The pumps shall be the centrifugal type and be rated for raw wastewater. Hence, the impellers can be designed either as canal or screw centrifugal types. A lifting system shall be provided to carry out the maintenance works. 

The discharge point of the supernatant shall be selected and designed by the Contractor. 

Minimum number of pumps Maximum daily operation time 

## 3.3.4.34 Odour Removal Unit (Bio-Filter) 

: 1 duty + 1 stand-by units :  16 hours/day 

The wastewater treatment plant shall not cause troublesome odor problems inside or outside the plant. The tenderer shall provide detailed calculations (e.g. volume and recycle rate from each potential source) for foul air to be extracted from the sources together with his proposal. Minimum recycle rate and locations foul air to be collected are as follows: 

- Inlet structure including stone trap (7 cycle/hour) 

- Screening building (12 cycle/hour) 

- Inlet, return, excess, primary sludge (if proposed) and dewatering facilities feeding pumping stations (12 cycle/hour), 

- All kind of sludge storage tanks, completely covered (7 cycle/hour), 

- Gravity thickener (if proposed) (7 cycle/hour), 

- Dewatering building and sludge screen (if proposed) building (12 cycle/hour), 

- Any other portion of the plant where odor problems are foreseen (7/12 cycle/hour), 

In addition to this, the ventilation of these units shall be provided in accordance with Section 3.3.11. 

In the design of odor units, the average and maximum H$_{2}$S concentrations in the foul air in the inlet pipe of unit shall be assumed at min. 30 ppm$_{v}$ and min.60 ppm$_{v}$ respectively and units shall be designed accordingly. 

The air ductwork dimensions shall be so selected that the minimum velocity in any duct shall not be less than 8 m/s to avoid clogging by settlement of solids. In any case, the air velocity in the duct shall not exceed 12 m/s. 

The odour removal system shall include the minimum following items, but not limited to: 

- bio-filter bed and bio-media to treat the foul air, which contain H$_{2}$S, NH$_{3}$ and similar odorous compounds, to be received from the odor releasing units 

- the extractor fan, 

- air ductwork between the extractor fan and the odor releasing units, 

- a pre-conditioning unit 

- sprinkler system for bio-media 

- service water and drainage connection for filtrate water from the bio-filter 

- (nutrient feed) media preparation and dosing system and necessary instrumentation. 

Operation and maintenance manual shall be prepared by the Contractor as well the other equipment. The media to be supplied for the bio-filter shall be commercially available with proper price regarding the media renewal. 

