Symptoms

• Efficiency reduction

• DO reduction in the aeration basin; and temporary bulking

• Mixed liquor dark colour

Main causes

• Insufficient aeration

• Wide oscillation of the organic loading rate

Investigations and analyses

• Measure DO concentration in the aeration basin specially in the dead zones

• Measure wastewater flow rate and organic concentration during peak time

Remedial actions

• Increase the volume of the aeration basin (raising the water level)

• Increase the aeration