the primary clarifiers’ bridge. Each  primary clarifier shall have a separate bridge (i.e. each bridge should work individually). If the shape  of clarifiers is circular, the bridge to be used shall be half bridge. The methodology of the sludge suction from the primary clarifier tanks shall be based on maintaining  the separate sludge suction from hopper of the tanks. The instrumentation and automation system  required for sludge suction shall be available from one hopper individually.  In order to achieve this aim, each sludge line from each hopper of the primary clarifier tank should  have one valve with electric actuator in accordance with 7.8.18. The operation status of the valves  should be monitored and controlled by the SCADA system. The settled sludge shall be pumped via primary sludge pumps to the gravity thickeners. * BOD$_{5}$ Reduction:  ≤25%  * COD Reduction:  ≤25%  * TSS Reduction:  ≤50%  * Total N Reduction:  ≤10%  * Total P Reduction:  ≤11% 