36 of 74  Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 3: Plant Description  The polymer shall be dosed by means of eccentric screw type pumps controlled by frequency  converters. Flow meters shall be installed on polymer dosing line incoming to each mechanical  thickener. Thickened excess sludge after the mechanical thickener shall be pumped via thickened excess sludge  pumps. The thickened excess sludge shall be pumped directly to the anaerobic digesters or to the  digested sludge storage tank. Quantity of excess sludge transferred to anaerobic digester or digested  sludge storage tank shall be measured. The pumps shall be speed controlled by means of frequency- converters. Adequate space within the unit shall be left for proper operation and maintenance of all  equipment. Access to the machines, pumps and components (such as valves and local control panels)  shall be secure and unhindered.  The capacity of the pumps shall be selected based on the below defined daily operation hours. Washing water shall be connected to both the suction and discharge lines of the thickened excess  sludge pumps and polymer dosing pumps. This washing system will engage automatically when the  pumps are not operated. Sludge out  : ≥ 6% DS  Operation hours, design  :  16 hours/day Minimum number of mechanical thickeners  : 3 (2 duty + 1 stand-by) units  Minimum number of thickened excess sludge pump  : 3 (2 duty + 1 stand-by)  Type of thickened excess sludge pump  : eccentric screw pump  Polymer preparation unit  : 1 duty  Minimum number of polymer dosing pumps  : 2 (1 duty + 1 stand-by)  3.3.4.25 Gravity Sludge Thickener for Primary Sludge For thickening of primary sludge, gravity thickeners shall be used to increase the dry solids content of  the primary sludge to minimum 5 % DS. The sludge screen shall be used before the gravity thickener.  The gravity thickener and sludge screen shall be in a building.  Inside building, the top of this tank shall be additionally covered to prevent the spreading of odor. This  top cover part shall be GRP and shall have transparent window covers so that the inside can be seen  during operation. Sludge screen shall be installed on the top of gravity thickener. The building shall  have a lifting system for maintenance and repair purposes. The waste collected from the sludge screen  should be conveyed to a container. The foul air from the gravity thickener and from the building shall  be collected and sent to the odor removal. The building door dimension and lifting equipment shall be  accordance with the requirements for repair and maintenance of all equipment in the building. The thickening device shall be the center-feed type and be equipped with perimeter weirs and  launders. Weirs shall be EN 1.4404 and launders shall be reinforced concrete. Weired supernatant  shall be transferred to the inlet structure of the anaerobic bio-phosphorus tank.  Minimum number of units  : 1 unit  Maximum surface loading rate  : ≤ 100  kg/(m²*day)  Thickened primary sludge after the gravity thickener shall be pumped via thickened primary sludge  pumps. The capacity of the pumps shall be selected based on the below defined daily operation hours. 3_Vol3_d4.3_Section 3_Plant Description_GIR_rev08 