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Primary Sedimentation Clarifiers

Application Problem: 

The customer had used a led (light-emitting diode) array, to monitor the floc blanket height 800 mm (30 inches) above and below the center feed well of the clarifier. This 1600 mm (60 inches) long array was very heavy and supported by extra cables from the bridge. The led array worked ok, when the density of the floc blanket was stable, but required periodic calibration. The led array also required periodic cleaning, to remove scum buildup and required two operators to pull the array to the bridge. If the blanket level was higher than the led array, the customer was unable to know how high the blanket was. If the blanket level was lower than the led array, the tank’s ability to filter out suspended solids diminished. The floc blanket was very dynamic due to hydraulic imbalance.


Hawk installed a high-frequency sonar transducer, optimized to cover the light density floc blanket. The ORCA sonar transmitter has a maximum range of 30 m (95ft), so the sonar could monitor the entire range of the clarifier, which was 6 m (20 ft) deep. The square designed clarifier was 45 m x 45 m (150 ft x 150 ft) square. The average flow was 125 megalitre per day (30 million gallons per day) to each clarifier. An automatic sludge cleaning device was also installed to remove buildup from the sonar transducer. The sludge cleaner has a factory guarantee. The second analog output from the ORCA transmitter was used to measure the water clarity between the floc blanket and the sonar transducer, like a simple turbidity meter. This provided feedback to the control room for the process problems. Hawk manufactures the largest range of sonar transducers, to provide optimized performance for all bed level density applications.

Ordering information: (complete system) Part no: OSIRDYX-OSIRT003S4XC6-OSIRMEL3-OSIRSC A

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