Comparison of polyacrylic acid and polyethylenimine in crystal violet removal from wastewaters by Polyelectrolyte Enhanced Ultrafiltration (PEUF)

Polyelectrolyte-based separation of toxic dyes is studied to estimate the potential of polyelectrolyte enhanced ultrafiltration (PEUF) using polyacrylic acid (PAA) (anionic polymer) and polyethylenimine(PEI) (cationic polymer). PEUF experiments are conducted to study the retention characteristics of crystal violet (CV) in the continuous cross flow system. Effects of the operating conditions, e.g., transmembrane pressure, feed polyelectrolyte concentration, feed dye concentration, ionic strength and pH on the permeate flux profile and observed retention have been investigated. The PEUF experiments showed that polyacrylic acid (PAA) allowed retention of CV in the order of 99 pour cent. The enhancement is primarily due to the formation of complexes between the anionic polymer and dye molecules However, when the cationic polyelectrolyte (PEI) was applied, the CV removal can reach around 60 pour cent. In the case of PAA, the retention of CV decreases with ionic strength, a high retention was obtained at pH range from 2 to 13; this effect was attributed to the increase of electrostatic interaction. The ionic strength and pH have no effect on the removal of CV in the case of PEI.