Experiment series in environmental engineering: Experiment 6 (NUS ChBE, AY 2004/2005 Semester 1)

Coagulation and flocculation are important processes in the removal of turbidity, suspended particles and natural organic material in water and wastewater treatment. Coagulation is an inexact science and requires an empirical approach to estimate the various important parameters that are important to the treatment process. In this study, jar tests are performed on a synthetic raw surface water consisting of 1 g/l of bentonite clay suspended in normal tap water (simulated reservoir water). The purpose of the study was to evaluate the optimum coagulant (alum) dosage, initial pH and flocculation time to remove turbidity from the synthetic water. The main mechanisms of coagulation between bentonite clay and alum are adsorption and charge neutralization and enmeshment of the colloidal particles in the Al(OH)₃ floc while that of flocculation are micro- flocculation, macro- flocculation and differential settling. The optimum alum dose and initial pH were determined to be 50 mg/l as Al₂(SO₄)₃.16H₂O and 5 respectively. The optimum initial pH determined was not in agreement with values reported in the literature. However, no optimum flocculation time could be determined due to inconclusive data. Further studies could focus on this area to investigate the optimum flocculation time to result in effective removal of turbidity from a bentonite clay synthetic water. Done by: Luo Jinjing, Lian Juan and Ng Wenfa