Effectiveness of tannins obtained from valonia as a coagulant aid for dewatering of sludge

For evaluating the tannin (natural polyelectrolyte) and AN913 (synthetic anionic polyelectrolyte) as a coagulant aid for treating raw water to remove suspended matter the tannin or AN913 was added to the synthetic water sample which was stirred and then allowed to settle. After a settled time a sample of the supernatant liquid was removed and its turbidity determined. For use as sludge conditioners the optimum polymer dose was determined. Formed sludge dewatering investigated for optimum pH and optimum dose of coagulant and coagulant aids. 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. As coagulant aids, tannin was more effective than AN913.