Optimization of chemical precipitation to improve the primary treatment of wastewater

Chemically enhanced primary treatment (CEPT) is a wastewater treatment method that serves as an attractive alternative to the conventional primary treatment, and it can also be used as an efficient preliminary step of the biological secondary treatment processes. CEPT adopts coagulation and flocculation and it accomplishes remarkable increases in the removal of common pollutants from the influent. The coagulants used in the present study were alum, sea-salt as a cheap coagulant, and homogenous mixtures of sea-salt (as a coagulant aid) and alum with different doses.These alternatives were tested in the direct precipitation of wastewater. The analytical hierarchy process was applied for the evaluation of different alternatives of coagulants according to four main criteria (i.e. removal efficiencies, sludge volume after 30min, coagulant cost, and pH variation). In addition, the removal efficiencies were divided into five subcriteria, including COD, BOD5, TSS, T-P, and T-N removals. The obtained results revealed that the removal efficiencies reached up to 87% of COD, 93% of BOD5, 94% of TSS, 96% of T-P, and 20% of T-N greatly reducing the settling time in the primary treatment to about 30min rather than 2h in the conventional primary sedimentation. This creates a simple procedure for the optimization of chemical precipitation for wastewater treatment.