Evaluation of tannin biopolymer as a coagulant aid for coagulation of colloidal particles

Tannin is a biodegradable anionic polymer. Tannin as a coagulant aid can be a potential substitute for synthetic anionic polyelectrolytes in water treatment because it can: (1) avoid the health effects from residual aluminum(III) and synthetic polymers, and (2) produce biodegradable sludge. In the present work, the coagulant characteristics of the tannin obtained from valonia were examined and whether or not tannin could be used a coagulant aid was determined. The effectiveness of tannin as a coagulant aid was investigated in jar test experiments. The jar test were conducted using water sample prepared in varying its pH and turbidity. In the turbidity removal from snythetic water, both Al2(SO4)3 + tannin and Al2(SO4)3 + AN913 showed significant improvement compared with Al2(SO4)3 only. However, tannin as a coagulant aid was more effective than AN913 and it significantly reduced the required doses of the Al2(SO4)3. The sludge filterability was determined by specific resistance measurements. Tannin and Al2(SO4)3 together gave a significant improvement comparing with Al2(SO4)3 only.