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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. 

## Return sludge pumps 

The pumps for return sludge shall be submersible pumps with frequency converters. The actual capacity of the pumps shall be regulated automatically based on the wastewater flow measured by the intermediate flow meter and a selected rate of return of activated sludge. The return rate shall be determined by the required sludge concentration in the activated sludge tanks. 

The total installed capacity of return sludge pumps shall be minimum 75% x Q$_{WW,h}$ without using the standby unit. 

The pumps shall be of the centrifugal type and be rated for return sludge. Hence, the impellers shall be designed either as canal or screw centrifugal types. 

The measured flow and status of the pumps should be monitored by the SCADA system. 

## Excess sludge pumps 

The pumps for excess sludge shall be submersible pumps or eccentric screw pump. 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. Service water connections shall be supplied so that the pump can be washed back on the suction and discharge lines. 

Minimum one additional stand-by excess sludge pump shall be provided. 

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Washing water shall be connected to both the suction and discharge lines of the sludge pumps. This washing system will engage automatically when the pumps are not operated. In addition, the service water line shall be installed to the appropriate places of the excess sludge pumping station and sufficient number of connection points shall be supplied. The treated water should be used for this purpose. 

## 3.3.4.21 Flow Measurement 

## 3.3.4.21.1 Inlet Flow Measurement 

A standard open channel measurement (ultrasonic) unit or in-line flow meter (electromagnetic) shall be installed downstream of the grit and grease removal tanks for continuous flow monitoring and recording. Regardless of type, easy access to flow meter for installation, dismantling and maintenance shall be secured and unhindered. In addition to this pH, conductivity and temperature of wastewater shall be measured at this unit. 

