الفهرس 
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Abstract
The present study provides a cost-effective and eco-friendly approach for chemically enhanced primary treatment (CEPT) of wastewater using the recovered alum from water treatment sludge as a coagulant. This approach was achieved after two phases of the present study. The first phase involves in investigation of the parametric conditions for alum recovery procedure by acidification. The results show that alum recovery percent reached up to 69.03%, and the reduction of sludge volume reaches its highest level at 90%. Moreover, the optimum pH level is 1.50 for alum recovery as indicated by maximum aluminum releasing, maximum reduction of sludge volume, and reasonable dosages of added sulfuric acid. On the other hand, the second phase of the present study is devoted to complete the process of CEPT of wastewater using the recovered alum in a developed model of hydraulic clari-flocculator. The obtained results revealed that the recovered alum is significantly better than the fresh alum according to viewpoint of the environmental impact. However, there are slight differences in the removal efficiencies of various wastewater characteristics when comparing the fresh alum with the recovered alum. The results revealed that the maximum differences in the removal efficiencies results from utilization of the fresh and the recovered alum were just 2.94% of BOD5, 8.11% of COD, 1.68% of TSS, 3.11% of PO4, and 11.33% of NO3.