27 of 74  Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 3: Plant Description  3.3.4.15 Secondary Clarifiers The secondary clarifiers shall be designed, constructed and equipped regarding the requirements set in  Table 2-1. The activated sludge liquor shall be collected from the activated sludge tanks and distributed into the  secondary clarifiers. In the clarifiers, suspended sludge and treated wastewater shall be separated by  sedimentation. The treated wastewater shall be drawn from the surface by overflow weirs and the  settled sludge shall be concentrated in the bottom hoppers. The concentrated sludge shall be returned  to the activated sludge tanks in order to secure a sufficient quantity of activated sludge in the tanks.  The return sludge pumping shall be proportional to the flow measured by the intermediate flow meter.  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 digested sludge storage tank or return sludge pumping station (as  the case may be). The clarifiers shall be constructed as either rectangular with their bases either flat or sloping towards  hoppers located in the edge of the tanks or circular tanks with their bases either flat or sloping towards  hoppers located in the center of the tanks.  Wastewater from the activated sludge shall gravitate to the clarifiers and shall be distributed into the  tanks. The weir channels shall be constructed along the perimeter or sidewalls.  Each clarifier tank shall have a separate moveable bridge. The bridge collector mechanisms shall be  sludge suction type or the scraper type with center well in the circular tanks or hopper well in the  rectangular tanks. The scraper mechanisms will be configured to fully sweep the clarifier slab with  each trip. All elements belong to clarifier mechanism that are below the water line shall be stainless  steel 1.4404. Center drives shall be provided with a torque indicator, and furnished with a mechanical  disengagement mechanism, whenever the rotating assembly is jammed.  The clarifiers shall be fitted with V-notch overflow weirs and scum boards and floating scum funnels  shall be installed. The removed scum shall be collected in a scum pit for pumping to the digested  sludge storage tank or return sludge pumping station (as the case may be).  Minimum number of secondary clarifier tanks for Stage 2 : 2 tanks  Minimum return sludge at maximum flow  : 0.75·Q$_{WW,h}$  Surface hydraulic load at maximum flow  :   1.6 m$^{3}$/m$^{2}$.hour for Q$_{WW,h}$  Sludge thickening time  :   2.0 hour  Sludge volume loading rate q$_{SV }$ : ≤ 500 l/(m$^{2}$·h)  Maximum weir load at maximum flow  : 10 m$^{3}$/m.h  Before discharging of the treated wastewater, disinfection by ultraviolet (UV) disinfection system  shall be applied. The wastewater shall be filtrated before UV disinfection by a microfiltration unit.  3.3.4.16 UV Disinfection System and Microfiltration  3_Vol3_d4.3_Section 3_Plant Description_GIR_rev08 