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 

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. 

## 3.3.4.35 Drainage of the Units 

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. 

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. 

 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 

