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The tanks shall be constructed as reinforced concrete structures. Each of the anaerobic tanks shall be equipped with submerged energy efficient mixers in order to ensure an efficient mixing of sludge and water and to avoid the settlement of sludge in the tanks. The proposed mixers by the Contractor shall be in accordance with the specifications given in Section 7.8.30. Each mixer has a separate lifting equipment compliant with Section 7.8.1 for the hoisting of the mixers. The mixers shall be designed for minimum horizontal velocity of the water of 0.3 m/s. Computational Fluid Dynamic (CFD) analyses for the mixers shall be submitted during the design stage and the mixers will be subject to the approval of the Engineer. 

The tanks shall be equipped with service bridges. The sprinkler system shall be designed and installed along the service bridges to prevent and/or remove the surface scum in the anaerobic bio-phosphorus tanks. The treated water should be used for this purpose. The drainage pit shall be designed and constructed on the bottom of each anaerobic tank. This drainage pit shall be equipped with the drainage valve that is extended spindle and manual operated. 

In addition to these, each anaerobic tank shall be equipped with one oxidation reduction potential (ORP) measurement devices, at the outlet of the tank. 

The volume of anaerobic biophosphorus tank should not be taken into consideration for sludge age determination. 

Minimum number of anaerobic bio-phosphorus tank for Stage 2 : 2 tanks 

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In addition to the anaerobic bio-phosphorus tanks, the Tenderer may suggest other hi-tech technologies (except phosphate electrodes and pre-fermentation) to support the biological phosphorus removal in order to minimize the chemical consumption to meet the phosphorus effluent concentration. In this case, all the necessary calculations, equipment specifications shall be provided together with his tender. 

## 3.3.4.10 Chemical Phosphorous Precipitation 

Biological phosphorus removal shall be supplemented by chemical phosphorus treatment. The chemical dosing facilities shall be designed for chemical phosphorus removal. The extra sludge quantities shall be taken into account in the design of the sludge treatment facilities considering that no biological enhanced phosphorus and other hi-tech phosphorus removal takes place. 

Chemical phosphorus removal shall be carried out by simultaneous precipitation of the iron trivalent (40% FeCl$_{3}$). 

The dosing system shall consist of as a minimum; 

- storage tanks 

- dosing pumps in accordance with Section 7.8.19.8 

- pulsation damper 

- filters 

- service water connection 

- pipes, valves and accessories 

