Bulking Control in Complete-Mixed Activated Sludge Process Using Combination of Metallic Coagulants and Static Magnetic Fields

Metallic coagulants have been used for more coagulation and flocculation of flocs in many wastewater treatment plants (WWTPs) in all parts of the world. The integration of different methods to improve the wastewater treatment process has been considered in recent years. In this case-control study, the effects of four main coagulants (ferric chloride, ferric sulfide, alum, and poly-aluminum chloride) on sludge volume index (SVI) with and without exposure of static magnetic fields (SMFs) have been investigated. Both methods significantly reduced SVI (mL/g), but the combination of SMFs and coagulants was more effective. Ferric chloride could control bulking or reduce SVI to less than 150 mL/g at concentrations of 0.0625 to 2 g/L when the SMFs intensity of 15 mT was used. The control of bulking in other coagulants happened when SMFs were added to coagulants at 0.0625-0.125 g/L concentration of coagulants (P < 0.05). With the application of SMFs, the highest reduction of SVI belonged to ferric sulfide (43.60%), followed by ferric chloride (18.40%), poly-aluminum chloride (PACl) (20.19%), and alum (19.80%). Without the application of SMFs, the highest reduction of SVI belonged to ferric chloride (38.36%), followed by alum (34.94%), PACl (25.43%), and ferric sulfide (6.69%).