Aerated Lagoon

Hi everyone 

I have a municipal wastewater treatment plant with aerated lagoon process with capacity 1500 cm/d and with:

• pretreatment part (screening and aerated grit removal tank)
• aerated lagoon ( 2900 m2) with 4 aerators with unit capacity 25 kg/h
• facultative lagoon (2800 m2) with 2 aerators  with unit capacity 25 kg/h
• Clarifier (490 m2)

This plant built since 1991 receive now 2500 m3/d.

The main problem is the bad quality of treated water (SS > 120 mg/l and whitish look) and the sludge fails to settle

How to do ?