Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 3: Plant Description  46 of 74  The Contractor shall design and construct the bio-media unit in line with the design criteria specified  above. This unit shall be reinforced concrete. The inner surfaces shall be painted with special epoxy  paint against corrosion and aggressive media. Perforated HDPE pipes shall be installed on its floor for  the distribution of the collected foul air. The unit shall be filled with bio-media. Water to be sprayed intermittently on the media bed shall flow downwards in the opposite direction of  the foul air flow and the media surface shall keep wet according to bacterial need of media. A drainage  system shall be provided to drain the water from the bottom of bio-media bed. The water, once filtered  down the media after sprayed intermittently on the media, shall under no circumstances be sprayed on  the media again or reused in the media bed. To provide protection against the atmospheric conditions and allow the inspection of the bio-filter bed,  the unit shall be covered with UV resistant, curved elements made of GRP. Pre-conditioning Unit 3.3.4.35 Drainage of the Units  A pre-conditioning unit made of HDPE containing PVC filling material and equipped with  moisturizing nozzles shall be provided and installed. The unit shall include a circulation pump having a stainless steel shaft and body together with its  standby pumps. Necessary stainless steel EN1.4404 (316L) piping work shall be done. pH adjustment  unit shall be equipped with dosage pumps together with its standby pumps. Control equipment  consisting of a heater in sufficient capacity together with its accessories, a thermometer, a moisture  analyzer, a flow meter, a gas analyzer, a pressure gauge and a pH meter shall be provided. All  necessary control units and panels shall be provided. The bio-media unit shall have a control room  (cabinet) for controlling and monitoring purposes. The following conditions should be met for the appropriate drainage of the units but not limited to;  The main drainage pit shall be designed, constructed and equipped to make the gravitational  discharge of the tanks possible, i.e. primary clarifiers, aeration tanks, bio-phosphorus tanks  and grit and grease removal tanks etc. The depth of this drainage pit shall be designed  considering minimum 1.5 m lower than the bottom level of the deepest tanks to be drained.  Each tank shall have the bottom drainage and the valve and these are installed in a suitable  location of that tank.   In order to discharge all sludge from primary clarifier tank and to drain the tanks completely,  the bottom level of the primary sludge pumping station shall be same with the primary  clarifier sludge hopper bottom level for the drainage purpose.   The drainage of the secondary clarifier shall be carried out by means of the return sludge  pumping station. For the complete drainage of the final clarifier tanks, the bottom level of the  The drainage pump capacity shall be so selected that the biggest tank shall be emptied in one  day. There shall be one stand by pump. Minimum two discharge lines for pumps shall be  provided in the drainage pit. One of these lines shall be directed to the plant discharge line  before outlet flow measurement and the other one shall be directed to the inlet of the plant. 3_Vol3_d4.3_Section 3_Plant Description_GIR_rev08 