New Polymeric Coagulants Tested in Water and Wastewater

Abstract

In this work, new polymeric flocculants are presented for use in water-treatment operations. Efficiencies are reported from results obtained by conventional bench-scale tests. These tests are carried out in three systems: a bentonite suspension, biologically treated wastewater effluents and chemically treated effluents. The polymers are water-soluble moieties of the zwitterionic type, which present considerable chain expansion in the presence of high ionic strengths or high salinity, in contrast to the behavior exhibited by common polyelectrolytes. In the case of biologically treated wastewater, 87% of turbidity removal is obtained with the polymer alone. In the case of chemically treated mixed industrial wastewater, the new polymers are compared with cationic and anionic polymers. This work illustrates that high efficiencies may be obtained using anionic or zwitterionic polymers. With 0.2 mg l⁻¹ of zwitterionic polymer and 20 mg l⁻¹ aluminum sulfate, removals of 38% and 96% in chemical oxygen demand (COD) and total suspended solids (TSS), respectively, can be obtained. For Mexico City's wastewater flow, the highest efficiencies are obtained with 250 mg l⁻¹ of Ca(OH)₂ and 0.1 mg l⁻¹ of zwitterionic polymer (48% COD and 87% TSS). In this particular case good results are also obtained using anionic flocculants with aluminum sulfate.

Keywords:

• Polymeric flocculants
• turbidity removal
• wastewater treatment
• zwitterionic polymers