Coagulation/flocculation of domestic sewage with organic polyelectrolytes

The removal of organic particles present in domestic sewage can be increased by coagulation/flocculation process as compared to the application of primary sedimentation tank, which only depends on plain settling. The aim of the present work is to study the effect of the variables affecting the removal efficiency of organic matter present in domestic sewage using a jar testing apparatus. Variables studied were, type and dose of flocculent/coagulant, G- value, rapid mixing, settling and flocculation time. The results showed that cationic Polyelectrolytes C-492 HMW and C-492 MMW can efficiently remove turbidity as high as 75% with doses as low as 10 mg/l. With application of C-581 and FeCl3, high doses of 50 mg/l and 25 mg/l were needed respectively. The results showed that decreasing settling time from 900 to 120 sec and flocculation time from 180 to 30 sec respectively did not affect the turbidity removal with Polyelectrolyte C-492 HMW. However, in case of rapid mixing, time played an important role in turbidity removal. The turbidity removal values were about 67 and 75% at rapid mixing time of 30 sec and G-value of 800 sec-1 respectively by C-492 HMW. Removal of total COD was about 52%, while removal of total phosphorous and total Kjeldahl nitrogen were 29 and 30%, respectively.