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Abstract
Donnan membrane process is used for alum recovery and re-use it as a coagulant instead of the commercial alum and thus reduce the cost of production and pollution caused by its plants, also it reduce the remaining sludge volume as well as solid content, through series of the laboratory experiments it has been achieved and verified that the best pH value of the used sludge is 3.1 to recover alum also the best volume ratio of the added sludge in the feed side to the H₂SO₄ in the recovery side is 4:1, as the used membrane is homogeneous nafion (117) and the best retention period is 24 hrs. This period shows featured results in the Al + 3 ion recovery (65 - 75 %), turbidity removal efficiency (70%), filterability enhancement of the remaining sludge (35%), solid content reduction for the remaining sludge (55%) also a negligible content of DOC and heavy metals in the recovered alum (less than 0.05%). Were also the possibility of applying donnan membrane process to a full scale (WTP) has been studied, as it was shown from the initial studies that it can produce sufficient alum needs for 69 WTP monthly, considering a capacity of 150,000 m³ / day