Comparative study between chemical coagulation/precipitation (C/P) versus coagulation/dissolved air flotation (C/DAF) for pre-treatment of personal care products (PCPs) wastewater

Abstract

For pretreatment of wastewater discharged from personnel care products (PCPs) factory, two treatment schemes were investigated. The 1st step in both schemes was chemical coagulation followed by precipitation in the 1st scheme and dissolved air flotation in the 2nd one. Ferric chloride (FeCl 3·6H 2O), alum (Al 2(SO 4) 3·18H 2O) and ferrous sulfate (FeSO 4·6H 2O) were used as coagulants. Lime (CaO) was used as coagulant aid and for pH adjustment. For C/P, the three coagulants investigated were found to be more or less similar in their performance. Maximum COD total removal obtained by ferric chloride, ferrous sulfate and alum was 75.8 ± 9.7, 77.5 ± 9.6 and 76.7 ± 9.9%, respectively. Corresponding BOD 5 total removal values were 78 ± 15.8, 78.7 ± 15.6 and 74.1 ± 19.3%, respectively. However, the optimum dose of ferric chloride and alum was 600 and 700 mg/l while that of ferrous sulfate was 850 mg/l. Alum produced a voluminous sludge, but with the least solids content. Ferric chloride produced compact sludge with a good settleability as reflected by the low sludge volume index (SVI) of 76.3 ± 28.8 ml/gTSS. In the coagulation–dissolved air flotation (C/DAF) experiments, the results showed that alum produced higher COD removal (77.5 ± 3.2%) as compared to ferric chloride (71.6 ± 2.9%) and ferrous sulfate (67.7 ± 3.7%). A cost evaluation of the initial investment and the running costs using the different coagulants at their optimum operating conditions were calculated. The investment and running cost for C/P process is higher by 27.3 and 23.7% than C/DAF.