Symptoms

• Presence of floating material on water surface

• Emanation of sulphides smell from clarifier

Main causes

• Sludge degradation due to high hydraulic retention time

• The trouble could take place in a limited zone of the clarifier due to the problems of the sludge collector mechanism.

Investigations and analyses

• Measure TSS in the settled sludge after sludge removal operation and if it is too high extend the extraction time

• Check the sludge collector mechanism

Remedial actions

• Increase the scraper velocity

• Increase the extraction time or the frequency of the sludge removal