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Abstract

Abstract
This research includes studying the effect of using natural coagulant aid "Walnut Coat" with alum and synthetic polyelectrolyte with alum also on turbidity removal compared with alum alone. A set of jar test was conducted on raw water of different turbidities (5, 10, 20, 40, 50, 80 and 100) NTU using different doses of coagulants and coagulant aids. Final turbidity, pH., were measured after settling. The obtained results indicated that the use of walnut coat with alum was effective in the removal of turbidities of (20, 40) NTU compared with alum alone. While the addition of polyelectrolyte with alum was found to be more effective for higher turbidities (50, 80, 100) NTU. Additionally, the average reduction in pH-value was more using walnut coat than that of using alum alone. Furthermore, walnut coat led to the formation of large, clear and easily settled flocs within the first 5 minutes of slow mixing, while same flocs appears at the end of 30 minutes of slow mixing with alum and polyelectrolyte as flocculant aid. Better sludge characteristics were obtained with walnut coat as flocculant aid, with low water content and high density which can be easily dried and disposed.
Key words: Turbidity, Tigris River, Alum, Walnut Coat, Polyelectrolyte, Coagulation, flocculation, Sedimentation.

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