Problem with ETP - Solids overflowing from final clarifier. Need a solution


We are having activated sludge process in our ETP (both industrial and sewage). Settling of biomass in jar is only upto 900ml even after 3-4 hours, will this indicate the presence of filamentous organisms. We are facing problem of solids overflow from final clarifier(floating problem). What would be remidial action for this situation? Our influent COD is around 1200-1400ppm, flow should be 4-5kl/hr, aeration tank volume 90kl, center feed clarifier volume 17kl. What is the general procedure for circulation of settled mass? Can anybody give details regarding this problem...

Seshagiri Rao