Abstract:

Coagulants play an important role in the treatment of water and wastewater and in the treatment and disposal of sludge. Aluminum sulfate, alum, is the common chemical coagulant used in the coagulation process. Recently polymers have been utilized in coagulation/flocculation processes for water purification. In this study, a natural indigenous coagulant is suggested as a substitute for alum or as an aid for alum. The coagulant characteristics of the tannins obtained from valonia were examined and whether or not tannins could be used as a primary coagulant and a coagulant aid was determined. Jar tests were done with a synthetic water prepared with varying pH and turbidity. It was found that the best slow stirring velocity and flocculation time were 45 rpm and 30 min, respectively. It was also found that tannins operated much better as a coagulant aid than as a primary coagulant. Tannin as a coagulant aid was more effective than synthetic anionic polyelectrolyte (AN913). At the optimum conditions with tannin, the turbidity decreased from 10 and 20 to < 0.02 and 0.9 FTU (formazin turbidity units), respectively.

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