Hi, Maymoun,  The Surface ...

Hi, Maymoun, 

The Surface Load of clarifier is calculated as 0.2 m3/m2.h(2500/24/490), which is too low for the final clarification(normally it is more than 1.0 for active sludge process ). Hence, the hydralic settling process will not cause the high SS effluent in this case. Given the BOD effluent data was not provided, we cannot analyze if the BOD load and aeration is ok for the system. However, I guess that over-aeration and degration of active sludge could be the main reason responsible for the high SS effluent, especially the total Hydraulic Retention Time (HRT) of aeration lagoon is more than 2 days. You can make a SV30 (sludge Volume) test to see the settlement character of the active sludge(I guess the SV30 may beyond 70%). In this case, you may: 1) decrase the aeration and make sure the Dissolved Oxygen(DO) is not more than 2.0 mg/l; and 2) supply the fresh active sludge into the lagoon (the fresh active sludge could be got from the dewatering sludge of the similar treatment facility); 3) discharge the surplus sludge from the clarifier. The restoration of the sludge sytem may take more than one weeks, you need to check the Mixed Liquor Suspend Solid  (MLSS) and SV30 from time to time and make sure they are around 3000-5000 mg/l and 20-30% respectively. 

Hope the above suggestion is helpful. 

Regards, 

Xujun