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High content of organic material in the collected grit

Symptoms

  • Quantity of grit removed higher than the normal

  • Dark colour of the grit removed

  • Mixture more doughy than the normal

  • Foul smell from the collected grit



Main causes

  • Low velocity and / or too high hydraulic retention time



Investigations and analyses

  • Analyse, daily, the volatile content in the collected grit

  • Measure the velocity corresponding to the different wastewater flow rate

  • Measure the air flow rate in case of aerated grit chamber



Remedial actions

  • If possible, reduce the number of the grit chambers working in parallel

  • In case of rectangular horizontal-flow grit chambers, reduce the water section or modify (reduce) the water level in the chamber by regulating the weir

  • In case of aerated grit chamber increase the air flow rate

  • Increase the velocity of roll or agitation

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